356 studies on protein. Almost none in people.

Last Friday, a review covering 356 studies came out. By Sunday, news headlines were already asking if your protein shake might be making you age faster.

What?

On July 31, Bailey Knopf and Dudley Lamming published a paper called "The hallmarks of protein and amino acid restriction in aging and longevity" in Cell Press Blue. They say that eating less protein can improve metabolic health and, in some species, might even help them live longer.

If you look closer, the paper gets specific fast. It's a narrative review, so it sums up existing studies instead of combining their data. Most of the strong evidence comes from research on flies, worms, mice, and rats. The best human data is from Lamming's own 43-day trial, where people on a low-protein diet lost weight and fat, and had lower fasting glucose, even though they ate more calories. That is a real result, but the study only lasted six weeks and only measured blood sugar and body fat. No one tracked how long anyone lived.

Paul Greenhaff, a professor of muscle metabolism at Nottingham, summed it up that same day. The main question "has not been addressed in humans."

So what?

The paper doesn't actually tell you to eat less protein. Instead, it says your protein needs depend on how active you are. Lamming himself said, "It's absolutely crystal clear that there are benefits of protein to muscle growth and exercise response of active individuals." But here's what the headlines missed: most people aren't very active, yet many eat as if they train much more than they really do.

I've made this point before. Last February, I said most people need 1.6 to 2.2 grams of protein per kilogram, then quickly added, "less if you're sedentary," and moved on. Those four words were actually the most important.

Think of protein as your body's repair budget. You use it for the work your body actually does. If you train, eating at the higher end of the range makes sense. If you don't train, you're paying the metabolic cost for muscle you never built.

There's something else you should know, though it doesn't make the science wrong. Lamming is on the scientific advisory board of a company working on mTOR inhibitors, and mTOR is central to his paper. He disclosed this, but I think it's important for you to know.

The other side of the story is strong too. In the Nurses' Health Study, nearly 49,000 women were tracked from 1984 to 2016. More protein in midlife, especially from plants, was linked to better odds of aging well. This result is about chronic disease, not muscle, and it only shows an association. For muscle, animal protein still has more leucine and a more complete amino acid profile. That difference matters most if you're not eating enough protein to start with. Once you get enough, studies stop finding a difference in strength or lean mass.

Now what?

• Count the lifting sessions you actually did last week, not the ones you planned. If you did two or more, stick with 1.6 grams per kilogram or more. If you did zero or one, drop to about 1.2.
• Are you over 65 or already losing strength? Ignore the headline. This review agrees with the usual advice. Your minimum is 1.0 to 1.2 grams per kilogram.
• Keep your protein intake steady throughout the week instead of loading up only on gym days. Your muscles stay sensitive to protein for 24 to 48 hours after you lift, so Sunday's chicken still helps pay for Saturday's workout.
• Compare what you eat on a typical day to your target number. If you go over it during a week when you didn't train, cutting out fortified snacks is the easiest way to adjust.

Stay healthy.
Andre