Seven Day Blackberry Feeding Affects the Energy Substrate Profile in Males And Improves Insulin Sensitivity

In the obesogenic environment, bioactive food components show promise in ameliorating metabolic dysfunction related to type 2 diabetes and metabolic syndrome. Preliminary animal studies on berries indicate that body composition, weight, and clinical markers of glucose regulation may be positively impacted by consumption of anthocyanin rich blue and black raspberries. The aim of our pilot study was to determine the influence of blackberry feeding on clinical markers related to glucose regulation as well as substrate utilization measured by indirect calorimetry in humans. This randomized, controlled, cross‐over study was conducted at the USDA Beltsville Human Nutrition Research Center. Fifteen overweight or obese male subjects (age range 31–69) were fed a controlled, high fat diet (40% en from fat) for 7 days that included either 600 g/d of fresh blackberries (BB) or an isocaloric amount of gelatin (control). There was a 7 day washout period between treatments. For the last 24 hours of each treatment period, subjects remained inside of a room‐sized indirect calorimeter, where a breakfast meal tolerance test (MTT, 75 g of sugar from waffle and syrup) was administered with their treatment, and timed blood draws (−15, 0, 30, 60, 90, 120, 180, 240 min) were collected and analyzed for glucose, insulin, and nonesterified fatty acids. Energy expenditure (EE), substrate oxidation, and respiratory quotient (RQ) were measured from gas exchange for the total 24 hr period as well as specific isolated time periods. Data were analyzed with mixed models using BMI, age, and treatment order, and their interactions with treatment as covariates. AUC of glucose was not different between BB and gelatin treatment (4286 vs 5027 mg·dL −1 ·min, respectively, p=0.17). However, AUC of insulin was lower after consumption of BB compared to gelatin (5322 vs 7325 uU·ml −1 ·min, p=0.008). During this 4 hr MTT period, EE was not different between the 2 treatments (BB, 405 kcal; gelatin, 399 kcal, p=0.79). However, preliminary data suggest that an interaction between BMI and treatment may be affecting RQ such that RQ is lower in higher BMI subjects fed BB compared to gelatin. Across the 24 hr period, RQ and EE were not different between the two treatments (.82 vs .83, 2184 vs 2124 kcal, respectively; BB vs gelatin treatments). However, during the 4 hr period that started with dinner, preliminary data suggest that a significant interaction of treatment and BMI for EE and RQ were observed (p=0.0385 and p=0.0059, respectively) where the BMI effect is the opposite of what was observed for the MTT time period; subjects with lower BMIs had a greater EE and lower RQ when fed BBs and the effect was attenuated with higher BMI subjects. The 24 hr stay in the calorimeter included 30 min of treadmill walking in the afternoon following the MTT. During this time period, a significant interaction of BMI with treatment demonstrated a decrease in RQ in higher BMI subjects fed BBs compared to gelatin (p for interaction = 0.041). In addition to improved insulin sensitivity, our data suggest a potential for anthocyanin rich BBs to change adiposity as RQ was indicative of preferential oxidation of fat for energy in higher BMI subjects during the MTT as well as during a bout of non‐strenuous activity. Further, beneficial effects of BBs may not be limited to overweight/obese subjects in terms of switching substrates to increase fat oxidation. More subjects are being enrolled to confirm these preliminary findings. Support or Funding Information This study is funded by the USDA.Serum insulin by treatment across the 4 hour meal tolerance test.Serum glucose by treatment across the 4 hour meal tolerance test.