The Fasting Mimicking Diet (FMD) is a dietary approach intended to replicate the benefits of intermittent fasting without the total food abstinence associated with traditional fasting. UCLA Health dietitian Shelby Yaceczko, DCN, RDN-AP, who specializes in clinical nutrition, provides insights into how FMD works, its potential health benefits, and what people should consider before embarking on this dietary plan.
As with any new diet plan, Dr. Yaceczko recommends first taking into consideration one’s overall health and talking it over with a health care provider.
Understanding the Fasting Mimicking Diet
The FMD is primarily plant-based and designed to produce fasting-like effects in the body by targeting blood glucose, ketone levels, and other biological markers.
Unlike traditional fasting, which restricts almost all eating and drinking with the exception of water and certain other liquids, the FMD permits a limited intake of specific nutrients to sustain the body. The diet is often set up in cycles – such as five consecutive days per month over three months.
“You can think of it as a low-calorie diet pattern designed to mimic fasting without fasting,” explains Dr. Yaceczko. “On an FMD, you’re allowed a limited intake of calories from specific food sources at certain times, so you won’t be completely fasting.”
The diet focuses on a macronutrient ratio of approximately 10% protein, 45% fat, and 45% carbohydrates, Dr. Yaceczko says. Generally, individuals consume around 40%-50% of their usual calorie intake on the first day, then reduce to 10%-20% for the next four days.
Health benefits of the FMD
In recent studies, the FMD has shown promising results in weight management, metabolic health, and chronic disease risk reduction.
According to Dr. Yaceczko, documented benefits include weight loss, decreased belly and liver fat, reduced cholesterol and blood sugar levels, and lowered blood pressure. Additionally, the diet may help reduce inflammation and cell damage in the body, processes associated with aging and disease.
One of the unique aspects of the FMD is its potential influence on cellular health, particularly through a process known as autophagy.
“FMD may potentially speed up autophagy, which eliminates bad cells in the body that cause disease and promote aging processes,” notes Dr. Yaceczko. This regenerative effect on cells is a key reason the diet is being studied for its effect on age-related diseases and cellular health.
Cardiovascular health and disease prevention
The FMD has also been linked to cardiovascular benefits. Some early findings suggest it may help reduce risk factors associated with heart disease, improve cholesterol levels and regulate blood pressure, which are vital components of heart health.
Research on the FMD’s effects on chronic diseases such as diabetes, cancer, and Alzheimer’s disease is also ongoing, though most studies have been conducted only on animals.
The potential of the FMD to support cancer treatment and recovery has drawn attention, as well. Though early studies have been promising, Dr. Yaceczko emphasizes caution.
“The FMD is being studied for its ability to extend median lifespan, reduce inflammation and cancer incidence, and increase results from anti-cancer treatments, but much of the research has only been done in animal studies,” she says.
As with any dietary intervention, clinical trials are essential to determine the FMD’s full effects on human health, Dr. Yaceczko says.
Safety considerations and who should avoid the diet
Although the FMD offers a range of potential health benefits, it is not suitable for everyone. Individuals who are pregnant or breastfeeding, those with a history of eating disorders, and people with existing medical conditions such as diabetes, kidney disease, or heart disease, should consult with their health care provider if considering the diet.
“Individuals who are considered at high risk of malnutrition or undernutrition should typically avoid fasting diet patterns,” Dr. Yaceczko warns. Additionally, those on medication should be sure to consult with a doctor before starting a fasting diet.
For those who do adopt the FMD, maintaining proper hydration is crucial. Dr. Yaceczko recommends consuming at least 70 ounces of water daily to prevent dehydration. The diet’s restrictive nature can also pose challenges, and long-term adherence may be difficult for some.
FMD vs. other fasting protocols
Unlike other intermittent fasting methods that require complete abstention from food for specific time intervals, the FMD allows for a limited amount of food intake. Dr. Yaceczko points out that this dietary flexibility can make the FMD more appealing to those who find traditional fasting too restrictive.
“For some, the FMD may be easier to adopt, given it allows for certain foods and nutrients during fasting days,” she explains. By offering a structured yet less restrictive fasting experience, the FMD has opened a door for individuals who wish to explore the benefits of fasting without entirely eliminating food.
A typical FMD meal plan
The FMD primarily includes non-starchy vegetables such as celery, zucchini, tomatoes, and leafy greens, along with whole fruits including berries, apples, and oranges. Healthy fat sources such as avocados, walnuts, and olive oil are also allowed, providing essential fats while limiting protein and carbohydrate intake.
The diet restricts high-glycemic foods such as white rice, white bread, bagels, refined sugars, processed foods, dairy, animal proteins, and starchy vegetables.
These dietary choices are intended to nourish the body while keeping calorie intake low enough to trigger fasting-like biological responses. However, Dr. Yaceczko stresses the importance of personalization.
“It’s essential to talk with your health care provider for individual calorie targets,” she advises, as caloric needs vary based on age, weight, and health status.
Is FMD right for you?
As interest in the diet grows, so does the need for more robust human studies to validate its safety and effectiveness, says Dr. Yaceczko.
“The Fasting Mimicking Diet is still a new diet pattern,” she says, “and we are learning more about it with new research studies coming out.”
While the FMD may be an appealing way to enhance cellular health and support healthy aging, it is essential to proceed with caution and prioritize an individualized approach, Dr. Yaceczko says.
Learn more about nutrition and diets from our UCLA Health GI dietitians.
