Home Mind + Body Nutrients & Diet Why You Should Try a Protein Fast (and How to do it)

Why You Should Try a Protein Fast (and How to do it)

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Of all the health trends in the past few years abstaining from certain types of calories seems to be the most common. Fasting has been a growing trend for many years with Silicon Valley types leading the charge [1]. Ketogenic diets are growing in popularity as is the new carnivore diet. The former restricts consumption of glucose and non-fat calories while the latter restricts just about everything minus animal protein.

While it might seem trendy, there are numerous purported benefits to all of these practices. Some are more well studied (such as in the case of fasting and to a lesser extent ketogenic diets) while others more anecdotal (such as the case of the carnivore diet). We're firm believers in n = 1 experimentation so if any of this resonates with you, keep doing what you are doing.

In this article, we'll cover why fasting from protein of any kind may be a highly beneficial new practice for health and longevity.

Towards the end we'll provide a few ways that you can start a protein fast to get the best results.

Protein Effects on Aging

There are numerous mechanisms by which protein effects healthful aging, but for our purposes we will focus on two:

  • IGF-1 (insulin-like growth factor-1)
  • mTOR (mammalian target of rapomycin)

First, let's look at IGF-1 and the trade off between performance and longevity. Adequate dietary protein (whether through animal or plant based products) can support muscle growth and elevated levels of IGF-1, which is an anabolic hormone released in the body.

IGF-1 helps increase neurogenesis (growth of new brain cells), prevents old brain cells from dying (neuroprotective), and supports physical robustness. In general, all performance indicators are enhanced through higher levels of IGF-1.

But this is a short-term approach…

High levels of IGF-1 can drastically reduce the lifespan in rodent and insect models. While animal models show lifespan reductions of 50% with higher levels of IGF-1, we can safely assume it is not that high in humans.

It is clear that high IGF-1, while beneficial in the short term, can drastically harm longevity and lifespan.

Reducing protein consumption doesn't immediately reduce IGF-1, but there is a correlation between dietary protein and levels of IGF-1. This is one reason why the fast mimicking-diet popularized by Valter Longo restricts protein to around 10% of the diet [2].

mTOR and Protein

One mechanism that is arguably most important for aging and longevity is called mTOR. This mechanism modulates another, more important, called autophagy.

This is getting scientific so we'll summarize autophagy as a process by which our cells start to recycle and repair dead organelles (basically a waste disposal system) in order to provide a more robust and healthy system. Without autophagy, our body never has a chance to get rid of dead and dying cells (which can lead to cancer among other detrimental health outcomes).

Autophagy is one of the key aspects that makes fasting so useful for longevity. The lack of calories allows internal mechanisms to begin and dispose of the “waste products” within our cells.

The important factor is that mTOR is the regulator of autophagy and mTOR is a protein sensor. This means that mTOR is sensing whether there is protein in the diet and suppressing the process of autophagy when protein is available.

The more the protein, the less likely autophagy will be reducing dead organelles and clearing out the cells.

Theoretically, it is possible to consume nothing but fat (through Bulletproof coffee, for example) and see many of the benefits of autophagy.

As Fung suggests, in theory it should be possible to consume hundreds (or even thousands) of calories from fat and not lose the benefits of autophagy. Because mTOR is a protein sensor, the hypothesis is, with no protein one can still see the positive effects.

Fat and Water Fasting

The thought of eating no food for multiple days can be overwhelming to some people. Indeed, fasting compliance in the scientific literature is 60 – 70% (meaning 30-40% dropped out) [3]. There are numerous types of fasting that can help (such as the fast mimicking diet or intermittent fasting), but another option may be a fat fast.

As Dr. Fung suggests, consuming hundreds and even thousands of calories from fat can provide a host of short-term benefits and theoretical health outcomes for longevity. In the short term, people fast with fat calories and experience benefits through elevated ketone bodies.

The ketone bodies in the brain are a great fuel source, which provide many people with enhanced focus, concentration, and mental performance. They also provide benefits on endurance (whether physical or mental) so that you can work longer at whatever work you are performing.

Consuming only fat probably increases the chances of consuming fewer calories than normal, which has elements that are similar to fast mimicking diet and others. The positive effects of eating fewer calories than one needs are well-researched and the calories from fat may make it more available to people who otherwise wouldn't fast.

Animal vs Plant Protein

Unfortunately for vegans, there is little different in the way the body utilizes amino acids that come from animals versus plants (at least as it relates to mTOR). Eating complete proteins from beans, rice, or other vegetables can influence mTOR in a way similar to animal protein. For other reasons, there are benefits of fasting from animal protein specifically, but that is outside the scope of this piece.

Whether you choose to go through an extended water only fast or try to receive the same benefits by only consuming fat, achieving a state where autophagy can clear out dead cells and organelles is imperative to maximize long-term health and support the aging process. There is still little evidence on whether these interventions will have the desired long-term effect, but by considering the existing science, you can take advantage of these mechanisms.


  1. https://www.entrepreneur.com/article/296577
  2. https://www.ncbi.nlm.nih.gov/pubmed/28235195?dopt=Abstract
  3. https://www.ncbi.nlm.nih.gov/pubmed/28459931?dopt=Abstract


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