Whether it’s the fact that we’ve been consuming more comfort foods and moving less during the pandemic (resulting in the dreaded “quarantine 15”) or the annual buzz around shaping up for summer, dieting continues to trend on social media. One diet in particular, the fasting-mimicking diet, is generating a lot of buzz — but what is it, exactly, and is it safe? It turns out, the fasting-mimicking diet isn’t primarily focused on weight loss (though it can lead to that), but other benefits such as slowing the aging process. We talked with experts to find out more.
What is the fasting-mimicking diet?
If fasting is the complete elimination of food, fasting mimicking (or fast mimicking) is a diet that allows food but in timed patterns that still produce the benefits of fasting. According to research, fasting and diets that mimic fasting can benefit the immune system and reduce markers associated with age-related disease, says Kylie Ivanir, MS, RD, of Within Nutrition and ReBody28.
The whole “getting older” part has a lot to do with fasting-mimicking diets surging in popularity. “People are wanting to work and perform much later in life, and therefore anti-aging science and biohacking have taken center stage recently,” says Ivanir. Immune conditions are also on the rise, which has led to more interest in this field, she adds.
A fasting-mimicking diet is low in calories, sugar and protein; moderate in carbohydrates; and high in unsaturated fats, says Ivanir. When following such a diet, timing is very important: Fasting-mimicking diets are designed to be followed only five days per month. After five days, you can resume regular healthful eating patterns.
The trademarked fasting-mimicking diet program out there is from a brand called ProLon, based on research from Valter Longo, PhD, director of the Longevity Institute at the University of Southern California, one of the top centers for research on aging and age-related disease. It’s a five-day fasting program that’s been scientifically developed and clinically tested to give you essential nutrition without activating your body’s “food sensing system” — aka, it sends your body into fasting mode (as if you were only drinking water) but you actually get to eat food on the plan.
How fasting-mimicking diets work
The benefits of fast-mimicking diets occur from activating autophagy, a process in the body of cell renewal and regeneration, says Ivanir. Autophagy causes damaged cells in the body to be replaced with younger, more effective immune cells. One small, randomized trial demonstrated that following a cycle of five days of a fasting-mimicking diet per month for three months reduced risk factors for age-related diseases. In addition, individuals in the trail experienced weight loss along with a reduction in total body fat, fasting glucose, blood pressure and other markers associated with aging and age-related disease.
ProLon’s program is specifically based on 20 years’ worth of scientific research from the USC Longevity Institute. It’s marketed as a calorie-restricted diet that triggers the natural process of cleaning and rejuvenating your cells, which supports healthy aging; helps you to positively impact your relationship with food; enhances performance by improving your mental clarity, focus and energy; and kickstarts weight loss.
On the ProLon plan, you receive five boxes of food — one to eat for each day. Day 1 transitions your body into fasting with 1,100 calories, while on Day 2, your body begins to enter ketosis (i.e., starts burning fat instead of sugar). Autophagy begins on Day 3 and continues through Days 4 and 5. From Days 2 through 5, you’re eating only 800 calories. Because calorie consumption is so low, it’s recommended that anyone in the middle of a fasting-mimicking period refrain from exercising during that time.
What you eat on a fasting-mimicking diet
When following the ProLon plan, all the guesswork of what to eat is removed because you simply consume what’s in the box each day, and that’s it. While the company doesn’t spell out exactly what is included and specific flavors of each item when you order, each box generally contains a variety of nut bars, soups, crackers and healthy fats such as olives, along with a selection of teas, an energy drink mix and a water bottle to ensure adequate hydration.
Can you follow a fasting-mimicking diet without buying the ProLon box? Not to the exact science, says Tara Scott, MD, chief medical officer and founder at Revitalize Medical Group in Akron, Ohio. She’s done the ProLon plan eight times personally and regularly holds group challenges with her staff. While a health coach on her team has analyzed the macros of the ProLon box and tried to come up with a DIY version of the fasting-mimicking diet, the contents of the actual ProLon box have been scientifically designed, so there’s no proof you’ll get the same metabolic effects, says Dr. Scott.
Are fasting-mimicking diets safe?
Dr. Scott recommends fasting-mimicking diets to people who are struggling with high cholesterol, high blood pressure, insulin resistance, pre-diabetes or high sugar, especially. She first tried ProLon’s program herself not because she had a weight problem (in fact, she is a marathon runner), but because she was pre-diabetic based on genetics. “Nothing else I was doing could get my sugar down,” she says.
In general, a fasting-mimicking diet such as ProLon’s is safe and effective, says Dr. Scott, who says you’ll generally see a loss of about 5 percent of your body fat the first time you try it. More benefits she sees in her patients following ProLon’s plan include a reset of gut bacteria, leading to a reduction in bloating and sugar cravings, and decreased joint aches and pains.
One big point to remember is that a fasting-mimicking diet should not be followed long-term. This method of eating is meant to last for only five days at a time, as it’s too low in calories, carbohydrates and protein to sustain your body in a healthy way beyond that, says Ivanir.
Fasting-mimicking diets are also not for everyone. “The restrictive cycle may be triggering for some individuals and can encourage disordered eating behaviors, and this diet is also not ideal for those who are pregnant or breastfeeding,” explains Ivanir. Anyone with a diagnosed health condition such as blood pressure issues, diabetes or cardiovascular disease should consult with their doctor before starting a fasting-mimicking routine. As research is still developing, a fasting-mimicking diet should only be undertaken under the supervision of a licensed healthcare professional, she adds.
What to know before trying the fasting-mimicking diet
There’s no way around it — you’ll be hungry while following the fasting-mimicking diet plan. It is all about caloric restriction, after all, to trigger the benefits, says Dr. Scott. Second, the price of the ProLon plan can be cost prohibitive for many. A five-day meal program for a first-time faster is regularly $249 (currently on sale for $199), though you can save a little money if you opt to order three boxes (to consume in three consecutive months) at once.
Still, the ProLon plan is a good way to help you kick start another kind of diet, says Dr. Scott. For instance, say you want to start following the keto diet and don’t know where to begin — you could follow the ProLon plan for five days and you’d be in ketosis and easily able to transition to keto from there. This particular diet is also vegan, gluten-free and dairy free, so if you were seeking to eliminate any of those from your diet, this would also be a good place to start, says Dr. Scott.
You should also understand that if you have a lot of weight to lose, the fasting-mimicking diet not be the right long-term plan for you. Most people will lose about 5 pounds the first time, maybe 5 more the second time, and so forth, but you won’t likely see double-digit weight loss from only following this plan.
Can you create your own fasting-mimicking diet?
If you want to try DIYing a fasting-mimicking diet plan, there are a few things to consider (though again, there are no guarantees you’ll get the same metabolic results as you would with ProLon).
First, consider protein. Ivanir says that for adults under 65 years old, protein intake should be around 0.31-0.31 grams per pound of body weight — lower than the general protein recommendation of about 0.8 grams per pound of body weight. “Protein is kept low because it can activate the mTOR pathway, a signaling pathway that plays a role in cell proliferation and growth,” explains Ivanir. “Reducing protein can turn this pathway off, which is thought to be beneficial.” (By the way, another method of activating the mTOR pathway is to increase consumption of leucine.)
Your main protein source on a fast-mimicking diet comes from beans, chickpeas, green peas and other legumes, says Ivanir. The goal is to minimize saturated fat and sugar while emphasizing whole grains, high-quality vegetables, olive oil and nuts.
Before beginning a DIY fasting-mimicking diet regimen, in addition to talking with a healthcare professional, you can set yourself up for success by creating a meal plan ahead of time, suggests Ivanir. “If you know what you are going to eat each [of the five days], it is much more likely you will stick to the plan,” she says. To do this, stock your fridge and pantry with the proper foods — such as whole grains and vegetables; protein such as high-quality fish; and healthy fats like olive oil, avocado, nuts and olives. “You might also consider telling friends and family you will see during this time about your plan to ensure they’ll support you,” says Ivanir.
Once you’ve done the planning, you may also want to ease into the diet slowly by eating higher calories the first day (about 50 percent of your usual intake), followed by a greater reduction the remaining days (think 35-40 percent of your usual intake), advises Ivanir. Some people may also benefit from using a multivitamin supplement during the diet to ensure they’re meeting all their nutrient needs. You can see how you’re feeling as you go, and make adjustments as needed, such as adjusting protein or carbohydrate intake slightly.
Finally, if you’re not ready to commit to five days a month following a fasting-mimicking diet, you can start small and begin to see some of the benefits. Ivanir recommends first aiming to reduce the amount of sugar and processed foods you’re consuming on a regular basis. “This will help to naturally detox your body and improve your anti-aging mechanisms,” she adds.