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What’s The Best Fasting Method For Longevity, Health, And Weight Loss?

What we eat, when we eat and how much we eat all impacts how long we live.  

For what to eat to live longer, we talk about the best longevity diet and foods here

So, that leaves the questions of when and how much to eat for optimal longevity — which we cover in this article.

Regarding how much to eat, almost a century of scientific research shows that eating less slows the rate of aging, extends lifespan, and reduces the risk of many aging-related diseases, including heart disease, Alzheimer’s and cancer.  

Eating less can be accomplished in two ways: through caloric restriction or fasting.  

This article is focused on fasting. We’ll first compare the research for caloric restriction vs. fasting, discuss the best method to fast, and will wrap up with some important things to consider when fasting. 

Let’s dive in! 

Caloric restriction versus fasting

Caloric restriction means eating less all the time, whereas fasting means eating less, sometimes.

With caloric restriction, instead of consuming, say, 2000 calories per day, one would consume 25 percent fewer calories per day. Caloric restriction has shown to extend lifespan and reduce the risk of many aging-related diseases (R,R,R).  

Around age 33, almost 60 percent of the calorie-restricted monkeys are still alive compared to 20 percent of the monkeys that could eat as much as they wanted. 
Source: Caloric restriction delays disease onset and mortality in rhesus monkeys. Science, 2009

However, it’s not easy to continuously eat less, and to do so for years or even the rest of your life. Some people believe you will always feel hungry, but this is also somewhat relative: after a while many people get used to it. 

In fact, caloric restriction does not have to be that difficult. A simple way to eat less is just by eating two meals per day. Not only will this save you some money, but a lot of time, too (no prep or eating time!)!

While caloric restriction means restricting calories throughout the day, fasting means going without food for specific periods.

Often, the boundaries between caloric restriction and fasting are somewhat blurry. After all, if you fast regularly then you’re also likely to restrict calories overall.

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Different forms of fasting and circadian eating plans

1. Intermittent fasting (technically speaking, it’s probably not what you think)

The most common form of fasting is called “intermittent fasting.”  Intermittent fasting means you fast during specific periods, mostly for 12 hours to up to 2 days, while at other times you eat as usual. However, technically, for it to be considered an intermittent fast, you would have to be consuming substantially fewer calories over the timeframe measured. If, however, you are consuming approximately the same or more calories, but eating only during a fixed number of hours (12 or fewer), it would be considered Time-Restricted Eating (TRE); more on this in the next section.

People have been labeling TRE as intermittent fasting so often that many now use the terms interchangeably.

2. Time-Restricted Eating (also called time-restricted feeding or time-restricted fasting)

During time-restricted eating, one eats only during a specific time window for the day, but does not restrict their calories (as that would constitute intermittent fasting). 

For example, you only eat within an 8 hour window, e.g., between noon to 8 pm. For the remaining 16 hours you don’t eat anything – you fast. This is called the 16/8 method. 

There are many variations of this. Some people only eat within a six or even four hour window, while other people simply skip breakfast or dinner every day.

But when is the best time of day to schedule your “eating window” for? 

Scientists believe your eating window is better set sooner in the day than later. 

The reason for this is that our metabolism changes throughout the day. In the morning up until about noon our body is best equipped to deal with food. In other words, to process the insulin, glucose, fats and amino acids and to handle the big increase in oxidative and inflammatory stress that goes together with every time you eat a meal.

In one study, men at risk for type 2 diabetes that adhered a 9-hour window eating period from 8 am to 5 pm had a 36% reduction in their glycemic response to a meal and reduced fasting triglycerides compared to men who ate during a more delayed 9-hour time window from noon to 9 pm (R). 

Another study showed that insulin sensitivity, blood pressure and oxidative stress improved significantly in men with prediabetes that ate in an 8-hour period (between 7 am and 3 pm) versus people who ate in a 12 hour period (from 7 am to 7 pm) (R). 

This and many other studies show that when you eat has a big impact on your metabolism and health! (R)

3. One-day fasting

As the name implies, one-day fasting involves going 24 hours without a meal. For example, some people choose to do this one day per week, while others do it every other day (this method is called “alternate-day fasting”). 

Another example is the 5:2 diet. During two non-consecutive days in the week one eats only 300 to 600 calories per day. This is not strictly fasting, but still one eats much less than one would normally do. 

4. Multiple-day fasting (sometimes also called prolonged fasting)

One can also fast for multiple consecutive days. For example, common routines include fasting for two days each week, or for 3 days every month, or 3 days every 3 months.

Fasting: how to do it well

As you can see, there are plenty of different ways to fast. But what’s the best way to fast for longevity? And what are some important things to take into consideration when fasting? 

Let us first say that almost every fasting method is healthy (as long you don’t overdo it and pay attention to some caveats we explain below). 

Fasting activates many geroprotective (“anti-aging”) mechanisms, like inducing autophagy which means cells will digest more waste material that otherwise accumulates which contributes to aging (R,R) and the activation of various protective genes, like those that code for sirtuins (R) or that reduce inflammation (R,R).

Even very short periods of fasting confer considerable health benefits. For example, when you fast for 12 hours or for one week, you will see improvements in metabolism, cellular repair, gene expression, insulin sensitivity, and so on (R) (Luckily, fasting for 12 hours is quite easy: just don’t eat anything after dinner (e.g., from 7 pm until 7 am the next day). 

It’s therefore not surprising that fasting can extend lifespan. For example, rats that fasted every other day lived 83 percent longer than rats that could eat whenever and as much as they wanted (R).

Mice that fasted for four consecutive days every two weeks lived on average 33 percent longer (64 weeks, compared to 48 weeks for non-fasting mice) (R):

Mice that fast for 4 days every 2 weeks live considerably longer than mice that can eat as much as they want. Source: Influence of short-term repeated fasting on the longevity of female (NZB×NZW)F1 mice. Mechanisms of Ageing and Development, 2000

What’s the best fasting method for longevity?

This brings us to the most important question: what’s the best way to fast? 

Likely, the best method to fast is a 3 day fast every month or every new season. So, at the start of every autumn, winter, spring and summer you fast for 3 days. 

3-day-fasting brings about the best health effects: you enter proper ketosis, induce strong autophagy and studies also show that 3 day fasts reboots stem cells and the immune system (R,R). 

With shorter fasts, you can’t get those effects (e.g. ketone induction), or the effects (like stem cell health and reprogramming) will be less robust. 

Proper ketosis is something you can only achieve after a minimum of 2-3 days of fasting period. Ketone levels in the blood start to increase sooner than that, but achieve significantly higher and more ideal levels after at least 2 days. 

In fact, if you start fasting, the following 4 things happen: 

First 4-6 hours after your last meal

The blood sugar levels from your last meal decline in the blood. That’s also why you start to feel hungry during this period. 

4 to 24 hours after your last meal

Given blood sugar levels get too low, the body starts to break down glycogen stores in the liver and muscles to produce  glucose, which is needed to maintain your blood sugar, which is required by the brain. Your body also starts to break down fats (triglycerides)into free fatty acids that enter your bloodstream to provide an alternative source of energy to glucose. 

1-3 day after your last meal

After about the first 24 hours, glycogen levels get depleted. Ketosis starts, as the body produces ketones. This is primarily to keep the brain working, but can be utilized by other organs as well. 

Normally, the brain relies on glucose (not fats or proteins) to function. Given glucose is hardly available at this point, the liver will produce ketones that will serve as another fuel for brain cells. 

Ketones are made from free fatty acids. Free fatty acids are released from fat cells that normally store fat as triglycerides. 

During fasting, the triglycerides in the fat cells are broken down into free fatty acids, which enter the blood and reach the liver where they are converted into ketones The ketones enter the blood and reach all tissues, including the brain. These ketones are acetone, acetoacetate and beta-hydroxybutyrate. Ketones have various health benefits, such as reducing inflammation, improving brain health and neurogenesis (creating of new neurons) and improving metabolism (R). Ketones are also the main reason why people often say they can think more clearly around the second or third day of fasting.

3 days after your last meal

Ketosis is strongly activated. The ketones exert various beneficial effects, especially for the brain. Other regulatory mechanisms are in full swing, like autophagy, increased insulin sensitivity, and improved stem cell maintenance. Stem cells are repaired and get extra maintenance (R). Levels of ghrelin, the hunger hormone, decline around day 3, so people start to experience much less hunger. IGF-1, a hormone that speeds up aging, now starts to significantly decline. Insulin levels are greatly reduced. The levels of the beta-hydroxybutyrate ketone are around 1.5-3 mM. 

As you can see, various very healthy and beneficial effects only spring into action after fasting for a minimum of 2-3 days, and ideally 3 days. 

After 3 days, ketosis really gets going, IGF-1 and insulin start to get really low, and stem cells start to maintain and protect themselves. 

That is why we at NOVOS are proponents of doing a 3-day-fast every month or every new season, assuming your healthcare professionals agree that you are in a healthy place to do so. 

Fasting is a great method to reduce the risk of various diseases, and to slow down aging and live longer. 

However, fasting can also entail risks and can even be dangerous. In many cases, fasting can be done wrong, so it’s important to take careful steps to mitigate any risks. 

Reasons why fasting can be dangerous or unhealthy  

1. Too much muscle breakdown

If you fast, especially longer than a day, you can start to suffer from muscle breakdown which can lead to muscle pain, including sometimes severe back pain. There are ways to mitigate this, as we explain below (like taking caprylic acid and electrolytes).  

2. Risk of further vitamin, mineral and other micronutrient deficiencies

Likely the biggest problem with regular fasting is that one aggravates or induces micronutrient deficiencies. Micronutrient deficiencies are very common. Most people, even those that eat healthy, are deficient in various micronutrients or take in suboptimal levels, typically without even knowing it. For example, studies show that about 70 percent of people are not consuming enough magnesium, a very important mineral for health and longevity. Many people are deficient in optimal levels of iodine, B vitamins, iron (especially women), omega-3 fatty acids, vitamin D, vitamin K, zinc and so on.

These deficiencies lead to all kinds of health problems, from brain fog and fatigue to an increased risk of cancer, Alzheimer’s and accelerated aging. 

We explain here why so many people are deficient and why the vitamin and mineral recommendations of governments are substandard

Fasting, which means eating less, can further lead to deficiencies, which in the long term can compromise your health and accelerate aging. 

So if you fast, make sure you take supplements. Because even if you eat healthy, you do need supplements

3. Losing too much weight

Fasting can lead to too much weight loss, especially in people who have a normal weight or are already thin or underweight. This is what you see with too much fasting, like with alternate-day fasting periods, in which you fast each other day, which can easily lead to too much weight loss. 

If you experience too much weight loss, it’s better to fast one day per week, or even better, for 3 days every new season, as we explained earlier.

4. Causing too much stress for your body

Fasting causes stress on the body. It induces stress hormones like cortisol and adrenaline. If you already have fragile health, or are underweight or weakened, have a chronic disease, have micronutrient deficiencies, or have an unhealthy gut microbiome, fasting can put too much stress on an already overstressed body. 

5. Being female

Studies seem to indicate that fasting could be less beneficial, or cause more side-effects, in women than in men. 

For example, in one study fasting improved insulin sensitivity in men but worsened it in women (R). This was during alternate-day fasting; a very intensive and demanding method of fasting, which we think is too taxing for the body. 

Also, studies in rodents show that fasting can have different effects on male versus female animals (R,R). 

Furthermore, women are more prone to micronutrient deficiencies, like iron or iodine. If they fast regularly, they can worsen these deficiencies and in the long term be worse off. 

So in general, women should be careful with fasting, and make sure to not overdo it. For example, instead of fasting every week, they could consider doing a 3 day fast every new season. 

6. Taking specific medications

If you fast, you don’t consume important electrolytes. These are minerals like magnesium, potassium, sodium and calcium. You need electrolytes to perform many important functions, like conducting nerve signals, contracting your muscles (including of your heart) and to regulate innumerable functions in your body. 

If you are a heart patient, or take medication that can already lead to reduced electrolytes (e.g. specific drugs that reduce hypertension) you could be at risk of more side-effects of fasting. 

One way to mitigate this problem is by taking electrolytes during fasting (see below). 


You should not fast when you: 

  • Are too thin or underweight or easily lose too much weight

  • Are malnourished and deficient in micronutrients

  • Have a chronic disease 

  • Already feel weak in general or suffer from suboptimal health 

  • Take medication that could interfere with fasting, especially ones that lower electrolytes (see further down)

  • Are pregnant or breastfeeding

  • Under eighteen years old. 


Fasting can be very healthy, if done properly. As mentioned earlier, it’s important to not overdo it. This means fasting too much (like every other day), which can cause too much stress on the body and lead to important deficiencies in micronutrients. 

Secondly, during fasting, we advise to do the following:

1. Take electrolytes (sodium, potassium, magnesium and calcium)

The body needs electrolytes to function properly (e.g. for nerve conduction, muscle contraction, etc). Taking these during fasting can reduce side effects (like dizziness, fatigue, brain fog, heart palpitations, etc.). 

For each day of fasting, one can consider taking a few grams of potassium, 400-500 mg of magnesium, 1000 mg of calcium, and around 1000 to 2000 mg of sodium. Ideally, these electrolytes are divided over two doses, one in the morning and one in the evening.

2. Take 1 tablespoon (15 ml) of caprylic acid up to three times per day during fasting 

This is more of a hack than a requirement. Caprylic acid is a medium chain fatty acid that has various health benefits. It’s a unique fat, in the sense that the brain cells can use it as energy (mostly, brain cells only use sugar or ketones to function properly). 

Caprylic acid can also be easily converted into ketones by the body, so when you take caprylic acid during fasting, you can get into ketosis faster and increase ketone levels. 

Another benefit is that caprylic acid contains some calories (15 ml, or one tablespoon of caprylic acid per day corresponds to 130 calories), so your body still has a little bit of energy. That way, you reduce the stress of too much fasting on the body, and reduce the muscle breakdown and muscle aches and cramps. 


Fasting is a great way to improve health, slow down aging, and reduce the risk of many aging-related diseases, like heart disease, type 2 diabetes and even Alzheimer’s and cancer.  

Humans are not made to eat all day as we are not accustomed to doing. In prehistoric times, we often could not eat during large parts of the day, or even for many days or weeks. 

Regular fasting is a natural state of the body and we should incorporate it  back into our lives to unlock the many health benefits. 

But it’s important to do fasting right, by making sure you are not worsening the micronutrient deficiencies that almost everyone is already suffering from, and by making sure you don’t fast too much or put excess stress on the body. 

Beyond fasting by actually eating nothing, there are also various “fasting-mimetics”: substances that can induce many of the health benefits or mechanisms you activate during fasting, like inducing autophagy, activating DNA protection, antioxidant enzymes, repair proteins, and so on. 

NOVOS Core contains various ingredients that can partially mimic a fasting state in the body, like glucosamine (by inducing autophagy – the digestion of proteins and other waste that otherwise accumulates during aging), fisetin (by improving metabolism and reducing inflammation), pterostilbene (by activating AMPK, an “energy deficiency sensor”), or microdosed lithium (by inducing autophagy). 

Learn more about those anti-aging ingredients here

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