Five-day fast: A guide to the fasting mimicking diet for weight loss

While eating during a fast might seem counterproductive, with the fasting mimicking diet you can enjoy meals while simultaneously experiencing the weight loss and health benefits of fasting. Its specially-designed meal plan allows you to eat while maintaining the body’s fasting state but avoiding the negative side-effects of conventional prolonged fasts. What is the fasting mimicking diet, how does it work and what are its weight loss benefits?

What is the fasting mimicking diet?

Fasting is the ancient practice of restrictive eating that can be used to lose weight through the process of ketosis, during which the body metabolises its fat reserves for energy. It has become the most popular diet method in the US, according to the International Food Information Council’s 2020 annual Food and Health survey [1]. In fact, everyone fasts to some extent every night when they sleep, during which the body’s insulin levels drop and signal to the body to burn fat instead of store it.

Popular types of fasting for weight loss are intermittent (alternating periods between fasting and feasting) and prolonged (fasting for longer than two consecutive days). Prolonged fasting is an effective way to lose weight and reset your body’s metabolism, however it can be accompanied by negative side effects including headaches and hunger that can deter those new to the fasting lifestyle.

The fasting mimicking diet differs from conventional prolonged fasting in that it allows you to continue to eat small, calorie-restricted meals with mostly plant-based ingredients including olives, vegetables, fruit, nuts, seeds and herbal teas, with less than half of the average daily food intake of a 2000kcal diet. So called ‘food fasts’ are considered to be just as effective as normal fasting and are an easier, more realistic way of fasting that people can actually sustain.

Even additional beverages like tea, coffee and sparkling water are allowed in moderation during this fast if you need a quick energy boost. Indeed, the fasting mimicking diet provides the right balance of fats, proteins and carbohydrates to limit hunger pangs associated with regular fasting while avoiding triggering the body’s nutrient-sensing pathways and maintaining the fasting state.

Developed by Dr Valter Longo, Director of the Longevity Institute at the University of Southern California, L-Nutra’s ProLon was the first fasting mimicking diet on the market and now has over 220,000 users. Dr Longo advocates the fasting-mimicking diet as a weight loss method that additionally helps to improve health and prevent disease. Designed to fit fasting around a busy lifestyle, the ProLon fast only lasts for five days out of every month, making it accessible from complete beginners to the most committed of fasters. Delivered directly to your door, the ProLon programme supplies nutritious, plant-based food, beverages and supplements for each day of the fast with the right balance of nourishment and energy while maintaining the fasting state.

Longevity.Technology readers can use the code LTECH15 to claim your 15% off any ProLon fasting plan.

How does the fasting mimicking diet work?

During prolonged fasting, the body’s metabolism switches from using readily available blood glucose from food to ketones produced from fat reserves through the process of ketosis. The fasting mimicking diet, as the name suggests, triggers this metabolic shift by simulating the fasting state. It is based on Dr Longo’s research into cellular nutrient sensors – how our cells know when there is enough food available (feast), and when they need to use stored glucose and fat for energy (fast).

ProLon meals use a combination of macronutrient and micronutrients that avoid triggering the body’s nutrient sensing pathways, inhibiting the same metabolic pathways as fasting. This starts ketosis, as the body metabolises fat reserves to produce ketones which feed the brain and result in weight loss. Fasting and the fasting mimicking diet also simulate stress resistance in cells, triggering autophagy – the process by which cells reuse their old or damaged cell components to rejuvenate [2].

These processes occur over the five days of the diet:

Day 1: On the first day of the fast, the body begins to transition into a fasting state. At this point, hunger hormones such as the gut hormone ghrelin may spike causing the dreaded hunger pangs, and within about 8-12 hours, the majority of blood glucose will have been used up by the body for energy. The human body is psychologically conditioned to crave food during the day (not to mention the modern tradition of consuming three full meals a day) so it may feel difficult to work against the body’s natural instincts and ignore hunger pangs. However, by resisting this first wave of hunger, insulin levels will remain low and the body will begin to switch to fat reserves for energy. Initially, you may experience a rapid amount of weight loss but this is likely from water, as glucose stores hold water that is released when the stores get emptied.
Day 2: After burning available glucose supplies, the body will switch to using its fat reserves for energy and start the production of ketones through ketogenesis. By the 48 hour mark, ketosis (fat burning) will begin. Weight loss through fat can start from as early as Day 2! The stress hormone cortisol starts to increase due to not eating, while ghrelin decreases. This hormonal shift can improve alertness and mental clarity and reduce hunger pangs. Feeling dizzy or lightheaded at this point could be a sign of mild dehydration as your body is not absorbing as much water from food (which usually makes up around 40% of your normal daily water intake). To make up for this deficit, up your water intake to more than usual and take the drinks included in the ProLon plan. However, over-consuming plain water during a fast can dilute blood electrolytes and exacerbate dehydration symptoms even more, therefore adding a small pinch of salt in every glass of water is recommended.
Day 3: The process of autophagy begins during the first few days of the fast and cells start to rejuvenate. Autophagy is achieved through the mild dietary stress that fasting places on the body, called hormetic stress. This triggers a cascade of hormones that simulate autophagy, weight loss and metabolic healing. Additional hormetic stressors like exercise, heat exposure and cold exposure also have this effect so are commonly used alongside fasting to enhance results [3]. Therefore it is recommended that you keep doing light exercise like walking or yoga during fasting, but save any strenuous exercise for after fasting. Exercise has the added benefit of keeping your body and mind occupied, distracting from any hunger pangs and the temptation to break your fast. Also on day 3, ketosis ramps up and hunger pangs should subside after a few days as the body adapts to the new eating pattern.
Day 4: Autophagy reaches a peak and users may experience the euphoria of a ‘fast high’, further reducing feelings of hunger. This may be related to increased levels of brain-derived neurotrophic factor (BDNF), a chemical released in the brain that improves mood.
Day 5: The final fast day, cellular renewal continues beyond day five with lasting results including weight loss and improved mental clarity, focus and energy. Post-fast, your bodyweight might creep back up a little, but this is common and is not your body regaining fat but rather it replenishing the water weight lost during fasting [4].

Weight loss benefits of the fasting mimicking diet

With the fasting mimicking diet, you can experience the same benefits as conventional prolonged fasting including weight loss and protection against disease. As the body switches to using fat reserves as its primary energy source, fat is burned through ketosis, causing weight loss while preserving muscle mass as the body does not need to use protein in muscle for energy.

By the end of the five-day fast, users may see a reduction in body fat, a smaller waist circumference, improved systolic blood pressure and metabolic health. When used for three consecutive months, ProLon helped people lose on average 5 lbs and 1.2 inches of waist circumference [5].

Weight loss associated with fasting lowers the risk of obesity-related diseases including diabetes and certain cancers.

Health benefits of the fasting mimicking diet

Long-term, fasting has been shown to effectively reduce inflammation and risk of related diseases such as Alzheimer’s, cardiovascular disease and arthritis [6].

Additionally, the cellular renewal achieved through autophagy can protect against diseases including cancer, cardiovascular disease and diabetes [2].

Fasting may even have anti-aging effects and is thought to reduce your biological age — the age based on the health of your cells rather than the years you have lived, which can be affected by lifestyle choices. Indeed, the Longo laboratory published key findings from randomised clinical trials proving that the fasting mimicking diet lowers the risk factors and markers of aging and age-related disease [7].

The fasting mimicking diet achieves the same benefits of fasting without fully restricting what you can eat and is easily adaptable to a busy lifestyle. ProLon recommends fasting every month to unlock the full weight loss benefits of fasting and the best metabolic health.