Perspective: Does Glycemic Index Matter for Weight Loss and Obesity Prevention? Examination of the Evidence on “Fast” Compared with “Slow” Carbs

Abstract

High-glycemic index (high-GI) foods (so-called fast carbs) have been hypothesized to promote fat storage and increase risk of obesity. To clarify whether dietary GI impacts body weight, we searched PubMed and the Cochrane Database of Systematic Reviews for observational studies reporting associations between BMI and dietary GI, and for meta-analyses of randomized controlled trials (RCTs) comparing low-GI and high-GI diets for weight loss. Data on 43 cohorts from 34 publications, totaling 1,940,968 adults, revealed no consistent differences in BMI when comparing the highest with the lowest dietary GI groups. In the 27 cohort studies that reported results of statistical comparisons, 70% showed that BMI was either not different between the highest and lowest dietary GI groups (12 of 27 cohorts) or that BMI was lower in the highest dietary GI group (7 of 27 cohorts). Results of 30 meta-analyses of RCTs from 8 publications demonstrated that low-GI diets were generally no better than high-GI diets for reducing body weight or body fat. One notable exception is that low-GI diets with a dietary GI at least 20 units lower than the comparison diet resulted in greater weight loss in adults with normal glucose tolerance but not in adults with impaired glucose tolerance. While carbohydrate quality, including GI, impacts many health outcomes, GI as a measure of carbohydrate quality appears to be relatively unimportant as a determinant of BMI or diet-induced weight loss. Based on results from observational cohort studies and meta-analyses of RCTs, we conclude that there is scant scientific evidence that low-GI diets are superior to high-GI diets for weight loss and obesity prevention.

The association of Carbohydrate Quality Index with cardiovascular disease risk factors among women with overweight and obesity: A cross-sectional study

“…Indeed, in previous studies, fiber intake was associated with obesity, WHR, WC, body weight, and BMI ( 54 , 56 , 63 – 65 ). Also, an association was seen between GI with body weight and obesity ( 66 ). In previous studies, an inverse association was seen between whole grains with central obesity and WC ( 67 , 68 ).…”

Competing paradigms of obesity pathogenesis: energy balance versus carbohydrate-insulin models

“…Furthermore, the typical prospective design comparing baseline diet with future weight change will not detect prior changes that have reached steady state by the time of the dietary assessment. In this situation, bias toward null associations may ensue; thus, the lack of consistent association involving GI and GL in cohort studies is difficult to interpret [123]. To better simulate an interventional study, the relationship of change in diet to change in weight over time can be examined.…”

Refined Grain Intake and Risk of Type 2 Diabetes

“…37 None of the cohort studies presented in Figure 2 adjusted for GI or GL in their statistical models, and thus it is possible that this could have influenced the results. However, application of GI values of foods from diet records and food frequency questionnaires used in all of the cohort studies is problematic, 39 and this may be especially true for white rice, with reported GI values ranging from 17 to 94. 40 Moreover, high consumption of white rice among Asian populations may not fully explain the higher T2D risk because high intake of white rice was not consistently associated with increased T2D risk across all Asian cohorts.…”