The study was approved by the Institutional Review Board of the David Geffen School of Medicine at the University of California, Los Angeles. Healthy men and postmenopausal women with body mass index (BMI) between 27 and 35 kg/m2 were recruited through internet advertisement and campus flyers. Subjects were excluded for conditions of type 2 diabetes or glucose intolerance, significant weight loss within 3 months, history of bariatric surgery, a history of alcohol or cigarette use, eating disorders, depression treated with medications and chronic diseases other than controlled hypertension and hypercholesterolemia. The study was registered at clinicaltrial.gov, NCT01142687.
Each subject gave informed consent prior to beginning the study. At the screening visit medical history, physical exam, electrocardiogram and fasting blood tests were performed. All eligible subjects were then started on the lead-in phase when all were instructed to consume maintenance calories and record food intake for 7 days to assure that they maintain constant weight within 1 kg. Subjects were then randomized double-blinded into placebo, 3 mg or 9 mg DCT groups for 4 weeks. Vital signs, anthropomorphic assessments, safety labs and adverse events were assessed weekly. The blood samples were sent to the UCLA Clinical Laboratory for analysis. Body composition and indirect calorimetric measurements are performed at day 0 and 28.
The dihydrocapsiate capsules of 1 mg and placebo were obtained from Ajinomoto Co (Ajinomoto Co., Inc. Japan). Dihydrocapsiate was synthesized enzymatically with vanillyl alcohol and 8-methylnonanoic acid. Following the esterification, filtration, extraction and evaporation are conducted. Refined rapeseed oil was used to dilute dihydrocapsiate to adjust the concentration. 200 mg of concentration adjusted dihydrocapsiate was packed in soft capsules, followed by drying. The placebo capsules to be used for the control group were prepared in the same manner as the dihydrocapsiate capsules.
The investigators and subjects were blinded to the identity of the capsules. Each subject was instructed to consume capsules containing either DCT or placebo three times per day within 30 minutes before breakfast, lunch and dinner in a manner designed to provide 0, 3, or 9 mg of DCT per day.
Very Low Calorie Diet (VLCD)
The VLCD plan consisted of eight servings per day of a very low calorie protein shake providing 100 kilocalories and 15 grams of high quality protein (Pro-Cal, R-Kane Products). Forty miliequivalent of K-Dur (potassium chloride tablet) were provided to all the subjects at the start of the meal plan and the dose was adjusted according to the weekly safety labs to maintain the potassium level within the normal range. Subjects consumed four additional servings on testing day one and day 28. Subjects were counseled by the registered dietician and physician for product compliance and possible side effects from the capsules.
Body weight was measured using a calibrated electronic scale and body composition was measured using an air displacement body plethysmograph (BOD POD, Life Measurements Instruments). Subject wore a swimsuit, biking shorts and a swim cap during the measurement.
Indirect calorimetric measurement
At day 0 and 28, subjects arrived at the facility in a fasting state. Basal metabolic rate (BMR) was obtained by measuring oxygen consumption and carbon dioxide production over 20 minutes using a Vmax hood (Cardinal Systems) while subjects remained recumbent at room temperature. Subject consumed a high protein test liquid meal over twenty minutes providing 400 kilocalories and 60 grams of protein. Oxygen consumption and carbon dioxide production was measured hourly over the next four hours for postprandial energy expenditure (PPEE). PPEE were adjusted by fat free mass (FFM).
Statistical analyses were carried out using SAS version 8.0.02 and a p value of 0.05 specified for statistical significance. For the evaluation of body weight and fat mass, the changes from baseline among groups were evaluated using 1-factor ANOVA. For the evaluation of changes in PPEE/FFM and RQ, the differences in mean change at each time point for different doses were evaluated using a mixed model with the change as a response variable and with dose, time point and dose-time point interaction as fixed effects. For evaluation of changes in BMR, the differences of mean changes with different doses were evaluated by using a mixed model with changes as response variables, and with doses as fixed effects.