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Intermittent fasting (IF) has been getting lots of attention recently. It was claimed that intermittent fasting having many advantages including weight loss, improved insulin sensitivity, heart health, reduced inflammation, and brain health. It is true? What does research say? Shall I practice intermittent fasting to lose weight?
What is intermittent fasting?
Intermittent fasting is an eating pattern that alternates between periods of eating and fasting. Unlike traditional diets that focus on what you eat, intermittent fasting focuses on when you eat.
What Research Shows
A systematic review with 9 randomized control trials showed that "IF had a reduction in body weight, BMI, fat mass, and triglyceride in adults aged over 40 with obesity without metabolic disease compared to regular diet, and IF did not cause a significant decrease in lean body mass, which suggests healthy and effective fat loss. However, more long-term and high-quality trials are needed to reach definitive conclusions." (Yao et al., 2024).
In this systematic review, the studies usually lasted 2-6 weeks, which was a very short term experiment. I would question the long term effect of intermittent fasting and whether their weight bounced back in 6 months or 1 year.
The second question I have for this research study is that what is the definition of regular diet in the control group? According the research, "regular diet is one that does not involve dieting, has no calorie restriction, and maintains the original eating patterns." As a dietitian, I care about the quality of a client's diet. Meal planning is helpful to improve the quality of the meal structure to achieve better health outcomes. Choosing healthy food options are important as well. However, in the control group, what is the added sugar intake in their diet? What is the meal timing? How often do they eat out? This is important information for me to evaluate and compare the diet. Simply restricting the meal timing does not provide me with enough information to reach an evidence-based conclusion.
In a randomized control trial, it shows that "the body weight in the subjects in the experimental group (EXP) group decreased by almost 2 kg and this decrease was visible in the remaining parameters related to body fat mass. The skeletal muscle mass did not change significantly, which indicates an actual decrease in the fat mass" (Domaszewski et al., 2020).
This seems to be a fantastic news. However, the research sample size was too small to generate a reliable conclusion. There were only 20 people in the control group and 25 people in the experiment group. 12% of research participants didn't follow the intermittent fasting, and so were excluded in the study. As a result, the experiment group were only 22 participants.
The research study only lasted for 6 weeks. The follow-up duration was too short. Weight loss is a long-term goal, and short-term weight loss doesn't mean a long-term success.
Fasting is a common practice for Muslims during Ramadan. It is once a year fasting for one month from sunrise to sunset. In this meta-analysis study, the research found a significant positive correlation for weight lost and body fat percentage reduction during the fasting period for those with obesity or overweight. No weight reduction was found in the population of normal weight. However, between 2 to 5 weeks later after the end of Ramadan, their weight bounced back to pre-Ramadan measurements. Therefore, the research concluded that weight loss effect for fasting is temporary if there is no long-term and lifestyle changes (Fernando et al., 2019).
A meta-analysis of randomized controlled trials showed that "intermittent fasting is not associated with greater or lesser weight loss than non-intermittent fasting diets." Intermittent fasting doesn't lead to reduction in blood pressure, fasting blood sugar, or LDL cholesterol in the obese (Silverii et al., 2023).
The research studies seem to show a conflicting result on this topic. More long-term research data is required with high quality and well-designed randomized control trials are required. As a dietitian, what time you eat is one of the important components that I assess. In addition, what food you eat makes a big difference in overall health, weight loss, cholesterol management, and diabetes prevention.
Cheers,
Elaine Dietitian
References:
Domaszewski, P., Konieczny, M., Pakosz, P., Bączkowicz, D., & Sadowska-Krępa, E. (2020). Effect of a Six-Week Intermittent Fasting Intervention Program on the Composition of the Human Body in Women over 60 Years of Age. International journal of environmental research and public health, 17(11), 4138. https://doi.org/10.3390/ijerph17114138
Fernando, H. A., Zibellini, J., Harris, R. A., Seimon, R. V., & Sainsbury, A. (2019). Effect of Ramadan Fasting on Weight and Body Composition in Healthy Non-Athlete Adults: A Systematic Review and Meta-Analysis. Nutrients, 11(2), 478. https://doi.org/10.3390/nu11020478
Silverii, G. A., Cresci, B., Benvenuti, F., Santagiuliana, F., Rotella, F., & Mannucci, E. (2023). Effectiveness of intermittent fasting for weight loss in individuals with obesity: A meta-analysis of randomized controlled trials. Nutrition, Metabolism and Cardiovascular Diseases, 33(8). https://doi.org/10.1016/j.numecd.2023.05.005
Yao, K., Su, H., Cui, K., Gao, Y., Xu, D., Wang, Q., Ha, Z., Zhang, T., Chen, S., & Liu, T. (2024). Effectiveness of an intermittent fasting diet versus regular diet on fat loss in overweight and obese middle-aged and olderly people without metabolic disease: a systematic review and meta-analysis of randomized controlled trials. The Journal of Nutrition, Health and Aging, 28(3), 100165. https://doi.org/10.1016/j.jnha.2024.100165
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