Same Weight Loss With Alternate-Day Fasting vs Cutting Calories

Marlene Busko

May 01, 2017

In a randomized trial of 100 obese adults, weight loss at 6 months and weight-loss maintenance and cardiovascular risk markers at 12 months were similar with an alternate-day-fasting regimen or a reduced-calorie regimen.

People in each of these two intervention groups lost about 5% more weight at 12 months than those in a no-intervention control group.

However, the dropout rate was higher in the alternate-day-fasting group (38%) than in the restricted-calorie group (29%) or the control group (26%), John F Trepanowski, PhD, from the department of kinesiology and nutrition at the University of Chicago, Illinois, and colleagues report in an article published online May 1 in JAMA Internal Medicine.

"This is the longest and largest study of intermittent fasting to date," senior author Krista A Varady, PhD, from the same department, told Medscape Medical News.

"I think a lot of people are interpreting [this study] as 'nothing happened,' but [people in the alternate-day-fasting group] did lose a clinically significant amount of weight," she stressed.

However, people in the alternate-fasting group ate more than the prescribed amount on fasting days and less on "feasting" days, whereas people in the daily-calorie-restriction group were more compliant with their prescribed regimen.

Nevertheless, "I really think that alternate-day fasting can be used as an alternative approach for someone who has failed with daily calorie restriction," Dr Varady said.

Invited to comment on the study, Yoni Freedhoff, MD, an obesity physician and assistant professor of family medicine at the University of Ottawa in Ontario, told Medscape Medical News, "While there are no doubt very vocal proponents of alternate-day (and other sorts) of fasting as a means to manage weight, what's clear from this study is that, as with every weight-management strategy, adherence is king.

"The best approach for one person is undoubtedly the worst approach for another," he added. "At the end of the day, whatever strategy a person employs to manage their weight, they'd better like it enough to stick with it, as temporary efforts generally only lead to temporary outcomes."

Intermittent Fasting vs Daily Calorie Restriction

The researchers began investigating the effect of intermittent-fasting on weight loss about 10 years ago and have published data from several clinical trials.

In 2011, another group of researchers enrolled 107 premenopausal women in a randomized controlled trial that compared intermittent fasting (2 days a week) or continuous calorie restriction for 6 months and reported similar weight loss and improved cardiovascular-risk markers in both groups (Int J Obes (Lond). 2011;35:714–727). These findings are used to support the "5:2 fast diet" that was featured in a BBC documentary in 2012 and is "probably the most popular diet in the UK right now," said Dr Varady.

In the current study, which ran from 2011 to 2015, Dr Varady and colleagues enrolled 14 men and 86 women who were 18 to 65 years old (mean age, 44) and had a body mass index (BMI) of 25 to 39.9 (mean BMI, 35). The participants were also sedentary and free of cardiovascular disease or diabetes.

They were randomly assigned to alternate-day-fasting, calorie-restriction, or control groups and told not to change their physical-activity habits.

People in the control group were instructed to stay the same weight and did not receive any nutritional guidance, but they were promised nutritional counseling and a 1-year gym membership if they completed the study.

During the weight-loss phase, participants in the alternate-day fasting group were instructed to consume 25% of their baseline calories (about 500 calories) at one meal (lunch) on a fasting day and then consume 125% of their usual calories split between three meals on a feasting day. The alternate-day pattern was repeated for 6 months.

People in the restricted calorie group were instructed to eat 25% fewer calories every day for 6 months.

For the first 3 months, participants in the two intervention groups came to the clinic to pick up weekly food supplies (Lean Cuisine plus fruits, vegetables, and other foods) to promote adherence to the program and help them see the types and quantities of foods they should be eating.

They met with a nutritionist weekly from months 4 to 6 and monthly during months 6 to 12 (the maintenance phase).

During the maintenance phase, people in the daily-calorie-restriction group reverted to eating 100% of calories they had been eating at baseline, while those in the other intervention group were instructed to eat 50% and 150% of their baseline calories on alternate days.

At 6 months, participants in both intervention groups had lost 6.8% more weight than those in the control group. At 12 months, participants in the alternate-day-fasting group and the restricted-calorie group had lost 6% and 5.3% more weight, respectively, than participants in the control group.

There were no significant differences in mean blood pressure, heart rate, triglycerides, fasting glucose, fasting insulin, insulin resistance, C-reactive protein, or homocysteine between the two intervention groups at 6 months and 12 months.

Many participants in the alternate-day-fasting group had difficulty sticking to the 500 calories every other day and transformed their diet into a "de facto" daily caloric-restriction diet as the trial progressed, and others simply withdrew from the study, the researchers report.

"Taken together, these findings suggest that alternate-day fasting may be less sustainable in the long term, compared with daily calorie restriction, for most obese individuals," they write.

Nevertheless, "a smaller segment of obese individuals may prefer this pattern of energy restriction instead of daily restriction," Dr Valady and colleagues continue. "It will be of interest to examine what behavioral traits (eg, ability to go for long periods without eating) make alternate-day fasting more tolerable for some individuals."

Since many participants had normal cholesterol levels and blood pressure at study entry, it is not surprising that cardiovascular-risk markers did not change in response to diet, they add.

The group hopes to conduct a 2-year study of obese individuals with prediabetes to see whether intermittent fasting might be linked with a lower risk of developing diabetes, Varady said.

The authors disclose that they have no relevant financial relationships.  

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JAMA Intern Med. Published online May 1, 2107. Article


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