Targeting dietary fat or glycemic load in the treatment of obesity and type 2 diabetes: a randomized controlled trial

The glycemic index issue

PURPOSE OF REVIEW

In recent years, many of the concerns surrounding the glycemic index have been addressed by methodological studies and clinical trials comparing diets carefully matched for other nutrients. These findings are reviewed together with new observational evidence for the role of the dietary glycemic index in the etiology of cardiovascular disease.

RECENT FINDINGS

The determination and classification of the glycemic index of a food product is now standardized by the International Standards Organization. Systematic studies using isoenergetic single and mixed meals have shown that glycemic index and/or glycemic load are stronger predictors of postprandial glycemia and insulinemia than carbohydrate content alone. In overweight individuals, a diet that combined modestly higher protein and lower glycemic index carbohydrates was the most effective diet for prevention of weight regain. New observational studies have reported increased risks of coronary heart disease associated with higher intakes of carbohydrates from high glycemic index foods. Epidemiological evidence has emerged linking dietary glycemic index to visceral fat and inflammatory disease mortality.

SUMMARY

There is growing recognition that replacing saturated fat with refined, high glycemic index carbohydrates increases postprandial glycemia and may be detrimental for weight control and predisposition to cardiovascular and inflammatory disease. In contrast, low glycemic index carbohydrates reduce risk.

Continuous glucose monitoring to assess the ecologic validity of dietary glycemic index and glycemic load

BACKGROUND

The circumstances under which the glycemic index (GI) and glycemic load (GL) are derived do not reflect real-world eating behavior. Thus, the ecologic validity of these constructs is incompletely known.

OBJECTIVE

This study examined the relation of dietary intake to glycemic response when foods are consumed under free-living conditions.

DESIGN

Participants were 26 overweight or obese adults with type 2 diabetes who participated in a randomized trial of lifestyle modification. The current study includes baseline data, before initiation of the intervention. Participants wore a continuous glucose monitor and simultaneously kept a food diary for 3 d. The dietary variables included GI, GL, and intakes of energy, fat, protein, carbohydrate, sugars, and fiber. The glycemic response variables included AUC, mean and SD of continuous glucose monitoring (CGM) values, percentage of CGM values in euglycemic and hyperglycemic ranges, and mean amplitude of glycemic excursions. Relations between daily dietary intake and glycemic outcomes were examined.

RESULTS

Data were available from 41 d of monitoring. Partial correlations, controlled for energy intake, indicated that GI or GL was significantly associated with each glycemic response outcome. In multivariate analyses, dietary GI accounted for 10% to 18% of the variance in each glycemic variable, independent of energy and carbohydrate intakes (P < 0.01).

CONCLUSIONS

The data support the ecologic validity of the GI and GL constructs in free-living obese adults with type 2 diabetes. GI was the strongest and most consistent independent predictor of glycemic stability and variability.

Dietary approaches to the treatment of obesity

Various dietary strategies can effectively reduce weight, as shown by this review. Those that are coupled with behavior therapy and ongoing support tend to produce longer lasting effects. Improvements in health parameters are observed with each dietary strategy. Improvements in diabetes and CVD risk factors have been observed with diets ranging from 10% fat to 45% fat. HP diets seem to be particularly effective in reducing fat mass and TAG, especially in individuals with dyslipidemia and who are at risk for type 2 diabetes. Likewise, LC diets have been shown to be effective in decreasing TAG and VLDL and increasing HDL. Although low-GI diets do not seem to be superior to any other diet for weight loss, there is evidence to suggest that they may provide some metabolic benefit for those with type 2 diabetes. Clearly, all of these diets have benefits but they can be realized only when they are followed. A common theme across studies is poor long-term adherence and weight regain. Dansinger and colleagues found a strong association between diet adherence and clinically significant weight loss, suggesting that “sustained adherence to a diet” rather than “following a certain type of diet” is the key to successful weight management.

Decreases in dietary glycemic index are related to weight loss among individuals following therapeutic diets for type 2 diabetes

This study assessed the effect of changes in glycemic index (GI) and load (GL) on weight loss and glycated hemoglobin (HbA1c) among individuals with type 2 diabetes beginning a vegan diet or diet following the 2003 American Diabetes Association (ADA) recommendations. The study was a 22-wk, randomized trial of 99 participants with type 2 diabetes who were counseled to follow 1 of 2 diet treatments. GI and GL changes were assessed based on 3-d dietary records. The relationships between GI/GL and changes in weight and HbA1C were calculated. In an intention-to-treat analysis (n = 99), the vegan group reduced GI to a greater extent than the ADA group (P < 0.05), but GL was reduced further in the ADA than the vegan group (P < 0.001). GI predicted changes in weight (P = 0.001), adjusting for changes in fiber, carbohydrate, fat, alcohol, energy intake, steps per day, group, and demographics, such that for every point decrease in GI, participants lost ~0.2 kg (0.44 lb). GI was not a predictor for changes in HbA1C after controlling for weight loss (P = 0.33). Weight loss was a predictor of changes in HbA1C (P = 0.047). GL was not related to weight loss or changes in HbA1C. A low-GI diet appears to be one of the determinants of success of a vegan or ADA diet in reducing body weight among people with type 2 diabetes. The reduction of body weight, in turn, was predictive of decreasing HbA1C.