FASTING ISN’T ANYTHING all that new. Certain religions have been advocating it for the practice for centuries – long, long before big-time diet books, Hollywood actors, and Internet fitfluencers began to talk about intermittent fasting.
Intermittent fasting (also abbreviated to IF) is an approach to eating that focuses on, well, not eating. Or at least when you should not eat.
There are all sorts of fasting schedules (16:8, 14:10, and more you can learn about here), though they tend to operate on the basic idea that if you’re restricting when you can eat, you’ll also limit your total caloric intake for the day and thereby reap the supposed rewards (weight loss being the biggie).
But there’s another form of fasting picking up traction in longevity circles. It’s called a “Fasting-Mimicking Diet” and differs from many major fasting schedules in one big way: you get to eat.
What is a fasting-mimicking diet?
THE FAST-MIMICKING DIET is a five-day eating plan that’s like a fast, except you can still consume calories while you’re on it.
You consume about 1,100 calories on day one and then 750 calories per day on days two through five while following a low-protein, low-sugar, high-fat, plant-based diet.
Note that most men need anywhere from 2,000 to 3,000 calories daily, according to the latest recommendations.
The diet is designed to be temporary, with its advocates suggesting a repeat of the diet a few times a year.
Valter Longo, Ph.D., a biologist and director of the USC Longevity Institute, invented the fasting-mimicking diet for patients with cancer. The goal was to develop an eating plan that could regenerate and rejuvenate patients’ cells and organs without depleting their blood sugar or electrolyte levels like a water fast could. Now, Longo says, most people can benefit from the plan.
Longo’s company ProLon, which sells the five-day fasting-mimicking diet in a box, says three cycles of the diet can “fuel your body into rejuvenation, longevity, and healthy living.” They tout metabolic health, cellular rejuvenation, fat-focused weight loss, a changed relationship with food, and more.
Some TikTokers even say the plan reduces bloating, makes their skin glow, and helps them reset after a period of not-so-healthy habits.
Benefits of a fasting-mimicking diet
SOME EMERGING RESEARCH does exist on the diet.
Over the past dozen years, scientists have studied the fasting-mimicking diet in Petri dishes, animals, and humans. (About a quarter of the studies are by Longo and his colleagues.)
Some small studies in humans suggest the fasting-mimicking diet could reduce body mass index, glucose, triglycerides, cholesterol, C-reactive protein (a marker of inflammation), insulin resistance, and liver fat, while boosting immune health and maybe even improving response to chemotherapy in patients with breast cancer.
“It’s probably giving the signal to the body to go into this fat-burning mode, where now insulin is working well, again, versus the fat storage mode, in which insulin resistance develops so that you can put away the fat,” says Longo. How, exactly? “After four or five days of fasting mimicking diet, we believe that either stem cells are turned on, or the cells that are not stem cells, they reprogram into stem-like cells,” says Longo. “So this is very, very clear in mice, and we’re starting to see evidence of that in people.”
And while the diet is short, Longo says it can help people build better habits. “We see a lot of people slowly undergoing a transformation,” says Longo. “I mean, it takes a while, but I think eventually they feel better while they’re doing this, and they gravitate very slowly, because within a couple months, it might take them a year or two to get that, but then slowly, they begin to go towards a much healthier lifestyle.”
So, in short, some preliminary research in cell and animal studies seems promising, but more clinical studies are needed to prove an effect in humans.
Risks of a fasting-mimicking diet
BEYOND THE FACT that the diet is not as well-studied as some proponents lead you to believe, there are other concerns.
It’s one-size-fits-all
The packaged fast-mimicking diet comes with plant-based soups, nut bars, olives, supplements, herbal teas, and a proprietary glycerol drink advertised to burn fat and preserve muscle. “It doesn’t sound very appetising,” says registered dietitian Janet Bond Brill, Ph.D. If you don’t like those foods, you’re out of luck – there are no substitutions.
It’s $$$
At about $200 for five days of food, ProLon is cheaper than eating at restaurants but more expensive than cooking from scratch.
“I think the appeal is that people are like yeah, OK, easy, just get me the food, tell me what to eat, and I don’t have to prepare anything, but I’d just as soon see people buy packaged salad and just real whole food, like bananas and spinach,” says Brill. “Eat a peanut butter and banana sandwich on whole grain.”
It’s intense
And, like any intense diet, the plan could be dangerous for certain people.
Longo says the diet has not caused problems for many of the million-plus people who’ve tried it, but he wouldn’t recommend it for anyone who needs to inject insulin or anyone with a very low body mass index.
Helen Agresti, a registered dietitian nutritionist in private practice and founder of Professional Nutrition Consulting, LLC, says the fasting-mimicking diet isn’t appropriate for anyone with a history of eating disorders. And if you have a pregnant person in your life, they should also steer clear.
Should you do a fasting-mimicking diet?
IF YOU’RE INTERESTED in trying a fast, maybe start elsewhere first.
Brill suggests intermittent fasting, which is cheaper and more customizable than the fasting-mimicking diet and backed by research suggesting it burns fat and increases autophagy, or cellular housekeeping, among other benefits.
An 18:6 plan is usually easiest for beginners, she says. You skip breakfast and eat during a six-hour window of the day. The 5:2 diet is closer to the fasting-mimicking diet – you eat just 600 calories during two consecutive days of the week and eat normally the other days.
Another option is try one of the easier, cheaper ways to reap benefits of fasting. “The way that I describe fasting within my practice to clients is: we’re actually already doing it, or we should be doing it, after we eat dinner, the remainder of the evening,” says Agresti. “We should not be eating before bedtime, and then during our sleep, we’re not eating. And then in the morning, when the sun is up, and we’re up, we should be hungry.”
This article originally appeared on Men’s Health UK.
Related:
Everything you need to know about fasting and its fitness benefits
