Seven Day Blackberry Feeding Lowers the Respiratory Quotient in Males And Improves Insulin Sensitivity

Abstract

Berries and/or berry extracts have been shown to reduce adiposity in animal models consuming a high fat diet, possibly due to alterations in energy substrate utilization. The objective of this research was to test the effect of berry intake on energy substrate use in humans consuming a high fat diet. In a placebo controlled crossover study design with 2 treatment periods, overweight/obese men (n=27) were fed a high fat diet (40% en fat) containing either 600 g/d blackberries (BB, 1200 mg/d flavonoids) or 600 g/d sweetened gelatin (calorie matched, flavonoid‐free control) for 1 week prior to a meal‐based glucose tolerance test (MTT) (75 g of sugar from waffle and syrup) and 24h stay in a room‐sized indirect calorimeter. Across the 24 hr period, the average RQ was significantly lower with the BB treatment (0.810 vs. 0.817, BB vs. gelatin, p=0.040) while energy expenditure (EE) was not different (2485 vs. 2439 kcal, p=0.11, BB vs. gelatin treatments). During the MTT, AUC of glucose was not different between BB and gelatin treatment (3488 vs. 4070 mg*min/dL, respectively, p=0.12). However, AUC of insulin was lower after consumption of BB compared to gelatin (6485 vs. 8245 uU*min/ml, p=0.0002). During this 4 hr MTT period, EE was not statistically different between the 2 treatments (BB, 452 kcal; gelatin, 440 kcal, p=0.20). However, there was a significant reduction in the RQ with BBs (BB, 0.84; gelatin, 0.85, p=0.004) which was independent of age or BMI. During the 4 hr period that started with dinner, the comparisons were similar, where a reduction in RQ and an increase in fat oxidation were observed with the BB treatment (0.818 vs. 0.836, 28 vs. 24 g, respectively; BB vs. gelatin treatments) with no difference in EE (493 vs. 483, p=0.26, BB vs. gelatin). The 24 hr stay in the calorimeter included 30 min of treadmill walking in the afternoon following lunch. During this time period, again there was a significant reduction in RQ with BB treatment (0.856 vs 0.871; BB vs. gelatin). Blackberry consumption may contribute to increased fat oxidation and improved glucose sensitivity in overweight males on a high fat diet. This is the first study to demonstrate the potential for blackberries to combat the metabolic effects of a high fat diet in human subjects. Mechanistic studies aimed at describing biochemical changes leading to these observations are underway.Support or Funding InformationSupported by the U.S. Department of Agriculture.