By Dr. Leandro Pucci, DCN, CNS, CKNS, LDN
GLP-1 medications such as semaglutide and tirzepatide change the nutrition question. Before treatment, most people with excess weight are trying to eat less. On treatment, appetite drops so sharply that the risk flips: the question becomes whether what you are still eating is enough to protect muscle, bone, and micronutrient status. How you answer it largely determines what you keep after the medication stops.
I work with many patients who are on, starting, or coming off a GLP-1. The ones who do best treat the medication as a window to rebuild eating patterns and muscle, not as a substitute for them.
GLP-1 receptor agonists mimic a hormone your gut releases after meals. They slow stomach emptying, increase insulin release when glucose is high, and act on appetite centers in the brain (1). Tirzepatide adds a second gut hormone, GIP. The practical result is earlier fullness, fewer cravings, and less interest in food. For a broader look at how these drugs compare with other peptides, see my guide to peptides for metabolic health.
The weight loss is substantial. In the STEP 1 trial, semaglutide 2.4 mg produced an average loss of 14.9% of body weight over 68 weeks (2). Not all of that weight is fat.
In a body-composition subgroup of STEP 1, lean mass accounted for roughly 40% of the total weight lost (2). Lean mass includes water and organ tissue, not only skeletal muscle, so this figure overstates muscle loss somewhat. It still matters, especially for:
A 2025 joint advisory from four professional societies, including the American Society for Nutrition and The Obesity Society, named muscle and bone loss, nutrient deficiencies from reduced intake, and weight regain after stopping as the main challenges of GLP-1 therapy. Their recommendations start with a baseline assessment of diet, strength, and body composition, then center on adequate protein and resistance training throughout treatment.
When total food intake falls by a third or more, nutrient density matters more than it did before. The gaps I see most often are protein, iron, vitamin B12, vitamin D, calcium, magnesium, and potassium, along with fiber and fluid. Gastrointestinal side effects make this harder. Nausea pushes people toward bland, refined carbohydrates, and slower gastric emptying combined with lower fluid intake leads to constipation.
This is not an argument for a long supplement list. It is an argument for testing at baseline and at intervals, and for building meals that cover these nutrients first. Supplements fill gaps that labs confirm.
1. Set a protein floor, then eat it first
In my practice I usually set protein at about 1.2 to 1.6 grams per kilogram of reference body weight per day, spread across two to four meals with roughly 30 to 40 grams each. Reduced appetite makes this hard, so protein goes first on the plate, before vegetables and starches. Liquid options (a protein shake, kefir, bone broth with added protein) help on days when nausea limits solid food. My protein-first strategy covers practical sources.
2. Train for strength, not only for calories
Resistance training is the signal that tells the body to keep muscle while fat is being lost. In a randomized trial of adults who had lost weight, those who combined liraglutide with a structured exercise program reduced body-fat percentage by 3.9 points over a year, about twice the reduction with either the drug or exercise alone. Only the combination group improved A1c, insulin sensitivity, and cardiorespiratory fitness (4). Two to three sessions a week that progressively load the major muscle groups is the target.
3. Build meals for a smaller appetite
Smaller, nutrient-dense meals work better than three large ones. Prioritize protein, colorful vegetables, and whole-food fats; go easy on high-fat fried meals, which tend to worsen nausea with slowed gastric emptying. Increase fiber gradually and pair it with fluid and electrolytes to prevent constipation. Alcohol is worth limiting: it adds calories without nutrients and can amplify GI side effects. Having prepared protein ready, as in my batch cooking guide, removes a lot of friction.
4. Monitor, don't guess
I check a baseline and periodic panel that includes a complete blood count, ferritin, vitamin B12, vitamin D, a complete metabolic panel (CMP), and fasting insulin and lipids, plus body composition every three months. Supplements are added when labs or intake tracking show a specific gap.
The trial data are consistent. In STEP 4, people who switched from semaglutide to placebo after 20 weeks regained 6.9% of body weight over the next 48 weeks, while those who continued lost a further 7.9% (5). In the STEP 1 extension, participants regained about two-thirds of their lost weight in the year after stopping, and most cardiometabolic improvements drifted back toward baseline (6).
That does not mean everyone needs the medication indefinitely. It means the exit needs a plan. What I look for before a taper:
The taper itself is a decision for the prescribing clinician. My role is to make sure the foundation underneath it is solid.
Semaglutide and tirzepatide are no longer in shortage, and the FDA has moved to restrict compounded versions (7). Compounded products, including those blended with B vitamins, are not FDA-approved and have not been tested in clinical trials. If you are using one, talk with your prescriber about where it is made and whether an approved product is an option.
How much protein should I eat on semaglutide (Ozempic, Wegovy) or tirzepatide (Mounjaro, Zepbound)?
A common clinical target is 1.2 to 1.6 grams per kilogram of reference body weight per day, divided across meals. Your target depends on age, kidney function, activity, and goals, so it is worth individualizing.
Will I lose muscle on a GLP-1?
Some lean mass loss is expected with any significant weight loss. Adequate protein and regular resistance training reduce it. Tracking body composition, not only the scale, tells you how you are doing.
Can I follow a low-carb or keto diet on a GLP-1?
Yes, many people do well with it, and it can help with blood sugar and cravings. The risk is very low total intake, so protein targets and electrolytes need deliberate attention.
Do I need supplements on a GLP-1?
Not automatically. Test first. Vitamin D, B12, iron, and magnesium are the most common gaps I find, and the need varies by person.
How do I avoid regaining weight after stopping?
Use the time on medication to build the habits and muscle that will carry you after it: consistent protein, strength training, sleep, and a plan for when appetite returns. Coordinate any taper with your prescriber.
On a GLP-1 or considering one? A nutrition plan built around your labs and body composition protects the results you are working for. Book a discovery call or read more about my metabolic health programs.
This article is for educational purposes and is not medical advice. Do not start, stop, or change a medication without your prescriber.
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