- Jennifer Middleton, MD, MPH
As obesity rates continue to rise, the elusive search for a solution persists. Intermittent fasting (IF) offers a simple approach; eat whatever you want within a designated time interval and then do not eat the rest of the time. Early, small studies suggested that intermittent fasting (IF) was more effective for weight loss than traditional calorie restriction diets, and IF's popularity has been boosted by disease-oriented studies demonstrating improvement in metabolic markers. A multitude of famous adherents have also contributed to IF's rising profile.
More recent, rigorous studies, however, may dampen the enthusiasm for IF. In 2018, a systematic review of intermittent fasting's effectiveness found similar rates of weight loss with IF compared to traditional calorie restriction. Later that year, a trial randomized 150 obese or overweight adults to either continuous energy restriction, IF using the "5:2" method (5 days a week of normal intake and 2 days a week of 25% intake), or placebo and then followed them for 50 weeks. It found that intermittent fasting "may be equivalent but not superior" to the traditional calorie restriction method.
And, now we have a new, 2020 randomized controlled trial. Researchers randomized 141 participants to either a "16:8" IF regimen (eat anything desired between noon-8 pm, then fast for the next 16 hours) or a "consistent meal timing" plan and then followed them for 12 weeks. The difference in weight loss between the two groups was non-significant (-0.26 kg [95% confidence interval −1.30, 0.78]). The IF group also demonstrated a decrease in lean muscle mass (-0.16 kg/m2 [95% CI -0.27, -0.05]) compared to the comparison group.
If this loss of muscle mass is replicated in other studies, IF's time might truly be up. This seemingly never-ending search for a "magic" diet plan additionally fails to account for the complex mechanisms behind obesity. Systemic environmental factors are the primary drivers of the obesity epidemic, not individual choice and a scarcity of willpower. The over-abundance of super-processed, inexpensive foods set humans, genetically hard-wired to crave fat and sugar, up for failure. Chronic stress and epigenetics affect both dietary preferences and metabolism. As long as we continue to neglect these powerful drivers of behavior, obesity will remain a public health crisis, one that COVID-19 will likely also continue to exploit.
You can read more in the AFP By Topic on Obesity, which includes this Curbside Consultation on "Obesity: Psychological and Behavioral Considerations."