Weight-loss drug found to shrink muscle in mice, human cells

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.

Even amongst traditional calorie deficits, rapid weight loss results in greater loss of muscle mass when compared to gradual weight loss, even if you lose the same amount of mass overall. I.e. you keep more muscle losing 0.5 lbs a week over 40 weeks than 2 lbs a week over 10 weeks.

> Even amongst traditional calorie deficits, rapid weight loss results in greater loss of muscle mass when compared to gradual weight loss,

This does not make any sense. Why would the body prefer anything over the most dense and available calorie store? Protein in muscle gives shit calories per gram, it is hard to build back and generally less available than fat: the number one energy store, doing exactly what it does.

I don't think anyone knows for sure, but I think the prevailing theory is it being a survival mechanism.

When our ancestors faced famine, it makes sense for the body to shed as much muscle as possible, since this reduces the metabolic rate in the medium-long term.

Muscle is more metabolically active than fat. Although fat can be used up for energy more readily, but muscle takes more energy to maintain. Burning fat just to maintain (unnecessary) muscle doesn't make sense in terms of survival.