People striving to lose weight have long been wooed by diet trends, hoping a new discovery or novel program will be their path to achieving a goal weight. Usually, research into the effectiveness of these diets lags behind media attention and public interest.True to form, that has been the case with the alternate-day fast, a popular diet trend
that features a day of fasting for each day of eat-whatever-you-want “feasting.”

Small studies and success stories have fueled the trend, but does the diet work? The May issue of JAMA Internal Medicine included findings from the first randomized controlled trial to compare the effectiveness of the alternate-day fasting diet with that of the restrictive diet and a control diet. Researchers randomized 100 participants into three groups: regular diet (control); diet supplying 75% of energy needs (restrictive); and the diet providing 25% of energy needs (fast) alternating with 125% of energy needs (feast). Overall, the alternate-day fasting group ate more than recommended on fasting days and less than recommended on unrestricted days, while the caloric-restriction group stuck fairly closely to the prescribed caloric intake. The dropout rate was highest in the alternate-day fasting group, with more than 38% of participants quitting, while 29% and 26% quit in the caloric-restriction and control groups, respectively.

The researchers monitored weight and a variety of health markers over 1 year. At the end of 6 and 12 months, they found similar weight loss results for the two diet groups: 6.8% for both alternate-day fasting and daily caloric restriction at 6 months; 6% for alternate-day fasting and 5.3% for daily caloric restriction at 12 months. There were no differences in blood pressure, heart rate, triglycerides, fasting glucose, fasting insulin, insulin resistance, C-reactive protein or homocysteine concentrations between these two groups. The alternate-day fasting group had higher HDL levels at 6 months (but not at 12) and higher LDL levels at 12 months. Ultimately, the diet consensus stands: The best diet is the one you can stick with.

Natalie Digate Muth, MD, MPH, RD

"Natalie Digate Muth, MD, MPH, RDN, FAAP, is a board-certified pediatrician and obesity medicine physician, registered dietitian and health coach. She practices general pediatrics with a focus on healthy family routines, nutrition, physical activity and behavior change in North County, San Diego. She also serves as the senior advisor for healthcare solutions at the American Council on Exercise. Natalie is the author of five books and is committed to helping every child and family thrive. She is a strong advocate for systems and communities that support prevention and wellness across the lifespan, beginning at 9 months of age."

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