‘Longevity’ is the new health trend, and animal studies suggest restricting protein could increase lifespan––but does this apply to humans? Here’s my response to a reader question from my weekly newsletter, the Vitamin.
Q–It is known that maintaining muscle mass and strength in old age requires strength training and increased protein intake. mTOR is activated during strength training. However, in terms of longevity, it is recommended to block mTOR (intermittent fasting, Rapamycin, consume less protein with a lot of leucine.) Maybe you have information on this matter?
The issue with this theory is that it’s based on mechanistic data (how a biological process might work in theory) and studies conducted in animal models. However, you have to question how applicable these findings are to humans.
Rodents, such as mice, have much faster metabolisms and shorter lifespans than humans––one human year equals about nine mice days.1 Because of their rapid metabolism, rodents break down and process nutrients, drugs, and other substances much quicker than humans. This can lead to differences in how their bodies react to treatments or dietary changes.
Due to their shorter lifespans, rodents also age and develop diseases much faster, making it tough to predict how long-term effects observed in rodents apply to humans, who live longer and have slower, more complex metabolic processes.
For example, one review paper points out that mice are less reliable as models for human disease because of how genes that are connected to disease differ between mice and humans, such that treatments observed in mice may not always predict what will happen in humans.2
Take the case of resveratrol in red wine—initial studies in mice suggested anti-ageing benefits, sparking excitement about similar effects in humans. However, the doses given to mice would translate to humans needing to drink hundreds, if not thousands, of glasses of wine daily. Even when adjusted for differences in metabolism and size, humans would still require 30 to 130 glasses per day to match the dosage used in these animal studies––a clearly impractical amount. When researchers later investigated the supposed health benefits of resveratrol in humans, they found no association between the levels of resveratrol found in a Western diet, health, and mortality risk.3
Don’t worry. I haven’t forgotten to answer the question. Let’s bring this back to protein restriction.
If you’re anything like me, when you hear a claim like “protein restriction can extend your lifespan,” your first thought is, “OK, but how many more years would it add?”
Well, nobody really knows because how could you possibly study this? You’d need a large number of people to eat a very low-protein diet over multiple years while controlling for all the other factors that could possibly affect health and longevity. And that’s if an ethics board approves a study like this due to the potential health risks of a prolonged low-protein diet (more on this in a second).
However, one study used mathematical models to see how changing the amounts of proteins, fats, and carbohydrates in the diet or reducing calorie intake could affect how long people live. They found changing the amount of fats and carbohydrates didn’t really affect lifespan, but reducing protein to the minimum recommended amount (12% of total calories) could, theoretically, increase lifespan by about 3.3 years.4
So you might add a few more years to your life by restricting protein, but at what cost? Adequate protein intake is important for a multitude of reasons. But it becomes even more crucial in older adults for preventing sarcopenia, or age-related muscle loss, which is linked to increased frailty and higher mortality risk.5
So much so that some researchers argue the current protein RDA (0.8g/kg) should be increased to 1.2g/kg to better support muscle maintenance and overall health in older adults.6 7
If higher protein intakes were so detrimental to our health and longevity, we wouldn’t see an association (in human studies, FYI) between higher protein intake and longevity.
Just recently, a study that involved tracking almost 50,000 women across ~30 years found eating more protein–especially plant protein–throughout midlife was linked with higher odds of healthy ageing and “with several domains of positive health status.” 8
Moreover, not all sources of protein are created equal. The term “protein restriction” often oversimplifies the issue by lumping all types of proteins together. There’s a significant difference between the effects of proteins from sources like chicken, fish, and plant-based options versus heavily processed meats.
Finally, we have to consider the broader picture of lifestyle factors that contribute to healthy ageing and longevity. For instance, spending more than 9 hours per day being sedentary versus less than 6 hours is associated with a 192% increase in the risk of death. On the other hand, 60 mins of physical activity (regardless of intensity) is associated with a ~50% reduction in the risk of death.9
A review of the literature suggests that physical activity could add an extra 2-4 years to your life (though it’s likely a bit more since this was a conservative estimate).10 In other words, being physically active could extend your life by as much, but more likely more than restricting protein (assuming that ~3-year figure is somewhat accurate).
Additionally, improving dietary habits and increasing physical activity had favourable effects on ageing biomarkers in healthy postmenopausal women. 11 Similarly, men undergoing an 8-week treatment that included diet, sleep, exercise, and relaxation guidance saw a ~3-year decrease in biological age.12
I mean, protein restriction might (and that’s a big might) extend your life slightly. But there’s a heap of human research suggesting dozens of other things that can help you not just live longer but have a better quality of life as you age. And I’d rather focus on those things than worry about unsubstantiated longevity hacks that almost always involve someone trying to sell you bullshit.
TL;DR
- Protein restriction extending lifespan may seem promising based on animal studies and mechanistic data, but it doesn’t hold up well when scrutinized in the context of human biology.
- Adequate protein intake, especially in older adults, is crucial for preventing muscle loss and maintaining overall health, directly impacting quality of life and longevity. Human studies consistently show that higher protein consumption, particularly from plant-based sources, is associated with better health outcomes and longevity.
- ‘Good’/’bad’ health doesn’t happen in a vacuum, and we have to consider all of the other factors that can contribute to healthy ageing, like a healthy diet and regular exercise.
- Instead of chasing unsubstantiated longevity hacks, focus on proven strategies that enhance lifespan and healthspan. After all, there’s no point in simply living longer if your quality of life deteriorates to the point where you can’t enjoy those extra years.
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