A systemic review and meta-analysis of randomised controlled trials found that intermittent fasting (alternate day fasting, TRF, periodic fasting, religious fasting) were associated with an improvement in cardiometabolic risk factors, including weight, waist circumference, fat mass, BMI, blood pressure, total cholesterol, triglycerides, fasting insulin, and insulin resistance, compared to a control group diet (Yang et al. 2021). The studies however small in their sample sizes, suffered a high degree of bias and were short term only.
Time Restricted Eating: The practice of extending the overnight fast to over 12 hours has become popular over the last few years. The 16:8 diet where food is only consumed in an 8-hour period is the most googled diet across the equatorial region across the world from Mexico to India.
Research that a long overnight fast is associated with blood lipid improvement (McAllister et al. 2020), reduction in blood pressure, and metabolic disease risk reduction (Melkani and Panda 2017).
However, a cross-sectional analysis of data from 1047 adults over 65 years of age found that a long overnight fasting time of at least 12 hours did not show beneficial associations with the examined biomarkers in older adults (Estrada-deLeon et al. 2022)
Alternative day fast more effective: A study of diets for weight loss in adults with prediabetes, the alternate day fast was shown to have more-significant reduction effects on body weight and body mass index than 16/8 Time Restricted Eating diet (Chair et al. 2022).
The 5-day fasting-mimicking diet (FMD), administered every four weeks for a period of two years, has been shown to ameliorate the detrimental changes caused by consumption of a high-fat, high-calorie diet (HFCD) in female mice.
Monthly FMD cycles inhibited the diet-mediated obesity by reducing the accumulation of visceral and subcutaneous fat without causing loss of lean body mass.
FMD cycles increased cardiac vascularity and function and resistance to cardiotoxins, prevented HFCD-dependent hyperglycaemia, hypercholesterolaemia and hyperleptinaemia and ameliorate impaired glucose and insulin tolerance.
The effect of monthly FMD cycles on gene expression associated with mitochondrial metabolism and biogenesis in adipocytes and the sustained ketogenesis in HFCD-fed mice indicate a role for fat cell reprogramming in obesity prevention. These effects of an FMD on adiposity and cardiac ageing could explain the protection from HFCD-dependent early mortality (Mishra et al. 2021).
The take home message for practitioners may be that different dietary interventions work for different people. We recommend the practice of restricting the window of eating ensuring a long overnight fast. For the treatment of metabolic syndrome, we recommend TRE with repeated cycles of the fasting mimicking diet. The practice of using the FMD back-to-back is being trialled for a more potent weight loss where rapid and significant weight loss is required, e.g. Where overweight is preventing surgery. However, in most situations the recommendation is to undertake the fasting mimicking diet one a month for three months and then reassess the outcome.
Chair, S. Y., H. Cai, X. Cao, Y. Qin, H. Y. Cheng, and M. T. Ng. 2022. 'Intermittent Fasting in Weight Loss and Cardiometabolic Risk Reduction: A Randomized Controlled Trial', J Nurs Res, 30: e185.
Estrada-deLeon, D. B., E. A. Struijk, F. F. Caballero, R. Ortola, P. Guallar-Castillon, J. R. Banegas, F. Rodriguez-Artalejo, and E. Lopez-Garcia. 2022. 'Association of prolonged nightly fasting with cardiovascular, renal, inflammation, and nutritional status biomarkers in community-dwelling older adults', Am J Clin Nutr.
McAllister, M. J., B. L. Pigg, L. I. Renteria, and H. S. Waldman. 2020. 'Time-restricted feeding improves markers of cardiometabolic health in physically active college-age men: a 4-week randomized pre-post pilot study', Nutr Res, 75: 32-43.
Melkani, G. C., and S. Panda. 2017. 'Time-restricted feeding for prevention and treatment of cardiometabolic disorders', J Physiol, 595: 3691-700.
Mishra, A., H. Mirzaei, N. Guidi, M. Vinciguerra, A. Mouton, M. Linardic, F. Rappa, R. Barone, G. Navarrete, M. Wei, S. Brandhorst, S. Di Biase, T. E. Morgan, S. Ram Kumar, P. S. Conti, M. Pellegrini, M. Bernier, R. de Cabo, and V. D. Longo. 2021. 'Fasting-mimicking diet prevents high-fat diet effect on cardiometabolic risk and lifespan', Nat Metab, 3: 1342-56.
Yang, F., C. Liu, X. Liu, X. Pan, X. Li, L. Tian, J. Sun, S. Yang, R. Zhao, N. An, X. Yang, Y. Gao, and Y. Xing. 2021. 'Effect of Epidemic Intermittent Fasting on Cardiometabolic Risk Factors: A Systematic Review and Meta-Analysis of Randomized Controlled Trials', Front Nutr, 8: 669325.