If you’re losing weight, does lifting weights reduce how much muscle you lose? Is it possible to entirely prevent muscle loss (or even gain muscle)?

Murphy & Koehler (2021)¹ did a meta-analysis on this question. They collected experiments where the experimental groups did resistance training while eating at an energy deficit (RT+ED), and the control groups did resistance training while eating a normal amount of food (RT+CON).

They found a strong association between change in lean mass and the magnitude of the energy deficit (slope = –0.325, p = 0.001). The meta-analysis predicts that you can eat at a deficit of 500 calories per day without losing any lean mass, but you will lose mass at a larger deficit.

(The meta-analysis also reported that participants gained strength in almost every study, even with larger calorie deficits. That’s useful to know, but I will focus on lean mass for this post.)

I should mention that what we actually care about is muscle loss, not lean mass loss. Lean mass includes anything that isn’t fat—muscle fibers, organs, glycogen, etc. Muscle mass is harder to measure. We don’t know what happened to study participants’ muscle, only their total lean mass.

Let’s set that aside and assume lean mass is a useful proxy for muscle mass.

The authors showed a plot of every individual study’s experimental group (RT+ED) and control group (RT+CON), along with a regression line predicting lean mass change as a function of energy deficit:²

But…does this regression line look a little odd to you?

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In this post I will explain the most impressive argument I heard in 2024.

First, some context:

There is an ongoing debate in the bodybuilding/strength training community about how much protein you should eat while losing weight.

Some say you should eat more protein if you’re losing weight:

If you’re eating less, your body is under extra pressure to cannibalize your muscles. Therefore, you should eat more protein to cancel this out.

The standard rebuttal:

Experimental trials have found that muscle gains max out when subjects eat 0.7–0.8 grams of protein per pound of bodyweight, and that’s true both when participants are maintaining weight and when they’re losing weight. There doesn’t appear to be a difference.

And the counter-rebuttal:

Almost all research looks at novice lifters. Experienced athletes have a more difficult time gaining muscle,¹ so losing weight will have a bigger negative impact on them, and therefore they need to eat more protein.

I used to believe this. Then I heard the most impressive argument of 2024.

I heard the argument in a YouTube video by Menno Henselmans:

It’s possible that in trained individuals there is a triple interaction effect, because that’s what you’re arguing here. If you’re saying that protein requirements increase in an energy deficit, but only in strength-trained individuals, then you are arguing for a triple interaction effect. […] That is very, very, very rare. Triple interaction effects, biologically speaking, simply do not occur much.

I didn’t understand what he was talking about. I spent two days pondering what it meant. On the third day, it finally clicked and I realized he was right.

To claim that trained lifters should eat more protein on an energy deficit, you’d need to believe that:

1. Above a certain level of protein intake (0.7–0.8 grams per pound), additional protein has no effect on muscle growth.²
2. Most of the time, trained athletes don’t need more protein than novices.
3. Novices don’t need more protein while losing weight than while maintaining/gaining weight.
4. HOWEVER, (a) among trained individuals who are (b) losing weight, the ones (c) who eat more protein (beyond 0.7–0.8 g/lb) gain more muscle.

The first variable (protein intake) has no interaction with muscle growth.

The second variable (trained vs. untrained) has no interaction with muscle growth.

The third variable (losing vs. maintaining weight) has no interaction with muscle growth.

The first and second variables together (protein intake + trained/untrained) have no interaction with muscle growth.

The first and third variables together (protein intake + losing/maintaining weight) have no interaction with muscle growth.

HOWEVER, when you put all three variables together, an interaction suddenly appears—a triple interaction effect.

This is a very strange claim. If all three variables together affect muscle growth, then you would expect each variable individually to affect muscle growth. And at least you would expect two out of three variables together to affect muscle growth.

(In fact, it is mathematically impossible to construct a differentiable function f(x, y, z) that is constant with respect to x, constant with respect to y, and constant with respect to z, but not constant overall. Although you could have a function f(x, y, z) where the slope with respect to each individual variable is close to 0, but not quite 0.)

Not to say a triple interaction effect can’t occur in the real world. It could be that muscle growth does depend on each of (protein intake, training experience, calorie deficit), but the relationships are so weak that the studies failed to pick them up.

But if you believe the studies’ results are correct, then it seems difficult—maybe even impossible—to still believe that trained lifters need to eat more protein while on a calorie deficit.

This was the best argument I heard in 2024 because:

• If you think about it, it’s obviously correct. It changed my mind as soon as I understood it.
• It’s difficult to come up with. (I’ve never heard anyone else make this argument.)

Notes

This research piece is not as rigorous or polished as usual. I wrote it quickly in a stream-of-consciousness style, which means it’s more reflective of my actual reasoning process.

My understanding of HIIT (high-intensity interval training) as of a week ago:

1. VO2max is the best fitness indicator for predicting health and longevity.
2. HIIT, especially long-duration intervals (4+ minutes), is the best way to improve VO2max.
3. Intervals should be done at the maximum sustainable intensity.

I now believe those are all probably wrong.

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Updated 2025-03-19 to add Catalina Crunch Cinnamon Toast.

(I write listicles now)

(there are only 7 eligible high-protein breakfast cereals, so the ones at the bottom are still technically among the 7 best even though they’re not good)

If you search the internet, you can find rankings of the best “high-protein” breakfast cereals. But most of the entries on those lists don’t even have that much protein. I don’t like that, so I made my own list.

This is my ranking of genuinely high-protein breakfast cereals, which I define as containing at least 25% calories from protein.

Many food products like to advertise how many grams of protein they have per serving. That number doesn’t matter because it depends on how big a serving is. Hypothetically, if a food had 6g protein per serving but each serving contained 2000 calories, that would be a terrible deal. The actual number that matters is the proportion of calories from protein.

My ranking only includes vegan cereals because I’m vegan. Fortunately most cereals are vegan anyway. The main exception is that some cereals contain whey protein, but that’s not too common—most of them use soy, pea, or wheat protein instead.

High-protein cereals, ranked by flavor

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Last updated 2025-05-05.

Outlive: The Science & Art of Longevity by Peter Attia (with Bill Gifford¹) gives Attia’s prescription on how to live longer and stay healthy into old age. In this post, I critically review some of the book’s scientific claims that stood out to me.

This is not a comprehensive review. I didn’t review assertions that I was pretty sure were true (ex: VO2 max improves longevity), or that were hard for me to evaluate (ex: the mechanics of how LDL cholesterol functions in the body), or that I didn’t care about (ex: sleep deprivation impairs one’s ability to identify facial expressions).

First, some general notes:

• I have no expertise on any of the subjects in this post. I evaluated claims by doing shallow readings of relevant scientific literature, especially meta-analyses.
• There is a spectrum between two ways of being wrong: “pop science book pushes a flashy attention-grabbing thesis with little regard for truth” to “careful truth-seeking author isn’t infallible”. Outlive makes it 75% of the way to the latter.
• If I wrote a book that covered this many entirely different scientific fields, I would get a lot more things wrong than Outlive did. (I probably get a lot of things wrong in this post.)
• When making my assessments, I give numeric credences and also use terms such as “true” and “likely true”. The numbers give my all-things-considered subjective credences, and the qualitative terms give my interpretation of the strength of the empirical evidence. For example, if the scientific evidence suggests that a claim is 75% likely and I understand the evidence well, then I rate the claim as “likely true”. If I only read the abstract of a single meta-analysis, and the abstract unequivocally supports the claim but I’m only 75% sure that the meta-analysis can be trusted, then I rate it as “true”. Both claims receive a 75% credence.

Now let’s have a look at some claims from Outlive, broken down into four categories: disease, exercise, nutrition, and sleep.

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