Sport Nutrition of Macronutrient Demands

Protein

The idea that protein requirements are increased by physical activity is intuitively attractive, and highprotein diets are a common feature of the diets of sportsmen and women. The available evidence shows an increased rate of oxidation of the carbon skeletons of amino acids during exercise, especially when carbohydrate availability is low. Protein contributes only about 5% of total energy demand in endurance exercise, but the absolute rate of protein breakdown is higher than at rest (where protein contributes about the same fraction as the protein content of the diet, i.e., typically about 12–16%) because of the higher energy turnover. 

It is often recommended that athletes engaged in endurance activities on a daily basis should aim to achieve a protein intake of about 1.2–1.4 g kg-1 day-1, whereas athletes engaged in strength and power training may need as much as 1.6–1.7 g kg-1 day-1. Those who take no exercise have an estimated average requirement of about 0.6 g kg-1 day and the recommended intake for these individuals is about 0.8– 1.0 g kg-1 day.

In strength and power sports such as weightlifting, sprinting and bodybuilding, the use of high-protein diets and protein supplements is especially prevalent, and daily intakes in excess of 2–4 g-1 kg-1 are not unusual. Scientific support for such high intakes is generally lacking, but those involved in these sports are adamant that such high levels of intake are necessary, not only to increase muscle mass but also to maintain muscle mass. 

This apparent inconsistency may be explained by Millward’s adaptive metabolic demand model, which proposes that the body adapts to either high or low levels of intake, and that this adjustment to changes in intake occurs only very slowly. This means that individuals such as strength and power athletes who consume a highprotein diet over many years will find that any reduction in protein intake will result in a loss of muscle mass. This is because of an upregulation of the activity of the enzymes involved in protein oxidation to cope with the high intake: activity of these enzymes remains high when there is a sudden decrease in intake, leading to a net catabolic effect.

Protein synthesis and degradation are both enhanced for some hours after exercise, and the net effect on muscle mass will depend on the relative magnitude and duration of these effects. Several recent studies have shown that ingestion of small amounts of protein (typically about 35–40 g) or essential amino acids (about 6 g) either before or immediately after exercise will result in net protein synthesis in the hours after exercise, whereas net negative protein balance is observed if no source of amino acids is consumed. 

These observations have led to recommendations that protein should be consumed immediately after exercise, but the control condition in most of these studies has involved a relatively prolonged (6–12 h) period of fasting, and this does not reflect normal behavior. Individuals who consume foods containing carbohydrate and proteins in the hour or two before exercise may not further increase protein synthesis if additional amino acids or proteins are ingested immediately before, during, or after exercise.

Various high (30%) protein, high (30%) fat, low (40%) carbohydrate diets have been promoted for weight loss, and some diets even suggest almost complete elimination of carbohydrate from the diet. Some of these diets have been specifically targeted at athletes, accompanied by impressive claims and celebrity endorsements. 

Proposed mechanisms of action of these diets include reduced circulating insulin levels, increased fat catabolism, and altered prostaglandin metabolism, but it seems more likely that these diets achieve weight loss simply by restricting dietary choice. These diets can be effective in promoting short-term weight loss, primarily by restricting energy intake (typically to 1000–2000 kcal day-1). There is no evidence to support improvements in exercise performance, and what evidence there is does not support the
concept.

Carbohydrate

Carbohydrate is an essential fuel for the brain, red blood cells, and a few other tissues. Fat and carbohydrate
are the main fuels used for energy supply in muscle during exercise. In low-intensity exercise, most of the energy demand can be met by fat oxidation, but the contribution of carbohydrate, and especially of the muscle glycogen, increases as the rate of energy demand increases. 

Carbohydrate oxidation rates of 3–4 g min-1 may be sustained for several hours by athletes in training or competition. When the glycogen content of the exercising muscles reaches very low levels, the work rate must be reduced to a level that can be accommodated by fat oxidation. In high-intensity exercise, essentially all of the energy demand is met by carbohydrate metabolism. Therefore, repeated short sprints place high demands on the muscle carbohydrate store, most of which can be converted to lactate within a few minutes.

Carbohydrate is stored in the body in the form of glycogen, primarily in the liver (about 70–100 g in the fed state) and in the skeletal muscles (about 300–500 g, depending on muscle mass and preceding diet). These stores are small relative to the body’s requirements for carbohydrate. Carbohydrate supplies about 45% of the energy in the typical Western diet. This amounts to about 200–300 g day-1 for the average sedentary individual, and is adequate for normal daily activities. 

In an hour of hard exercise, however, up to 200 g of carbohydrate can be used, and sufficient carbohydrate must be supplied by the diet to replace the amount used. Replacement of the glycogen stores is an essential part of the recovery process after exercise: if the muscle glycogen content is not replaced, the quality of training must be reduced, and the risks of illness and injury are increased. Low muscle glycogen levels are associated with an increased secretion of cortisol during exercise, with consequent negative implications for immune function.

When rapid recovery is a priority, replacement of carbohydrate should begin as soon as possible after exercise with carbohydrate foods that are convenient and appealing. Thereafter, the diet should supply sufficient carbohydrate to replace the amount used in training and to meet ongoing demands of other tissues. Some recommendations for carbohydrate intake after training or competition are shown in Table. For athletes preparing for competition, a reduction in the training load and the consumption of a high-carbohydrate diet in the last few days are recommended. This maximizes the body’s carbohydrate stores and should ensure optimum performance, not only in endurance activities, but also in events involving short-duration high-intensity exercise and in field games involving multiple sprints.

The high-carbohydrate diet recommended for the physically active individual coincides with the recommendations of various expert committees that a healthy diet is one that is high in carbohydrate (at least 55% of energy) and low in fat (less than 30% of energy). However, where energy intake is either very high or very low, it may be inappropriate to express the carbohydrate requirement as a fraction of energy intake. With low total energy intakes, the fraction of carbohydrate in the diet must be high, but the endurance athlete with a very highenergy intake may be able to tolerate a higher fat intake. Recommendations, as in Table, should be framed in absolute amounts relative to body mass, i.e., grams of carbohydrate per kilogram body mass. 

The type of carbohydrate eaten is less important than the amount. It is valuable to choose nutrientrich carbohydrates and to add other foods to recovery meals and snacks to provide a good source of protein and other nutrients. The presence of small amounts of protein in recovery meals may promote additional glycogen recovery when carbohydrate intake is less than optimal or when frequent snacking is not possible. Protein taken at this time may also stimulate protein synthesis in muscles, as described above. Carbohydrate-rich foods with a moderate to high glycemic index (GI) provide a readily available source of carbohydrate for glycogen synthesis, and should be the major fuel choices in recovery meals.

Fat

Fat is an important metabolic fuel in prolonged exercise, especially when the availability of carbohydrate is low. One of the primary adaptations to endurance training is an enhanced capacity to oxidize fat, thus sparing the body’s limited carbohydrate stores. Studies where subjects have trained on high-fat diets, however, have shown that a highcarbohydrate diet during a period of training brings about greater improvements in performance. 

Even Table Suggested carbohydrate intakes for athletes in training Immediate postexercise recovery (0–4 h): 1 g per kg body mass per h, consisting of several small snacks Daily recovery (moderate duration/low intensity training): 5–7 g kg-1 day-1 Daily recovery (moderate–heavy endurance training): 7–12 g kg-1 day-1 Daily recovery (extreme training: 4–6 h or more per day): 10–12 g kg-1 day-1 when a high-carbohydrate diet is fed for a few days to allow normalization of the muscle glycogen stores before exercise performance is measured, the exercise capacity remains less after training on a high fat diet. 

It must be recognized, though, that these shortterm training studies usually involve relatively untrained individuals and may not reflect the situation of the highly trained elite endurance athlete where the capacity of the muscle for oxidation of fatty acids will be much higher. For the athlete with very high levels of energy expenditure in training, the exercise intensity will inevitably be reduced to a level where fatty acid oxidation will make a significant contribution to energy supply and fat will provide an important energy source in the diet. 

Once the requirements for protein and carbohydrate are met, the balance of energy intake can be in the form
of fat. Fat also serves other important functions in the diet. As well as providing essential fatty acids, it acts as a vehicle for the transport of fat-soluble nutrients. Some athletes try to minimize their fat intake, but this is not wise.

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Sport Nutrition of Macronutrient Demads

Source: Nutritional Supplement

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Nutrition For Training

The training load of athletes varies greatly between individuals, depending on the nature of the sport and the level of competition, and it also varies over time in relation to the competitive season. Training may consist of high-intensity resistance training, brief but intense sprints, prolonged moderate intensity efforts, or technical work. Each places different demands on the muscles, cardiovascular system, and other tissues, and each has different energy requirements. The aim of training is to induce changes in body tissues and organs that will improve exercise performance, but different adaptations are required in different sports. Increasing muscle mass, strength, and power is a key objective in many sports, but in other sports, these changes would hinder, rather than help, performance. The training stimulus, therefore, must be specific to the objectives of the event. 

Within limits, the greater the training stimulus – consisting of the intensity, duration and frequency of individual training sessions – the greater the adaptation that takes place. As mentioned above, nutrition is important in promoting recovery between training sessions to allow an increase in the training load that can be sustained without succumbing to illness and injury, and also in allowing more effective adaptations to each bout of training. This may be important in complex sports such as soccer, where different training objectives must be achieved and where the training must also accommodate practice of a variety of skills.

Influence of Exercise Training on Energy Balance Energy must be supplied by the diet to meet immediate energy needs (body functions, energy for activity, and growth) and for the maintenance of body energy stores. Energy stores, consisting primarily of fat, but including the key carbohydrate stores in liver and muscle, play a number of important roles related to exercise performance, since they contribute to size and function (e.g., muscle mass) as well as providing fuel for exercise. Athletes try to manipulate these factors towards the characteristics that offer advantages to their sport: this may mean a change in body mass, a change (usually a reduction) in body fat, a change (usually an increase) in muscle mass, and optimization of muscle and liver carbohydrate stores.

Not all athletes are able to correctly identify goals that are suitable for their sport and for their individual make-up. This can lead to various problems, including excessive restriction of energy intake in an attempt to achieve an unrealistically low body mass. If energy intake is too low, and especially if carbohydrate intake is inadequate, it may not be possible to sustain the training load without the risk of chronic fatigue, injury and illness. If an energy deficit is incurred, it may lead to changes in metabolic and hormonal function, which affect performance, growth and health. One outcome of low energy availability in female athletes is a disturbance of reproductive function and menstrual regularity. Other problems are likely to occur in male athletes. 

There is a real danger that the focus on achieving a specific body mass and body composition, may become  more important than achieving success in competition. Monitoring of body mass can provide a useful index of energy balance in some situations, but other biomarkers are generally better. Measurement of body fat stores, usually by measurement of skinfold thickness, can be helpful in setting targets and in monitoring progress. Other markers, such as measurement of urinary ketone levels, can identify athletes who are failing to achieve an adequate carbohydrate intake. 

Problems are most likely to occur when the energy expenditure is either very high or very low. Athletes with very high energy demands are likely to be training at least twice per day, leaving limited opportunities for eating the large amounts of foods that are necessary. Athletes with low energy demands and who must restrict energy intake to achieve a low body mass have two main problems: they must cope with constant hunger and they must also be careful in their selection of foods to ensure that they achieve an adequate intake of essential nutrients. 

An athlete’s energy requirements are set primarily by the training load and by body mass, although there is also a large interindividual variability even when these factors are constant. Measurements of oxygen uptake, heart rate, and other variables made after exercise show that the metabolic rate may remain elevated for at least 12 h and possibly up to 24 h if the exercise is prolonged and close to the maximum intensity that can be sustained. After more moderate exercise, the metabolic rate quickly returns to baseline level. 

Therefore, it seems likely that the athlete training at near to the maximum sustainable level and who already has a very high energy demand will find this increased further by the elevation of postexercise metabolic rate: this will increase the difficulties that many of these athletes have in meeting their energy demand. The recreational exerciser, for whom the primary stimulus to exercise is often to control body mass or reduce body fat content, will not exercise hard enough or long enough to experience substantial elevations of metabolic rate after exercise.

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Nutritional For Training

Source: Nutritional Supplements

Image: bodyhealthnfitness.com

Assesment of Nutritional Status

Assesment of Nutritional Status. Stability of body weight requires that energy intake and expenditures are balanced over time.The major categories of energy output are resting energy expenditure (REE) and physical activity; minor sources include the energy cost of metabolizing food (thermic effect of food or specific dynamic action) and shivering thermogenesis.

The average energy intake is about 2800 kcal/d for men and about 1800 kcal/d for women, though these estimates vary with age, body size, and activity level.Dietary reference intakes (DRI) and recommended dietary allowances (RDA) have been defined for many nutrients, including 9 essential amino acids, 4 fat-soluble and 10 water-soluble vitamins, several minerals, fatty acids, choline, and water (Tables 60-1 and 60-2, pp.400 and 401, in HPIM-16). The usual water requirements are 1.0–1.5 mL/kcal energy expenditure in adults, with adjustments for excessive losses.The RDA for protein is 0.6 g/kg body weight. Fat should comprise <30% of calories, and saturated fat should be < 10% of calories.At least 55% of calories should be derived from carbohydrates.

Malnutrition

Malnutrition results from inadequate intake or abnormal gastrointestinal assimilation of dietary calories, excessive energy expenditure, or altered metabolism of energy supplies by an intrinsic disease process. Both outpatients and inpatients are at risk for malnutrition if they meet one or more of the following criteria:

• Unintentional loss of >10% of usual body weight in the preceding 3 months
• Body weight <90% of ideal for height (Table )
• Body mass index (BMI: weight/height2 in kg/m2) < 18.5

A body weight <90% of ideal for height represents risk of malnutrition, body weight <85% of ideal constitutes malnutrition, <70% of ideal represents severe malnutrition, and <60% of ideal is usually incompatible with survival. In underdeveloped countries, two forms of severe malnutrition can be seen: marasmus, which refers to generalized starvation with loss of body fat and protein, and kwashiorkor, which refers to selective protein malnutrition with edema and fatty liver.In more developed societies, features of combined protein- calorie malnutrition (PCM) are more commonly seen in the context of a variety of acute and chronic illnesses.

Etiology

The major etiologies of malnutrition are starvation, stress from surgery or severe illness, and mixed mechanisms.Starvation results from decreased dietary intake (from poverty, chronic alcoholism, anorexia nervosa, fad diets, severe depression, neurodegenerative disorders, dementia, or strict vegetarianism; abdominal pain from intestinal ischemia or pancreatitis; or anorexia associated with AIDS, disseminated cancer, or renal failure) or decreased assimilation of the diet (from pancreatic insufficiency; short bowel syndrome; celiac disease; or esophageal, gastric, or intestinal obstruction).Contributors to physical stress include fever, acute trauma, major surgery, burns, acute sepsis, hyperthyroidism, and inflammation as occurs in pancreatitis, collagen vascular diseases, and chronic infectious diseases such as tuberculosis or AIDS opportunistic infections.Mixed mechanisms occur in AIDS, disseminated cancer, COPD, chronic liver disease, Crohn’s disease, ulcerative colitis, and renal failure.

Clinical Features

• General—weight loss, temporal and proximal muscle wasting, decreased skin-fold thickness
• Skin, hair, nails—easily plucked hair, easy bruising, petechiae, and perifollicular hemorrhages (vit.C), “flaky paint” rash of lower extremities (zinc), hyperpigmentation of skin in exposed areas (niacin, tryptophan); spooning of nails (iron)
• Eyes—conjunctival pallor (anemia), night blindness, dryness and Bitot spots (vit.A), ophthalmoplegia (thiamine)
• Mouth and mucous membranes—glossitis and/or cheilosis (riboflavin, niacin, vit.B 12, pyridoxine, folate), diminished taste (zinc); inflamed and bleeding gums (vit.C)
• Neurologic—disorientation (niacin, phosphorus), confabulation, cerebellar gait, or past pointing (thiamine), peripheral neuropathy (thiamine, pyridoxine, vit.E), lost vibratory and position sense (vit. B12) Laboratory findings include a low serum albumin, elevated PT, and decreased cell-mediated immunity manifest as

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Assesment of Nutritional Status

Source: Manual of Medicine

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Sources and Types of Dietary Fiber

The main sources of dietary fiber in most Western diets are well characterized, and high-quality data are available for both food composition and dietary intakes. This is not always true for diets in developing countries, however, and this problem bedevils attempts to investigate the importance of fiber by making international comparisons of diet and disease. Another problem is that different analytical approaches give slightly different values for the dietary fiber content of foods, and do not reflect the physical and chemical properties of the different polysaccharide components. 

The use of enzymic hydrolysis to determine the ‘unavailable carbohydrate’ content of foods was refined by Southgate, and his technique was used for the 4th edition of the UK standard food tables, The Composition of Foods published in 1978. The 6th edition, published in 2002, contains values for nonstarch polysaccharides, derived using the Englyst technique, but recommends use of AOAC methods for food labeling purposes. A comparison of values for nonstarch polysaccharides and dietary fiber values obtained

by the AOAC method is given in Table 2.

In the UK about 47% of dietary fiber is obtained from cereal products, including bread and breakfast cereals. The level of cell wall polysaccharides in a product made from flour depends on the extraction rate, which is the proportion of the original grain present in the flour after milling. Thus a ‘white’ flour with an extraction rate of 70% usually contains about 3% NSP, whereas a ‘wholemeal’ flour with an extraction rate of 100% contains about 10% NSP. The terms ‘soluble’ and ‘insoluble’ fiber have been coined in order to partially overcome the problem of the lack of correspondence between the total analytical value for fiber and the physical properties of the measured polysaccharides. 

By adopting the Englyst technique for the separation and chemical analysis of nonstarch polysaccharides it is possible to specify both the soluble and insoluble fiber content of foods. Some representative values for soluble and insoluble fiber in cereal foods are given in Table 3, and those for fruits and vegetables, which provide a further 45% of the fiber in UK diets, are given in Table 4. 

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Source: Guide to Nutrition Supplements

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Source of Calcium Dietary

Food Sources

The majority of dietary calcium in industrialized countries comes from milk products; one serving (i.e., 250 ml milk or yogurt or 40 g cheese) contains approximately 7.5 mmol (300 mg). Nondairy sources (fruits, vegetables, and grain products) supply approximately 25% of total calcium. When substantial amounts of grains are consumed, for example, in breads or as maize products, these can be important sources, although the calcium in cereals tends to be less bioavailable than that in dairy products. Other foods high in calcium include tofu set with a calcium salt, kale, broccoli, and, increasingly, calcium-fortified juices and cereals. No matter what the source, a high percentage of people in both industrialized and less wealthy countries fail to meet recommended guidelines for optimal calcium intake.

Bioavailability

Several dietary constituents decrease the bioavailability of calcium in food. Increasing fiber intake by, for example, replacing white flour by whole wheat flour in a typical Western diet has long been associated with negative calcium balance even when calcium intakes meet recommended levels. Likewise, the fiber in fruits and vegetables can cause negative calcium balance. In cereals, hytic acid is the main constituent of fiber that binds calcium, making it unavailable for absorption. The fermentation of bread during leavening reduces phytate content substantially, making calcium more bioavailable. In fruits and vegetables, the uronic acids in hemicellulose are strong calcium binders, as is the oxalic acid present in high concentrations in foods such as spinach. 

Calcium bioavailability from beans is approximately half and that from spinach approximately one-tenth of the bioavailability from milk. In contrast, calcium absorption from low-oxalate vegetables, such as kale, broccoli, and collard greens, is as good as that from milk. The difference in calcium absorption between the various forms of supplements is not large. Dietary fat does not affect calcium absorption except in individuals with diseases that impair fat malabsorption (e.g., short bowel syndrome, celiac disease, and pancreatitis). In these conditions, the calcium forms an insoluble and unabsorbable ‘soap’ with the unabsorbed fat in the alkaline lumen of the small intestine, potentially resulting in impaired bone mineralization. 

In addition, the luminal calcium is not available to precipitate the oxalates, meaning that the free oxalates will be hyperabsorbed leading to increased risk for renal oxalate stones. Neither dietary phosphorus nor a wide range of phosphorus-tocalcium ratios affect intestinal calcium absorption in very low-birth-weight infants and adults. Lactose improves calcium absorption in young infants, in whom absorption of calcium is predominantly by passive transport. In adults, the presence of lactose in the diet has little effect on the efficiency of calcium absorption. 

Effects of High Calcium Intakes 

Calcium can inhibit the absorption of both heme iron (found in meat, fish, and poultry) and non-heme iron. The mechanism by which this occurs remains controversial, but the inhibition probably occurs within the mucosal cells rather than in the intestinal lumen. This interaction is of concern because calcium supplements are taken by many women who may have difficulty maintaining adequate iron stores. Approximately 300–600mg of calcium, as a supplement or in foods, reduces the absorption of both heme and nonheme iron by approximately 30–50% when consumed in the same meal. 

The inhibitory effect on iron absorption is inversely related to iron status so that it is relatively unimportant above a serum ferritin concentration of approximately 50–60 mg/l. Thus, consideration should be given to monitoring the iron status of menstruating women with low iron stores who take calcium supplements. There is no inhibitory effect when calcium and iron supplements are consumed together in the absence of food, and inhibition may be less with calcium citrate. In the past, it was common to restrict dietary calcium in patients with a history of calcium oxalate stones. However, recent data suggest that a severe calcium restriction in patients with oxalate stones is not only ineffective but also can lead to bone demineralization. For the prevention of recurrent stone formation, a diet restricted in oxalate, sodium, and animal protein is probably most effective. Only if absorptive hypercalciuria is present should a moderate calcium restriction be imposed.

Long-term consumption of approximately 1500– 2000 mg calcium per day is safe for most individuals, although there will be some reduction in the efficiency of iron absorption. However, higher intakes from supplements (62.5 mmol or 2.5 g per day) can result in milk–alkali syndrome (MAS), with symptoms of  hypercalcemia, renal insufficiency, metabolic alkalosis, and severe alterations in metabolism. Based on risk of developing MAS, the upper limit for calcium intake is 2500 mg per day for adults and children.

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Source: Guide to Nutrition Supplements

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Sources of Vitamin C Dietary and High Intakes

It is apparent from the list of rich sources of vitamin C in Table 3 that the major determinant of vitamin C intake is the consumption of fruit and vegetables; deficiency is likely in people whose habitual intake of fruit and vegetables is very low. However, clinical signs of deficiency are rarely seen in developed countries. The range of intakes by healthy adults in Britain reflects fruit and vegetable consumption: the 2.5 percentile intake is 19mg per day (men) and 14 mg per day (women), while the 97.5 percentile intake from foods (excluding supplements) is 170 mg per day (men) and 160 mg per day (women). Smokers may be at increased risk of deficiency; there is some evidence that the rate of ascorbate catabolism is 2- fold higher in smokers than in nonsmokers.

There is a school of thought that human requirements for vitamin C are considerably higher than those  discussed above. The evidence is largely based on observation of the vitamin C intake of gorillas in captivity, assuming that this is the same as their intake in the wild (where they eat considerably less fruit than under zoo conditions), and then assuming that because they have this intake, it is their requirement— an unjustified assumption. Scaling this to human beings suggests a requirement of 1–2 g per day.

Intakes in excess of about 80–100mg per day lead to a quantitative increase in urinary excretion of unmetabolized ascorbate, suggesting saturation of tissue reserves. It is difficult to justify a requirement in excess of tissue storage capacity. A number of studies have reported low ascorbate status in patients with advanced cancer—perhaps an unsurprising finding in seriously ill patients. One study has suggested, on the basis of an uncontrolled open trial, that 10 g daily doses of vitamin C resulted in increased survival. Controlled studies have not demonstrated any beneficial effects of high-dose ascorbic acid in the treatment of advanced cancer.

High doses of ascorbate are popularly recommended for the prevention and treatment of the common cold. The evidence from controlled trials is unconvincing, and meta-analysis shows no evidence of a protective effect against the incidence of colds. There is, however, consistent evidence of a beneficial effect in reducing the severity and duration of symptoms. This may be due to the antioxidant actions of ascorbate against the oxidizing agents produced by, and released from, activated phagocytes, and hence a decreased inflammatory
response.

Scorbutic guinea pigs develop hypercholesterolemia. While there is no evidence that high intakes of vitamin C result in increased cholesterol catabolism, there is evidence that monodehydroascorbate inhibits hydroxymethylglutaryl CoA reductase, resulting in reduced synthesis of cholesterol, and high intakes of ascorbate may have some hypocholesterolaemic action. There is limited evidence of benefits of high intakes of vitamin C in reducing the incidence of stroke, but inconsistent evidence with respect to coronary heart disease.

Regardless of whether or not high intakes of ascorbate have any beneficial effects, large numbers of people habitually take between 1 and 5 g per day of vitamin C supplements. There is little evidence of any significant toxicity from these high intakes. Once the plasma concentration of ascorbate reaches the renal threshold, it is excreted more or less quantitatively with increasing intake. Because the rate of ascorbate catabolism increases with increasing intake, it has been suggested that abrupt cessation of high intakes of ascorbate may result in rebound scurvy because of ‘metabolic conditioning’ and a greatly increased rate of catabolism. While there have been a number of anecdotal reports, there is no evidence that this occurs.

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Source: Guide to Nutrition Supplements

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Dietary Antioxidants

The human endogenous antioxidant system is impressive but incomplete. Regular and adequate dietary intakes of (largely) plant-based antioxidants, most notably vitamin C, vitamin E, and folic acid, are needed. Fresh fruits and vegetables are rich in antioxidants (Figure 6), and epidemiological evidence of protection by diets rich in fruits and vegetables is strong. To decrease the risk of cancer of various sites, five or more servings per day of fruits and vegetables are recommended. However, it is not known whether it is one, some, or all antioxidant(s) that are the key protective agents in these foods.

Furthermore, it may be that antioxidants are simple co-travellers with other, as yet unidentified, components
of antioxidant-rich foods. Perhaps antioxidants are not ‘magic bullets’ but rather ‘magic markers’ of protective elements. Nonetheless, the US recommended daily intakes (RDIs) for vitamin C and vitamin E were increased in 2000 in recognition of the strong evidence that regular high intakes of these antioxidant vitamins are associated with a decreased risk of chronic disease and with lower allcause mortality.

To date, research on dietary antioxidant micronutrients has concentrated mainly on vitamin C and vitamin E. This is likely to be because humans have an undoubted requirement for these antioxidants, which we cannot synthesize and must obtain in regular adequate amounts from food. However, there are a plethora of other dietary antioxidants. Some or all of the thousands of carotenoids, flavonoids, and phenolics found in plant-based foods, herbs, and beverages, such as teas and wines, may also be important for human health, although there are currently no RDIs for these. 

Furthermore, while there are recommended intakes for vitamin C, vitamin E, and folic acid, these vary among countries, and there is currently no agreement as regards the ‘optimal’ intake for health. In addition, there is growing evidence that other dietary constituents with antioxidant properties, such as quercetin and catechins (found in teas, wines, apples, and onions), lycopene, lutein, and zeaxanthin (found in tomatoes, spinach, and herbs) contribute to human health.

Zinc (found especially in lamb, leafy and root vegetables (vegetarian), and shellfish) and selenium (found especially in beef, cereals, nuts, and fish) are incorporated into the antioxidant enzymes SOD and glutathione peroxidase,
and the elements are themselves sometimes referred to as antioxidants. The levels of ascorbic acid, alfa-tocopherol, folic acid, carotenoids, and flavonoids within the body are maintained by dietary intake. While the role and importance of dietary antioxidants are currently unclear, antioxidant defense can be modulated by increasing or decreasing the intake of foods containing these antioxidants. 

There are a number of reasons for recommending dietary changes in preference to supplementation for achieving increased antioxidant status, as follows.
1. It is not clear which antioxidants confer protection.
2. The hierarchy of protection may vary depending on body conditions.
3. A cooperative mix of antioxidants is likely to be more effective than an increased intake of one antioxidant. 

4. Antioxidants, including vitamin A, Beta-carotene, vitamin C, selenium, and copper, can be harmful in large doses or under certain circumstances.
5. Antioxidant status is likely to be affected by the overall composition of the diet, e.g., the fattyacid and phytochemical mix.
6. The iron status of the body, environmental conditions, and lifestyle undoubtedly affect antioxidant demand.
Antioxidant defense, therefore, is likely to be optimized through a balanced intake of a variety of antioxidants from natural sources rather than by pharmacological doses of one or a few antioxidants.

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by Umaee

 Source  : Guide to Nutrition Suplement

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Vegetarian Diets

Adequate Vegetarian Diet Patterns

There are many individuals who have little or no risk of dietary inadequacy from their vegetarian eating patterns; for example, an adult male who regards himself as a vegetarian (also referred to as a meat avoider, or semi-vegetarian) but has a dietary pattern that consists solely of occasionally avoiding red meat about half of the time with no other dietary alterations. Such an individual is unlikely to need further dietary assessment.

Some characteristics of sound, adequate vegetarian diet patterns include the following:

• Use of a nutritionally sound food guide of diet planning; vegan and vegetarian food guides that conform to the latest recommendations of expert groups may help to ensure that nutrient needs will be met with balance and without excessive intakes.
• If diet alone does not meet the RDAs, regular use of appropriate vitamin mineral supplements plus use of a nutritionally sound food guide.
• Vegans and some other vegetarians sometimes have multiple food avoidances; intakes of nutrients likely to be deficient can be increased by use of rich sources of whole foods, foods fortified with the nutrients falling short, and/or vitamin or mineral supplements.
• Consumption of a wide variety of food groups and foods within each group.
• Membership of a family with a long history of adherence to healthy vegetarian eating styles.
• Avoidances are limited to a few foods or are sporadic in nature.

Signs of Possibly Inadequate Vegetarian Diet Patterns

The more of the following characteristics that apply, the higher the potential risk of inadequacy and the greater the need for further assessment. Diet First it is important to examine what food groups, foods, or products are avoided or de-emphasized on vegetarian diets, and then some additional characteristics of dietary patterns, personal characteristics, and belief systems that further increase risk of dietary inadequacy and other health problems:

• Many types and extensive avoidance of animal food groups. Assessment of the nutritional adequacy of vegetarian eating patterns begins by examining animal food groups (red meat, poultry, fish and seafood, milk and milk products, eggs) and specific foods within these that are avoided entirely or eaten only in minimal amounts. Unless other foods or food groups rich in these nutrients or nutrient-containing dietary supplements are used, problems may arise.
• Many types and extensive avoidance of fortified foods, nutrient-containing dietary supplements, and processed foods. Some vegetarians believe that fortified foods (highly fortified cereals, calcium fortified soy milk and/or juices, B12 fortified yeast), processed foods (frozen, canned, and in extreme cases cooked foods for raw food eaters), and nutrient-containing dietary supplements (vitamins, minerals, fatty acids) should be avoided for various philosophical, ideological, or religious reasons, and refuse to use them. Usage needs to be assessed since such avoidances limit options for nutrition intervention strategies.
• Few acceptable foods and supplements. Foods and groups that are stressed and emphasized on the vegetarian diet should be noted. If very few foods or food groups are acceptable for one reason or another, or if only special foods are permitted (organic, nonprocessed, etc.) this may further limit intakes. Some vegetarians are willing to use both fortified foods and nutrient-containing dietary supplements. Use of these may have implications for health and should be recorded. Nutrient intervention strategies for increasing intakes of nutrients falling short in diets may be limited since such individuals may refuse to use fortified foods and/or dietary supplements.
• Many practices such as fasting, altered diet during illness, and use of special foods for medicinal purposes. These practices may further increase risks of nutritional inadequacy. If medical care or treatment is avoided, additional risks may accrue.

Other practices Other practices must also be considered:

• Other lifestyle practices with beneficial potential health impacts. Vegetarians have other health habits and lifestyles that alter risks for chronic diseases for the better, such as nonsmoking, abstinence from alcohol, and high levels of physical activity. Therefore, differences in their health outcomes are probably due to a range of factors, and not solely to differences in their diets.
• Lack of ongoing health surveillance by a physician. Lack of medical supervision increases the chances that preventable or treatable health problems will be dealt with expeditiously.

Personal characteristics Among these are the following:

• Nutritionally vulnerable because of age or physiological condition. The very young, the old, the rapidly growing, pregnant and lactating women, pubertal children, the elderly, and the ill and frail all fall into this group. Individuals at especially high risk are those with chronic diseases and conditions that alter nutritional needs who also have inadequate dietary intakes.
• Low weight for height. If weight for height, as measured by body mass index, is below 18.5 or if unintentional weight loss has totaled more than about 5–7 kg (10–15 pounds), there is reason for concern.
• Rapid weight loss. Unintentional loss of more than 5% of weight in a month is a cause for concern.

Beliefs Ideology is also important:

• Deeply held beliefs in alternative philosophical or religious systems that govern food choice. Some individuals feel bound to make their diets conform to their ethical, philosophical, or religious systems. This can further constrain choice and nutrient intakes.
• Membership of a quasi-philosophical or religious group that includes vegetarian diets that are not planned in line with nutritional recommendations by experts. Some groups, e.g., the Seventh-Day Adventists or certain other lacto-ovo vegetarian groups, make a conscious effort to incorporate the recommendations of expert groups, such as those of the Food and Nutrition Board/Institute of Medicine and Health Canada in English-speaking North America into the regimens they recommend. In such cases, the group support provided may be of positive benefit and help to ensure nutritional adequacy. However, at times in the past other groups have insisted on regimens that did not incorporate such recommendations. For those who are active in such groups, the group’s support may reinforce negative attitudes toward meeting such expert recommendations.

Using the characteristics above, it is usually possible to sort out those consuming vegetarian diets who are at low or no risk of inadequacy from those who may potentially have problems and need further assessment and counseling.

Current Vegetarian Eating Patterns and Practices

Until about 40 years ago, in Western countries virtually all of the common vegetarian eating patterns involved avoidance of animal flesh (meat and poultry); categorization of vegetarian patterns was relatively straightforward and consisted simply of differentiating between those who ate no animal foods at all (vegan vegetarians), those who also consumed milk and milk products (lacto vegetarians), and those who ate eggs as well (lacto-ovo vegetarians).

This simple categorization scheme broke down in the 1960s and 1970s as a result of greater exposure to the cuisines of other cultures, new Eastern religions and philosophical systems with a vegetarian tradition, and other influences, which led to the emergence of new patterns of vegetarianism. Today, myriad vegetarian eating patterns exist, and they cannot be easily described by focusing on a single dimension, such as animal food intake. Meatless and vegetarian eating patterns and life styles are growing in popularity today. They continue to be fostered by a greater availability and variety of meat alternatives and analogs for animal products.

There is also a good deal of favorable publicity about phytochemicals with supposedly beneficial health effects. At the same time, concerns about the healthfulness of animal foods have been triggered by publicity on the bovine spongiform encephalopathy (BSE) epidemic in the UK, a later epidemic of hoof and mouth disease in cattle, and most recently an epidemic of SARS spread from animals to people. Worries about saturated fat/trans fat coronary artery disease links, dietary fat and cancers, food safety, and other factors probably also contributed to the increased prevalence of vegetarian eating.

At the same time, vegetarian eating patterns are much more heterogeneous today than in the past. The availability and variety of plant foods, as well as commercially available and tasty meat analogs has greatly increased. Fortified foods today include soy milks fortified with vitamins B12 and D and a highly bioavailable form of calcium, and highly fortified breakfast cereals. These foods and nutrientcontaining dietary supplements make it easier for vegans and vegetarians to obtain nutrients that would otherwise be low or lacking.

Conformity to Nutritional Recommendations

Well-planned vegetarian diets have nutritional profiles that are in line with recent expert recommendations. A well-planned vegetarian diet pattern, if sustained throughout adulthood, may reduce risks of coronary artery and other chronic degenerative diseases associated with excessive weight. Generally, vegetarian diets tend to be low in saturated fat and cholesterol and high in complex carbohydrates, dietary fiber, magnesium, potassium, folic acid, and antioxidant nutrients such as vitamins C and E. They also tend to be relatively low in energy. Thus, the diet-related risks for a number of chronic degenerative diseases associated with intakes of these nutrients may be decreased on vegetarian diets. Some risks are clearly lower; for example, vegetarians generally tend to have lower weight for height than do nonvegetarians. Constipation tends to be less of a problem in this group, perhaps due in part to the higher intake of dietary fiber.

Conclusions 

Vegetarian diets should be planned in accordance with expert nutritional recommendations. When this is followed, such diets are healthful and nutritionally adequate. When they are not planned, the nutrients that are  likely to fall short usually differ somewhat from those on nonvegetarian diets. In some cases these deficits can be remedied by dietary counseling. In others differences between ideologies about diet and nutrient needs are such that acceptable dietary strategies cannot be found. Nutrition scientists and practitioners can help vegetarians who seek their advice by monitoring the nutritional status of high-risk individuals, by identifying food sources of specific nutrients, and by suggesting dietary modifications that may be necessary to meet individual needs when intakes fall short.

Salam

by Umaee

Source: Nutrisional Suplement (Vegetarian Diets)

Food and Drug Administration Pregnancy Categories

Food and Drug Administration Pregnancy Categories

A. Controlled studies performed in pregnant women do not demonstrate a risk to the fetus during the first trimester of pregnancy with no evidence of risk in the second or third trimesters. The possibility of fetal harm appears highly unlikely.

B. Either studies in reproducing animals do not demonstrate a fetal risk but there are no controlled studies in pregnant women, or animal reproduction studies have shown adverse effects (other than a decrease in fertility) that were not confirmed in controlled studies in pregnant women in the first trimester and there is no evidence of a risk in later trimesters.

C. Either study in animals has demonstrated adverse effects on the fetus (teratogenic, embryocidal, or other effects) and there are no controlled studies in women, or studies in women and animals are not available. These drugs should be given only if the potential benefits of the drug justify the potential or unknown risk to the fetus.

D. There is positive evidence of human fetal risk, but the benefits from administration in pregnant women may be acceptable despite the risk. For example, if the drug is needed in a life-threatening situation or for a serious disease for which safer drugs cannot be used or are ineffective, administration may be indicated.

X. Animals or human studies have demonstrated fetal abnormalities or there is evidence of risk to the fetus based on human experience, or both. The risk of the use of the drug in pregnant women clearly outweighs any possible benefit. The drug is therefore contraindicated in women who are or may become pregnant.

Salam

by Umaee

source: clinical handbook's of prescriotion drugs (WZFWS95V82ZM)

image: pregnancyandbaby.com

Understanding Food and Food–Drug Synergy

Nutrition has a unique and important role in the prevention and treatment of chronic disease. From a prevention perspective, many individuals modify their diet, even subtly, to modify their risk of chronic diseases. Some commonreasons for dietary modifications include improving blood lipid profile, controlling blood glucose, maintaining a healthy body weight, and ensuring adequate calcium in the diet to maintain a strong skeleton. While using foods to promote health seems intuitive, delineating the complex interactions
within a food and among different foods is challenging and at times perplexing.

Moreover, when combining foods with drugs, there are additional interactions, positive or negative, that can influence health outcomes. Using the diet to promote optimal health requires knowledge of the beneficial effects resulting from these interactions among foods, individual food components, and/or drugs. There are multiple interactions that can occur among foods; components within a food; components from different foods; foods and drugs; or individual food components and drugs. Because of the wide variety of interactions, there is a vast potential for synergistic relationships to be observed.

What is food synergy and food–drug synergy? In the context of this article, food synergy encompasses the following:
• The interaction of two or more components within a food or of two or more foods working together such that the potential health benefit is greater than the effect of the single component or food;
• The additive effects of multiple foods or food components that confer a health benefit;
• The ability of a food or food component to attenuate or negate an unwanted side effect of another food or food component.

Similarly, food–drug synergy includes the following:
• The interaction of a food (or food component) and a specific drug that confers a greater health benefit than either the food (or food component) or drug alone;
• The additive effects of a drug in combination with a food (or food component) that confer a health benefit;
• The ability of a food (or food component) to attenuate or negate a negative side effect of a drug.

Salam

by Umaee

source: Food Drug Synergi and Safety

image: hispanically***.com