Dietary glycemic index: health implications.

Weight loss can be achieved by any means of energy restriction, but the challenge is to achieve sustainable weight loss and prevent weight "creep" without increasing the risk of chronic disease. The modest success of low fat diets has prompted research on alternative dietary strategies, including high protein diets and low glycemic index (GI) diets. Conventional high carbohydrate diets, even when based on wholegrain foods, increase postprandial glycemia and insulinemia and may compromise weight control via mechanisms related to appetite stimulation, fuel partitioning, and metabolic rate. This paper makes the case for the benefits of low glycemic index diets over higher protein diets. Both strategies are associated with lower postprandial glycemia, and both are commonly labeled as "low glycemic load," but the long-term health effects are likely to be different. A large body of evidence, which now comprises observational prospective cohort studies, randomized controlled trials, and mechanistic experiments in animal models, provides robust support for low GI carbohydrate diets in the prevention of obesity, diabetes, and cardiovascular disease. Although lower carbohydrate, higher protein diets increase the rate of weight loss, cohort studies and meta-analyses of clinical trials suggest the potential for increased mortality.

Carbohydrates--the good, the bad and the whole grain.

Weight loss can be achieved by any means of energy restriction, but the challenge is to achieve sustainable weight loss and prevent weight 'creep' without increasing the risk of chronic disease. The modest success of low fat diets has prompted research on alternative dietary strategies including high protein diets and low glycemic index (GI) diets. Conventional high carbohydrate diets, even when based on whole grain foods, increase postprandial glycaemia and insulinemia and may compromise weight control via mechanisms relating to appetite stimulation, fuel partitioning and metabolic rate. This paper makes the case for the benefits of low glycemic index diets over higher protein diets. Both strategies are associated with lower postprandial glycemia and both are commonly labelled as 'low glycemic load' but the long-term health effects are likely to be different. There is now a large body of evidence comprising observational prospective cohort studies, randomised controlled trials and mechanistic experiments in animal models, that provides robust support for low GI carbohydrate diets in the prevention of obesity, diabetes and cardiovascular disease. While lower carbohydrate, higher protein diets also increase the rate of weight loss, cohort studies and meta-analyses of clinical trials suggest the potential for increased mortality.

Glycemic index, glycemic load, and chronic disease risk--a meta-analysis of observational studies.

BACKGROUND: Inconsistent findings from observational studies have prolonged the controversy over the effects of dietary glycemic index (GI) and glycemic load (GL) on the risk of certain chronic diseases. OBJECTIVE: The objective was to evaluate the association between GI, GL, and chronic disease risk with the use of meta-analysis techniques. DESIGN: A systematic review of published reports identified a total of 37 prospective cohort studies of GI and GL and chronic disease risk. Studies were stratified further according to the validity of the tools used to assess dietary intake. Rate ratios (RRs) were estimated in a Cox proportional hazards model and combined by using a random-effects model. RESULTS: From 4 to 20 y of follow-up across studies, a total of 40 129 incident cases were identified. For the comparison between the highest and lowest quantiles of GI and GL, significant positive associations were found in fully adjusted models of validated studies for type 2 diabetes (GI RR = 1.40, 95% CI: 1.23, 1.59; GL RR = 1.27, 95% CI: 1.12, 1.45), coronary heart disease (GI RR = 1.25, 95% CI: 1.00, 1.56), gallbladder disease (GI RR = 1.26, 95% CI: 1.13, 1.40; GL RR = 1.41, 95% CI: 1.25, 1.60), breast cancer (GI RR = 1.08, 95% CI: 1.02, 1.16), and all diseases combined (GI RR = 1.14, 95% CI: 1.09, 1.19; GL RR = 1.09, 95% CI: 1.04, 1.15). CONCLUSIONS: Low-GI and/or low-GL diets are independently associated with a reduced risk of certain chronic diseases. In diabetes and heart disease, the protection is comparable with that seen for whole grain and high fiber intakes. The findings support the hypothesis that higher postprandial glycemia is a universal mechanism for disease progression.

Comparison of 4 diets of varying glycemic load on weight loss and cardiovascular risk reduction in overweight and obese young adults: a randomized controlled trial.

BACKGROUND: Despite the popularity of low-glycemic index (GI) and high-protein diets, to our knowledge no randomized, controlled trials have systematically compared their relative effects on weight loss and cardiovascular risk. METHODS: A total of 129 overweight or obese young adults (body mass index, > or =25 [calculated as weight in kilograms divided by the square of height in meters]) were assigned to 1 of 4 reduced-fat, high-fiber diets for 12 weeks. Diets 1 and 2 were high carbohydrate (55% of total energy intake), with high and low GIs, respectively; diets 3 and 4 were high protein (25% of total energy intake), with high and low GIs, respectively. The glycemic load was highest in diet 1 and lowest in diet 4. Changes in weight, body composition, and blood chemistry profile were studied. RESULTS: While all groups lost a similar mean +/- SE percentage of weight (diet 1, -4.2% +/- 0.6%; diet 2, -5.5% +/- 0.5%; diet 3, -6.2% +/- 0.4%; and diet 4, -4.8% +/- 0.7%; P = .09), the proportion of subjects in each group who lost 5% or more of body weight varied significantly by diet (diet 1, 31%; diet 2, 56%; diet 3, 66%; and diet 4, 33%; P = .01). Women on diets 2 and 3 lost approximately 80% more fat mass (-4.5 +/- 0.5 [mean +/- SE] kg and -4.6 +/- 0.5 kg) than those on diet 1 (-2.5 +/- 0.5 kg; P = .007). Mean +/- SE low-density-lipoprotein cholesterol levels declined significantly in the diet 2 group (-6.6 +/- 3.9 mg/dL [-0.17 +/- 0.10 mmol/L]) but increased in the diet 3 group (+10.0 +/- 3.9 mg/dL [+0.26 +/- 0.10 mmol/L]; P = .02). Goals for energy distribution were not achieved exactly: both carbohydrate groups ate less fat, and the diet 2 group ate more fiber. CONCLUSION: Both high-protein and low-GI regimens increase body fat loss, but cardiovascular risk reduction is optimized by a high-carbohydrate, low-GI diet.

Dietary approaches to overweight and obesity.

For years dietary guidelines for the treatment of overweight and obesity have advised a low-fat, high carbohydrate diet. Recent meta-analyses have shown that weight loss achieved with ad libitum low-fat diets is typically in the range of 3-4 kg. Although clinically significant, this weight loss is modest, usually regained on cessation of the intervention and the low-fat messages have not impacted on the ever increasing rates of overweight and obesity. Alternative approaches include low-glycemic index and high protein diets. Both effectively reduce the glycemic load of the diet and early studies suggest they may be effective in increasing satiety, reducing ad libitum energy intake and may improve fat oxidation by reducing insulin demand. Both approaches can be used within the context of a reduced-fat diet, with evidence emerging to suggest this may improve weight and body composition outcomes.