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Is the Fasting-Mimicking Diet Safe? 

By Fitoru | 18 November 2019
bottled water, apple and healthy meals in foil trays

A fasting-mimicking diet (FMD) is a weight-loss strategy that offers up the benefits of fasting but with no actual fasting required. It’s the latest trend, and you’re probably wondering if it works, how it works, and whether or not it’s a safe way to lose weight. We have the details so you can decide.

What Is the Fasting-Mimicking Diet?

Conceived by Dr. Valter Longo, the fasting-mimicking diet calls for restricting calorie intake during certain periods of time. Dr. Longo and the team at the Longevity Institute of the University of Southern California found that calorie restriction promotes the immune system and improves age-related risk factors for humans

These are feats achieved thanks to the metabolic pathways that are triggered during a fasted state, including autophagy (cellular cleanup and recycling), increased stem cell activity, and lower insulin-like growth factor (IGF-1) signaling. Dr. Longo’s book The Longevity Diet goes into more detail about the health benefits of fasting and the clinical trials he conducted showing that the fasting-mimicking diet can lower blood glucose, blood pressure, inflammatory C-reactive protein, and cholesterol levels. 

Sounds pretty impressive…so, what and when can you eat on a fasting-mimicking diet plan?

The Fasting-Mimicking Diet Plan

A fasting-mimicking diet is a moderate-carb, moderate-fat, low-protein diet. It also caps your calorie intake at 40% of your usual diet, but not every day. Between 2 and 5 days of the week you’re required to eat between 500-1,000 calories max, but you can eat as normal for the remaining days. 

A 5-day fast looks essentially like this:

  • Day 1: Consume 1,000 calories at a macronutrient ratio of 55% fat, 35% carbs, and 10% protein.
  • Days 2-5: Consume fewer calories, between 500 and 700, at a ratio of 45% fat, 45% carbs, and 10% protein.
  • Day 6: Return to your normal caloric intake, eating nutritious foods like meats, vegetables, fruit, and dairy.

If you aren’t interested in meal planning and just want to try this diet for the health care benefits, you can buy a 5-day meal package called ProLon which takes the guesswork out of this fasting diet. For those who prefer to prepare their own meals, we have a list of FMD-approved foods.

Fasting-Mimicking Diet Foods

The ProLon fasting-mimicking diet consists of foods like nut bars, tomato and mushroom soups, herbal teas, and oils. Here’s a clearer breakdown of what’s FMD-approved and what isn’t.

FMD-Approved Foods

Nuts, seeds, olives, low-carb veggies, and thin soups are generally approved, including:

  • Nuts and nut bars containing coconut, almond, honey, and nut butters
  • Kale and other dark, leafy greens
  • Decaffeinated herbal teas like hibiscus and spearmint
  • Nutritional yeast and seeds like flax, pumpkin, and chia 
  • Dark chocolate, cocoa powder, and nibs
  • Quinoa and healthy soups like minestrone, tomato, and mushroom blends flavored with lemon juice or fresh herbs
  • Olives, a high-fat snack that is still officially approved in moderation
  • Algal oil, which is vegetarian and full of omega-3 fatty acids

Foods to Avoid on FMD

The above-listed foods are in the official ProLon package along with a couple of proprietary supplements, and though people are encouraged only to eat those foods during fasting days, if you’re attempting the fasting-mimicking diet on your own, here are foods you should definitely avoid.

  • Starchy carbs like bread, pasta, potatoes, rice, and other grains
  • Fruits, no matter their sugar or carb content
  • High-protein foods like animal meats and eggs
  • Foods with added fats or sugar 

The first day will most likely be the hardest to adjust to on the FMD meal plan, but the improvements this diet make to your blood sugar levels and cognitive performance may be worth the sacrifice. Not to mention the loss of belly fat (including the visceral fat that endangers your vital organs). After a few consecutive days of fasting you may just see a drastically healthy change to your body weight and composition. 

What Is the Fasting-Mimicking Diet?

Health Benefits of Fasting-Mimicking Diets

The benefits claimed by the ProLon Fasting-Mimicking Diet are supported by Dr. Longo’s studies and other scientific research that’s been done on fasting practices. 

1. Weight Loss

One of Dr. Longo’s studies found that during a 3-month period the fasting group lost 6 pounds more than the control group, and with far greater losses in belly fat. Other studies unconnected to Dr. Longo and his team also show that intermittent fasting practices can improve weight-loss efforts by 47% more than continuous calorie restriction, and very-low-calorie diets like FMD have been proven to lead to weight loss.

2. Cholesterol and Blood Sugar Control

Dr. Longo’s study also recorded drops in the blood sugar and cholesterol levels (as much as 20 mg/dl) of the FMD group. That information can be trusted based on other studies done with animal models: 4 days of the FMD plan every week over a 2-month period showed reduced insulin resistance, the rejuvenation of damaged pancreatic cells, and improved stability of blood glucose levels in diabetic mice.

3. Anti-Inflammatory Properties

Inflammation contributes to a multitude of chronic diseases, including diabetes, cardiovascular conditions, and cancers. Studies reveal that intermittent fasting practices reduce the inflammation markers C-reactive protein (CRP), interleukin 1 beta (IL-1β), interleukin 6 (IL-6), and tumor necrosis factor-alpha (TNF-α).

One study showed that people participating in alternate-day fasting for Ramadan experienced lowered levels of proinflammatory cytokines. Another study showed that when mice with multiple sclerosis were put on an FMD plan for 30 days they had significantly lower levels of proinflammatory cells linked to autoimmune diseases compared to mice placed on a ketogenic diet for 30 days.

Fasting-Mimicking Diet vs. Intermittent Fasting vs. Keto: What’s the Difference?

Is the FMD plan really that different from intermittent or alternate-day fasting? And what about the low-carb keto diet? Here are the distinctions.

  • Intermittent fasting: The fasting-mimicking diet is indeed one of many forms of intermittent fasting. Intermittent fasting is an umbrella term that covers cyclical fasting practices, daily fasting hours, and more.
  • The ketogenic diet: The ketogenic diet is a high-fat, moderate-protein, low-carb diet, meaning it has some overlap with the FMD ratios, but is very strict in its ratios of 75% fats, 20% protein, and 5% carbs for daily caloric intake. 

All that being said, the FMD plan does help your body maintain a semi-ketogenic state due to the calorie restriction, and ketosis itself mimics fasting, though to achieve the metabolic state of full ketosis (which is characterized by rapid body fat loss), the macronutrient ratios would have to be adjusted.

Ketosis is a secondary metabolism that uses the ketones derived from fat to fuel the body instead of using the easy energy in sugar and carbs. This ketogenic metabolism evolved to help keep us alive during times of famine, so it (just like the fasting-mimicking diet) safely starves the body just enough to get a better health outcome.

Should You Try the Fasting-Mimicking Diet?

The FMD plan may not be for everyone. The intermittent fasting practices that make it beneficial to your health can be had without the cost or the specific nutrition restrictions of the ProLon meal kit, and if your goal is weight loss, the ketogenic diet may be the better route, as it actively targets body fat and has a lot more filling recipes available.

Above and beyond the cost of the meal kit and the severe restrictions on food types, the ProLon kit is not recommended for those who are allergic to sesame, celery, oats, soy, or nuts, and should not be followed by anyone malnourished, underweight, pregnant, breastfeeding, or with serious medical conditions like kidney disease or diabetes. The keto diet, on the other hand, can help those with diabetes actually manage the disease better.

Functional Fasting 

The fasting-mimicking diet, like other intermittent fasting practices, has real health benefits for those fit enough to follow the restrictions. That being said, the FMD plan is not the only way to utilize fasting in small pockets that fit your busy life: ask yourself when you want to fast and find the plan that best suits you.


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