Slowing Down Aging with Intermittent Protein Restriction

One serving (140 g) of pasta contains 8 grams of protein. (Photo by ex.libris)

I've written a lot about the health benefits of caloric restriction and intermittent fasting on this blog. But what if those same benefits could be had by periodically restricting protein intake?

According to Ron Mignery, author of "Protein Cycling Diet" (which is free, by the way), staying away from protein every once in a while shares a lot of the health effects of caloric restriction and intermittent fasting. Obviously, protein cycling is much easier, because it's not the energy intake but the protein intake that matters. Here's a quote from the introductory chapter:

Protein cycling is intended as a way for you to live longer and healthier with minimal interference with your normal routine and diet. It is based on well-established observations that animals and people who have endured periods of famine have extended life spans compared to those who have not and on more recent observations that periodic protein restriction alone can accomplish the same thing.

The key to the benefits of protein cycling is autophagy, a process in which a cell consumes a part of itself for energy. Starvation is one way of inducing autophagy: since there is no external source of energy, the body begins to use its own cell material to keep things running smoothly. This also happens to be an effective way of getting rid of accumulated junk in the cells, something which is difficult to do otherwise.

Mignery argues that autophagy is the reason why calorie restriction (CR) and intermittent fasting (IF) work the way they do, and that by the same logic, protein cycling should extend life too. He also points out that protein cycling may be something we're evolutionarily adapted to:

Before we managed fire, our days were governed by the sun. In the tropics, the sun is down for 12 hours every day. Without fire, there is little to do in the dark but sleep. So our ancestors likely fasted at least 12 hours every night even if they ate continually throughout the day. A 12 hours fast with our ancestors' diet may have been sufficient to induce autophagy and perhaps they were already protein cycling.

So what does a protein cycling diet look like in practice? Mignery gives a lot of interesting calculations in his book, which I urge you to check out, but let's skip straight to the conclusion:

From the table we can see that 3 days a week of protein restriction would be sufficient to counteract an exponential accumulation that doubles every 2.5 years. This then is my most recommended regime: three 24 hour periods each week where very little protein is consumed.

Sound familiar? If you're a long time reader of this blog then it should, because three days of not eating protein per week is pretty much what the 24/24 hour cycle version of intermittent fasting (also known as "alternate-day calorie restriction" and "alternate-day feeding") looks like. Since you're not consuming any calories during a fast, you're obviously not consuming any protein either.

So, it seems that whatever benefits protein cycling has, intermittent fasting has too. But that is not the point, of course. The point Mignery makes is the opposite: that the benefits of intermittent fasting can be had without restricting all calories as long as you restrict proteins. Yes, you read correctly. Unlimited carbs and fat.

But before you order that vegetarian pizza with extra cheese to kickstart your protein fast, there's a small caveat: protein is in almost everything. And, unfortunately for our purposes here, only very little is needed to keep autophagy at bay:

A less active adult male of any weight or caloric consumption gets his minimal protein requirement when the calories he gets from protein exceed 4% of his total caloric intake.

For someone on an average 2,000 kcal diet, that would mean less than 80 kcal (or 20 grams) from protein is acceptable. Anything above that is a bad idea during a protein fast. Thus, commonly known protein-rich foods such as meat, fish, eggs, beans and lentils are obviously out of the question.

But even carbohydrate-based foods are surprisingly high in protein. For example, cooked pasta contains 6 grams of protein per 100 grams. Even rice, which has the lowest protein percentage of grains consumed in the Western diet, still has 2 g protein per 100 g. Even if you ate nothing but rice for your daily calories, you would get enough protein to prevent autophagy.

So you would have to be very careful in constructing your diet during the protein restriction periods. In practice, I think you would have to reduce total energy intake during a protein fast and choose foods that are low in protein. Fats and oils (with little to no protein) could be enjoyed liberally, while carbs (some of which come with fairly large quantities protein) would need more careful attention.

That said, if Mignery is right, protein cycling still seems easier than intermittent fasting – and much easier than caloric restriction. If you're unwilling to cut back on your total food intake or do zero-calorie fasting but would like to have some of the benefits associated with IF and CR, I encourage you to read the book. Perhaps you will find protein cycling a good place to start.

At this point, I'm not entirely convinced that either intermittent fasting or protein cycling will have the same benefits as caloric restriction, which has been studied more extensively and in a wider range of species. It's not clear to me that autophagy alone is the reason why CR works, or even why IF works.

That said, it does seem clear that autophagy has a wide range of positive health effects. Anything that reduces and reverses the accumulation of junk inside the body seems like a worthwhile effort to me. I suspect autophagy will continue to receive attention within the next few years.

For more information on caloric restriction and intermittent fasting, see these posts:

Intermittent Fasting: Switching from Alternate-Day Fasting to Condensed Eating Window
Intermittent Fasting: Understanding the Hunger Cycle
Caloric Restriction Improves Memory in the Elderly
Anti-Aging in the Media: New York Times on Caloric Restriction and Resveratrol