For today’s Dear Mark, I’m answering a question about the optimal diet for longevity. An article sent in by a reader claims that a recent mouse study has identified the perfect diet for everyone, but especially for older people: a high-carb, low-protein one. They even manage to throw in some stuff maligning the paleo diet (they just can’t resist).
Find out below if the claim holds water. Let’s go:
What’s your take on this new study claiming that the best diet for longevity is a high-carb, low-protein one?
Researchers placed mice on a bunch of different diets to see how they’d affect levels of fibroblast growth factor 21, or FGF21. The 25 diets ranged from 5-60% protein and 5-75% fat or carbohydrate. They tried pretty much every permutation and found that the low-protein, high-carb combo produced the greatest increase in FGF21.
FGF21 “plays a role” in longevity, immune and metabolic health, energy metabolism, and appetite. Implicit in the study’s aims is that higher FGF21 is a good thing. It helps us live longer and healthier. If all that’s true, of course we’d want to find the macronutrient ratio that increases FGF21 most.
FGF21 is ultimately a marker of mitochondrial stress (PDF). By doing things that boost FGF21—which include fasting, low-calorie diets, low-carb/high-fat diets, and even acute exercise—we are applying a moderate amount of stress to our mitochondria. This is a good thing, provided the fasting doesn’t lapse into starvation, the diets don’t become chronic deprivation diets, and you allow sufficient recovery from the exercise. It’s hormesis: apply a stressor and bounce back stronger than before.
With most hormetic stressors, the benefits turn into negatives if the exposure persists or accumulates. There’s the chance of getting too much of a bad thing.
Is there any evidence of too much FGF21 being bad for us?
Among Chinese males, those with the highest FGF21 levels are more likely to have a heart attack and to have another within 30 days of the last one.
Both the highest and lowest FGF21 levels are associated with an increased risk of cardiovascular disease and death from heart attack.
Higher levels of FGF21 are linked to fatty liver, cardiovascular disease, and other metabolic disorders.
Independent of other risk factors, high serum FGF21 predicts the severity of atherosclerosis.
FGF21 may not be causing these things, but its elevated presence is at least a marker of something bad going on.
What does this all mean?
We have human evidence that various FGF21 genetic variants can help determine how well a person does on high-carb diets and low-carb diets. Those with the C variant lost more weight, waist circumference, and body fat on a high carb diet and less on the low-carb diet. Meanwhile—and this wasn’t reported in the study abstract—those with the T variant lost more weight, body fat, and waist circumference on the low-carb diet and were still losing body fat after two years.
I guess what I’m saying is this: Go with the diet that works for you.
All these things will increase FGF21 in the manner that’s likely to be healthiest without getting into excessive, chronic elevation.
What about the original article’s contention that older people should eat high-carb, low-protein diets to stave off death?
We know that in older individuals, a higher protein intake is healthiest because as we age, we get less efficient at processing protein. We need more protein. Research shows that more protein promotes all the things we need to remain healthy and functional as the years accumulate.
Seniors who eat a half pound of red meat each day enjoy better physical function, get stronger, and build more lean muscle mass. That lean mass becomes ever more important the older we get. It’s a reserve for illness, injury, and bedrest. It keeps us spry and vibrant. It makes us strong; strong enough to take care of ourselves and actually engage with the outside world.
Mark Sisson is the founder of Mark’s Daily Apple, godfather to the Primal food and lifestyle movement, and the New York Times bestselling author of The Keto Reset Diet. His latest book is Keto for Life, where he discusses how he combines the keto diet with a Primal lifestyle for optimal health and longevity. Mark is the author of numerous other books as well, including The Primal Blueprint, which was credited with turbocharging the growth of the primal/paleo movement back in 2009. After spending three decades researching and educating folks on why food is the key component to achieving and maintaining optimal wellness, Mark launched Primal Kitchen, a real-food company that creates Primal/paleo, keto, and Whole30-friendly kitchen staples.