Written by the Spacemilk team · Last updated October 2026

Protein matters more on a GLP-1 medication because most people eat less, and part of the weight lost can be lean mass, which includes muscle. Your prescriber or a registered dietitian should set your protein target. The approach experts most often recommend is getting enough protein and pairing it with regular strength training.

Why does protein matter more on a GLP-1 medication?

GLP-1 medications include semaglutide (sold as Ozempic and Wegovy) and tirzepatide (sold as Mounjaro and Zepbound), which acts on the GLP-1 receptor and a second hormone receptor, GIP. A 2025 joint advisory from the American College of Lifestyle Medicine, the American Society for Nutrition, the Obesity Medicine Association and The Obesity Society notes that these medications reduce how much people eat by 16% to 39% compared with placebo (Mozaffarian et al., 2025, The American Journal of Clinical Nutrition). The advisory notes that adequate protein "may be difficult to achieve due to reduced appetite and/or taste aversions."

The second reason is body composition. In the STEP 1 trial of semaglutide, a sub-study of 140 participants measured body composition with DXA scans. Over 68 weeks, total fat mass fell by 19.3% and total lean body mass fell by 9.7% (Wilding et al., 2021, Journal of the Endocrine Society; main trial: Wilding et al., 2021, New England Journal of Medicine). Summarizing the trial, the advisory reports that of an average 13.6kg weight reduction, 8.3kg (62%) was fat mass and 5.3kg (38%) was lean body mass, which includes muscle and other non-fat tissue. Because muscle is about half of lean mass, the authors estimate that roughly 20% of the weight lost was muscle.

For context, fat fell faster than lean mass, so lean mass made up a larger share of body weight by the end. The advisory also notes similar losses with other approaches that produce large weight reductions, such as bariatric surgery and very low-calorie diets, and lists adequate protein and strength training to preserve lean mass among its priorities.

How much protein do you need on a GLP-1?

Your number should come from your prescriber or a registered dietitian. For reference, these are the figures the joint advisory gives:

Reference point	What the advisory says
0.8 g per kg of body weight per day	The recommended daily allowance for the general adult population (currently under review)
1.2–1.6 g/kg/day	Higher targets that "have also been proposed during active weight reduction"
80–120 g/day	An absolute target that "may enhance adherence while ensuring adequate intake"
2 g/kg/day or more	Prolonged intake at or above this level "should be avoided"

Source: Mozaffarian et al., 2025.

The advisory also says it's unclear whether targets should be based on actual body weight, an adjusted weight or lean mass, because using actual weight can overestimate protein needs in people with obesity. That's one more reason to get your number from a clinician who knows your health history, especially if you have kidney disease or have been told to limit protein.

Protein on its own isn't the whole answer. The advisory states that more protein "alone is likely inadequate to support the preservation of muscle mass in the absence of structured resistance/strength training," and recommends that GLP-1s be prescribed with an exercise program aiming for strength training at least three times a week plus at least 150 minutes of moderate aerobic activity.

How do you get enough protein when your appetite is low?

These strategies come from the joint advisory; your dietitian can tailor them to you.

• Eat protein first. Starting a meal with protein-rich foods makes it more likely you'll get enough protein before you're full.
• Go smaller and more often. The advisory suggests a small breakfast, then small meals every 3 to 4 hours, notes that vomiting is more likely after large meals, and says avoiding large or high-fat meals can help with diarrhea.
• Choose lower-volume protein foods. Fish, eggs, Greek yogurt, cottage cheese, nuts and seeds, and nut butters pack protein into smaller portions.
• Try liquid protein. Smoothies and protein drinks are often more appealing than heavier foods when your appetite is low, and the advisory notes that some people meet their protein targets with high-protein shakes.
• Keep fluids up. The prescribing information for these medications warns that nausea, vomiting and diarrhea can lead to dehydration (Zepbound prescribing information, FDA).

What should you look for in a protein powder if GI side effects are an issue?

Nausea, diarrhea, vomiting and constipation are among the most common side effects listed on the FDA labels for these medications (Wegovy prescribing information; Zepbound prescribing information). The Zepbound label notes that most nausea, vomiting and diarrhea happened while the dose was being increased, and decreased over time. A label can't tell you how a powder will sit with you, but it does tell you what's in it.

• Sugar. The advisory counsels limiting added sugars and sugar-sweetened beverages. Look for 0g sugar or very little.
• Sugar alcohols. Sweeteners like sorbitol, xylitol and erythritol bother some people's stomachs. The FDA requires foods that could supply 50g of sorbitol a day to carry the warning "Excess consumption may have a laxative effect" (21 CFR 184.1835).
• Lactose. Milk-based proteins can contain lactose, and about 36% of people in the United States have trouble digesting it (NIH/NIDDK). If dairy doesn't agree with you, look for a lactose-free protein.
• Serving size and volume. Check the scoop size and how much liquid it calls for. A drink you can finish comfortably, or sip over a morning, may be easier than a large shake.
• Fat and fiber. The advisory notes that avoiding fatty or high-fiber foods in the first few days of treatment can help with nausea. Check both on the panel.
• Complete protein. Look for all nine essential amino acids, or a PDCAAS (protein quality score) of 1.0.

For a deeper look at choosing a protein when your stomach is sensitive, read Protein powder for a sensitive stomach.

Where does Spacemilk fit?

Spacemilk is a protein powder, not a weight-loss product. It isn't designed to work with any medication, and it hasn't been studied in people taking GLP-1s. Here's what's in it:

• 20g of complete protein per serving (PDCAAS 1.0), isolated from non-GMO baker's yeast
• 100 to 120 calories per serving, depending on the flavor (Unflavored 100, Chocolate 120)
• 0g sugar and 1.5g fat per serving, with 1 to 3g of fiber depending on the flavor
• No lactose, no sugar alcohols and no gums like xanthan or guar. Flavored versions use a small amount of konjac fiber for texture and are sweetened with Reb M (a sweetener fermented from rice) and thaumatin. Unflavored is a single ingredient: yeast protein isolate.
• Formulated to be low in FODMAPs (not certified)
• Free from all nine major allergens: dairy, soy, gluten, eggs, tree nuts, peanuts, fish, shellfish and sesame
• Every batch third-party tested, with results published on our testing page

If you want an easy way to add protein on low-appetite days, Spacemilk Complete Protein is one option: 20g of complete protein in a drink you can sip. Ask your prescriber what protein target is right for you.

Talk to your prescriber first if…

• you have kidney disease or have been told to limit protein
• you have nausea, vomiting or diarrhea that is severe or won't go away, or you can't keep fluids down
• you have slowed stomach emptying (gastroparesis) or another stomach condition
• you're pregnant, planning a pregnancy or nursing
• you have a food allergy, including a known yeast allergy
• you're unsure how much protein, or what kind of exercise, is right for you

This page shares nutrition facts and published guidance, not medical advice.

Frequently asked questions

How much protein should I eat on a GLP-1?

Ask your prescriber or a registered dietitian. A 2025 joint advisory notes that targets of 1.2–1.6 g per kg of body weight per day have been proposed during active weight reduction, against 0.8 g/kg/day for adults generally. Your number depends on your health and body composition.

Can eating more protein stop muscle loss on a GLP-1?

No food can promise that. The advisory says more protein alone is likely inadequate to preserve muscle without structured strength training, and recommends the two together.

Has yeast protein been studied in people taking GLP-1 medications?

No. Yeast protein, the protein in Spacemilk, was shown in a 2024 double-blind randomized controlled trial to match whey for building lean muscle and strength in men over 40 doing resistance training. That study wasn't in people taking GLP-1 medications, so it doesn't tell us anything about lean mass on these drugs. The full summary is on our Science page.

Is Spacemilk a weight-loss product?

No. Spacemilk is a protein powder. It isn't made to work with any medication, and we make no claims about weight, appetite or blood sugar.

Where can I find more answers?

See our FAQ, or compare proteins in Yeast protein vs whey.