Fast-mimicking diet: benefits, side effects and how to get started

Your diet is a crucial factor in achieving a healthy and well-functioning body. The foods you consume on a daily basis sustain your body’s energy and nutritional needs. With this, you must start your journey to healthy eating habits by choosing a diet. Among the popular fast-emerging types of diets in the fitness world is the ‘fast-mimicking’, an easy and effective eating diet plan.

Fast-mimicking diet (FMD) is somewhat similar to the 5:2 fasting diet, in which you eat about 25 percent of your regular caloric intake for two days and then normally eat for five days. However, for the fast-mimicking diet, it is the other way around. You do the eating only for two days and be in a calorie deficit for five days. Not to mention, this diet is associated with longevity. 

What is a fast-mimicking diet? 

Although it is called the fast-mimicking diet, you don’t necessarily need to do complete fasting. People who follow the fast-mimicking diet eat about 500 to 600 calories on fasting days which don’t have to be consecutive. 

The fast-mimicking diet is a kind of intermittent fasting (IF) plan that limits one’s calorie intake for several days while eating whatever he wants during the other days of the week. It is like tricking your cells into thinking they are not being fed.

With its scheduled eating and reduced calorie-intake concept, the fast-mimicking diet is more like modified fasting, where you don’t totally abstain from eating, compared with the conventional idea of fasting, but you consume a small amount of nutrient-dense foods [1]. 

Moreover, the main idea is to feed your body with just enough calories to make it seem satiated but not full. You must allow your body to enter gluconeogenesis, referring to the process that the body converts fat and other non-carbohydrates to glucose. 

Aside from its eating schedule in a week, the fast-mimicking diet depends on simple whole foods that are low in protein and sugars. In fact, a typical day of a person following the FMD looks like this:

  • Nut butter bar and herbal tea for breakfast. 
  • Only a small serving of soup with kale crackers for lunch. 
  • The snack is only a few olives. 
  • For dinner, just another small bowl of soup. 
  • Taking supplements that have glycerin drink with multivitamins and DHA contents. 
Fast-mimicking diet vs intermittent fasting
Photograph: rawpixel.com/Freepik

Fast-mimicking diet vs intermittent fasting

As mentioned, the fast-mimicking diet is only a type of intermittent fasting, but what makes them exactly different? Basically, the FMD allows you to eat food in small amounts all throughout the day but in a low-calorie deficit that is specific to your body’s needs, such as carbohydrates, fats and protein. Meanwhile, intermittent fasting completely restricts you from consuming food within a period of time. 

The days when you are allowed to eat are called the eating window, in which you are free to eat whatever you want, whether you are following a fast-mimicking diet or intermittent fasting. Although the fast-mimicking diet offers a wide range of health benefits, most especially in obesity prevention, intermittent fasting has much more to offer. 

Intermittent fasting does not allow you to indulge in food as you should be fasting for particular days, making it a healthier diet plan compared with the fast-mimicking diet, where you only reduce your calorie intake when you are not on the eating window. Despite being a healthier option, intermittent fasting is not for everyone as fasting can be a lot to manage; hence, the fast-mimicking diet is more beginner-friendly [2]. 

How does it work?

For five days, you must eat very little in order to follow the rules of the fast-mimicking diet. It works by tricking the body into thinking it is fasting, but technically, it is not. As your body perceives that it is fasting, it undergoes autophagy, which switches on a repair mode and cleans out damaged cells to keep the body functioning properly. 

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Benefits of the fast-mimicking diet

The fast-mimicking diet is found to be helpful in the different areas of the body’s function, including managing weight, improving brain function, lowering inflammation and preventing type 2 diabetes and cardiovascular disease, all of which are essential in lengthening the lifespan.  

Weight management

In the earlier research on the fast-mimicking diet, animals were used as participants to understand the extent of FMD in weight management. Through different animal studies, the fast-mimicking diet was found to be helpful in metabolism and lifespan. 

In one human clinical trial, the effects of a fast-mimicking diet seem to be similar to the animal studies. The study was participated by one hundred healthy individuals who followed FMD five days a month for three months.

At the end of the study, the participants were found to lose weight and visceral fat and drop blood pressure, blood sugar, blood cholesterol and markers of inflammation [3]. 

Furthermore, another study conducted a large randomized trial that shows a fast-mimicking diet as an effective weight loss method with its typical calorie restrictions. The participants were found to reduce weight and improve risk factors, including cancer, diabetes and cardiovascular disease. 

Additionally, it was found that the fast-mimicking diet can promote weight loss of about 6 pounds or 2.7 kilograms for three months. The claim comes from research that compared two groups of people who completed three cycles of the fast-mimicking diet within three months. The fasting group was found to reduce belly fat compared with the control group [4]. 

The fast-mimicking diet has similar benefits to prolonged fasting. By following the diet, your body will use your body’s fat reserves as the primary energy source. Eventually, ketosis will occur, helping with weight loss and preserving muscle mass.

Your body does not need to use your existing protein in muscles for energy while you are on a fast-mimicking diet, resulting in a reduction of fat and improvements in metabolic health. 

The mentioned research above use healthy participants, so how about people who are already overweight or obese? Can the fast-mimicking diet help them as well? The answer is partly yes.  

In a study conducted for 16 weeks with obese men as participants, the researchers found that intermittent fasting can provide around 47 percent more weight loss than continuous calorie restrictions.

Also, a very low-calorie diet can promote weight loss; however, if the fast-mimicking diet is much more effective compared with other diets or fasting methods for obesity is still a bit blurry. 

Lower cancer markers

Here’s another interesting health benefit of the fast-mimicking diet: its capacity to lower cancer markers. Following the studies about the fast-mimicking diet, scientists have further discovered that there is a drop in insulin-like growth factor, which refers to a biomarker for cancer growth. There is also an increase in the activity of stem cell production that indicates the regeneration of healthy cells. 

The good news does not stop there, as the fast-mimicking diet is found to be helpful in improving the success of cancer chemotherapy and experiencing fewer side effects of radiation therapy for cancer patients [5]. However, note that the claim still needs more research, but the provocative data suggested looks promising. 

Specifically, the fast-mimicking diet may help patients with breast cancer by enhancing the quality of life and illness-related perceptions. One major factor of cancer development is aging, as it changes the environment of cells, causing damage. Thus, ensuring to keep the cell environment healthy can decrease the incidence of cancer markers. 

In a study conducted to determine the effects of a fast-mimicking diet in post-surgery, the patients as participants were found to have higher emotional well-being scores and lower fatigue, nausea and insomnia symptoms compared with non-adherent participants on their regular diets. 

Support a healthy brain

Among the many studies conducted about the fast-mimicking diet, there is also a result that recurs over and over again, which is its ability to support a healthy brain. 

Initially, the animal studies found that mice experienced extended longevity, reduced visceral fat, lowered cancer incidence and skin lesions, rejuvenated immune system and delayed bone mineral density loss. And, of course, there was a remarkable brain change detected when the mice followed the fast-mimicking diet for four consecutive days, twice a month [6]. 

Furthermore, another study has backed up the claim that the fast-mimicking diet is good for the brain. The researchers used old mice as subjects, and they administered the fast-mimicking diet cycles among them.

In the end, they discovered that the fast-mimicking diet could promote brain growth, which is scientifically known as hippocampal neurogenesis. Also, the mice showed improved cognitive performance. Although the claim needs to be conducted in human trials, this still shows a promising effect of the fast-mimicking diet [7]. 

Moreover, other studies also dug deep into the fast-mimicking diet’s potential role in bettering Alzheimer’s disease.

One relevant study suggests that following the fast-mimicking diet’s eating plan for four months will not only improve cognitive performance and behaviour in a mouse model of the disease, but it can also lower the levels of tau in the brain [8]. People with Alzheimer’s disease have high levels of tau, which is a protein that tangles in the brain, causing damage to neurons.

supports a healthy brain

When we age, our capacity to keep our cognition declines and interestingly, the fast-mimicking diet can help boost the formation of new neurons in the central nervous system. In addition, the fast-mimicking diet can also improve motor learning and memory [9]. The claims come from a mice study; hence, further clinical research in humans is needed to strengthen the fast-mimicking diet as beneficial to seniors.

Helps with type 2 diabetes and cardiovascular disease 

Type 2 diabetes and cardiovascular disease are two of the major death-causing diseases in the world. Despite being fatal, type 2 diabetes and cardiovascular disease are preventable with the right health choices, and among them is through a fast-mimicking diet. 

Let’s start first with type 2 diabetes which we commonly hear of as a lifestyle disease, as it directly occurs because of one’s eating habits and daily lifestyle choices.

Some studies suggest that adapting the fast-mimicking diet for three consecutive months can lower visceral fat while enhancing glucose metabolism at the same time. It also improves IGF-1 signals, which is a hormone that contributes to regulating growth hormone and insulin sensitivity in people with type 2 diabetes [10]. 

Some other research reports following animal studies revealed that the fast-mimicking diet could improve blood glucose levels and β cell function in mice [11]. However, further intense research is still needed to explore the benefits of pairing the fast-mimicking diet with exercise and other healthy lifestyle changes to prevent and address type 2 diabetes.

Moving on to the beneficial effects of the fast-mimicking diet on cardiovascular disease. Well, the diet seems to contribute to reducing one’s risk of cardiovascular disease and to prove the claim, a study was conducted involving one hundred healthy men and women who did the fast-mimicking diet.

In the end, the researchers discovered that the fast-mimicking diet could lower blood pressure, triglycerides, LDL and total cholesterol and C-reactive protein, which is a marker of systemic inflammation [12]. 

Side effects of a fast-mimicking diet

Despite its many promising health benefits, the fast-mimicking diet has some side effects you must know before starting to use it. Although the majority of the side effects are only temporary, you may still want to prepare your body. Some of the prominent ones are the following:

  • Dizziness and headache
  • Fatigue or feeling of tiredness
  • Hunger
  • Sugar cravings
  • Weakness

Downsides of the fast-mimicking diet

If you are thinking of doing the fast-mimicking diet, it is better to know its downsides as well for you to have a wise decision that suits your health needs and lifestyle routines. 

You become dependent on a company’s packed food. 

Most of the time, people who do a fast-mimicking diet need a food service to provide them with pre-packed foods that are calculated based on their everyday calorie needs. It can be a pretty hassle for you to do it yourself unless you have time to do a weekly diet prep. Also, you are not allowed to eat anything aside from the meals provided by the food service. Hence, dieters often rely on or become dependent on certain food services that can be pricey over time. 

There are no customized food variations for your body’s needs. 

Individualisation is often neglected by the food provider, as they usually prepare food within limited food sets and in batches. By doing generalized food preparations, the body types and certain nutritional needs of dieters are not taken into consideration, resulting in unsustainable fitness goals and ineffective processes. 

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Normally, pre-packed foods have high levels of sodium content.

To make the pre-packed foods last for a week, you may need to add more sodium, and this has become problematic for some fast-mimicking dieters, most especially if you have certain medications. The sodium content of some packaged soups is found to be high, given their low-calorie amount. For instance, one soup has only 120 calories but contains 830 mg of sodium, which makes it still unhealthy.

Uses of the fast-mimicking diet

Now, let’s talk about why a fast-mimicking diet is for you by understanding its uses in your body. Some of the uses of the fast-mimicking diet are the following: 

Helps you enter ketosis more easily

The fast-mimicking diet as a type of intermittent fasting is the perfect method to get ketosis, which refers to a metabolic state that happens when your body uses fat for energy instead of glucose. From the fast-mimicking diet, you can ease your way to following the keto diet, which is another type of healthy, high-fat diet. 

Reduces inflammation and help treat autoimmune conditions

Aren’t we all done with inflammation that gives us many infections and injuries? Well, here’s the answer–the fast-mimicking diet. In a 2016 study, the fast-mimicking diet was discovered to be beneficial in reducing pro-inflammatory cytokines, increasing corticosterone levels and suppressing autoimmunity. The researchers concluded that the fast-mimicking diet is safe and feasible and has the potential to be an effective treatment for relapsing-remitting multiple sclerosis (RRMS) [13]. 

Supports healthy blood sugar levels

If you want to simply regulate your blood sugar levels, the fast-mimicking diet can help you. In the early research studies, the fast-mimicking diet is found to be a great contributor to any diabetes concerns, particularly in regulating blood sugar levels.

It also presents positive results on the regeneration of β-cells, which is a type of cell found in the pancreas primarily responsible for synthesising insulin. Furthermore, it has been shown to reverse β-cell failure and help rescue mice from having type 1 and 2 diabetes [14]. 

People who are NOT ideal for a fast-mimicking diet

Although a great diet plan, the fast-mimicking diet is not for everyone. There are people who are not advised to follow the fast-mimicking diet due to certain allergies and medications.

Individuals who are allergic to nuts, soy, oats, sesame seeds or celery are not ideal dieters of the fast-mimicking diet. Some of the recommended foods to eat during a fast-mimicking diet include the mentioned ones. 

Also, a fast-mimicking diet is not advisable for pregnant and breastfeeding mothers and people with any dietary restrictions, like a low-fat diet, most especially if they commonly experience fever or diarrhoea. Don’t even try to adapt the fast-mimicking diet to your children as well; it is not designed for kids. 

Underweight people should not follow the fast-mimicking diet as well because they may eventually adopt an eating disorder, which can cause them to be anaemic from having inadequate protein intake in the past. 

Additionally, people who often have infections or recurring health issues because of recent injury or illness should not follow the fast-mimicking diet; this type of diet plan may cause them to be more vulnerable and become immuno-compromised. Hence, it is better to consult a physician before deciding to try a fast-mimicking diet. 

People who are ideal to do a fast-mimicking diet

The fast-mimicking diet is generally designed for people who want to be healthy and lose weight. The diet is perfect for overweight or obese people as it can help them lose weight in the healthiest way possible. 

People who are ideal to do a fast-mimicking diet

It is also great for people who simply want to be on top of their diet and increase their health span. Though it needs a doctor’s clearance, the fast-mimicking diet is an effective way to help people with chronic health conditions, including those with blood pressure issues, diabetes, cardiovascular disease and forms of cancer.  

There are important things you need to know if you are interested in trying the fast-mimicking diet; these are the following: 

  • Preparing your body for the calorie deficit is a must. You should eat healthy foods and do exercises weeks before even starting. 
  • Only eat a minimum of 50 to 100 calories every day during your fasting periods. 
  • Drink plenty of water and avoid certain drinks, like sugary drinks, soda, coffee and alcoholic beverages. 
  • During your fasting/calorie deficit days, you must not eat ultra-high fat foods or processed foods. 
  • When you want to drink tea, choose decaffeinated herbal tea with no added sugar. 
  • Don’t cheat! Strictly follow the diet plan for it to become effective; otherwise, your efforts may be wasted. Think about the two days eating window in a week; in there, you can eat whatever you want! 

The stages of a five-day fast-mimicking diet 

Here’s what happens each day during the fast-mimicking diet [15]. 

DayWhat happens?
Day 1 Your body starts to transition into a fasting stage. It upregulates fat burning and prepares to begin autophagy, the cellular clean-up.  
Day 2The fat-burning process that’s happening in your body further increases and cellular clean-up is improved. 
Day 3 The cellular clean-up continues, and your body begins to reach ketosis, the process by which your body fat is burned to be the primary fuel source of your body. 
Day 4 Still, cellular cleaning and renewal continue along with fat burning. 
Day 5 The fast is completed and re-feeding beyond day 5 is to fuel overall wellness. 

6 strict rules of the fast-mimicking diet 

  • Rule 1: Follow the calorie restriction – You must only eat 900 or fewer calories every day to mimic the benefits of a whole month of full-time calorie restriction. You should calculate the calories in the foods you eat every day and add them up to achieve 900 calories or less. 
  • Rule 2: It should be purely vegan Here’s an interesting rule in the fast-mimicking diet that is not emphasized enough by many: animal proteins or dairy products are not allowed during your five-day period. The diet is a one hundred percent plant-based meal plan.
  • Rule 3: You must eat only whole foods The fast-mimicking meal plan is free of ultra-high fat foods or heavily processed foods. You should only include whole foods in your diet, which can be vegetables, whole grains like oats, brown rice and barley, nuts, beans, fish and shellfish. 
  • Rule 4: It is free of sugar, including fruits – If you eat fruits every day, it is time to set them away temporarily for five days, as the fast-mimicking diet is free of sugar, including fruits’ fructose. Ideally, you must avoid eating fruits with too much sugar content. 
  • Rule 5: It is lectin-light – Another rule to take note of: you are not allowed to eat plants with a high content of harmful lectins. Ideally, you may need to soak beans and legumes and pressure-cook them to remove most lectins. 
  • Rule 6: It is highly nutritious – The sole purpose of the fast-mimicking diet is to help you achieve a more healthy body, aside from losing weight, of course. You should maximize micronutrients and minimize macronutrients in order to get the best results from this diet. Making your diet diverse and nutrient-dense with low calories is the ideal meal plan. Also, don’t misunderstand calorie restriction to starving yourself.

The bottom line 

The main question we always answer is ‘how does this affect longevity?’ The fast-mimicking diet is actually popular in anti-aging studies. It is known to help promote longevity and reduce the risk of fatal diseases by just following it for five days each month within a three-month period. 

In fact, prolonged fasting, with only water for two to four days, can reboot your immune system when applied periodically over months or years. It can result in the clear-out of damaged cells and the regeneration of new ones; this can be seen as the reduced appearance of wrinkles and age-related changes [16].

Think of the fast-mimicking diet as reprogramming your body to slow down the signs of aging. You prevent yourself from having fatal diseases, improving your skin with its stem cell-regeneration effects, slowing your bone mineral density loss, keeping your brain function healthy, and the best part, you lose weight. 

The health expert behind the research, Valter Longo, who is the affiliate principal investigator of the Eli and Edythe Broad Center for Regenerative Medicine and Stem Cell Research, is positive about this direction of research and hopes to introduce the diet as disease prevention and treatment. 

The current research studies of the fast-mimicking diet show promising results. Hence, don’t wonder if this diet plan will be the first-ever safe and effective intervention that prolongs longevity and health span in the future. 

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[1] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6816332/ 
[2] https://www.shape.com/healthy-eating/diets/fasting-mimicking-diet 
[3] https://pubmed.ncbi.nlm.nih.gov/28202779/ 
[4] https://www.drlamcoaching.com/blog/benefits-of-a-fasting-mimicking-diet/ 
[5] https://pubmed.ncbi.nlm.nih.gov/27314084/ 
[6] https://pubmed.ncbi.nlm.nih.gov/26094889/ 
[7] https://www.cell.com/cell-reports/pdf/S2211-1247(22)01258-X.pdf 
[8] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3982836/ 
[9] https://fullscript.com/blog/improve-concentration-naturally 
[10] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6816332/ 
[11] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6245873/ 
[12] https://fullscript.com/blog/high-blood-pressure-hypertension 
[13] https://prolonfmd.com/wp-content/uploads/2016/10/cell-press-may-2016.pdf 
[14] https://www.sciencedirect.com/science/article/pii/S0092867417301307 
[15] https://prolonlife.com/pages/fasting-mimicking-diet
[16] https://gero.usc.edu/2019/04/18/eat-less-live-longer-the-science-of-fasting-and-longevity/ 

Photograph: FoToArtist_1/Envato
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