MUSCLE LOSS WITH GLP-1 AND GIP AGONISTS: WHY IT HAPPENS AND HOW A DEXA BODY COMPOSITION SCAN CAN HELP

GLP-1 and GIP agonists such as Mounjaro (tirzepatide) are extremely effective for weight loss, with many patients losing 10 to 20% of their total body weight. While this is beneficial for metabolic health, an important part of safe weight management is ensuring that the weight you lose is mostly fat — not muscle. Research shows that all forms of rapid weight loss, including medically assisted weight loss, can lead to some degree of lean mass reduction unless monitored and supported properly.

A DEXA body composition scan is the most accurate way to see exactly how much of your weight loss is fat, muscle, and visceral fat. This allows you and your clinician to optimise the treatment, preserve muscle, and protect long-term health.

1. Reduced appetite
   These medications significantly suppress appetite. While this helps with calorie control, it can also lead to under-eating protein and essential nutrients.
2. Rapid weight loss
   When weight comes off quickly, the body loses both fat and muscle unless resistance training and adequate protein intake are maintained.
3. Lower energy intake
   With lower calorie intake, the body may prioritise energy conservation. Muscle tissue is metabolically costly to maintain, and the body may break it down if nutritional intake is insufficient.
4. Reduced spontaneous activity
   Many people naturally decrease day-to-day movement when eating less, contributing to muscle loss.

Clinical trials consistently show that approximately 20% to 40% of total weight lost on GLP-1 and GIP therapy comes from lean mass. Lean mass includes muscle, water, and organ tissue — but muscle makes up the majority of the lean reduction. This does not mean treatment is unsafe, but it highlights the importance of monitoring and preventing avoidable muscle loss through nutrition, resistance training, and DEXA tracking.

Muscle mass is critical for metabolic rate, strength, balance, joint support, insulin sensitivity, and healthy ageing. Excessive muscle loss can make a patient more prone to weight regain in the future, as a lower metabolic rate makes long-term maintenance harder.

A DEXA body composition scan is the best tool for separating fat loss from muscle loss. It provides precise data on:

– total body fat percentage
– fat distribution
– visceral fat
– total lean and muscle mass
– muscle distribution in arms, legs, and trunk

Unlike standard scales, DEXA shows whether weight loss is healthy and whether adjustments are needed. This is especially important for patients on GLP-1/GIP therapy who want to avoid unnecessary muscle loss.

Most patients benefit from repeating a DEXA scan every 8 to 12 weeks. This interval helps identify early trends and ensures any decline in muscle mass is addressed promptly.

1. Increase protein intake
   Aim for around 1.2 to 1.6 grams of protein per kilogram of body weight per day. With appetite suppression, patients often unintentionally under-eat protein.
2. Prioritise resistance training
   Strength training is the single best method to preserve or even increase muscle during weight loss. Two to three sessions per week focusing on major muscle groups is ideal.
3. Avoid extreme calorie restriction
   While medication reduces appetite, it is important to eat enough to support muscle maintenance. Very low calorie intake accelerates muscle loss.
4. Maintain daily activity
   Aim for regular steps and movement throughout the day. Light activity helps preserve lean mass.
5. Ensure adequate nutrients
   Low appetite can cause micronutrient deficiencies. Balanced intake of vitamins and minerals supports recovery and energy levels.
6. Monitor progress with DEXA
   Regular DEXA scans show whether fat loss is occurring while muscle is being preserved. If lean mass is dropping too quickly, your plan can be adjusted early.

Bodyweight alone cannot distinguish between fat loss and muscle loss. Two people could each lose 5 kg, but one might lose mostly fat while the other loses large amounts of muscle. DEXA reveals exactly what is changing and ensures you are losing weight in a healthy and sustainable way.

– Anyone on Mounjaro or similar medications
– Patients starting or progressing through a weight-loss programme
– Individuals concerned about muscle loss
– Older adults at higher risk of sarcopenia
– People wanting a healthy, toned physique
– Anyone aiming for safe, medically supervised fat loss

GLP-1 and GIP medications are powerful tools for weight reduction, but preserving muscle is essential for long-term health, longevity, and metabolic stability. A DEXA body composition scan is the most accurate method for tracking fat loss versus muscle loss throughout treatment.

By combining medication with adequate protein, resistance training, and regular DEXA monitoring, you can ensure that you lose fat, protect your muscle, and achieve sustainable, healthy weight loss.

DEXA.LONDON is dedicated to providing the highest-quality body composition and bone-health scanning in London. Our service uses clinical-grade DEXA technology, offering detailed, medically robust body composition reports in a clear, easy-to-understand format. Whether you are starting GLP-1/GIP treatment, monitoring progress, tracking muscle change, or assessing visceral fat, DEXA.LONDON gives you the precise data you need to make informed decisions about your health. Located on Harley Street and operated by 3Beam Imaging Centre, DEXA.LONDON provides fast appointments, expert analysis, and repeatable scans ideal for tracking your journey over time.