We’ve all seen it, clients buzzing with excitement because they’ve finally shifted a few kilos. The number on the scale is going down and everything seems to be on track. But then the complaints start trickling in. “I feel a bit weaker,” “my lifts have stalled,” or “I just feel flat.” That’s when we start to realise that not all weight loss is good weight loss.
Because yes, fat is coming off, but so is muscle. And losing muscle during a calorie deficit is the sort of progress that comes back to bite you. That’s why as fitness professionals and nutrition coaches, preserving lean body mass (LBM) should always be part of the plan, not just shifting weight for weight’s sake.
It’s a principle we drill into learners on our nutrition courses. Because it doesn’t matter if it’s a client on a meal plan, post-surgery or even using GLP-1 medication, the risk of losing muscle is real.
Let’s take a look at why it happens, why it matters and what we can actually do about it.
The Unwanted Side Effect of Dieting
Whenever we create an energy deficit, the body taps into its reserves. Ideally, we want that to be body fat. But unless we’re strategic about it, muscle gets broken down too.
Studies show that during weight loss, up to 45% of the total weight lost can come from lean tissue. This is more so the case when there is an absence of strength training or adequate protein intake (Cannavaro et al., 2025). That’s a big problem, because LBM isn’t just about aesthetics or athletic performance. It plays a massive role in metabolic rate, insulin sensitivity, mobility and injury prevention.
And once you start losing muscle, it’s harder to stop. Metabolic rate drops, you burn fewer calories at rest and your body becomes more efficient at storing fat. This in turn makes fat regain more likely once you stop dieting. Definitely not the original goal.
Why It’s Harder to Regain Muscle Than Fat
And what’s really annoying is that rebuilding muscle is a slower, more resource-intensive process than regaining fat. Your body can pile fat back on pretty quickly when you return to maintenance or surplus, but rebuilding lost muscle is harder work. This is even more difficult for older adults or sedentary individuals.
And in those with obesity, it’s even trickier. A growing body of research shows that individuals with excess fat mass often experience anabolic resistance, where their muscles don’t respond to dietary protein or exercise in the same way as someone leaner would (Beals et al., 2016; Guillet et al., 2009). So once muscle is lost, it takes more effort to regain it and even more to keep it.
Resistance Training and High-Protein Diets
Resistance training is non-negotiable during a diet if the goal is to keep muscle. It’s the strongest signal we can send to the body that muscle is still needed. Strength training stimulates muscle protein synthesis (MPS), which helps maintain and potentially build muscle even when energy intake is reduced.
But it’s not just lifting weights. Nutrition needs to match the effort. For most adults in a calorie deficit, 1.6–2.2 grams of protein per kg of body weight per day is a good target, ideally spread across the day and anchored around training sessions. Quality matters too, as in complete proteins with all the essential amino acids are best.
Where Amino Acids Come In
This is where things get interesting. Even with the best training programme and a high-protein diet, some people struggle to hit their targets. Maybe their appetite tanks during a cut. Maybe they’re recovering from bariatric surgery. Maybe they’re on a GLP-1 like semaglutide and can barely manage half a chicken breast.
That’s when amino acid supplementation including essential amino acids (EAAs), can play a role.
EAAs include the nine amino acids your body can’t make on its own, and they’re critical for triggering and sustaining MPS. Among them, leucine is a standout as it activates the mTORC1 pathway, which is like flipping the switch for muscle building. But leucine alone isn’t enough. You need the full blend of EAAs to actually build and maintain muscle tissue.
That’s why EAAs outperform BCAAs when it comes to preserving muscle in a deficit.
Take the recent Cannavaro et al. (2025) review. It summarised several studies where EAA supplementation helped maintain or improve LBM during calorie restriction. For example, in a 2024 study, women following a very-low-energy ketogenic diet (VLEKD) were given 8g of EAAs per day during the refeeding phase. Those who took the supplement maintained more muscle mass, lost more fat and had stronger grip strength compared to the non-supplemented group.
Other studies in older adults have shown similar results. When EAAs were added to meal replacements in hypocaloric diets, participants experienced greater fat loss and less muscle loss compared to isocaloric controls (Coker et al., 2022). Some even showed increased thigh muscle cross-sectional area without any training at all.
So, Are BCAAs Pointless?
No.
BCAAs (leucine, isoleucine, valine) are part of the EAA family and do help stimulate MPS to a degree. But taking them alone when you’re eating enough protein doesn’t offer much additional benefit.
In fact, in several studies, BCAA supplementation didn’t prevent muscle loss during calorie restriction unless protein intake was otherwise too low (Ooi et al., 2021). And even then, EAAs were more effective.
So while BCAAs support energy during training and help with muscle recovery, they’re not a substitute for whole protein or a full-spectrum EAA blend in this situation.
When Supplements Really Matter
There are other situations where EAA supplementation becomes more than just a nice-to-have:
- Very low-calorie diets: EAAs are a quick, efficient way to boost protein quality when overall food intake is low.
- Post-bariatric surgery: Appetite and gastric volume are limited, EAAs can provide high-quality amino acids without requiring large portions.
- On GLP-1 medications: Appetite suppression often leads to unintentional under-eating, including protein. EAAs are an easy way to top up intake without adding bulk.
- Older adults: Muscle response to protein is reduced with age, so a leucine-rich EAA formula can help reach the anabolic threshold.
- Busy or stressed clients: Those who regularly skip meals or under-eat during dieting phases may benefit from targeted EAA support around training or between meals.
What We Can Do
First, nail the basics. Resistance training, daily movement and hitting a solid protein target will do most of the heavy lifting when it comes to keeping muscle. But when those boxes are already ticked or hard to meet, EAA supplements can help close the gap.
Encourage clients to:
- Spread protein intake across the day, aiming for 25–35g per meal.
- Add an EAA supplement around training, particularly in a fasted or low-protein state.
- Monitor body composition, strength and function, not just scale weight.
- Be aware of energy levels, recovery and hunger. Not all weight loss is worth celebrating if it’s dragging performance down.
And if they’re on GLP-1s or recovering from surgery, reassure them that targeted amino acid support can help preserve their hard-earned muscle while they manage their health.
It’s time to move the conversation beyond just “weight loss.” Because if you’re losing muscle along with the fat, you’re trading short-term results for long-term problems.
Whether it’s through training, diet or smart supplementation, keeping hold of lean mass should be a priority for every weight loss client. And in cases where food alone isn’t cutting it, essential amino acids can offer a powerful, evidence-based way to help preserve muscle during a deficit without derailing progress or making things complicated.
Weight loss might be the goal, but let’s make sure it’s the right kind of weight that’s coming off.
Reference
- Cannavaro, D., Leva, F., Caturano, A., Berra, C.C., Bonfrate, L., & Conte, C. (2025). Optimizing Body Composition During Weight Loss: The Role of Amino Acid Supplementation. Nutrients, 17(12), 2000. Click here to review the full research article.
- Beals, J.W., Sukiennik, R.A., Nallabelli, J., Emmons, R.S., van Vliet, S., Young, J.R., Ulanov, A.V., Li, Z., Paluska, S.A., & Wolfe, R.R. (2016). Anabolic sensitivity of postprandial muscle protein synthesis to the ingestion of a protein-dense food is reduced in overweight and obese young adults. The American Journal of Clinical Nutrition, 104(4), 1014–1022. Click here to review the full research article.
- Guillet, C., Delcourt, I., Rance, M., Giraudet, C., Walrand, S., Bedu, M., Duche, P., & Boirie, Y. (2009). Changes in basal and insulin and amino acid response of whole body and skeletal muscle proteins in obese men. The Journal of Clinical Endocrinology & Metabolism, 94(8), 3044–3050. Click here to review the full research article.
- Annunziata, G., Verde, L., D’Orsi, V., Caprio, M., Gorini, S., Savastano, S., Colao, A., Muscogiuri, G., & Barrea, L. (2025). Supplementation with essential amino acids in the early stage of carbohydrate reintroduction after a very-low energy ketogenic therapy (VLEKT) improves body cell mass, muscle strength and inflammation. Journal of Translational Medicine, 23, 111. Click here to review the full research article.
- Coker, M.S., Barati, Z., Murphy, C.J., Bateman, T., Newcomer, B.R., Wolfe, R.R., & Coker, R.H. (2022). Essential amino acid enriched meal replacement improves body composition and physical function in obese older adults: A randomized controlled trial. Clinical Nutrition ESPEN, 51, 104–111. Click here to review the full research article.
- Ooi, D.S.Q., Ling, J.Q.R., Sadananthan, S.A., Velan, S.S., Ong, F.Y., Khoo, C.M., Tai, E.S., Henry, C.J., Leow, M.K.S., & Khoo, E.Y.H. (2021). Branched-chain amino acid supplementation does not preserve lean mass or affect metabolic profile in adults with overweight or obesity in a randomized controlled weight loss intervention. The Journal of Nutrition, 151(4), 911–920. Click here to review the full research article.
Become a PT and Help Clients Keep the Muscle and Shift the Fat
Looking to support clients through smarter weight loss strategies? The Nutrition & Exercise Specialist & Master Diplomas™ from TRAINFITNESS could be exactly what you need. In a 2025 review, researchers found that up to 45% of weight lost during dieting can come from lean body mass. This is a concerning figure for anyone trying to improve health, strength or performance. But the same review showed that supplementing with essential amino acids (EAAs) helped preserve muscle mass, improve grip strength and promote greater fat loss, particularly when paired with structured nutrition and exercise plans. On this course, you’ll explore the science behind these outcomes and learn how to apply evidence-based strategies to support clients during calorie restriction, post-bariatric surgery or while using GLP-1 medications such as Ozempic & Wegovy . If you want to become a personal trainer specialising in nutrition, this diploma gives you the tools to guide clients toward results that last. And this is not just on the scales, but in strength, function and health.
Nutrition & Exercise Specialist/Master – Distance Study, In-Person & Live-Virtual
