I'm always so baffled by warnings about losing muscle when losing weight.

Of course you do! If your body is tens of pounds lighter, then you don't need the extra muscle to lug it around. This paper is about reduction in heart muscle, and of course your heart doesn't need to be as strong because there's less blood to pump and less tissue to fuel.

When you gain weight, you also increase the muscles needed to carry that weight around. If you see someone obese at the gym doing the leg press, you may be astonished at how strong their legs are. When you lose weight, you don't need that muscle anymore.

Our bodies are really good at providing exactly the amount of muscle we need for our daily activities (provided we eat properly, i.e. sufficient protein), so it's entirely natural that our muscles decrease as we lose weight, the same way they increased when we gain weight. Muscles are expensive to keep around when we don't need them.

Obviously, if you exercise, then you'll keep the muscles you need for exercising.

But this notion that weight loss can somehow be a negative because you'll lose muscle too, I don't know where it came from. Yes you can lose muscle, but you never would have had that muscle in the first place if you hadn't been overweight -- so it's not something to worry about.

From the article: "...explains this rate of muscle decline is significantly higher than what is typically observed with calorie-reduced diets or normal aging and could lead to a host of long-term health issues..."

The warning isn't that you're losing muscle during weight-loss with these drugs. It's that the ratio of muscle vs fat loss is much greater with the drugs compared to traditional weight loss methods.

It's been well studied that if you exercise and eat enough protein while losing weight, you can retain more muscle.

Losing a lot of lean mass is incredibly detrimental to your longevity and quality of life.

> Our bodies are really good at providing exactly the amount of muscle we need for our daily activities

The problem is that the average joe's daily activity is incompatible with an healthy muscle mass. After 30 if you don't actively exercise you lose muscle mass, if you're obese, 50 and starve yourself or take drugs that make you lose more muscles than necessary you won't gain them back ever unless you do some form of serious resistance training

https://hips.hearstapps.com/hmg-prod/images/triathlete-aging...

I'm not qualified to interpret results, but this paragraph stuck out to me:

> Using mice for the study, the researchers found that heart muscle also decreased in both obese and lean mice. The systemic effect observed in mice was then confirmed in cultured human heart cells.

So it also happened for already lean mice (though no mention of whether they still lost fat), and for cultured human heart cells (so not a by-product of needing less muscle to pump blood through a shrunken body).

> Our bodies are really good at providing exactly the amount of muscle we need for our daily activities

That is exactly the risk. Our bodies are really good at it. But we are taking drugs that may change what our bodies do. Even a small bit of extra heart muscle loss may push as below where our bodies would have left us naturally. Is that dangerous? Are there people who need to worry about it? How do we know whether or not that should be a concern? It raises questions, and is worthy of discussion, even if we do land at answers that say it is an acceptable level of risk.

I wondered about exactly this.

The study is actually a published letter [1], and it doesn't appear to account for this. Science Direct even published a study about this in 2017 [2]:

> Weight loss, achieved through a calorie-reduced diet, decreases both fat and fat-free (or lean body) mass. In persons with normal weight, the contribution of fat-free mass loss often exceeds 35% of total weight loss, and weight regain promotes relatively more fat gain.

We already know how to reduce the effect of this, the person simply needs to increase exercise as the weight is lost in order to maintain lean muscle mass.

[1] https://www.sciencedirect.com/science/article/pii/S2452302X2...

[2] https://www.sciencedirect.com/science/article/pii/S216183132...

When you gain weight, you also increase the muscles needed to carry that weight around. If you see someone obese at the gym doing the leg press, you may be astonished at how strong their legs are. When you lose weight, you don't need that muscle anymore.

Anyone can put up impressive #s on a leg pres. Try the bench press instead. No one impressed by leg press.

In regard to the oft claim of obese people being stronger or more muscular, not really. Studies show that obese people carry only a tiny extra 'lean body mass' compared to non-obese people when matched for height, age, and gender, and much of this extra mass is organs, not muscle. Otherwise, the extra weight is just water. Sometimes it is even less because obesity impairs movement, leading to muscle loss due to inactivity.

If obese people seem strong it is because the fat reduces the range of movement for certain lifts like the squat and bench press, so it's possible for obese people to put up impressive numbers owing to having to move the weight less distance. Same for pushing movements, e.g. linemen, as being heavier means more kinetic energy, but this is not the same as being stronger in the sense of more muscle output. This is why obese people are not that impressive at arm curls or grip strength relative to weight, but wirey guys can curl a lot relative to weight or have a lot of grip strength. An obvious example of this is overweight women having worse grip strength compared to men; the extra fat does nothing.

I don't mean to target your comment specifically because it's obvious you know the difference, but I'm continually annoyed by the conflation of fat and muscle as "weight," even by medical professionals who should know better.

We should not be talking about losing "losing weight" as a substitute for saying "losing fat," which is what most people mean. Likewise, when people say they want to "gain weight", they almost always mean they want to "gain muscle."

Why does this matter? Trying to manage one's health or fitness as "weight" gives (most) people the wrong idea about what their weight number represents, and what to do to improve their level of fitness and dial in on the anatomically appropriate amount of body fat. As an example, it's possible (although admittedly unlikely) for one to work hard to gain muscle and strength while reducing body fat and stay exactly the same weight the whole time. Their overall health, fitness, and longevity will be significantly improved but pop fitness will tell them that they haven't made any progress at all.

> When you gain weight, you also increase the muscles needed to carry that weight around.

I can't figure out how relevant that is. From what I've seen of obese people they always struggle with limited mobility, which often only improves with physiotherapy (or other forms of exercises). Sumo wrestlers are huge but can move faster than an equivalent obese person because (I assume) they have stronger muscles due to their regular regimented training and diet. Does this mean they have more muscle mass than fat compared to an equivalent obese person? Does more muscle mass indicate stronger muscles?

And obviously the heart is going to reduce muscle now that it doesn't need to pump blood through heaps of fat.

Then a study concentrates no comparing muscle weight loss by traditional dieting, that is a change in what someone eats, to weight loss via drugs.

It is not immediately clear if the muscle loss happens faster (probably) what the immediate impact of that is, and whether or not you lose more muscle mass on one or the other.

What they need is to design some sort of mouse gym.

I'm always so baffled by people commenting without reading the article first.