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Abstract
Background: Adipose tissue inflammation is a possible link between obesity and type 2 diabetes mellitus. In obesity adipose tissue macrophages (ATMs) are thought to undergo a phenotypic switch to a pro-inflammatory state resulting in chronic low-grade inflammation that is correlated with insulin resistance. The mechanism producing this phenotypic switch is unclear. This pilot study seeks to explore the hypothesis that the pro-inflammatory state of ATMs in obesity occurs due to an environment of metabolic dysfunction and nutrient excess characterized by elevated levels of free fatty acids, glucose, and insulin.
Methods: Sixteen overweight or obese individuals with evidence of insulin resistance were randomized to follow either a control diet based on the United States Department of Agriculture’s 2010 Dietary Guidelines for Americans or the Anti-Inflammatory Milieu (AIM) diet designed to reduce the exposure of ATMs to the hypothesized pro-inflammatory stimuli. The AIM diet had a low glycemic load, low insulinemic index, and a low content of long-chain fatty acids. Subjects followed the diet for twelve weeks while attending bi-weekly group meetings. At baseline and at the intervention conclusion subjects were tested for markers of metabolic activation on ATMs, and adipose tissue expression of pro-inflammatory and anti-inflammatory markers. An exit survey was used to conduct an exploratory analysis of the feasibility for free-living individuals to adopt each study diet.
Results: No significant differences between the AIM and USDA diet groups were observed in the changes in levels of metabolic activation markers or number of ATMs, or in adipose tissue expression of inflammatory markers. Weight loss occurred in all but one of the sixteen subjects with an average weight change in the AIM group of -5.8 ± 3.9 kg and an average weight change in the USDA group of -5.0 ± 3.2 kg. A non-significant trend towards a moderate increase in the average numbers of ATM and downstream inflammatory markers was observed in each diet group. No significant differences were seen in subject perceptions of the study diet experience between diet groups. Subjects in each diet group tended to regard the diets as feasible and satisfying.
Discussion: This study suggests that a diet aimed at minimizing daily exposure of adipose tissue to glucose, insulin, and long-chain fatty acids provides no unique benefit to decreasing adipose tissue inflammation compared with the generally recommended 2010 USDA Dietary Guidelines. Weight loss among subjects in each diet group may have contributed to potential increases in inflammatory markers. Beyond the presumed benefit of weight loss, it remains uncertain if either study diet is beneficial or harmful in the long term with regard to adipose tissue inflammation and associated co-morbidities. Overall the study participants were a motivated group of individuals who felt that they benefited from both study diets, and who are likely to continue the study diets in the future.
