Keto’s Anti-Aging Benefits Might Not Extend to Endurance Athletes

Published April 13, 2023 11:13AM

Of all the diet fads to capture the imagination of endurance athletes, none has been quite as polarizing as keto. Although it is a essentially a reboot of fad diets that have come and gone numerous times in the past (Atkins is the best known of these) adherents to the ketogenic diet tend to treat it as though it is something novel and new and that it is the only diet an athlete should consider if they want to attain peaks in body composition, performance and lengthen their lifespan. They also claim keto can be a fountain of youth, helping athletes crack the anti-aging code through their eating habits.

Nutritionists, on the other hand, as well as a fair representation of coaches in the endurance world, are not persuaded. This group of people who are less convinced by the marketing and sales extolled by social media personalities has for some time now pushed back against the keto craze, pointing out that the ketogenic diet is not suitable for athletes training for and participating in endurance sports. They also highlight evidence that often flies in the face of the bold claims being made in support of keto.

So what is a ketogenic diet? Is there any evidence to support any of the main claims put forth by its proponents, or alternatively, those who are opposed to it? Finally, what should we take from a paper recently published that seems to suggest that the ketogenic diet may have some real benefits to counter the effects of aging, but not for athletes?

What is the Ketogenic Diet?

The cells of our bodies depend on carbohydrates for their most easily metabolized fuel. To make use of them, cells have a locked door system that must be opened with a key to allow the entry of carbohydrates and this key is insulin, a hormone secreted by the pancreas whenever levels of sugar are high in the bloodstream.

Decades ago, scientists postulated that the western diet was leading to higher rates of obesity, diabetes and cardiac disease because of the recurrent spikes in insulin associated with repeated ingestion of sugary foods. They believed that shifting the emphasis to high protein and high fat foods would reduce these insulin spikes and potentially decrease what they thought was a cause of morbidity and mortality.

These diets have come in many forms and been called various names, but all have one important thing in common: They are very low in carbohydrates. Most restrict total sugars to 50g or less per day. The body metabolizes the high quantities of fats and proteins to ketones that are then used as an alternative fuel by cells, albeit much less efficiently than carbs.

A lot of research has been done on ketogenic diets, and a few things can be said about them:

Ketogenic diets have also been found to play an important role in preserving muscle architecture and function in older lab animals, and it has been suggested that this may be an important finding with implications in humans as well.

Aging and Mitochondria

As we age, our muscles undergo significant changes related to both a decrease in the number and size of muscle fibers and to a change in the type of muscle fibers from those that have high metabolic rates to those that have slower ones (this process is collectively referred to as sarcopenia). It has been hypothesized that a major reason for these changes is a deterioration in the health of mitochondria within the cells.

Mitochondria are tiny organelles within all of our cells that act as the cells’ furnaces. It is here that fuels are burned with oxygen and converted to other forms of energy. With advancing age, mitochondrial health declines, and with it, the health of muscle fibers. A leading theory now postulates that the loss of mitochondria is what leads to the age-related changes in muscle fibers over time.

A recent paper in Exercise and Sport Sciences Reviews by Suraj Pathak and Keith Baar of UC Davis summarized the current state of research in this area and evaluated whether a ketogenic diet could have benefits to athletes in terms of preserving muscle mass and function with advancing age. Consumption of a ketogenic diet shifts metabolic processes within the mitochondria and has been shown to preserve mitochondrial health in lab animals. Similar experiments are not yet available in human subjects, but many researchers are optimistic that the results would be similar.

The theory is that the mechanism by which a ketogenic diet protects mitochondria in part results from activation and enhancement of a specific enzymatic pathway that is required for the metabolism of these alternative fuels. Activation of peroxisome proliferator-activated receptor (PPAR) leads to improved handling of ketones and fats and allows for bypassing of the preferred pathways that handle carbohydrates.

But according to Pathak and Baar’s research, there are two problems with this theory related to the ketogenic diet for older individuals who are athletes.

The first relates to the fact that men and women who remain physically active as they age have a lower rate of sarcopenia than do their more sedentary compatriots. In fact, in lab experiments the effect of exercise is to maintain mitochondrial and muscle health in a similar fashion as a ketogenic diet in older animals.

Second, the main molecular changes induced by a ketogenic diet that are thought to confer protection against sarcopenia also, paradoxically, impair exercise performance. As the researchers say, “…even though it is already clear that ketogenic diets have been successful at improving muscle size and function in disease and aging animal models, a ketogenic diet fails to improve elite athletic performance likely because one of the key molecular changes that underlies the muscle adaptation to the diet (PPAR activation) is the same thing that decreases high-intensity performance.”

For these very important reasons, a ketogenic diet should be considered only with caution, especially when it comes to older athletes competing in endurance sport.

And so, as is typical for fad diets, the hype tends to be out of proportion to the reality. While a ketogenic diet may offer some benefits to older, more sedentary individuals, those who are active (and particularly those who pursue endurance sport) would be best served by adhering to a more traditional, well-rounded diet that includes carbohydrates.