You May Be Eating Too Little Protein to Lose Fat — Especially If You're on a GLP-1

Add up the protein you eat before dinner. For most of my clients trying to lose weight, it's under 20 grams.

The day usually looks like this: toast or a smoothie for breakfast, a salad for lunch, and then everything lands on one big dinner. If that's your day, you're not doing anything unusual. It's how most women eat when they're trying to be "good." The problem is that this pattern quietly works against the one thing that keeps your metabolism running: your muscle.

Why muscle decides whether the scale moves

Your muscles are your main calorie-burning engine. As they shrink, so does your metabolism. And in a calorie deficit, which is what every weight-loss attempt is, your body doesn't only pull from fat. If protein is scarce, it can pull from muscle for fuel too. This gets more pronounced after 40, when we naturally start losing muscle each decade unless we actively work to keep it.

The result is the pattern I see constantly in my practice: eat less, lose a little, stall, eat even less, stall harder. Less muscle, slower metabolism, and a scale that won't budge no matter how little you eat. The fix is rarely more restriction. It's usually more protein, placed differently across the day.

The 30-gram rule, updated

You may have heard that your body can only use 20 to 30 grams of protein at a time and the rest is wasted. That rule needs an update. Newer research found that when people ate a large 100-gram dose of protein, very little of it was burned off as waste, the muscle-building response lasted longer instead. So a big protein dinner isn't "wasted."

But there's still a practical cap on how much your muscles can put to work in one sitting, and it's personal: it depends on your body weight and how much muscle you carry, not one magic number. Research on protein distribution suggests roughly 0.4 grams per kilogram of body weight per meal to get the most muscle-building benefit, for many women, that works out to about 25 to 30 grams, and older adults may need more per meal, not less, because muscle responds less eagerly to protein as we age.

Here's why the spread matters. Muscle building isn't switched on all day. It turns on when enough protein shows up at once. A toast-and-salad day may flip that switch once, at dinner. The real problem isn't your big dinner, it's the ten empty hours before it, when your muscle had nothing to work with.

If you're on a GLP-1, this matters even more

GLP-1 medications like semaglutide are powerful appetite tools. But they shrink your appetite without knowing anything about your muscle. And when appetite drops, protein is often the first thing to go, it's filling, it takes effort to prepare, and a few crackers feel easier.

Research presented at the Endocrine Society's 2025 meeting found that roughly 40 percent of the weight lost on semaglutide came from lean mass, including muscle, and the people most at risk were women, older adults, and those eating too little protein. Higher protein intake appeared protective. The same study found that losing more muscle was linked to smaller improvements in blood sugar, which means muscle loss may blunt part of the benefit you're taking the medication for in the first place. It was a small study, so the exact numbers will keep being refined, but the direction is consistent with what I see in practice.

My clients on GLP-1s are often eating so little that hitting protein targets by accident is impossible. When you only have appetite for a small amount of food, that food has to be mostly protein. Eat the chicken before the rice. Drink the protein shake before the snack. On these medications, protein-first isn't a nice-to-have, it's how you make sure the weight you lose is mostly fat.

What to actually do

Aim for 25 to 30 grams of protein, three to four times a day, starting with breakfast. Three ounces of chicken, fish, or beef is about the size of a deck of cards and delivers roughly 20 to 26 grams, depending on the protein. Greek yogurt, eggs with cottage cheese, a quality protein shake, any of these can turn a 5-gram breakfast into a 25-gram one. If you strength train, even a couple of times a week, that protein has an even better chance of staying on your frame as muscle.

And notice what this advice isn't: it isn't eating less. Most of the women I work with need to eat more of the right thing, more often, for the scale to finally move in the right direction. My clients are usually shocked when adding food is what breaks the stall.

If you're on a GLP-1, or considering one, and want to make sure the weight you lose is fat and not muscle, this is exactly what I help my clients do. You can work with me privately through my four-month programs, reach out through my application page and I'll take it from there.

Fix your gut, fix your life.

Sarah Mirkin, RDN, CPT, is a registered dietitian specializing in IBS, SIBO, and weight management at Kitchen Coach. This article is general education, not medical advice; talk with your physician before changing your diet or medication.