Effects of Intermittent Energy Restriction Alone and in Combination with Sprint Interval Training on Body Composition and Cardiometabolic Biomarkers in Individuals with Overweight and Obesity
Question
Does combining twice-weekly 5:2 intermittent fasting with low-volume sprint interval cycling produce better body composition and cardiometabolic outcomes than fasting alone or SIT alone?
Summary
In adults with overweight or obesity, 16 weeks of 5:2 intermittent fasting drove most body-weight and fat-mass improvement, while low-volume supervised cycling sprint intervals mainly improved cardiorespiratory fitness. Combining fasting with SIT did not reduce weight or fat more than fasting alone. The SIT protocol was very short and well attended, but it was not enough by itself to meaningfully change body composition or most cardiometabolic biomarkers.
Methodology
- Adults with overweight or obesity recruited in Melbourne, Australia.
- 34 participants.
- Magnetically braked cycle ergometer plus 5:2 fasting diet.
- Work intervals: 20 seconds at 150% VO2peak.
- Recovery: 40 seconds active rest at 50 W.
- Intensity: 150% VO2peak for work intervals; HR and Borg RPE monitored.
- About 10 minutes total including 3 minute warm-up and 3 minute warm-down.
- SIT 3 sessions/week on non-fasting days; fasting 2 nonconsecutive days/week.
- 16 weeks.
- Randomized three-arm intervention trial
- Body weight and composition, VO2peak, Blood pressure and pulse wave velocity, and Lipids and glucose regulation were tracked.
Outcomes
Body weight and fat mass
IF and IF/SIT reduced body weight and fat mass more than SIT alone, with no significant difference between IF and IF/SIT.
Body weight group x time p=0.004; fat mass group x time p=0.002; IF and IF/SIT lower than SIT at 16 weeks p<0.05.
Visceral adipose tissue
VAT decreased significantly within IF/SIT at 16 weeks but between-group differences were not significant.
Time effect p=0.001; IF/SIT within-group p=0.004; IF trend p=0.07.
VO2peak
Exercise was required for cardiorespiratory fitness gains; SIT and IF/SIT improved VO2peak whereas IF alone did not.
Time p=0.001, group p=0.001, group x time p=0.002; SIT p=0.03 and IF/SIT p=0.001 vs IF.
Blood pressure and biomarkers
Blood pressure, lipids, glucose and insulin resistance effects were minimal or mixed; LDL and glucose AUC improved only in IF/SIT in change analyses.
No main effects for BP/PWV; LDL reduction in IF/SIT p<0.01; glucose tolerance AUC reduction in IF/SIT p<0.05.
Insights
- Very short cycle SIT can improve VO2peak, but users seeking fat loss likely need diet/energy-balance support or more exercise volume.
- Pairing SIT with fasting improved fitness plus some metabolic markers, but did not outperform fasting alone for weight/fat loss.
- For app programming, 20-second hard / 40-second easy bike intervals are time-efficient but should be framed as fitness-oriented, not a standalone weight-loss tool.
Limitations
- Small final sample and low male numbers, with pooled sex analysis.
- Free-living diet and activity were not tightly controlled.
- Self-reported food logs and physical activity measures may be biased.
- No continuous energy restriction comparator.
- SIT volume may have been too low to test body composition effects.
Safety
- No adverse events were reported in the the paper.
- Participants were screened for chronic disease, smoking, pregnancy, menopause, and contraindicating medications.
- SIT participants had to attend at least 85% of sessions to remain in final analysis.