Research has shown that drastically cutting back on calories can slow your metabolism and force your body into starvation mode.
Not only does it make you grumpy, being hungry all the time in the name of weight loss usually backfires when happy hour comes calling or when your cheat day turns into a cheat week. A human only has so much willpower, amiright?
So when we heard that a plan called the Fasting Mimicking Diet was getting a lot of buzz for its five-day-a-month fasting plan, we had to find out for ourselves if it was legit. After all, “fasting” is basically code for starving yourself. No bueno.
Plus, research has shown that drastically cutting back on calories can slow your metabolism and force your body into "starvation mode," making it harder for you lose weight and keep it off.
However, this diet promotes the idea of "fasting with food." That means eating tiny meals, which you purchase from the company, for just five days a month, to shift your body into a fasting state without completely giving up food.
Fasting Mimicking Diet fans swear by it, but is this plan legit—or even safe? Experts weigh in.
The Fasting Mimicking Diet is based on research from the Longevity Institute at the University of Southern California—specifically, a study published in the journal cell metabolism, which tested how yeast reacted when deprived of food for a short period of time.
The study authors found that yeast actually had a longer life expectancy when deprived of food. Over the next couple of years, the researchers then ran similar experiments with mice and eventually humans.
In the most recent study of people aged 19 to 75 on a fasting diet, the study authors found that people who went on a fasting diet for five days a month over a period of three months lost weight and had a reduction in their risk of heart disease.
One of the researchers in the original yeast study, Valter Longo, Ph.D., went on to develop the Fasting Mimicking Diet that's trending today.
Here's how the plan works: The first step is to fill out a 10-question assessment about your health, age, food allergies, prescriptions, and more.
Then, if you pass, you can purchase the pre-packaged, plant-based, low-carb, low-protein, low-calorie meals. They start at $299 per five-day supply.
On the Fasting Mimicking Diet, you'll consume between 1,100 calories on the first day and 750 calories during days two through five.
The meals are one size fits all, according to their website. If you don't pass the assessment, you're directed to speak with your physician about starting the plan.
A physician can order it for you and monitor your health on the diet.
After day five on the Fasting Mimicking Diet, followers are encouraged to start easing into their normal eating habits by day seven, according to the company's website.
ProLon, the company behind the diet, states that the fasting period “allows your body to trigger a set of protectionist measures that the body developed during natural selection, when food was scarce and not easy to find and store.”
The fasting period also “allows your body to optimize its performance, rejuvenate its cells, and thrive under such circumstances.” So there's that.
According to their site, the food you eat on this plan consists of soups, kale crackers, supplements, energy bars, and plant-based energy drinks.
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Beth Warren, R.D.N., founder of Beth Warren Nutrition and author of Living a Real Life With Real Food, says that the calorie intake on the five-day “fast” is well below the minimum requirement she'd prescribe to her patients.
However, it's definitely possible to lose weight on this diet in the short term, says Scott Keatley, R.D., of Keatley Medical Nutrition Therapy.
“For those who are overweight, decreasing weight by five to 10 percent has been shown to do everything this diet claims,” he says.
Keatley says that lowering your calories by this much creates a hormetic effect, which makes your body stronger while decreasing body weight and fat.
But, of course, any time you go on a calorie-restricted diet you’re going to lose weight—at least in the short term. As for the long term, New York-based R.D. Jessica Cording says going super-low calorie for five days a month on the Fasting Mimicking Diet is probably not helpful for weight loss.
“While it may help someone meet their weight-loss goals in the short term, I'm more concerned about the long-term behavioral aspect of someone looking to lose weight," she says.
That's because following this program doesn't teach dieters the lifestyle changes necessary to help them lose weight on their own and maintain it over time, like meal planning, cooking at home, listening to your hunger and fullness cues, and watching your portion sizes.
Cording suggests that if someone has to fast for five days a month to maintain the weight they want, there may be some “underlying issues” with their diet that need to be addressed.
Warren agrees. “The significant calorie restriction alone may cause weight loss for some people,” she says.
“However, the diet states that the other 25 days per month people can eat what they want, which would inevitably work against those benefits.”
Keatley points out that, while the diet claims to have other health benefits, the evidence is kind of weak.
“We're unsure what the long-term effects of a diet like this are and we don't know if this diet reduces incidences of disease, since they claim to only reduce the bio-markers we associate with diseases,” he says.
There’s also a chance that people could throw their metabolism out of whack and end up gaining weight in the long-term, Keatley adds.
Don't expect the Fasting Mimicking Diet to give you long-term results.
If weight loss and maintaining that goal weight are your main objectives, experts recommend taking a closer look at your overall diet instead and figuring out where you can make smarter choices.