Fasting Isn’t the Dieting Secret Weapon You Think

Researchers compared alternate-day fasting to a traditional calorie-reduction diet and found surprising results.

Intermittent fasting has become one of the most popular diets for those trying to lose weight. The belief is that restricting eating to 4-8 hours per day can lead to improved calorie burning, better regulation of glucose, and improved digestion. There are many adherents who believe they have proven that intermittent fasting is a good, safe, and healthy diet choice.

However, according to an article on the effect of alternate-day fasting in JAMA Internal Medicine, there may not be a significant benefit to fasting.

A team of Chicago researchers studied 100 obese adults over the course of three years. The patients were assigned at random to one of three groups: control group (with no dietary changes), daily calorie-restricted diet group (consuming 75% of calorie needs), and alternate-day fasting group (25% calorie needs on fast days, 125% of calorie needs on “feast” days). The researchers monitored the patients for a year, then evaluated the effects of the various diets.

As expected, the control group saw minimal change in their weight loss. The other two groups, however, saw visible results: they lost between 5 and 6% of their original body weight over the course of a year. The alternate-day fasting group lost 6% while the daily calorie restriction group (the normal dieters) saw a 5.3% reduction in body weight.

The mean age of the 100 participants (86 women and 14 men) was 44. It was found that the dropout rate was highest in the alternate-day fasting group (38%), versus the daily calorie restriction group (29%) and control group (26%).

The subjects in the alternate-day fasting group ate more than prescribed on fast days, and less than prescribed on feast days, while those in the daily calorie restriction group generally met their prescribed energy goals. There were no significant differences between the intervention groups in blood pressure, heart rate, triglycerides, fasting glucose, fasting insulin, insulin resistance, C-reactive protein, or homocysteine concentrations at month 6 or 12.

Mean high-density lipoprotein (HDL) cholesterol levels at month 6 significantly increased among the participants in the alternate-day fasting group, but not at month 12, relative to those in the daily calorie restriction group. Mean low-density lipoprotein (LDL) cholesterol levels were significantly elevated by month 12 among the participants in the alternate-day fasting group compared with those in the daily calorie restriction group.

The researchers concluded that there wasn’t much difference between the groups and that alternate-day fasting does not produce superior weight loss or weight maintenance compared with daily calorie restriction. There was also a higher rate of recidivism which should be noted as impactful. Which seems to take us back to the good old idea of watching your calorie counts. Everything old is new again.


1. John F. Trepanowski, Cynthia M. Kroeger, Adrienne Barnosky, Monica C. Klempel, Surabhi Bhutani, Kristin K. Hoddy, Kelsey Gabel, Sally Freels, Joseph Rigdon, Jennifer Rood, Eric Ravussin, Krista A. Varady. “Effect of Alternate-Day Fasting on Weight Loss, Weight Maintenance, and Cardioprotection Among Metabolically Healthy Obese Adults.” JAMA Internal Medicine, 2017.