Why Fasting Every Other Day May Not Lead to Long-Term Weight Loss

It sounds like a dieter’s dream. You eat whatever you want one day and then fast the next.

Called alternate-day fasting, the diet allows you to indulge — a lot — followed by eating in a way that severely restricts calories. But according to one new study, this approach isn’t beneficial for weight loss, especially long term.

The study, published in JAMA Internal Medicine, involved 100 obese adults with a healthy metabolism and was designed to compare the effects of alternate-day fasting with daily calorie restriction on weight loss, weight maintenance and heart disease risk.

Study participants were randomly assigned to either the alternate-day fasting diet where they ate 25 percent of their normal calorie needs on fast days and 125 percent of their calorie needs on feast days; a normal diet where they ate 25 percent fewer calories a day; or a control group where they didn’t stick to any specific diet.

Researchers discovered something interesting: weight loss for the alternate-day fast group and the calorie-restricted group was about the same. Alternate-day fasters lost 6 percent of their body weight while those on a restricted-calorie diet lost 5 percent.

The alternate-day fast group ate more calories on fast days and fewer calories on feast days than they should have, which may explain their weight loss. However, they were more likely to quit their diet than the calorie-restricted group who ate normally. Thirty-eight percent of the group quit compared to 29 percent of the calorie-restricted group and 26 percent of the control group.

I can’t say I’m shocked. In the study, alternate-day fasters had to stick to a 500-calorie diet for the entire day — which is nearly impossible. Eating a hearty breakfast alone would put you over that mark. Though researchers said some people on the diet were successful and lost 20 to 50 pounds in a year, dieting like this isn’t sustainable long term.

The study indicated as much — those who ate a normal, balanced diet were able to stick to their calorie requirements better than those who endured the ongoing cycle of feast or famine. Even if you eat a lot of protein on fast days, like the researchers recommended in the study, you’ll still encounter a huge calorie deficit that leads to less energy and forces your body to go into “starvation mode,” which makes it hold on to calories for longer, thereby slowing weight loss.

The body has a natural way of correcting itself, so fasting likely will create bouts of hunger that lead you to overeat. On top of that, eating whatever you want every other day isn’t the best way to lower your risk for heart disease, high blood pressure, diabetes and other chronic conditions.  In fact, LDL cholesterol levels were significantly elevated after one year in the alternate-day fasting group compared to those in the calorie restriction group.

The most effective approach is making small lifestyle changes over the long term. These will be much more lasting than binging and fasting on an alternate-day schedule.