[Retric]

What’s relevant is subjective. I’ll agree it’s far from as important as obesity, but the point is some of this adaptation is good.

As to loss of muscle mass from rapid weight loss, that’s very true but slightly overstated as regaining muscle can occur ~10x as fast as it takes to grow it in the first place. Someone without a significant calorie deficit barring nutritional deficiency or other impediment will regain whatever muscle mass is required for their lifestyle quite quickly. However, people don’t train with weighted vests as among other things it targets the wrong muscle groups.

[cthalupa]

>muscle mass is required for their lifestyle

The problem here is that the overwhelming majority of people that need GLP-1s have lifestyles that are not conducive to health and have less muscle mass than would be healthy to begin with.

Which is what has me so confounded by this claims - these people already have less muscle than they should for optimal health. Losing any is a significant issue. And without lifestyle intervention, they're not going to regain any of that lost muscle.

GLP-1 drugs are phenomenal and a huge win for health outcomes. But that doesn't mean we shouldn't be telling people the truth about their downsides and what they need to do to counteract them.

[Retric]

Let’s ignore GLP-1, and assume an individual slowly dieted to that exact same weight. What’s going to happen over the following year(s) is their lifestyle causes identical muscle loss.

In that context is this a long term downside of GLP-1 or their lifestyle?

Treating lean muscle mass as an inherent good makes sense when it’s adapted to a person’s current lifestyle. It doesn’t make sense when it’s a temporary situation.

[cthalupa]

False dichotomy - much of the muscle loss happens because of the rapid weight loss. If you diet more slowly and are not at very high levels of relative musculature you’re not going to lose nearly as much even in the long run, at least prior to advanced age. The newly skinny person might lose some muscle mass on their legs if they dieted down slowly, but it is significantly less likely that they will lose all of the other body-wide muscle mass that they do with rapid weight loss.

Your body will hold on to a surprising amount of muscle. Even people that take PEDs can drop back down to natural testosterone levels and keep ~80% of their gains in the long term. (Actual gains, not the temporary glycogen and intra-muscular water retention that you see with some compounds on cycle.) It takes significant effort for them, but they’re trying to hold on to supraphysiological levels, vs. someone who is trying to hold on to what is already on the lower end of the physiological range.

[Retric]

> False dichotomy

No, you’re looking at the short term effects on a largely irrelevant metric (volume) while ignoring the underlying mechanisms at play.

> Your body will hold on to a surprising amount of muscle.

It’s only surprising if you ignore what going on at the cellular level. Gaining fat or muscle eventually involves gaining new cells and structures like capillaries not just increased the volume of existing cells. This is a really slow process in muscle, but those new cells stick around and can rapidly adapt to stimulus as long as you have a sufficient diet.

So yes in rapid weight loss your individual muscles cells become smaller and less capable but that’s very quick to recover. Longer term, you’ll hit the exact same homeostasis point based on stimulus and long term diet.

PS: If this seems like voodoo magic it’s simply a very old evolutionary response to starvation that predates hominid development. Being able to fairly rapidly lower energy expenditure over say winter and then recover is a major advantage.

[cthalupa]

> Gaining fat or muscle eventually involves gaining new cells and structures like capillaries not just increased the volume of existing cells. This is a really slow process in muscle, but those new cells stick around and can rapidly adapt to stimulus as long as you have a sufficient diet.

It's an open question if hyperplasia even occurs in adult humans, and if so, under what conditions. MSC proliferation and differentiation is a thing, but none of this is actually particularly relevant to the discussion at hand.

> So yes in rapid weight loss your individual muscles cells become smaller and less capable but that’s very quick to recover. Longer term, you’ll hit the exact same homeostasis point based on stimulus and long term diet.

I'm not talking about hypothetical situations where people treat this more like a cut and then turn their lives around when it comes to resistance training and protein intake, because we know that in large part they don't. We know that a good portion of people on GLP-1 medications become sarcopenic and stay that way. And this whole thread basically started because someone was claiming that the muscle loss was good!

I'm not saying GLP-1s are bad or rapid weight loss is bad - I'm just saying you need to take steps to avoid muscle loss. And a huge amount of people on GLP-1s don't know about or understand these risks.

[Retric]

> I'm just saying you need to take steps to avoid muscle loss.

Do you have any evidence that long term lifestyle isn’t going to result in similar levels of strength?

> if hyperplasia even occurs in adult humans

It definitely occurs in other mammal muscle and some human tissue, and there’s studies supporting it occurring in human muscle. Myofibre splitting for example definitely occurs. https://pubmed.ncbi.nlm.nih.gov/16625366/

I’ll admit there’s controversy here, but I think the default position should be human biology is similar to other mammals unless someone demonstrates otherwise. Otherwise our unwillingness to preform experiments on humans and the expense of primate experimentation is going to create a scientific bias.