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Nutrition During Weight Loss with GLP‑1 Medications
Medications such as semaglutide and other glucagon-like peptide-1 (GLP-1) receptor agonists have changed how we approach weight loss. For many people, these treatments make it easier to reduce appetite and lose weight in a way that was previously difficult to achieve. However, an important part of the conversation is often overlooked: what happens to nutrition as food intake decreases?
These medications work, in part, by reducing hunger and slowing digestion. They act on receptors for GLP-1, a naturally occurring hormone involved in appetite regulation. More specifically, GLP-1s can delay gastric emptying, meaning food leaves the stomach more slowly, which makes a person feel fuller longer. They may also reduce hunger and cravings. While this supports reductions in body weight, it can also lead to lower overall food intake and fewer calories consumed per day.
This may unintentionally reduce the intake of healthy life sustaining nutrients the body depends on every day. Emerging research indicates that people using GLP-1 medications may consume insufficient amounts of key nutrients, including protein, iron, calcium and several vitamins (1). On top of reducing appetite, common GI side effects of nausea, vomiting and constipation can make regular eating more difficult. These findings identify a potential nutritional risk, but they do not mean that every patient will develop a deficiency.
Protein is particularly important during this process. During any weight loss, whether through medication, diet or surgery, the body loses not only fat but also some lean tissue. The amount varies considerably between people and studies (2). Lean mass includes muscle, but also water, organs and other non-fat tissue, so it is not an exact measure of muscle mass.
Without adequate protein intake, lean tissue loss in proportion to overall body mass lost may be more elevated, with potential effects on strength and recovery. Including protein with each meal may prevent the loss of excess lean tissue. Eggs, dairy products, fish and beans are possible sources. Protein-rich snacks or protein shakes may be useful when food intake is limited, although they are not necessary for everyone.
Adequate protein combined with regular exercise, including strength training when medically appropriate, may help preserve lean tissue. No strategy can completely prevent muscle loss, and individual recommendations should reflect a person’s health and abilities (3).
Vitamins and minerals such as vitamin D, iron and B vitamins are needed in small amounts but play vital roles in bone and muscle health, oxygen transport, immune function and energy levels. Inadequate intake may contribute to health concerns, although symptoms such as fatigue are nonspecific and require proper assessment.
Nutrient-dense foods may include whole grains such as oats, leafy greens, bell peppers, other vegetables and fruit such as berries, depending on individual tolerance. These foods can also provide fiber, which supports bowel regularity. Current research suggests that reduced dietary intake during GLP-1 therapy may increase nutritional insufficiency risk, particularly when nutrition is not actively monitored (3).
People using these medications should generally stay hydrated, especially when experiencing digestive symptoms. Increasing fibre gradually and consuming enough fluid may be helpful to prevent constipation, but individual fluid needs can vary.
Despite this, structured nutritional support is not always part of routine care. Unlike bariatric surgery, where regular nutritional monitoring is standard, formal systems to assess and support nutrition during GLP-1 therapy remain limited, representing an important gap in care (5).
For individuals using these therapies, the goal is not simply to lose weight, but to do so in a way that supports overall health. Paying attention to protein intake, including nutrient-dense foods and maintaining regular follow-up may help protect lean tissue and reduce the risk of deficiencies. Patients should avoid starting supplements without professional advice. A doctor or another qualified provider can determine whether dietary changes, laboratory testing or supplementation are needed concurrently with GLP-1 use.
Weight-loss medications can be powerful tools, but nutrition remains the foundation that supports their long-term success.
At Clinique Michel Gagner, we provide individualized obesity care based on each patient’s health, treatment history and goals. Our specialists and registered dietitians offer medical and nutrition consultations as part of a personalized weight management approach.
We also assess patients considering bariatric surgery, with nutritional services included for up to three months after a procedure. You can review our bariatric surgery fees and included services or complete our two-minute weight-loss questionnaire to determine where to begin.
1. Johnson B, et al. Investigating nutrient intake during use of GLP‑1 receptor agonists: a cross-sectional study. Frontiers in Nutrition, 2025.
2. Karakasis P, et al. Effect of glucagon-like peptide-1 receptor agonists and co-agonists on body composition: Systematic review and network meta-analysis. Metabolism, 2025.
3. Sibal R, et al. Macronutrient, Micronutrient Supplementation and Monitoring for Patients on GLP-1 Agonists: Can We Learn from Metabolic and Bariatric Surgery?. Nutrients, 2025.
