Blog

You are eating less, and the scale is going the right way. Here is the part nobody mentions when they hand you the prescription: eating less does not only burn fat. It also tells your muscles to slow down rebuilding themselves.

Muscle is not built once and kept. Your body is taking it apart and putting it back together all the time. When the rebuilding keeps up, you keep the muscle. When it falls behind, some of the weight you lose is muscle, and that is the weight you want to keep: it holds you upright, keeps your metabolism up and keeps you from looking deflated.

This post is about why eating less tips that balance, why it tips further after 40, and the two things that tip it back. If you want the plan built for you, Greatest Workout does it in three taps.

What happens when you eat less

In one carefully controlled study, 12 active adults ate enough for 10 days, then about 20% less than they needed for 10 days. Protein stayed the same the whole time, at a good amount: 1.5 g per kg of body weight. Their muscle-building was still about 19% lower when they ate less (Pasiakos et al., 2010).

That is a small study, and 10 days is short. But the direction is the point: a calorie deficit turns down muscle-building on its own, even when protein is good. On a GLP-1 the deficit can be bigger than that, and it lasts months.

Why fast weight loss is the hard case

A review of the research on dieting found that more protein together with strength training preserved muscle during weight loss, and sometimes added some. When the weight loss was moderate, 1.6 g of protein per kg a day preserved lean mass. But when the deficit was large and the weight came off fast, protein could not fully stop the loss (Phillips, 2014).

Fast weight loss with a big deficit is a fair description of the first months on a GLP-1. That is why the trials found so much of the weight lost was lean tissue, and why “eat more protein” on its own is not the whole answer.

After 40, it is slower

Two more studies explain why age makes this worse.

After the same leg workout and the same drink of amino acids, muscle-building rose within 1–3 hours in younger men, and only after 3–6 hours in older men (Drummond et al., 2008). The older muscle still responded. It just took longer to get going.

And the amount matters more. In 35 men averaging 59 years old, 170 g (6 oz) of beef, about 36 g of protein, raised muscle-building more than smaller servings, and more again after a workout (Robinson et al., 2013). “Some protein” is not the same as enough protein.

What fixes it

There are two levers, and you need both. The full version is here; this is the short one.

1. A protein number, not a vague goal. Greatest Workout uses 1.6 g per kg of body weight a day, the amount that preserved lean mass with moderate weight loss in the review above. For an 85 kg (187 lb) person, that is about 136 g. For healthy, active people, 1.4–2.0 g per kg has been judged safe, including for the kidneys and bones (ISSN position stand, 2007).

If you have reduced kidney function, or diabetes with any kidney involvement, a protein target is a conversation with your doctor first. Take the number to whoever prescribed your medication.

2. A reason for the muscle to stay. Protein is the material; lifting is the signal that the muscle is still needed. You do not have to lift very heavy. In one study, light weights taken close to failure raised muscle-building as much as heavy weights taken to failure, and kept it raised longer (Burd et al., 2010). What matters is that the last few reps are hard. That is good news if your joints are not what they were.

When you can only face one real meal

This is the part GLP-1 users ask about most. You are full after half a plate. Spreading protein over four meals is the easy way to hit the total, and if you can do it, do it. But plenty of days you cannot.

You may have read that the body cannot use more than 20–30 g of protein at a meal. That idea looks only at muscle-building and ignores muscle breakdown. Counting both, two protein researchers found no practical upper limit to the benefit of protein at a meal (Deutz and Wolfe, 2013). That is an opinion paper, not a new experiment.

There is one trial that tested it. Older hospital patients who ate about 72% of their day’s protein at lunch gained lean mass over six weeks, while those who spread the same protein over four meals did not (Bouillanne et al., 2013). They were in hospital and under-nourished, which is very different from you, so take it as “one big protein meal can work”, not “one big meal is better”.

What that means in practice:

• The daily total matters most. Spread it if you can.
• At the meal you can eat, protein goes first and does not get cut down to 30 g because of a rule that does not hold.
• An evening protein snack is a reasonable place to find what you are missing. Protein before bed is used to build muscle overnight (Trommelen and van Loon, 2016), though the studies compared it with nothing, not with the same protein earlier, so the benefit may simply be the extra protein.

What this does not prove

None of these studies is about GLP-1 medication. They are about the situation a GLP-1 puts you in: eating less and losing weight, often after 40. Most are small, and most measure muscle-building over a few hours, which is a clue about muscle gained over months, not proof of it.

What they add up to is consistent and has not changed in years: in a calorie deficit, protein plus strength training is how you keep the muscle, and getting older makes both matter more. That is enough to act on. It is not enough to promise you a number.

We keep the studies behind the program, with who was in each one and how strong it is, on our research page.

Put it to work

You need a protein number that fits your weight and a training plan short enough to finish on a small appetite. Get your plan in three taps: your program, your protein target and your first week of workouts, free.

---

For educational and informational purposes only. This is not medical advice, and the protein target in particular is not appropriate for everyone. Talk to the clinician who prescribed your medication before changing how you eat or train.

The scale is the reason this problem hides.

It cannot tell 2 lb of fat from 2 lb of muscle, and on a GLP-1 it is going down either way. So the single number most people check every morning is the one number that cannot answer the question they should be asking, and it keeps giving them good news while the answer gets worse.

You do not need a DXA scanner. You need four measurements, three of which cost nothing, and a baseline taken early enough to compare against.

Take the baseline now. Not after you have lost 20 lb. The comparison is the whole point, and a measurement with nothing to compare it to tells you almost nothing.

1. Your working loads, at a fixed effort

This is the most sensitive early signal you have, and if you are following a program you are already collecting it.

The protocol: keep the same lifts for at least eight weeks, and record the load and reps for each set at a consistent effort level. Not your maximum — maximum testing in an energy deficit is a bad trade. Use a fixed rating of perceived exertion: the weight that leaves you about three reps short of failure.

What it tells you: if the weight that leaves you three reps short is drifting down over a month, while your bodyweight is also dropping, something is going in the wrong direction. Holding your loads while losing weight means your strength relative to your size is improving, which is the outcome you actually want.

What it does not tell you: it is confounded by sleep, stress, fuelling on the day and technique. One bad session is a bad session. A four-week trend is data.

This is why the Preserve program keeps the same lifts for all eight weeks — goblet squat, trap bar deadlift, Romanian deadlift — and moves only the sets, reps and effort. A fixed lift turns the logbook into a measuring instrument. The app logs every set, so the trend is already there rather than something you have to reconstruct.

2. Grip strength

Grip is the most widely used clinical screen for low muscle strength, it takes thirty seconds, and a dynamometer costs about as much as a month of protein powder.

The protocol: seated, elbow at 90°, upper arm against your side. Three squeezes per hand, maximum effort, thirty seconds between. Record the best of the six. Same protocol, same time of day each time, ideally not straight after training.

The clinical cut-points (EWGSOP2, the European consensus definition used for probable sarcopenia). They were set for older adults; if you are younger, the change from your own baseline matters more than these numbers:

	Below this is a flag
Men	27 kg
Women	16 kg

What it tells you: crossing below those numbers, or dropping substantially from your own baseline, is a reason to talk to your clinician. It is a standard clinical screen, not a fitness metric.

What it does not tell you: grip is a proxy. A strong grip does not prove your legs are fine, and forearm-heavy training inflates it.

3. Five-times sit-to-stand

Lower-body function, no equipment, thirty seconds.

The protocol: a standard chair against a wall. Arms folded across your chest — no pushing off. Stand fully upright and sit back down, five times, as fast as you safely can. Time it from “go” until you are fully upright for the fifth time.

The cut-point: more than 15 seconds for five rises is the EWGSOP2 cut-point for low muscle strength. Alongside grip, it is used to flag probable sarcopenia.

What it tells you: leg strength and power, which is the thing that decides whether you can get off the floor at 75.

What it does not tell you: it is affected by knee and hip pain, and by practice. Do it twice at baseline and use the second one.

4. Photographs, in the same place and the same light

Unfashionable, and better than it sounds.

The protocol: front, side, back. Same spot, same light, same time of day, same minimal clothing, every four weeks. Relaxed, not flexed.

What it tells you: body composition changes that the scale is hiding in both directions. Four weeks apart they are useless; four months apart they are frequently the clearest evidence you have.

What it does not tell you: anything on its own week to week, and nothing you should judge yourself by on a bad day.

What a good trajectory looks like

Over three months on a GLP-1, with protein and lifting in place:

• bodyweight down
• working loads flat or up
• grip flat
• sit-to-stand flat or faster
• photos showing the shape changing faster than the scale

Flat strength on falling bodyweight is a win. It means you are getting stronger relative to your size, and it is the normal outcome when the two levers are in place — not an exceptional one.

What should worry you

• loads drifting down over a month at the same effort
• grip dropping more than a couple of kg from your own baseline
• sit-to-stand getting slower
• weight falling fast — more than about 1% of bodyweight a week, sustained. Faster loss has been linked to more lean-mass loss in some studies, though no exact threshold is established

Any of those, in combination with the medication, is worth a conversation with whoever prescribed it. Faster is not better in this one respect, and a dose that is driving weight off at a rate your protein intake cannot support is a thing your prescriber can adjust.

If you are already below the grip or sit-to-stand cut-points, that is a reason to see somebody, not a reason to train harder. Those are clinical screening thresholds. Treat them as such.

On “strength standards” tables

You will find plenty of tables saying a man should squat his bodyweight or deadlift 1.5×. Those are coaching conventions, not research, and they are close to useless for this purpose.

The reason is simple: you are changing the denominator. If you squat 100 kg at 100 kg bodyweight and then squat 95 kg at 85 kg bodyweight, every standards table says you improved, and what you want to know is whether you lost 5 kg of squat. General population norms answer a different question than the one you have.

On a GLP-1 the only benchmark that means anything is your own, taken early. That is why this post has protocols and your-own-baseline comparisons in it rather than a table of what other people can lift.

Start here

Take all four measurements this week. It is about twenty minutes, once, and it is the difference between knowing what your weight loss is made of and guessing.

Then read the two posts that explain what the measurements are for: how much muscle actually comes off on a GLP-1, and the two levers that protect it.

Greatest Workout logs your sets and your protein, so the trend is already there when you go looking for it.

---

For educational and informational purposes only. This is not medical advice. The cut-points quoted here are clinical screening thresholds, and being below one is a reason to see a clinician. Talk to whoever prescribed your medication before changing how you eat or train.

The previous post covered the problem: between a quarter and two-fifths of the weight lost in the big GLP-1 trials was lean tissue, because an energy deficit costs lean mass, the appetite suppression takes protein down with everything else, and nothing in the process tells your body the muscle is still needed.

There are exactly two levers. Everything else is detail.

Lever one: eat enough protein

A 2025 joint advisory from four obesity and nutrition societies puts protein for people on GLP-1s at 1.2–1.6 g per kg of body weight per day during active weight loss (Mozaffarian et al., 2025). That is well above the 0.8 g/kg everyday allowance, which is set to prevent deficiency, not to protect muscle while you lose weight.

Greatest Workout uses 1.6 g/kg, the top of that range, because 1.6 is roughly where the resistance-training literature stops showing extra benefit from extra protein: a 2018 meta-analysis put the plateau at about 1.6 g/kg, with wide uncertainty, in people who were not dieting (Morton et al., 2018). If you are lifting — and the second half of this post argues you should be — the higher number is the relevant one.

For an 85 kg person that is about 136 g a day. Four meals, 34 g each.

On a GLP-1 this is the hard part, and it is harder than it sounds. You are full after half a meal. Protein is the most satiating thing on the plate, so it is the first thing you stop finishing. People routinely arrive at a GLP-1 appetite eating 60-70 g a day without noticing the change, because nothing hurts and the scale is going the right way.

What tends to work, from coaching people through it:

• Protein first, every meal. Not as a rule of thumb — literally eat it first, before the rest of the plate, because you will not get back to it.
• Four smaller meals beat three. Your stomach capacity is the binding constraint, so take more runs at it.
• Liquid calories are not cheating here. A shake is 25-30 g that requires no appetite at all. This is the one situation where drinking your protein is straightforwardly the right answer.
• Weigh it for a week, once. Almost nobody’s estimate survives contact with a kitchen scale, and the error is nearly always in the same direction.

The caveat that matters: if you have reduced kidney function, a high protein intake is a conversation with your doctor, not a blog post. Same if you are on a GLP-1 for type 2 diabetes with any degree of nephropathy. Take the number to whoever prescribed the medication. And if you are carrying a lot of extra weight, a target worked out from your total body weight can overstate what you need; ask them what weight to base it on.

Lever two: give the muscle a reason to stay

Muscle is metabolically expensive. A body in an energy deficit that is never asked to produce force will get rid of it, because keeping it costs something and buys nothing.

Resistance training is the signal that it still buys something. That is the whole mechanism — not “exercise”, not cardio, not steps. Something heavy enough that your body concludes the tissue is load-bearing.

What the evidence actually says. The general case is strong and old: resistance training plus adequate protein preserves lean mass during an energy deficit, across decades of studies in dieting, bariatric surgery and ageing. The GLP-1-specific case is early — the most-quoted result is a case series of three people who did resistance training three to five times a week, prioritised protein, and ranged from losing 6.9% of lean soft tissue to gaining 5.8%, while losing 13-33% of their body weight.

Three people is three people. You will see “resistance training cuts muscle loss to under 10%” quoted as though it were a trial result. We could not find a trial behind it; the closest figure we know of is one person in that case series, who lost 8.7% of their weight as lean tissue. The honest summary is: the mechanism is well established, the general evidence is strong, and the GLP-1-specific trials are still recruiting.

That is more than enough to act on. It is not enough to promise you a number.

Why a GLP-1 needs a different program

This is the part generic advice gets wrong. “Lift three times a week” is correct and useless, because the program most people would pick is one they cannot complete on this medication.

You have less fuel. An hour of volume work is built on the assumption that you ate enough yesterday. On a GLP-1 appetite you did not. Long sessions do not fail because you lack discipline; they fail because there is nothing in the tank by set fourteen.

So the sessions get shorter and heavier. Load is the signal that preserves muscle; volume is what drives hypertrophy in a surplus, and you are not in a surplus. In a deficit, heavy and brief keeps what you have. Long and moderate mostly makes you tired and hungry, and you are already both.

Three days, not five. Recovery is slower when you are under-eating. The fourth and fifth sessions of a five-day split, on a GLP-1, are usually where adherence dies.

The same lifts for weeks. You are not trying to grow; you are trying to hold ground and demonstrate it. Keeping the lifts fixed means the number on the bar is a measurement, not a comparison between two different exercises.

In practice, the Preserve program is three 40-minute full-body sessions a week for eight weeks: squat and push, hinge and pull, total body. One key lift per day — goblet squat, trap bar deadlift, Romanian deadlift — with the sets, reps and effort moving week to week while the lifts stay put. Five exercises a day, six on the total-body one. Nothing exotic, because exotic is not the problem.

Greatest Workout builds that program and your protein number around your medication, which is the part that is tedious to do by hand.

What does not matter as much as the internet thinks

Cardio is not the enemy. Zone 2 walking is good for you, does not meaningfully compete with recovery at sane volumes, and helps with the appetite and mood swings. It just does not protect muscle, so it does not substitute for the lifting.

Creatine is probably worth it and is not a lever. Cheap, well-studied, safe in healthy people. It belongs in the “small, free wins” column, not in the same sentence as protein and lifting.

The timing of your protein matters far less than the total. Spread it out because it is easier to hit the total that way, not because the window is magic.

How to know whether it is working

The scale will not tell you. It cannot distinguish 2 lb of fat from 2 lb of muscle, and on a GLP-1 it is going down either way, which is exactly why this problem hides.

The third post in this series is about the measurements that do tell you, none of which need a DXA scanner.

---

For educational and informational purposes only. This is not medical advice, and the protein target in particular is not appropriate for everyone. Talk to the clinician who prescribed your medication before changing how you eat or train.

The drugs work. That part is settled — people lose weight on semaglutide and tirzepatide that they could not lose any other way, and for a lot of them it is the first thing that has ever worked.

The question nobody answers properly is what the weight is made of.

The numbers

Both of the big trials measured body composition in a subset of participants with DXA scans, which is the part of the results that does not make headlines.

In the STEP 1 substudy of semaglutide 2.4 mg, about 40% of the weight lost was lean soft tissue — 95 people scanned.

In the SURMOUNT-1 substudy of tirzepatide, it was about 26% — 124 people scanned.

So somewhere between a quarter and two-fifths of what came off was not fat. On 30 lb of weight loss that is roughly 8 to 12 lb of lean tissue, depending on which drug and which person.

Those are small subsets of large trials, and the two numbers are not directly comparable — different populations, different durations, different amounts of total weight lost. But the size of the effect is not in dispute. It is large enough to matter.

“Lean mass” is not “muscle”

This is where most articles on this subject go wrong, in both directions.

DXA does not measure muscle. It measures lean soft tissue, which is everything that is not fat and not bone: muscle, yes, but also water, glycogen, the blood volume that supports a larger body, and the organs themselves. All of those legitimately get smaller when a body gets smaller.

So the 40% figure is not 40% muscle. Some of it is water you were carrying. Some of it is glycogen that left with the carbohydrates. Some of it is the extra tissue that existed to service extra body mass and is not needed at the new size.

Some lean mass loss is normal and appropriate. A person who loses 50 lb and keeps every gram of lean tissue has done something strange, not something admirable.

The problem is not that the number is above zero. The problem is the proportion — and the proportion in those trials is higher than it needs to be, because nothing in the trials was designed to protect it.

Why it happens

Three things stack up, and they compound each other.

An energy deficit alone will do it. This is not special to GLP-1s. Any sizeable calorie deficit costs lean tissue unless something actively protects it. Bariatric surgery patients, people on very low calorie diets, anyone losing weight fast — same pattern.

The appetite suppression works on protein too. This is the part that is specific to these drugs, and it is underrated. The medication does not selectively reduce your appetite for the foods you were overeating. It reduces appetite, full stop. Protein is the most satiating macronutrient and usually the hardest to finish when you are full early — so protein intake tends to fall further, proportionally, than anything else. People on a GLP-1 frequently end up eating well under the protein a person not losing weight would need, at exactly the moment they need more of it.

There is no signal to keep it. Muscle is expensive. A body that is short of energy and is never asked to produce force will shed it, because there is no reason not to. Nothing about taking a weekly injection tells your body that the muscle is still required.

That last one is the one you can do something about, and it is why the answer is not a different drug or a different diet. If you want to keep it, something has to ask for it. A training program built for a GLP-1 appetite is a different thing from a normal training program, and that difference is the subject of the next post in this series.

Why it matters past the mirror

Three reasons, in rough order of how much they should worry you.

Function. Lean mass is how you get off the floor, carry things, and stay upright when something unexpected happens. This matters more the older you are, and GLP-1s are widely prescribed to people in their fifties and sixties, where losing 10 lb of lean tissue is not cosmetic.

What you weigh afterwards is made of something. If you lose 30 lb with 10 lb of lean tissue in it, and later regain 15 lb, the regain is predominantly fat. Do that twice and the same number on the scale describes a substantially different body. This is the mechanism behind “I weigh what I did five years ago but I look worse”.

Resting metabolism. Lean tissue is metabolically active, so less of it means a lower daily energy expenditure, which makes maintenance harder at the very point you stop the drug. This effect is real but it is routinely overstated in fitness marketing — it is a meaningful contributor, not the whole story of weight regain.

What this does not mean

It does not mean the drugs are bad, and it does not mean you should stop taking one. For many people the metabolic benefit of losing a large amount of fat dwarfs the cost of the lean tissue that came with it. That is a conversation for you and whoever prescribed it, and nothing on this page is medical advice.

It means the lean tissue is a variable you can influence, and that almost nobody is told so.

The next two posts are about doing that: what actually protects muscle on a GLP-1, and how to tell whether it is working without a DXA scanner.

If you would rather skip to the thing itself, Greatest Workout builds the program and the protein target around your medication and your schedule.

---

For educational and informational purposes only. This is not medical advice. Talk to the clinician who prescribed your medication before changing how you eat or train.