Popular weight-loss medications like semaglutide (Ozempic) and tirzepatide (Mounjaro) can dramatically reduce appetite and food intake, but new research shows most users aren't receiving adequate nutrition guidance to prevent serious health risks including muscle loss and vitamin deficiencies. A comprehensive review from the University of Cambridge and University College London found that despite the rapid rise in these medications' use, structured nutritional support has failed to keep pace.

How Do GLP-1 Weight-Loss Drugs Actually Work?

Glucagon-like peptide-1 (GLP-1) receptor agonist medications mimic a natural hormone released after eating. These drugs reduce appetite, increase feelings of fullness, and help curb food cravings. The result is dramatic: calorie intake can drop by 16 to 39 percent, making these medications highly effective for people living with obesity.

However, this powerful appetite suppression creates a hidden problem. "Obesity management medications work by suppressing appetite, increasing feelings of fullness, and altering eating behaviors, which often leads people to eat significantly less," explains Dr. Adrian Brown, an NIHR Advanced Fellow at University College London's Centre of Obesity Research. "However, without appropriate nutritional guidance and support from healthcare professionals, there is a real risk that reduced food intake could compromise dietary quality, meaning people may not get enough protein, fiber, vitamins, and minerals essential for maintaining overall health".

What Happens to Your Body Composition During Treatment?

One of the most concerning findings involves what actually gets lost during weight loss. Research suggests that lean body mass, including muscle, can make up as much as 40 percent of the total weight lost during treatment with these medications. This means that if someone loses 50 pounds, roughly 20 pounds of that could be muscle rather than fat.

Loss of lean muscle mass increases the likelihood of weakness, injuries, and falls. Low intake of key vitamins and minerals can trigger additional problems including fatigue, weakened immune function, hair loss, and osteoporosis.

Why Isn't Nutrition Support Being Provided?

The research identified only 12 studies examining diet and nutrition alongside treatment with semaglutide or tirzepatide. These studies varied widely in how they delivered dietary advice and measured nutrition outcomes, making it difficult to draw firm conclusions about best practices.

In the United Kingdom, when semaglutide is prescribed through the National Health Service (NHS), it's intended to be part of a broader program that includes a reduced-calorie diet and increased physical activity with professional support. However, around 1.5 million people in the UK are currently using GLP-1 drugs, and an estimated 95 percent obtain them privately. In these private settings, additional nutrition advice and follow-up support are often not provided.

Dr. Marie Spreckley of the University of Cambridge emphasizes the urgency: "Use of GLP-1 receptor agonist therapies has increased rapidly in a very short period of time, but the nutritional support available to people using these medications has not kept pace. Many people receive little or no structured guidance on diet quality, protein intake, or micronutrient adequacy while experiencing marked appetite suppression".

How to Support Healthy Weight Loss on These Medications

Experts recommend drawing lessons from nutrition care used after weight-loss surgery, which creates similar appetite suppression and food intake reduction. Dr. Cara Ruggiero, a researcher from the Medical Research Council Epidemiology Unit at the University of Cambridge, outlines evidence-based strategies:

• Prioritize high-quality protein: Include protein sources distributed evenly across meals to help preserve lean muscle mass during periods of reduced appetite and rapid weight loss.
• Focus on nutrient-dense foods: Rather than counting calories, emphasize foods packed with vitamins, minerals, and other essential nutrients that support overall health.
• Eat smaller meals more frequently: Research suggests that eating smaller portions spaced throughout the day may help ease side effects like nausea and make the medications easier to tolerate, especially early in treatment.
• Personalize fat intake guidance: The available evidence does not support strict low-fat diets alongside these medications, though some observational studies found that people taking the drugs often consumed high levels of total and saturated fat, suggesting personalized guidance aligned with national dietary recommendations may be helpful.

What Experts Say About the Gap in Care

Dr. Spreckley notes that if nutritional care is not integrated alongside treatment, there is a real risk of replacing one set of health problems with another. "If nutritional care is not integrated alongside treatment, there's a risk of replacing one set of health problems with another, through preventable nutritional deficiencies and largely avoidable loss of muscle mass. This represents a missed opportunity to support long-term health alongside weight loss," she explains.

The research team is now launching a new project called AMPLIFY (Amplifying Meaningful Perspectives and Lived experiences of Incretin therapy use From diverse communitY voices) to explore how people experience these medications in daily life and what information and support patients find most useful. This real-world perspective could help improve future care.

If you're considering or currently using these medications, seek out a registered dietitian who understands how GLP-1 drugs work and can provide personalized nutrition guidance. The goal isn't just weight loss—it's sustainable weight loss that preserves muscle, prevents nutrient deficiencies, and supports long-term health.