Here's the idea: During your "fasting" days, you seriously restrict your calorie intake. But during "feast" days, you can go all out and eat whatever you like. But does this method actually work?
For a new study, researchers from the University of Illinois at Chicago divided 100 obese but metabolically healthy patients into three groups. During the first six months, one group tried alternate-day fasting (eating 25 percent of their calorie needs on fast days and 125 percent of their calories on feast days), the second group tried daily calorie restriction (consuming 75 percent of their calorie needs each day), and the third group, the control, had no intervention. During the last six months of the year-long study, the "weight maintenance" phase, the groups increased their calorie intake: The alternate-day fasting group consumed 50 percent of their calorie needs on fast days and 150 percent on feast days, and the calorie restriction group consumed 100 percent of their calorie needs each day.
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A quick note on what those fast-day calorie restrictions actually were: During fast days, participants were expected to limit themselves to about 500 calories a day. Everyone's calorie requirements are different, depending on things like height, weight, activity level—the list goes on. But the Dietary Guidelines for Americans say young women should aim for 1,800 to 2,400 daily calories, according to the office of disease prevention and health promotion. So, 500 calories a day is seriously restrictive, and not necessarily recommended unless you are under the guidance of a professional (as was the case in this study).
The results, published in JAMA Internal Medicine, showed that after a full year there wasn't much difference between the groups. Basically, the researchers found that alternate-day fasting didn't produce superior weight loss, weight maintenance, adherence to the diet, or any improvement in risk indicators for heart disease when compared to those who just restricted their calories.
Not surprisingly, the study had a lot of dropouts, too: 13 alternative-day fasting participants, 10 calorie restriction participants, and 8 control group participants left the trial before the end. And, as you might have guessed, multiple alternate-day fasting dropouts said the program was just too difficult to follow.
So, it sounds like alternate-day fasting is a pretty unpleasant experience, and it doesn't necessarily work. Which is fair since calorie counting doesn't work for everyone, and what happens to your body when you skip a meal isn't pretty. While no singular weight-loss method works for everyone, this particular diet sounds like a write-off—so feel free to pass on fasting.
