GLP-1s, lean mass, and the floor you still have to build.

I'm going to say something up front that might surprise you given the tone of a lot of my writing. I think GLP-1 medications are a genuine medical advance. I think the research on them is real. I think they're helping people for whom other approaches haven't worked. I'm not anti-GLP-1, and I don't think you should be either.

I also think a lot of people taking them right now are going to look back in 5 years and wish they'd done one thing differently. That one thing is the topic of this post.

What GLP-1s actually do

Semaglutide (Ozempic, Wegovy), tirzepatide (Mounjaro, Zepbound), and similar GLP-1 receptor agonists work by mimicking a hormone your body naturally produces to regulate appetite and blood sugar. They slow gastric emptying (food stays in your stomach longer), reduce appetite signals in the brain, and improve insulin sensitivity. The result, for a lot of people, is significant weight loss without the same white-knuckle willpower that previous approaches required [1].

The weight loss is real. For people with type 2 diabetes, obesity, or significant metabolic dysfunction, these medications can change the trajectory of health in ways that previous approaches couldn't. I'm not here to argue with the data.

> My concern isn't whether GLP-1s work. They work. My concern is what you're losing along with the fat.

The part that doesn't get talked about enough

Here's the piece that most of the GLP-1 conversation is missing. When you lose weight through any aggressive calorie deficit, a significant portion of the weight you lose is lean mass (muscle, bone, water) along with fat. The ratio depends on several factors, but the most important one is whether you're doing resistance training and eating enough protein during the weight loss period.

Research on GLP-1 users in clinical trials has found that roughly 25-40% of the weight lost is lean mass if the patient isn't actively training and prioritizing protein [2]. That's not a footnote. That's a quarter to nearly half of the weight you lost being muscle, not fat.

Muscle loss has downstream consequences you don't see in the mirror for a year or two. Reduced metabolic rate means weight regain becomes easier later. Reduced strength means reduced balance, reduced function, reduced quality of life. And reduced muscle mass in middle age accelerates all the age-related problems I wrote about in my post on strength training after 35.

Losing weight fast while losing 30% of it as muscle isn't winning. It's winning now and paying for it later.

What I tell clients who are on or considering a GLP-1

I'm not going to tell someone on a GLP-1 to stop taking it. That's between them and their doctor. What I tell them is this: if you're going to take one, build the foundation that protects you from the downside.

1. Resistance train, seriously, at least 2-3 times per week. This is the single most important variable for preserving lean mass during weight loss. Every study on weight loss + resistance training shows dramatic improvements in lean mass retention compared to diet alone [3]. You don't need to become a bodybuilder. You need to lift real weights against real resistance 2-3 times a week, consistently, the entire time you're losing weight.

2. Eat enough protein, probably more than you think. During weight loss on a GLP-1, the protein target I'd aim for is closer to 1.0g per pound of current bodyweight, or 1.2-1.6g per kg. That's higher than normal because you need extra amino acids to protect against the catabolic pressure of the calorie deficit. The challenge with GLP-1s is that they suppress appetite, which makes it hard to eat enough, which makes protein a priority. Protein shakes become really useful here.

3. Don't lose weight too fast. The faster you lose, the more of the loss is muscle. A loss rate of roughly 0.5-1% of body weight per week is the research-backed sweet spot for preserving lean mass [4]. If your GLP-1 is pushing you faster than that, talk to your doctor about titrating down. Slow is better.

4. Get bloodwork every few months. GLP-1s affect a lot of things besides hunger. Nutrient absorption, muscle, bone, thyroid. Regular bloodwork catches drift before it becomes a problem. This is one of the places I lean on working with a naturopath or functional medicine practitioner who can interpret the labs in context.

5. Have a long-term plan, not just a GLP-1 plan. What happens when you come off the medication? Most people regain weight, because the medication was managing appetite, not teaching habits. The only defense against regain is the habit stack you built during the weight loss window. Resistance training, protein, sleep, daily movement. Build those during the weight loss, and the weight regain story changes.

Where I actually stand

I said it at the top and I'll say it again. I'm not against GLP-1s. They're a genuine medical advance. For some people, they're the right tool.

I'm against using them without building the foundation that keeps the weight loss healthy and the results lasting. I've coached people who used GLP-1s well and came out the other side leaner, stronger, and with a better relationship to food than they'd had in decades. I've also seen people come off them 20 pounds lighter but 15 pounds weaker, with reduced bone density and a metabolism that's going to fight them for years.

The difference wasn't the medication. It was whether they built the floor underneath it.

The foundation stays the same regardless

Here's the honest version that doesn't sell as well on Instagram. GLP-1s don't change the foundational work. They change the pace at which you can lose weight. They don't remove the need to train, eat enough protein, sleep, and build sustainable habits.

If you're taking one, the 10 pounds you lose because the medication reduced your hunger doesn't mean the training and protein and sleep stop mattering. It means they matter more, because they're the only thing standing between you and the muscle loss version of this story.

If you're considering one, talk to your doctor, make an informed decision, and commit to the foundation before you start. Resistance train. Eat protein. Sleep. Move daily. Those four things are what determines whether the GLP-1 is a tool that helped you or a shortcut that cost you lean mass you can't get back easily.

The research is real. The benefits are real. The trade-offs are also real. Know them, plan for them, and build the floor that protects against them.

There are still no shortcuts

Even with the best medical advances AI and medicine are bringing us in the next decade, the foundation doesn't change. Eat enough protein. Train your body. Sleep. Move every day. Manage stress. These are the things that don't have shortcuts, even when other things do. The medical advances give you a tool. You still have to do the work.

Sources

• [1] Wilding et al., *Once-Weekly Semaglutide in Adults with Overweight or Obesity*, New England Journal of Medicine, 2021.
• [2] Wilding et al., supplementary data on lean mass loss during GLP-1 use. Multiple replication studies report roughly 25-40% of weight loss as lean mass when resistance training and protein are not prioritized.
• [3] Longland et al., *Higher compared with lower dietary protein during an energy deficit combined with intense exercise promotes greater lean mass gain and fat mass loss*, American Journal of Clinical Nutrition, 2016.
• [4] Helms et al., *Evidence-based recommendations for natural bodybuilding contest preparation*, Journal of the International Society of Sports Nutrition, 2014. Review of weight loss rate and lean mass retention.