GI and Weight Loss and Appetite

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Although many of the popular diet books promote the use of low GI foods in their diets, there is minimal evidence to suggest that a low GI diet contributes to weight loss. The diet books claim that high GI foods are digested rapidly causing blood glucose to surge and an oversecretion of insulin, both contributing to insulin resistance, increased appetite, overeating, and weight gain. However, figure 1 illustrates the glucose response to carbohydrate loads containing 50 g of glucose from dextrose, rice, corn, potato, and bread [36]. Although the peak responses differ slightly they occur at approximately the same time. Furthermore, the actual change in glucose is only ~20mg/dl (1 mmol/l). Reporting the results in percentage of change as is done with the GI often distorts the small to modest changes in glycemic responses. Actual changes in postprandial glucose levels would be more useful.

In reviewing weight changes in the 12 studies in persons with type-2 diabetes in table 2, one study reported more weight loss on the high GI diet, 1 study reported more weight loss on the low GI diet although the calories were also less in that arm, and 10 studies reported no differences in weight loss. Heilbronn et al. [25] asked the question does reducing the GI of a high carbohydrate diet confer a benefit during energy restriction. After 4 weeks of an energy-restricted diet, subjects were randomized to a low or a high GI diet. There was no difference in weight loss between the groups.

Raben [37] reviewed weight loss on high versus low GI diets and concluded that no clear pattern of difference between low and high GI in terms of decreased food intake or weight loss is shown. In 20 studies (6 days to 6 months in duration), the average weight loss in 4 studies was 1.5 kg on the low GI diet, in 2 studies 1.6 kg on a high GI diet, and in 14 studies there was no difference in weight loss between the high and the low GI diets. It was concluded that there was no evidence that low GI foods are superior to high GI foods for long-term body weight control.

On the other hand, Pawlak et al. [38] concluded that based on epidemio-logical evidence and a small weight loss study in adolescents there was support for a role of the GI in disease prevention and treatment, weight loss and satiety. Their hypothesis is that recommended lower intakes of dietary fat for weight loss has actually contributed to the increase in obesity, and that reduced dietary fat results in compensatory increases in the consumption of high GI carbohydrate, principally refined starchy foods and concentrated sugar. Because they are rapidly digested such foods cause a large increase in postprandially glucose and insulin causing a decrease in satiety and weight gain.

The recently released US Dietary Guidelines for Americans, however, strongly recommend calorie control to manage body weight. They state: 'When it comes to weight control, calories do count - not the proportions of carbohydrate, fat and protein in the diet. . . . The healthiest way to reduce

Time (min)

Fig. 1. Glucose response to 50 g of digestible carbohydrate from dextrose, rice, corn, potato and bread. Reprinted with permission from Crapo et al. [31].

Time (min)

Fig. 1. Glucose response to 50 g of digestible carbohydrate from dextrose, rice, corn, potato and bread. Reprinted with permission from Crapo et al. [31].

calorie intake is to reduce one's intake of added sugars, solid fats, and alcohol - they all provide calories, but they do not provide essential nutrients.'

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