What You Need to Know About The Fasting-Mimicking Diet


Fasting diets are going mainstream. In a society where it’s customary to eat three large meals each day while snacking throughout, the idea of fasting may seem extreme. Generally, fasting involves eating no or very little caloric-containing food and beverages for periods ranging from 12 hours to a couple of weeks.

Any type of fasting involves calorie restriction, which may lead to a lower overall energy intake and weight loss. While we often think of fasting as a weight loss strategy, many researchers who study fasting aren’t focused on that at all. Instead, they are shedding light on the role of fasting in disease prevention and longevity. There are many forms or methods of fasting, such as intermittent fasting and water fasting.

A recent fasting trend is the Fasting Mimicking Diet (FMD), which is based on research carried out at two of the world’s leading centers for biomedical and longevity research located at the University of Southern California, the Longevity Institute and the Diabetes and Obesity Research Institute.

What is the Fasting Mimicking Diet?

The FMD is a patented program created by Dr. Valter Longo, director of the Longevity Institute at the University of Southern California. Initially, he studied fasting in mice and found that two to five days of fasting each month reduced disease risk. The research was then expanded to people with similar results. (1)

The FMD is a type of modified fasting. Instead of abstaining from food completely like a traditional fast, you consume small amounts of food – but you do it in such a way that provides the benefits of fasting.

close up of a salad on a white plate

The fasting-mimicking diet controls food portions which can help you manage and maintain your weight.

Dr. Longo has since begun selling a five-day weight loss program called the ProLon Fasting Mimicking Diet through L-Nutra, a nutrition technology company that he founded. (2) Outlined below are some of the principles of the FMD. (3)

An overview of the Fasting Mimicking Diet

A fast-mimicking diet usually lasts five days. Intake of carbohydrate, protein, and calories are kept low, while fat intake is high. Calories are reduced to approximately 40% of normal intake, which helps keep you nourished and puts less stress on the body than normal fasting would, while providing the same results.

Day one of the diet provides approximately 1090 calories (10% protein, 56% fat, 34% carbohydrate), while days two through five provide only 725 calories (9% protein, 44% fat, 47% carbohydrate). (3)

The fast is then followed by a 25-day “refeeding” period, during which individuals return to a regular diet. It is recommended to repeat the five-day fasting, 25-day refeeding cycle three to four times in a row to maximize its effects. (3)

Fasting Mimicking Diet food list

The FMD is based on a whole food-derived and plant-based eating pattern. (3)

Nutrient guidelines are as follows:

  • Carbohydrates should come from complex carbohydrate plant sources (e.g., quinoa, buckwheat, whole-wheat pasta, beans, fruits, and vegetables)
  • Protein should come from plant-based sources (e.g., tofu, tempeh, pulses, lentils) (2)
  • Fats should come primarily from oils (e.g., coconut oil, olive oil) and nuts (e.g., almonds, walnuts) (2)
  • Sugar intake should be kept below 30 g on day one and below 20 g on days two through five (2)
pea soup with peas next to it

The FMD that mimics the effects fasting, promoting cellular protection and regeneration, while still providing all of the essential nutrients.

Fasting Mimicking Diet benefits

While limited studies have examined the effects of FMD specifically, preliminary evidence suggests that the FMD provides benefits similar to those experienced with regular fasting. This evidence is summarized below, along with general benefits of dietary patterns that incorporate fasting.

Improved weight loss

A clinical trial examined the effects of a FMD on markers and risk factors for aging and age-related diseases. One hundred healthy participants from the United States were randomized into two groups. One followed three months of an unrestricted diet and the other group consumed the FMD for five consecutive days per month for three months. Participants in the FMD group lost an average of 2.6 kg (almost 6 lbs). This weight reduction was due in part to a reduction in total body fat and trunk fat. (4) Although this is a relatively small study, led by the developer of the ProLon Fasting Mimicking Diet, other studies have shown that dietary patterns that incorporate fasting are effective in promoting weight loss.

In a small pilot study, 13 women and six men with metabolic syndrome were instructed to limit food consumption to 10 hours each day, maintaining a 14-hour fast each night, for a period of 12 weeks. Participants were instructed not to consciously reduce their caloric intake or change their diet during the 10-hour eating window. Over the 12 weeks, participants lost an average of 3.3 kg, about 3% of their body weight. This change also led to a 3% reduction in abdominal fat and a 4% reduction in waist circumference. (5)

Reduced blood sugar and cholesterol

The same small study conducted by Dr. Longo also found that the FMD group experienced a significant drop in blood sugar and cholesterol levels. Blood sugar levels dropped an average of 0.8 mg/dl and cholesterol levels dropped an average of 11 mg/dl including a small drop in LDL cholesterol (the bad cholesterol). However, when compared to the control group eating an unrestricted diet, these results were not significant. (4)

More studies have suggested that fasting may improve blood sugar control. In one study, 10 obese individual diagnosed with type 2 diabetes followed an intermittent fasting protocol for two weeks. This consisted of fasting for a period of 18 to 20 hours each day, with participants allowed to eat whatever they choose during the eating period. The intermittent fasting yielded a significant increase in the incidence of fasting blood sugars that were at target and a favorable decrease in high blood sugar after eating. (6)

Other research has found that incorporating fasting into your routine can be especially beneficial when it comes to heart health. In this study, sixteen obese individuals, 12 women and four men, participated in alternate-day fasting for eight weeks. Participants were found to have reduced levels of LDL cholesterol by 25% and triacylglycerol levels that were 32% lower compared to baseline. (7)

Reduced inflammation

Some studies have found that fasting can help to decrease levels of inflammation in the body and help to promote better overall health. While acute inflammation is a normal immune process that helps fight off infections, chronic inflammation can have serious health consequences, including heart disease, diabetes, cancer, multiple sclerosis, and inflammatory bowel disease. (8)

A recent study showed that intermittent fasting reduced the release of pro-inflammatory cells called monocytes in blood circulation. In fact, during periods of fasting, these cells go into “sleep mode” and are less inflammatory than monocytes found in those who were fed. (9)

In another study, individuals practicing alternate-day fasting for the religious holiday of Ramadan were found to have lower markers of inflammation compared to the weeks before or after. (10)

Slowed aging and cognitive decline

One of the primary reasons that Dr. Longo developed the FMD was to slow the aging process and the risk of certain diseases by promoting the body’s ability to repair itself through cellular regeneration. (11)

The process by which old and damaged cells are recycled to produce new healthier ones is called autophagy. Fasting has been shown to optimize autophagy, which might help to slow cellular aging and mental decline. (12)

Scientists at Georgia State University in Atlanta showed that fasting, or restricting calorie intake, can produce a molecule that delays vascular aging. In studying mice, they saw that starving mice produced the molecule beta-hydroxybutyrate, a molecule that is produced by the liver and used as an energy source when glucose is not available. Researchers also found that beta-hydroxybutyrate can prevent one type of cell aging known as senescence. (13)

elder couple working out outdoors

Fasting has been shown to optimize autophagy, which might help to slow aging and mental decline.

Side effects of the Fasting Mimicking Diet

With all the potential benefits of the FMD, there are also some drawbacks to consider. ProLon states that symptoms frequently seen with fasting diets include:

Less common side effects include:

Many of these symptoms make up what is called the “keto-flu”, which is the result of the body’s rapid excretion of sodium and fluids and carbohydrates are restricted. (14) Most of the symptoms resolve either during or immediately after completion of the diet, however, can last for a couple of weeks in some individuals. (15)

Should you try the Fasting Mimicking Diet?

The FMD is considered to be safe for most healthy individuals and may provide several health benefits. However, whether the diet is more effective than other methods of intermittent fasting is still unclear. Anyone thinking of trying the FMD or any other type of fasting diet should consult their healthcare practitioner prior to starting, particularly those with pre-existing medical conditions.

According to ProLon, the FMD is not advised for certain individuals, including:

  • Individuals under the age of 18 years or over the age of 70 years
  • Women who are pregnant and/or breastfeeding
  • Individuals who have a troubled relationship with food, including disordered eating
  • Individuals who are underweight and/or malnourished
  • Anyone with certain diagnosed medical conditions
  • Individuals with different dietary needs that would not be met with the diet guidelines (16)

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 help to promote weight loss and reduce blood sugar, cholesterol, and inflammation.

Only one human study on the diet has been carried out to date, and more research is needed to fully validate its benefits.