The Fasting-Mimicking Diet: What You Need to Know

Over the past few years, the concept of fasting has gone mainstream. For some dieters, it’s become an effective way to lose weight. For longevity buffs, it may be one way to improve health. Indeed, fasting has been linked to a lower risk of diabetes, improved cardiovascular health, better brain function, weight loss, and more. (17) But, in places where eating three meals per day is the norm, the thought of fasting may be daunting.

For those who find most forms of fasting difficult, there may be a solution: the fasting-mimicking diet.

What is the fasting-mimicking diet?

The fasting-mimicking diet (FMD) is a type of modified fast. Instead of totally abstaining from food, as you would during a traditional fast, you consume small amounts of nutrient-dense food. Typically lasting five days, some research suggests that the FMD provides all of the health benefits of fasting without completely foregoing food. (27)

Pioneered by biogerontologist and cell biologist Valter Longo, PhD at the University of California, Los Angeles (UCLA), FMD uses calorie restriction to mimic the effects of fasting in the body while still consuming some food. Done properly, calorie restriction has been shown to provide the essential nutrients you need while also potentially extending lifespan and reducing the risk of age-related diseases. (16)

The fasting-mimicking diet vs. intermittent fasting

The fasting-mimicking diet is different from intermittent fasting because it allows you to eat small amounts of food throughout the day that provide specific amounts of the three key macronutrients—carbohydrates, fats, and protein. Intermittent fasting (IF), on the other hand, involves consuming no food at all for a specific amount of time. When you do eat (known as your eating window), there are typically no food restrictions. Although both FMD and IF have been shown to confer multiple health benefits, you can get considerably more out of IF if you trade in unhealthy and addictive ultra-processed foods for minimally processed foods. (14)(19)(27) Less processed food tends to be higher in fiber and nutrients, resulting in greater satiety. (8)

Did you know? People have been safely fasting since antiquity for religious, cultural, and health reasons. (19)

A fasting-mimicking diet allows you to eat small amounts of nutrient-dense food while still experiencing the health benefits of a more traditional fast.

The fasting-mimicking diet meal plan

During a FMD, which typically lasts for five days, you follow a very low-calorie, low-protein meal plan before resuming your normal eating pattern for the rest of the month. You can do it just once or you can do it monthly for up to six months.

The diet contains specific macro- and micronutrient amounts. Each day provides:

• 43 to 47% carbohydrate
• 44 to 46% fat
• 9 to 11% protein

The first day consists of about 1,100 calories. Days two through five contain approximately 725 calories per day. (27)

Currently, there is a pre-packaged FMD diet available that was created by Dr. Longo designed to eliminate the guesswork. It’s plant-based and does not include gluten, GMOs, or any animal products. Each box delivers five days of soups, bars, snacks, teas, supplements, and a glycerol solution designed to protect lean muscle mass while keeping you in a fasted state. (26)(27) While this offers precise nutrition based on whole foods, it might be possible to recreate the benefits of the commercial FMD by following the macronutrient recommendations and dietary principles of the pre-packaged kit. However, a “fasting-mimicking diet do-it-yourself” approach has not been clinically studied and should only be implemented when recommended and monitored by your integrative healthcare professional to ensure safety and efficacy.

6 health benefits of a fasting-mimicking diet

Preliminary studies and clinical trials suggest that a FMD provides an array of benefits similar to those experienced with intermittent fasting.

Autoimmune disease

According to a recent study in the journal Arthritis and Rheumatology, autoimmunity—where the body’s immune system attacks its own healthy cells and tissues—is on the rise in the United States. (6) In a 2017 study, researchers at UCLA noted that both the type and levels of nutrients found in the FMD can influence key immune cells called lymphocytes, providing a possible positive impact on several autoimmune diseases, including multiple sclerosis (MS), rheumatoid arthritis (RA), and type 1 diabetes. (4)

In one animal study of MS—which is among the most common autoimmune disorders—researchers reported that a FMD reduced the diseases’ severity and completely reversed symptoms in 20% of the subjects. (5)(23) They found that a FMD not only increased corticosterone and regulatory T-cell levels, it also reduced inflammation and improved nerve function by repairing the protective myelin sheath that surrounds axons. (5)

Animal studies suggest that a fasting mimicking diet could foster the formation of new brain cells.

Cognition

Maintaining cognition is one of the most cited concerns among people as they age. (11) Research in the journal Cell Metabolism reported that a FMD can foster the formation of new neurons in the central nervous system and improve motor learning and memory. (2) As this study was conducted on mice, further clinical research is needed to confirm these benefits for people entering their senior years.

Other studies have begun to address FMD’s potential for those with Alzheimer’s disease. One study found that four months of a FMD eating plan not only improved cognitive performance and behavior in a mouse model of the disease, it also reduced levels of tau in the brain. (18) Tau is a protein that forms tangles in the brains of those with Alzheimer’s disease and can damage neurons. (15)

Type 2 diabetes

Although type 1 diabetes is an autoimmune disorder, type 2 diabetes is often considered a lifestyle disease. (10) Practicing an FMD for three consecutive months has been found to reduce visceral fat while improving glucose metabolism and IGF-1 signaling, a hormone that, among other things, plays a role in regulating growth hormone and insulin sensitivity in individuals with type 2 diabetes. (1)(27) Other research reports the FMD’s ability to improve blood glucose levels and β cell function in mice. (28) More research is needed to explore the benefits of pairing FMD with exercise and other healthy lifestyle changes for preventing and addressing type 2 diabetes.

Heart disease

Cardiovascular disease is the leading cause of death in America. (3) Practicing a FMD may help to reduce some of the risk factors that contribute to this condition. In a human trial involving 100 healthy men and women, researchers found that the FMD, when practiced monthly for three months, lowered blood pressure, LDL (bad) and total cholesterol, triglycerides, and C-reactive protein (a marker of systemic inflammation). According to the findings, systolic blood pressure was reduced by 4.5 + 6.0 mmHg while diastolic BP dropped 3.1 + 4.7 mmHg. The researchers also noted that both cholesterol and triglycerides were reduced more in participants whose levels were already elevated at the start of the study. Waist circumference—an important risk factor for cardiovascular disease—also improved during the trial. (21)(27)

Longevity

When it comes to longevity, anthropologist Ashley Montagu once remarked that “the idea is to die young as late as possible.” Practicing a FMD monthly for at least three months has been shown to extend healthspan and lifespan by reducing IGF-1 levels, oxidative damage, and inflammation while optimizing energy metabolism and boosting cellular protection in mice. (1)(2)(13) The FMD restricts protein intake, and this has been shown to increase both health and longevity. (2) What’s more, some research has documented the ability of the FMD to trigger autophagy, the body’s process of breaking down old or damaged cells and recycling their components into new, healthy cells. (25)

Practicing a fasting mimicking diet once a month for at least three months may enhance weight loss.

Weight loss

Many people try a FMD in hopes of losing weight. Studies do show that three consecutive cycles of the FMD can reduce body weight, total body fat, and waist circumference. It’s been found to also increase lean body mass. These results may persist for several months after the three-month FMD program has been completed. (7)(27)

Side effects of a fasting-mimicking diet

Although a FMD can provide numerous health benefits, there may be some temporary side effects. Those most frequently reported include:

• Dizziness
• Fatigue
• Headache
• Hunger
• Sugar Cravings
• Weakness (20)

Should you try a fasting-mimicking diet?

FMD is considered safe for most individuals and may provide several health benefits. (24) However, whether the diet is more effective than other methods of intermittent fasting is still unclear.

FMD is not advised for certain individuals, particularly:

• Individuals who suffer from an eating disorder (22)
• Those under the age of 18 years (9)
• Women who are pregnant and/or breastfeeding (12)

The bottom line

The FMD is a modified fasting diet in which you consume small amounts of food in a way that still provides the benefits of fasting. It may promote healthy aging and weight loss while also improving cardiovascular, cognitive, immune, and metabolic health. A fasting-mimicking diet may be a simple and effective way to enjoy those benefits without time-restricted eating or other traditional forms of fasting. However, more research is needed to confirm many of the proposed health benefits. It’s also wise to consult your healthcare practitioner prior to beginning a FMD or any type of dietary changes such as IF or time-restricted eating, especially if you have an existing medical condition.