Are Fasting Diets Safe?

Jenna Birch
by Jenna Birch
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Are Fasting Diets Safe?

Another day, another story about a celebrity on the latest liquid diet, juice cleanse, or fasting regimen. Fasting diets are gaining in popularity, but for many of us they may not be feasible or even healthy.

The trendiest plans are juice cleanses and the new 5:2 Diet. A juice cleanse requires a person to go on an all-juice diet for a period of time—which could be as short as 24 hours, or as long as 2 weeks—to flush the system of toxins and drop weight in a hurry, especially before a big event. Meanwhile, the 5:2 Diet, recently profiled in The Wall Street Journal, restricts calories to around 500 a day for women and 600 a day for men during two fasting days per week, and then dieters eat whatever they’d like the other five days. Both the 5:2 Diet and juice cleanses ultimately create a calorie deficit that leads to weight loss.

But the question remains: are fasting diets safe? If done right, they could be. Physician nutrition specialist Melina Jampolis, M.D., says she will occasionally recommend a restrictive regimen. “I’m not a big fan of juice cleanses or fasting diets,” she says. “If prolonged, they can lead to loss of lean body mass fairly quickly, due to a protein deficiency that can drop metabolism. I do, however, believe that something like the 5:2 diet can work, because it is easier to stick with than being ‘on a diet’ and restricting calories seven days a week.”

Still, Jampolis, author of The Calendar Diet, isn’t sold on the idea, and has adapted the 5:2 approach. “I prefer to allow my patients a little more structure 5 days a week—maybe eating 80 to 100 percent of their normal intake with a few treats built in—and then going moderately low-calorie a couple days a week.” Jampolis insists her patients follow two primary guidelines while on a fast or cleanse:

Get enough lean protein “This will preserve muscle mass, and can help with hunger, as well,” says Jampolis. For women, that’s about 46 grams. For men, it’s more like 56 grams.

Control sugar intake Especially if the regimen includes juicing. “If someone wants to have a few mainly-green juices throughout the day to control hunger and boost nutrients, I’m OK with that, but they really need to watch the sugar content,” says Jampolis. However, for diabetic dieters it’s not a good idea. “It’s better to go with three protein smoothies on low-cal days if diabetics want to follow a liquid diet, and then throw some fruit and greens in the smoothies.”

Restricting your food intake in a minor way can also improve your weight loss results. Instead of starting a full-blown restrictive regimen, try simply foregoing solid foods until noon. Start the day with a healthy, pre-made green juice at breakfast instead of feasting on a calorie bomb like a bagel with cream cheese. You can also experiment with eliminating snacks, says NYC-based dietitian Lisa Moskovitz, R.D. “Skipping meals often leads to overeating at the next sitting, but skipping that extra snack between meals might actually help with weight loss, or prevent overeating,” says Moskovitz. “Many people eat more meals and snacks than necessary,” she says.

By restricting your access to snack foods, you might weight coming off at a healthy, steady pace. “Snacks are usually low in nutrients and high in calories—think chips, cookies, and other processed or bagged food items,” says Moskovitz. “These types of foods are not only high in calories, but they can spike blood sugars which, in turn, can increase appetite and cravings later on that day,” she says. “By avoiding extra eating between meals, it’s easier to create the calorie deficit needed to produce weight loss, and stop cravings at the same time.”

You should always talk to your doctor before starting a restrictive regimen. Have you ever tried a fasting diet? What did you think?


About the Author

Jenna Birch
Jenna Birch

Jenna Birch is a health and lifestyle writer. She has written for many web and print publications, including Marie Claire, Runner’s World, and As a nutrition and fitness junkie, she’s a lifelong athlete, major college sports fan and developing yogi—but still can’t resist the allure of an occasional chocolate lava cake. (Everything in moderation, right?) For more, visit her at or follow her on Twitter.  


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