Strength Training While Losing Weight: For Women and Men

01What this is about

If you are a woman and think strength training is “not for me” because you are afraid of getting too muscular: this article is for you. It applies just as much to men.

The scale shows three kilos less, but you do not feel fitter? Then it is worth looking at what was actually lost. When you lose weight, body fat is not the only thing that goes down. Fat-free mass decreases too. That includes muscle, but also water, organs and bone. Part of this is normal, because a lighter body needs less muscle mass. More important than the pure amount are strength and muscle quality.

Many people have two worries: that losing weight leads into a spiral where they have to eat less and less, and that strength training will make them “too muscular”. This article shows what is true about both and what is not.

02What the science says

How much muscle is lost without training?

A common saying is that a quarter of every kilo lost is fat-free mass. Researchers call this rule a rough approximation at best. How much it really is depends, among other things, on your starting weight, the size of your deficit and how active you are.

A later model calculation with data from about 900 adults with overweight arrived at roughly 2 to 2.5 kilos of muscle per 10 kilos of weight loss in men and roughly 1 to 1.5 kilos in women, without targeted training. These are estimates, not a guarantee.

What strength training changes

A large review pooled 25 studies with a total of 1,608 adults with overweight. 15 of them included only women. Everyone lost weight through dieting, and some also trained with weights. Those who did strength training lost less fat-free mass and more fat. For preserving fat-free mass the effect was small to moderate and the certainty of the evidence moderate; for fat the certainty was high.

Body weight barely differed, by 0.32 kilos on average, which is not meaningful. So the scale does not show the difference.

This also shows in older adults: in a study of 160 people aged 65 and over with obesity, those who did strength training lost 2 percent of lean mass over 26 weeks. The group that only did endurance training lost clearly more.

And the fear of “too much muscle”?

A review of many studies found no meaningful difference in muscle growth between women and men. A more recent overview of 29 studies arrives at similar relative gains. In absolute numbers men are slightly ahead, because they start with more muscle mass.

For scale: in one study, 20 young women trained hard with their whole body five times a week for twelve weeks. Depending on the group, their lean mass rose by 1.1 to 1.9 kilos. The study was co-funded by the dairy industry. If you train only twice a week, you will end up below that. This is our own assessment, not a study result.

On top of that, results vary widely. In a study with 585 people, 342 of them women, the gain from arm training ranged from barely measurable to substantial. So you will not become a bodybuilder overnight.

Beginners in a deficit

The picture here is mixed. In one study, 40 young men ate about 40 percent below their needs for four weeks and trained six days a week. Both groups kept their lean mass. The group with 2.4 grams of protein per kilo of body weight even gained 1.2 kilos. But the program was very intense and is not an everyday model.

In another study with 90 women with overweight, the participants combined diet and training for 16 weeks. The group with more protein and dairy gained lean mass, the middle group kept it, and the low-protein group lost some. This study was also co-funded by the dairy industry.

On average across many studies, muscle gains are slowed in a deficit, while strength still increased. Realistically, that means: keeping muscle is well supported. Some beginners can gain a little, but you cannot expect that as a rule.

Your needs drop, but not because of muscle alone

At rest, muscle burns about 13 kcal per kilo per day, fat tissue only about 4.5 kcal. A worked example, not a study result: if you lose 2 to 2.5 kilos of muscle, you burn roughly 26 to 33 kcal less per day at rest.

The larger part of the falling need comes from elsewhere. A lighter body also burns less during movement, and the body adjusts to eating less. How strong this adaptation is, is disputed among researchers.

As a rule of thumb from a calculation model, the maintenance needs of an average adult with overweight fall by about 24 kcal per kilo lost, if activity stays the same. At 10 kilos that is around 240 kcal. This is an approximation, not a measurement.

A thought example, not a study result

Imagine Tom. He wants to lose ten kilos and cuts radically. Part of his weight loss is muscle, his body needs less energy, the plateau arrives, and Tom thinks: I have to eat even less. With a moderate deficit and two normal strength sessions per week, he gives his muscles a reason to stay. His body has to adapt less, and he gets to eat more. That the need is a bit lower after ten kilos is normal and not a setback.

What the studies do not say

• The benefit for fat-free mass showed in studies up to five months. In longer studies it was no longer clearly detectable. Whether that is due to the effect or to many participants dropping out, namely 25 to 49 percent, is unknown.
• Most studies were supervised. For blood sugar, blood fats and blood pressure, the review found no benefit.
• Without a diet, strength training alone barely reduced fat mass; endurance training was more effective there.
• Strength training does not cancel out the falling need: in one study, resting energy expenditure fell equally in the strength and the endurance group.

03How to put it into practice

1. Normal strength training is enough. The WHO recommends that adults do strength training of moderate or higher intensity on at least two days per week, working all major muscle groups. Full-body sessions with basic exercises are enough, you do not need a special program. Exactly how you train, meaning sets, repetitions and rest, depends on you and we discuss it individually.
2. Increase gradually. In studies there were also injuries to muscles and joints.
3. Keep the deficit moderate. The bigger the calorie gap, the bigger the share of muscle in what is lost.
4. Think about protein and sleep: You can read more in “Protein: How Much You Actually Need” and “Sleep: Why It Controls Hunger and Metabolism”.
5. Reassess your needs after a few kilos. A plateau often means that your needs have adjusted, not that you are doing too little.
6. Do not drop endurance. In the study with older participants, the combination of strength and endurance did best for physical function.