Why Protein Is Essential During GLP-1 Treatment and After Bariatric Surgery
Blog by Dr Q Cheng, Bariatric Surgeon Sydney
When people begin their weight loss journey with GLP-1 medications or bariatric surgery, much of the focus is understandably on the number on the scales. However, successful weight loss is about far more than simply losing kilograms. The real goal is to improve your overall metabolic health, reversing obesity related medical problems and lose excess body fat while preserving lean muscle mass [1,2]. One of the most important factors in achieving this is ensuring an adequate intake of protein.
Why is protein important in our diet?
Protein is the body’s primary building block. It plays a crucial role in maintaining muscle, repairing tissues, supporting the immune system, producing hormones and enzymes. It is also important in keeping our hair, skin and nails healthy [3]. During periods of weight loss especially when caloric intake is significantly reduced, the body can begin breaking down muscle in addition to fat for our daily energy. Without enough dietary protein, this loss of muscle can occur more rapidly, leading to reduced strength and an overall slower metabolism [4]. This not only has immediate impacts but can ultimately affect weight loss maintenance over the long term.
How GLP-1 and Bariatric surgery impacts diet?
This is particularly important for people taking GLP-1 medications such as Semaglutide or Tirzepatide. These medications are highly effective because they reduce appetite and increase satiety, with an overall effect of reducing our caloric intake. While this reduction in food intake is beneficial for weight loss, it also means many people unintentionally consume much less protein than their bodies require [5]. If patients simply eat less without prioritising protein-rich foods, they may lose valuable muscle mass alongside body fat. This is why nutritional quality becomes just as important as the quantity of food we consume.
Not all weight loss is created equal. Two people may each lose 10 kg, but the composition of that weight loss can be dramatically different. Prioritising adequate protein intake and resistance exercise helps maximise fat loss while preserving valuable muscle mass, leading to better strength, a healthier metabolism and improved long-term weight maintenance.
The same principle applies and perhaps even more so after bariatric surgery. Following procedures such as sleeve gastrectomy or gastric bypass, the stomach’s capacity is dramatically reduced. Patients become full quite quickly, meaning every bite needs to provide as much nutritional value as possible. Protein should therefore always be prioritised at every meal [1,2]. By eating protein before vegetables or carbohydrates, patients are more likely to meet their nutritional needs despite their smaller meal sizes. Adequate protein also supports wound healing after surgery, reduces the risk of nutritional deficiencies and helps patients recover more effectively as they return to normal activities [2]. For any patient of the practice, you would have heard us talk about the bariatric plate which highlights the recommended change in food composition. This is one of the core principles with any weight loss therapies.
Why muscle mass is important
One of the most overlooked aspects of weight loss is the importance of preserving muscle. Muscle is far more than something that contributes to physical appearance—it is metabolically active tissue that helps the body burn energy even while at rest. Losing excessive muscle during weight loss can reduce resting metabolic rate, increase fatigue and make long-term weight maintenance more challenging. Preserving muscle allows patients to remain stronger, more active and better able to sustain their results over time.
Adequate protein intake also plays an important role in preventing sarcopenia – the progressive loss of muscle mass and strength that can occur with ageing, illness and rapid weight loss [3]. As more people use GLP-1 medications and undergo bariatric surgery, we as healthcare professionals are increasingly recognising that the true marker of successful treatment is change in body composition rather than the weight number reflected on scales [6]. The combination of sufficient protein intake, regular resistance exercise and ongoing physical activity provides the best opportunity to preserve lean muscle while reducing body fat.
What are good protein options and how much do you need?
Protein requirements vary between individuals depending on body size, age, physical activity and medical history. Many patients who have undergone bariatric surgery are advised to consume over 60 grams of protein each day, while those taking GLP-1 medications may benefit from protein intakes based on their ideal body weight [1,2]. Because every patient is different, personalised advice from our experienced bariatric dietitian is essential to ensure your nutritional needs are being met.
Fortunately, there are many excellent sources of protein that can be incorporated into everyday meals. These include lean chicken, fish, eggs, Greek yoghurt, cottage cheese, tofu, legumes and lean red meat are all excellent options [7]. During the early recovery period after bariatric surgery, some patients may also benefit from protein supplements or shakes to help with their daily protein targets. These should complement a balanced diet rather than replace whole foods.
Why Exercise Physiology is important
Protein alone is not enough to maintain muscle. Resistance exercise whether through weight training, resistance bands, Pilates or bodyweight exercises help provide the stimulus needed for the body to preserve and build lean muscle tissue [8]. Even two or three strength-based sessions each week can make a significant difference when combined with an adequate protein intake. This partnership between nutrition and exercise is one of the most effective strategies for achieving healthy, sustainable weight loss.
Ultimately, weight loss should never be viewed simply as eating less. Whether you are taking a GLP-1 medication or have undergone bariatric surgery, your body still requires high-quality nutrition to function at its best. Prioritising protein helps preserve muscle, supports recovery, maintains strength and promotes a healthier metabolism. This would allow you to lose weight in a way that protects your long-term health. At our clinic, we encourage every patient to think beyond the scales and focus on building healthy habits that will support lasting success for years to come.
References
- Australian & New Zealand Metabolic and Obesity Surgery Society (ANZMOSS).
Clinical Practice Guidelines for Bariatric Surgery. https://anzmoss.org/ - American Society for Metabolic and Bariatric Surgery (ASMBS). Mechanick JI, Apovian C, Brethauer S, et al. Clinical Practice Guidelines for the Perioperative Nutrition, Metabolic, and Nonsurgical Support of Patients Undergoing Bariatric Procedures – 2019 https://pubmed.ncbi.nlm.nih.gov/32202076/
- Deutz NEP, Bauer JM, Barazzoni R, et al. Protein Intake and Exercise for Optimal Muscle Function with Aging. Clinical Nutrition. https://pubmed.ncbi.nlm.nih.gov/24814383/
- Jastreboff AM, Aronne LJ, Ahmad NN, et al. Tirzepatide Once Weekly for the Treatment of Obesity. New England Journal of Medicine. 2022;387:205–216. https://www.nejm.org/doi/full/10.1056/NEJMoa2206038
- Bennett JP, Lim S. The Critical Role of Body Composition Assessment in Advancing Research and Clinical Health Risk Assessment across the Lifespan. J Obes Metab Syndr. 2025 Apr 30;34(2):120-137. doi: 10.7570/jomes25010. Epub 2025 Apr 8. PMID: 40194886; PMCID: PMC12067000. https://pubmed.ncbi.nlm.nih.gov/40194886/
- Phillips SM, Fulgoni VL, Heaney RP, et al. Commonly Consumed Protein Foods Contribute to Nutrient Intake, Diet Quality, and Nutrient Adequacy. American Journal of Clinical Nutrition. https://pubmed.ncbi.nlm.nih.gov/25926509/
- American College of Sports Medicine (ACSM) ACSM Position Stand: Progression Models in Resistance Training for Healthy Adults. Medicine & Science in Sports & Exercise. 2009;41(3):687–708. https://pubmed.ncbi.nlm.nih.gov/19204579/
