Written by Chrystal Moulton, Staff Writer. Low glycemic diet significantly reduces BMI and insulin resistance.
Obesity is a growing public health issue affecting millions of people worldwide. So far, researchers have not been able to agree on the best plan of action to specifically help obese individuals lose weight and maintain good health.(1,2) Information on the effects of glycemic index on weight has also been inconsistent. However, in the current study (1), researchers wanted to determine whether glycemic index had an effect on weight loss.
The GLYNDIET study was designed as a randomized, parallel-controlled clinical trial lasting for 6 months. The study was designed with three objectives.(2) The primary objective was to evaluate the effect of glycemic index on weight loss, satiety, glucose and insulin metabolism, as well as other biomarkers of stress and inflammation. Participants were recruited from outpatient obesity clinics in Spain. Eligible subjects were between the ages of 30-60 years old with a body mass index (BMI) between 27-35 kg/m2. Subjects were randomized into 1 of 3 diet intervention groups:
» Low glycemic diet = 40% of energy from fat, 42% from low glycemic index carbohydrates, and 18% energy from protein (glycemic index = 34)
» High glycemic diet = 40% of energy from fat, 42% from high glycemic index carbohydrates, and 18% energy from protein (glycemic index = 62)
» Low-fat diet = 30% of energy from fat, 52% from high glycemic index carbohydrates, and 18% energy from protein (glycemic index = 65)
All diet interventions had equal amounts of calories but differed in the glycemic index of carbohydrates. Total fiber also did not differ between the protocols. Dietitians met individually with volunteers to advise what foods were in compliance with their designated diet. Volunteers were also given a folder with recommendations and bi-weekly menus. Physical examinations were performed at baseline, 15 days, and monthly thereafter, until the end of the trial. Dietary assessment and physical activity was performed at baseline, 1st, 3rd, and 6th month of the protocol. Satiety and blood parameters were evaluated at baseline and at the end of the trial.
In all, a total of 94 eligible participants who were randomized into the 3 diet intervention groups completed the trial. Baseline characteristics between groups were not significantly different. At weeks 16, 20, and 24, the low glycemic diet group showed significant decreases in BMI compared to the low-fat diet group (p<0.05). Overall decrease in BMI, at the end of the study, was very significant in the low glycemic diet group compared to the low-fat diet group (p<0.01). Furthermore, insulin resistance significantly decreased in the low glycemic diet compared to the low-fat diet after 6 months (p<0.005). Significant reduction in hunger was also observed in the low glycemic diet group compared to the high glycemic diet group (p=0.048).
Table 1. Changes in insulin after 6 months
| Baseline | After 6 months | |
| Fasting plasma insulin (mU/mL) ‡ | ||
| LGI diet | 5.96 ± 0.49 | -1.41 ± 0.34* |
| HGI diet | 4.44 ± 0.48 | -1.10 ± 0.35 |
| LF diet | 4.94 ± 0.49 | -0.09 ± 0.34 |
| HOMA-IR † | ||
| LGI diet | 1.20 ± 1.01 | -0.62 ± 0.54* |
| HGI diet | 0.90 ± 0.69 | -0.58 ± 0.33 |
| LF diet | 1.07 ± 1.08 | -0.39 ± 0.42 |
‡ significant difference between diet groups p= 0.019; † p-value between diet groups (p=0.009); * significant difference compared to LF diet (p<0.005). LF- low-fat, LGI- low glycemic index, HGI- high glycemic index. HOMA-IR is a clinical test for insulin resistance.
Overall, low glycemic carbohydrate diet was more effective in promoting weight loss than a low-fat diet. Furthermore, insulin sensitivity improved in the low glycemic diet group compared to the low fat diet group. Despite the positive results, researcher mentioned that the data could not be applied to obese individuals with type 2 diabetes as that population was not represented in the current study. Furthermore, subjects in the study were accustomed to a Mediterranean diet, and thus may not be generalizable to non-Mediterranean populations. Further research will be needed to confirm the current results.
Source: Juanola-Falgarona, Martí, et al. “Effect of the glycemic index of the diet on weight loss, modulation of satiety, inflammation, and other metabolic risk factors: a randomized controlled trial.” The American journal of clinical nutrition 100.1 (2014): 27-35.
© 2014 American Society for Nutrition
Posted May 22, 2014.
Chrystal Moulton BA, PMP, is a 2008 graduate of the University of Illinois at Chicago. She graduated with a bachelor’s in psychology with a focus on premedical studies and is a licensed project manager. She currently resides in Indianapolis, IN.
References:
- Juanola-Falgarona M, et al. Effect of the glycemic index of the diet on weight loss, modulation of satiety, inflammation, and other metabolic risk factors: a randomized controlled trial. Am J Clin Nutr. 2014 Apr 30.
- Juanola-Falgarona M, et al. Design and methods of the GLYNDIET study; assessing the role of glycemic index on weight loss and metabolic risk markers. Nutr Hosp. 2013 Mar-Apr;28(2):382-90.
