Branched-Chain Amino Acids in relation to food preferences and insulin resistance in obese subjects consuming walnuts: A cross-over, randomized, double-blind, placebo-controlled inpatient physiology study

Background&aims: To assess whether the concentrations of circulating Branched-Chain Amino Acids (BCAAs) change after walnut consumption and, whether these changes are associated with alterations in markers of insulin resistance and food preferences. Methods: In a crossover, randomized, double-blind, placebo-controlled study, ten subjects participated in two 5-day inpatient study admissions, during which they had a smoothie containing 48 g walnuts or a macronutrient-matched placebo smoothie without nuts every morning. Between the two phases there was a 1-month washout period. Results: Fasting valine and isoleucine levels were reduced (p =.047 and p <.001) and beta-hydroxybutyrate levels were increased after 5-days of walnut consumption compared to placebo (p =.023). Fasting valine and isoleucine correlated with HOMA-IR while on walnut (r = 0.709, p =.032 and r = 0.679, p =.044). The postprandial area under the curve (AUC) of leucine in response to the smoothie consumption on day 5 was higher after walnut vs placebo (p =.023) and correlated negatively with the percentage of Kcal from carbohydrate and protein consumed during an ad libitum buffet meal consumed the same day for lunch (r = −0.661, p =.037; r = −0.628, p =.05, respectively). Conclusion: The fasting and postabsorptive profiles of BCAAs are differentially affected by walnut consumption. The reduction in fasting valine and isoleucine may contribute to the longer-term benefits of walnuts on insulin resistance, cardiovascular risk and mortality, whereas the increase in postabsorptive profiles with walnuts may influence food preference. Trial registration clinicaltrials.gov: Number: NCT02673281, Website: https://clinicaltrials.gov/ct2/show/NCT02673281.