Protein plays a role in longevity through multiple conflicting variables. Which ones are more important depends on who you ask.
In the longevity space, the debate as to whether protein intake should be limited or maximized remains hotly contested. It’s easy to find arguments from experts in the field claiming that protein consumption increases the rate of aging. On the other hand, you will find many arguing that we should be consuming large amounts of protein to maximize healthspan. This article will breakdown the reasoning behind both sides and finally give my own opinion on the topic.
Arguments for a High Protein Diet
The basis for high protein diet recommendations largely revolve around the belief that it will lengthen healthspan. Remember that healthspan, among other things, is the amount of time that we can spend functionally independent and physically able to do the things we want to do in life. Examples include being able to take your dogs for a walk, play with your grandchildren, travel, grocery shop, etc. Run through the mental exercise of picturing yourself when you’re 80 years old and ask yourself: what will I want to be able to do at this age? Chances are a significant number of activities you’ll want to be able to do will require some degree of physical ability which will require some degree of muscle mass and function.
Preventing sarcopenia
As we age, not only does it become harder for us to gain muscle, a condition called anabolic resistance, but it actually becomes easier and easier for us to lose muscle. This phenomenon is known as sarcopenia, the progressive loss of muscle mass and strength as we age, and the negative effect it has on people is staggering. It may be the reason someone stops going on family trips, as they are too weak to travel. It may be the reason why someone falls, breaks their hip, and never fully recovers. It may be the reason someone is confined to a nursing facility, unable to care for themselves independently. And unfortunately this condition is all too common among our elderly. According to the NIH, sarcopenia affects up to 55% of people over the age of 80.
In order to prevent sarcopenia, the goal would be to enter our elderly years with a good amount of muscle mass. Since anabolic resistance begins in one’s 30’s and 40’s, making it gradually harder to build muscle, it would make most sense to use one’s youthful years to accumulate lean muscle and then in one’s 50’s and onward do everything to maintain that muscle. Two crucial elements of muscle building is providing the biological signal to the muscle to grow (resistance training) and providing the resources for the muscle to grow (protein). Ergo, the argument for high protein diets.
Improving glucose disposal
There are a number of other benefits to healthspan that come with increased lean muscle mass, but I’ll briefly mention one more. Muscle is a “sink” for glucose, or sugar, that floats around in our blood. In fact, 80-90% of circulating glucose gets taken up by muscle. In metabolic disease such as diabetes, individuals have difficulty getting glucose, which becomes toxic at high levels over long periods of time, out of the blood and into muscle. One way of preventing this very common disease is to increase the size of the “sink” one has for glucose. We can do this by increasing muscle mass which requires significant amounts of protein consumption.
Arguments against a High Protein Diet
The reasoning behind recommendations to limit protein intake comes from the geroscience field which studies the biological drivers of aging. One incredibly important protein that is known to drive aging is mTOR (mammalian target of rapamycin). mTOR’s job in a nutshell is to sense the amount of nutrients available to a cell and then tell it to go down one of two paths: grow and proliferate, or recycle and repair. Excessive growth and proliferation through a highly active mTOR actually leads to a number of issues within the cell that likely contribute to more rapid aging and thus increases the risk of developing age-related diseases like cardiovascular disease, cancer, and dementia. In contrast, recycling and repairing which happens when mTOR is turned off decreases the risk of age-related disease and increases lifespan.
Protein activates mTOR
Amino acids, which are the building blocks of protein, are able to activate mTOR leading to cellular signals to grow and proliferate. This fact forms the basis for those in the longevity field who argue against high protein diets. However, a number of other molecular signals are known to activate mTOR, two of them being glucose and insulin. Those who are unable to remove glucose from the blood and put into muscle, such as diabetics, will also have high insulin levels. This may explain why diabetes is a risk factor for multiple age-related diseases, since glucose and insulin activate mTOR and accelerate the rate of aging. And, as explained previously, those with less healthy lean muscle have a smaller “sink” to dispose of glucose, predisposing one to diabetes.
What we don’t know about mTOR
Additionally, there is still a significant amount about mTOR that we do not yet understand. One question that remains is in what specific tissues of the body does mTOR get activated in response to different signals like amino acids versus glucose/insulin and how does each affect or not affect the rate of aging? Another is how different lengths of mTOR activation affect longevity: if you think of mTOR as a button, will quickly pressing the button on and off affect aging differently than holding down the button all the time? Another factor to consider is antagonistic pleiotropy: does mTOR activation in youth affect aging differently than mTOR activation later in life? All of these important questions that need to be considered when arguing against protein intake due to mTOR activation are, as of now, unanswered.
My personal opinion
As a physician who regularly takes care of elderly patients, I am well accustomed to the diseases and disabilities that afflict us as we age. Because of this, understand that I come from a place of bias when I say I am currently more concerned about sarcopenia than I am about mTOR when it comes to protein intake. If we limit protein consumption decreased functional ability later in life to me seems inevitable. On the other hand, the little that we know about mTOR and it’s effects on laboratory animals in my mind isn’t enough to outweigh the guaranteed risk of muscle loss with age. From my perspective, we need much more research to tease apart the nuances of mTOR before we can in good faith recommend limiting protein intake to patients, and even then the recommendations must be personalized to the individual.
So how much protein would I recommend? Again, that would depend upon individualized factors that I won’t get into here, but for the vast majority of us I would recommend erring on the side of too much protein than too little. The RDA recommends a measly 0.8 grams of protein per kilogram of body weight per day. To maintain muscle, research suggests a minimum of 1.0 grams of protein/kg of body weight. To build muscle, typically individuals will need somewhere in the ballpark of 1.4 to 2 grams of protein/kg of body weight daily. Finally, enough can’t be said about the source of protein. Not all protein sources are made equal. Opt for healthy protein sources such as lean unprocessed meats, fish, eggs, beans, tofu, and greek yogurt while avoiding processed meats such as hot dogs, bacon, burgers, sausage, etc.
As should always be true and encouraged in honest science and medicine, I reserve the right to change my opinion in the face of new evidence.