PURPOSE: The objective of the present study was to investigate the effects of the 16/8 diet on cardio-metabolic risk factors in competitive male runners.
METHODS: This ongoing study is a randomized cross-over intervention that consists of two 4-week arms: a “normal diet” arm (ND: 12 hours fasted and 12 hours fed) and a “16/8” (TRF: 16 hours fasted and 8 hours fed) arm along with a 2-week washout. Sixteen subjects will complete the study and will participate in 4 test days (12 hour fasted), one at the beginning and end of each arm, where they will undergo a DXA scan, resting energy expenditure measurement and a fasting blood draw for biomarker quantification. Overall calories, macronutrient intake and exercise training will be held constant over the 2 interventions. Preliminary
RESULTS: Data on 9 subjects shows no significant differences between groups in changes in body mass (+0.41 ND vs. -0.72 kg TRF, p=0.25), fat mass (-0.29 ND vs. -0.63 kg TRF, p=0.65), fat free mass (+0.56 ND vs. -0.25 kg TRF, p=0.18) and body fat (-0.42 ND vs. -0.61 % TRF, p=0.72) with the 4 week intervention. Changes in resting energy expenditure (+152.3 ND vs. +11.3 kcal TRF, p=0.18), resting respiratory exchange ratio (-0.003 ND vs. -0.04 TRF, p=0.36), blood glucose (-3.9 ND vs. -1.9 mg/dl TRF, p=0.61), total cholesterol (+1.0 ND vs. -3.0 mg/dl TRF, p=0.68), HDL cholesterol (-1.7 ND vs. 0.0 mg/dl TRF, p=0.71), LDL cholesterol (0.0 ND vs. -3.8 mg/dl TRF, p=0.41), and triglycerides (+17.9 ND vs. *4.3 mg/dl TRF, p=0.46) also did not differ between interventions.
CONCLUSION: So far, with limited power, there does not appear to be any physiological health benefits in male runners adhering to a 16/8 diet when compared to a normative eating timeframe.