Why We Lose Muscle When We’re Losing Weight

It is known that when we lose weight (regardless of whether or not we use medications), in addition to losing fat mass, we inevitably lose muscle mass, as well. This is because to lose weight, we need to create a negative energy balance where we are burning more calories than we are taking in, resulting in a calorie deficit, which can impact how our body utilizes/burns energy stores.  

When we eat, our body breaks down the nutrients into amino acids, fatty acids, and glucose to be used by our tissues. Glucose is the main energy source for our cells, tissues, and organs and is derived primarily from carbohydrates _[3]. Any glucose not immediately used is stored as glycogen in the liver, muscles, and fat cells _[4]. When we are in a caloric deficit, like losing weight, our body will first utilize glycogen stores in the liver for energy _[5]. When those stores are depleted, our bodies will recruit fat and muscle stores to be metabolized for fuel. When not in an energy deficit, we can access these stores without causing significant muscle breakdown and rebuild protein stores to maintain our muscle mass efficiently. However, during an energy deficit in which our caloric intake is lowered, our bodies experience increased rates of protein breakdown and reduced rates of protein rebuilding/synthesis to preserve energy, resulting in a loss of muscle mass _[2]. 

So while some muscle mass loss is to be expected as we lose weight, if we are not mindful about mitigating this loss through intentional diet and exercise modifications, individuals are at risk for developing sarcopenic obesity (a combination of high body fat percentage and low levels of skeletal mass and functionality) which can increase the risk of developing metabolic diseases, and can lead to frailty, falls, and disability _[6]. Additionally, significant decreases in muscle mass levels can cause a down-regulation of metabolic processes, resulting in a lower metabolism, reduced protein turnover, and higher rates of weight plateauing _[2]. 

While many individuals speculate that the use of GLP-1 receptor agonist medications such as Ozempic and Mounjaro are directly contributing to the increased rates of weight-loss-induced muscle wasting, it is important to clarify that losing muscle in addition to fat mass when losing weight is not unique to GLP-1 RA medications and occurs not from using the medication, but in doing so without incorporating muscle-preserving diet and exercise modifications _{[7] [8]}. Additionally, a recent study showed that semaglutide and liraglutide (the active compounds in GLP-1 RA medications Ozempic/Wegovy and Saxenda/Victoza, respectively) might be protective against obesity-induced skeletal muscle atrophy _[9]. 

To preserve muscle mass when losing weight (either with or without the use of GLP-1 RA medications), it is imperative that patients engage in regular exercise _[10] – with emphasis on strength training – and consume adequate amounts of protein _[11]. During our initial visit, we will discuss nutrition recommendations, provide examples and meal ideas to achieve adequate protein consumption, review physical exercise guidelines, and recommend best engaging in muscle-preserving activities. While we want you to see a change in the number on the scale, ensuring that you maintain healthy levels of lean muscle mass through your weight loss journey is our highest priority!