According to Marian Neuhouser, PhD, of the Fred Hutchinson Cancer Research Center in Seattle, and colleagues, compared with a high-glycemic load diet, one with a low-glycemic load was associated with a significant reduction in high-sensitivity C-reactive protein (P=0.02) in people with a body mass index of 28 to 40 kg/m2. There was also a trend toward an increase in adiponectin (P=0.06), a beneficial hormone that increases insulin sensitivity and fatty acid oxidation, the researchers reported.
Foods with low glycemic loads include various fruits and vegetables, cheese, milk, and yogurt and the participants' weight remained steady throughout the study.
"Although weight loss and maintenance of energy balance should remain one of the critical components of any lifestyle intervention for the overweight and obese, the results from this study suggest that diet composition, particularly carbohydrate quality, plays a key role," they wrote.
"Adhering to a low-glycemic load diet may help individuals at risk of obesity-related metabolic dysfunction improve their overall health."
High-glycemic load diets lead to rapid increases in blood glucose and insulin concentrations, whereas low-glycemic load diets result in less dramatic responses. Low-glycemic load diets have been shown to improve insulin resistance and glucose homeostasis in patients with diabetes, but it had been unknown whether such diets could improve the health of people without diabetes or other conditions.
So Neuhouser and colleagues conducted the Carbohydrates and Related Biomarkers Study, a randomized, crossover study comparing the effects of low- and high-glycemic load diets on biomarkers of inflammation and adiposity in healthy adults. The study included 80 participants, half who had a normal weight (BMI 18.5 to 24.9 kg/m2) and half who were overweight or obese.
All completed two 28-day feeding periods in random order; the researchers provided all foods. The diets were designed to maintain weight and contained the same macronutrient content (15% protein, 30% fat, and 55% carbohydrate).
The diets during the two periods differed by glycemic load (250 or 125) and by fiber content (28 and 55 grams/day for the high-glycemic and low-glycemic load diets, respectively).
The researchers measured body composition and serum levels of various biomarkers of inflammation and obesity, including high-sensitivity C-reactive protein (hs-CRP), amyloid A, interleukin-6, leptin, and adiponectin. Adherence was similarly high for both diets.
In the analysis of all participants, there were no differences among the biomarkers based on diet. The analysis stratified by baseline body fat mass, however, yielded some differences.
In the participants with low body fat mass (less than 32% for women and 25% for men), levels of hs-CRP were higher but not significantly so (P=0.09) and interleukin-6 concentrations were significantly higher (P=0.02) with the low-glycemic load diet.
The researchers said that it was unclear why the low-glycemic load diet might have increased inflammation in these individuals.
"It is possible that other, unmeasured aspects of the controlled diet that were new to them triggered slight increases in inflammation," they wrote.
For individuals with high body fat mass, the low-glycemic load diet was associated with a significant 0.24-mg/L reduction in hs-CRP and a nonsignificant 0.21-mg/L increase in adiponectin. Both differences are substantial, according to the researchers.
"We interpret the study findings to suggest that low-glycemic load diets influence two critical mechanisms linked to adverse health outcomes: inflammation and synthesis of adipose-derived peptides," they wrote.
"Our observation that the low-glycemic load diet reduced inflammation biomarkers only in the overweight and obese, but not normal weight participants, suggests that those who may already be slightly insulin resistant or at risk for insulin resistance may benefit the most from a low-glycemic load dietary pattern." Another reason that might explain the possible beneficial effects of the low-glycemic load diet is the difference in fiber content, which was about twice as high in the low-glycemic load diet.
"Fiber is well known to be inversely associated with inflammatory factors, although the exact mechanism is unclear," the authors wrote.
They acknowledged some limitations of the study, including the young age of most of the participants (mean age 29.6), the possibility that some deviations from the study diets were not reported, and the limited number of biomarkers examined.
- This study shows that a low glycemic diet reduced high-sensitivity CRP and tended to increase adiponectin serum concentrations in participants with high body fat mass.
- Note that low-glycemic load diets improve insulin resistance and glucose homeostasis in individuals with diabetes.
Neuhouser M, et al "A low-glycemic load diet reduces serum C-reactive protein and modestly increases adiponectin in overweight and obese adults" J Nutr 2012; DOI:10.3945/jn.111.149807.