Role in Nutritional Management of Diabetes

Diabetes mellitus is characterized by either an absolute or relative lack of insulin, which has short-term and long-term consequences. Diabetic people may develop both microvascular complications (mainly affecting the eyes, kidneys, and nerves) and macrovascular complications (essentially accelerated development of atherosclerosis presenting mainly as heart attack and peripheral vascular disease). Medical management aims to replace the insulin, or modulate its production or efficacy using oral (hypoglycemic) drugs, in a metabolic environment enhanced by good control of diet and body composition. Medical management also aims to achieve early detection of complications and other risk factors for cardiovascular disease by regular testing of blood and urine biochemical variables and blood pressure and by regular physical examination of the eyes, neurological, and cardiovascular systems.

Control of dietary energy intake (in relation to the varying demands for growth, maintenance, physical activity, etc.) remains the key feature of dietary control affecting metabolic fluxes, blood glucose levels, and body weight. Views on the appropriate proportional sources of energy from fat, carbohydrate, and protein have changed enormously over the last century from seriously energy-restricted high-fat diets (with percentage energy from fat as high as 70% raising some doubts about the level of compliance) through to very high-carbohydrate diets (sometimes 60–65% energy from carbohydrate) used in specialist centers in the US. Today, for most diabetic patients in most countries the target is to achieve 50–55% energy from carbohydrate sources. 

Prior to the 1970s, when the move towards high-carbohydrate diets began, the high fat content of the diet along with less tight blood glucose (and urine glucose) control than is customary today was partly responsible for the high relative mortality from cardiovascular disease seen among diabetic patients. At that time young male diabetics were up to nine times more likely to die from heart attack than matched nondiabetic individuals. Reduction of fat in the diet and achievement of an optimal distribution from saturated, monounsaturated, and polyunsaturated sources (<10%, 10–20%, and no more than 10%, respectively, for patients with diabetes in the UK) remain a major aspect of dietary management of diabetic people in order to reduce the risk of developing coronary heart disease.

Control of blood glucose is critical in order to achieve avoidance of prolonged periods of hyperglycemia, which is associated with glycation of proteins and the risk of development of microvascular complications, and avoidance of hypoglycemia with its attendant risks of coma. In day-to-day practice, the avoidance of hypoglycemia is very important to patients and any new method of achieving normalization of blood glucose profiles is an advance. Dietary fiber offered such an advance from the mid 1970s when some forms (notably isolated polysaccharides such as guar gum, a glucomannan, and pectin, polygalacturonic acid) were shown to reduce the area under the blood glucose and insulin curves after acute test meals. Subsequent long-term
(6-week) clinical trials showed that diets high in foods containing soluble dietary fiber, such as beans, oats, and barley, were more effective in reducing the area under the 24-h blood glucose profiles than diets containing more high-fiber foods based on wheat products.

Research in this area led David Jenkins to describe (in 1981) the concept of the ‘glycemic index’ (GI) which is a numerical expression of the ability of a food to raise blood glucose levels. In practice it is measured by comparing the blood glucose response to a 50-g carbohydrate portion of food with the response to 50 g glucose (in some papers the comparison is with a 50-g carbohydrate portion of bread). The dietary fiber (especially soluble fiber) content of a food slows down the rate of digestion and absorption of starch in foods giving flatter blood glucose responses and a lower GI; however, the structure of the starch (whether amylose or amylopectin) influences its rate of degradation and the extent to which the starch granules are hydrated by processing (including cooking) is also important.
The physical structure of the food (particularly the extent to which plant cells are intact), the presence of fat, which may slow gastric emptying, and the presence of some ‘antinutrient’ substances may all influence the GI. Low-GI diets have been shown in many clinical trials to improve important variables that are secondary indicators of blood glucose control, and to reduce blood lipids. Low-GI diets may be particularly helpful to patients who are frequently troubled by episodes of hypoglycemia though adequate proof of this is still awaited. 

Low-GI diets are not just relevant to treatment of diabetes but have been shown in two large-scale epidemiological surveys published in 1997 to result in a significant reduction in the risk of development of maturity onset (type 2) diabetes in middle-aged American men and women. Thus, there is good reason to believe that there should be greater emphasis on the GI of diabetic diets and the fiber content, as well as emphasis on GI for those at risk of developing diabetes, especially the older obese person. Expert committees in many developed countries of the world have set target values for dietary fiber intake for diabetic patients (e.., the American Diabetes Association (ADA) recommends 20–35 g day-1 total dietary fiber by the AOAC method) and many, especially the Australian Diabetes Association and with the notable exception of the ADA, have recommended an increase in low-GI foods.

In 2003 even Diabetes UK (the UK Diabetes Association) noted that there might be merit in taking account of GI in dietary management for those with diabetes. Some physicians believe that the GI of foods is too complex an issue for patients to grasp, but in essence simply requires a partial substitution of bread and potatoes with pasta products, an increased use of high-fiber breakfast cereals including oats, increased use of beans and lentils, and emphasis on the use of temperate fruits (e.g., apples and pears).
Obesity (body mass index (weight in kilograms divided by height in meters squared) in excess of 30 kgm-2) is becoming more prevalent in developing countries and attracts an increased risk of the development of diabetes mellitus; a high proportion of established type 2 diabetics are obese and overweight. In the popular diet book ‘The F-Plan Diet,’ published in 1982, Audrey Eyton claimed that dietary fiber would help people lose weight by a number of mechanisms including reducing the efficiency of dietary energy absorption and by making people feel full for longer after meals thus having an overall effect on reducing food intake. At the time of publication these ideas were hypothetical - subsequent investigation has shown that increasing fiber intake two- or threefold by a variety of dietary changes can increase fecal energy losses by 75–100 kcal day-1. 

Studies on the effects of dietary fiber on postprandial satiety where experimental meals are carefully designed to differ little except for fiber content have given variable results. However, there is a clear effect of fiber on chewing (the number of chews necessary to eat the same energy equivalent of food) where high- and low-fiber types of commonly consumed foods are eaten and this may have an important satiating effect. Clinical trials of highfiber weight loss regimens have given variable results. Double-blind placebo-controlled trials using pressed barley fiber and pectin tablets compared to a starch control have been undertaken in Scandinavia and have demonstrated statistically significantly greater weight losses in the fiber-treated groups up to 26 weeks of treatment. It seems reasonable to conclude that under some conditions the right kind of high-fiber diet can facilitate weight loss, but may not always do so.

Diabetic people are more likely to have dyslipidemia than nondiabetic people. When control of diabetes is lost, patients may demonstrate gross hypertriglyceridemia due to increased production of very-low-density lipoprotein (VLDL) particles in the liver as a consequence of the increased flux of free fatty acids from the peripheral tissues. At the same time total and LDL cholesterol may be raised. Improvement in diabetic control often achieves normalization of blood lipids, but where hyperlipidemia persists there may be a place for use of dietary fiber, especially soluble fiber, and especially oat Beta-glucan-containing foods as an adjunct to dietary and pharmacological therapy (see above).


by Umaee
Source: Nutritional Supplement
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