Does Alternate-Day Fasting Really Work?

The standard accepted diet typically involves eating three times a day, preferably “square meals”.  Of course, the optimal diet for each person is dependent on a variety of other factors like exercise, health conditions, physiology, age, etc.  But when it comes to diet trends—that is, strategic decisions about losing weight or optimizing energy, etc—a new study argues that alternate-day fasting might be effective at improving overall health. 

Often shortened to ADF, alternate-day fasting is a specific type of intermittent fasting, which is categorized by cycling between periods of eating and not eating (fasting) over a certain period of time.  Specifically, Delnor Hospital Northwestern Medicine Metabolic Health and Surgical Weight Loss Center bariatric endocrinologist Dr. Elizabeth Lowden explains that alternate-day fasting typically includes both a period of regular food intake that alternates with full fasting; which means no food at all. Sometimes, though, the fasting period can be characterized by intake of only about 500 calories per day. 

The thing is, we do not have a lot of clinical data on ADF.  This makes it harder to understand its efficacy. Fortunately, this study is the largest of its kind to investigate the overall effects of strict adherence to ADF (in healthy people).  For this study, then, the 60 participants were instructed to alternate not eating for 36 hours and then eating as much as they wanted within the following 12 hours, for a duration of 4 weeks. 

Study author Frank Madeo explains, “Strict ADF is one of the most extreme diet interventions, and it has not been sufficiently investigated within randomized controlled trials.”

Over the course of the study, each person’s glucose was monitored to make sure they were not eating on their fasting days.  Also, each person was instructed to keep a food diary, regardless of the type of diet they were following. 

A professor at the Karl-Franzens University of Graz Institute of Molecular Biosciences, in Austria, Madeo goes on to say, “We aimed to explore a broad range of parameters, from physiology to molecular measures. If ADF and other dietary interventions differ in their psychological and molecular effects, complex studies are needed in humans that compare different diets.”

At the end of the study, the researchers found that those on the ADF diet experienced some benefits, including:  reduced belly fat and weight, higher ketone levels, lower levels of inflammation biomarkers, and lower cholesterol levels.