Losing excess weight can improve blood pressure, blood sugar, sleep and heart health. But when you lose a significant amount of weight, you do not lose fat alone. Some lean mass is usually lost too, and some of that may be muscle.
This can happen with any substantial weight loss, but it is particularly relevant now that medical weight-management treatments can help people lose larger amounts of weight than was often possible before.
Lean mass includes muscle, as well as water and other non-fat tissue, so lean-mass loss does not mean that all of it is muscle. The aim is to lose excess fat while maintaining as much muscle, strength and function as possible.
How much muscle do you actually lose?
Studies looking at body composition during significant weight loss, including trials of modern medical weight-loss treatments, show that most of the weight lost is fat, but some lean mass is lost as well.
The proportion varies between studies and treatments, but in the SURMOUNT-1 body-composition study around three quarters of the weight lost was fat mass and around one quarter was lean mass. Because lean mass includes more than muscle, this does not mean that a quarter of the weight lost was muscle. It does show that muscle can be lost during substantial weight loss and is worth protecting.
Why muscle matters more as you get older
Muscle plays a key role in strength, mobility, balance, endurance and staying active. From midlife onwards, both muscle mass and strength tend to decrease gradually as we age.
A successful weight loss outcome isn’t measured only by the number of kilograms lost. It also means reducing excess fat while preserving muscle mass, strength and physical function.
Protein matters more when you are eating less
Protein provides the amino acids needed to maintain and repair muscle, so getting enough becomes particularly important during weight loss.
This is especially relevant during medical weight-loss treatment because appetite can fall considerably. Portions become smaller, meals may be skipped and overall food intake can fall quite quickly.
For many adults losing weight, around 1.2 to 1.6 grams of protein per kilogram per day is often used as a guide when maintaining muscle is a priority, although this needs to be individualised. The right amount depends on body size, age, activity level and medical history, and people with kidney disease or other relevant conditions may need specific advice.
Protein can come from meat, fish, eggs, dairy products, beans, lentils, tofu and other protein-rich foods. In practice, making sure there is a good source of protein at meals is often more useful than becoming too focused on exact numbers.
Resistance exercise helps preserve muscle
Regular resistance exercise is the other important part of protecting muscle during weight loss. Using and loading the muscles gives the body a reason to maintain them while weight is coming down.
This might involve free weights, gym machines, resistance bands or body-weight exercises, depending on fitness, experience and any injuries. Walking, cycling and swimming are still important for heart health and general fitness, but they do not provide the same stimulus for maintaining muscle.
Protein and resistance exercise work together. Protein provides the building blocks needed to maintain and repair muscle, while resistance exercise gives the muscles the stimulus to stay strong.
Faster weight loss is not always better
It is easy to assume that the faster the weight comes off, the better the treatment is working. With medical weight-management treatment, that is not necessarily the case.
The aim is not to suppress appetite to the point where someone is barely eating. Treatment should produce useful weight loss while still allowing enough food and nutrition to maintain health, activity and muscle.
If weight is falling very quickly but food intake has become very low, strength is dropping or exercise has stopped because of weakness or tiredness, the treatment plan should be reviewed. That may mean looking again at nutrition, the pace of weight loss or the treatment dose rather than simply trying to lose weight faster.
Weight loss is only one part of improving health
Losing excess weight can make a big difference to health, but it is only one part of the picture. Smoking has a major effect on the risk of heart disease, stroke and cancer, while heavy alcohol intake can raise blood pressure, affect the liver and disrupt sleep.
Poor sleep, ongoing stress and physical inactivity can also affect energy, appetite and general health. Medical weight management works best when it sits alongside these other parts of health rather than replacing them.
What about testosterone?
Excess weight and low testosterone are often linked in men, and testosterone may improve as weight and general health improve.
For some men, particularly younger men with excess weight and low testosterone, weight management may be an important first step. But ongoing symptoms such as low sex drive, reduced energy, poor motivation or erection problems still need proper assessment, particularly if testosterone is clearly low.
In men with genuine testosterone deficiency, treatment can improve symptoms and increase lean mass. Feeling better may also make it easier to stay active and exercise regularly while working on weight.
Testosterone is not a treatment for obesity, however, and should not be prescribed simply as a way of preventing muscle loss during weight reduction.
How our Weight Management Service works at H3 Health
At H3 Health, our Weight Management Service looks at weight as part of men's overall health rather than simply as a number on the scales.
That includes weight and waist measurement, blood pressure, blood sugar, cholesterol, sleep, alcohol, smoking, diet and activity levels, as well as any symptoms that may suggest another health issue.
Where medical weight-management treatment is appropriate, reviews are not only about how much weight has been lost or whether the dose should change. We also look at whether food intake and protein remain adequate, whether strength and activity are being maintained, and whether someone is becoming weaker or struggling to exercise as weight comes down.
As someone gets closer to their target weight, the focus starts to shift towards maintenance. For some people, ongoing medical treatment may remain part of that plan; for others, the dose or treatment may change over time. Nutrition, resistance exercise and maintaining strength remain important whichever approach is taken. Contact us for more information.
The bottom line
Losing excess weight can bring substantial health benefits, but some muscle can be lost along the way, so protecting it should be part of the plan from the beginning.
Getting enough protein, continuing regular resistance exercise and avoiding weight loss that is so rapid that food intake, strength or activity start to suffer can all help.
The aim is to lose excess fat while maintaining muscle, strength and the ability to stay active.
References
Ma C, Avenell A, Bolland M, et al. Effects of weight loss interventions for adults who are obese on mortality, cardiovascular disease, and cancer: systematic review and meta-analysis. BMJ. 2017;359. doi:10.1136/bmj.j4849.
Look M, Dunn JP, Kushner RF, et al. Body composition changes during weight reduction with tirzepatide in the SURMOUNT-1 study of adults with obesity or overweight. Diabetes Obes Metab. 2025;27(5):2720–2729. doi:10.1111/dom.16275.