Fast and Slow Weight Loss Rates Are Equally Effective at Changing Body Composition

Ideally, when you want or need to lose weight, you want it to be fast. There is always a trade-off, of course. If you want to lose weight fast, you can’t eat very much, at least not compared to what you’re used to.

One of the main issues with a strict diet is hunger. That can be troublesome, sure, but let’s say you’re prepared to deal with it. You accept that you’ll go hungry a lot, just so you can lose weight faster and get it over with.

Another issue is the risk of losing muscle along with the fat weight you want to get rid of. Losing muscle during weight loss is not a good thing. Not only do you slow down your metabolism, making it easier to regain the weight you lost, but you also lose strength and functionality.

A new study examined the long-term effects of moderate calorie restriction compared to severe calorie restriction on weight loss, muscle mass, and bone density. It was quite a large and long study, with 101 overweight women dieting for a year. They were placed randomly into two groups. The first group cut their calories by 25–35%. That’s a moderate deficit. Not too hard to handle, but it takes longer to reach your target weight. The other group restricted their energy intake by a whopping 65–75%, a massive and severe deficit.

The subjects were encouraged to exercise, but it wasn’t mandatory or supervised. In other words, this wasn’t a strength-training study. The positive thing about that is that we get to see the effects of calorie restriction itself.

At 12 months, there was a large difference between the groups. The women who had cut their calories by 65–75% had lost twice as much body weight and body fat as the moderate group. They did also lose more lean mass, but this extra decrease in muscle mass was proportional to the total weight lost. This means that they women who dieted much harder and lost much more weight didn’t lose any more muscle mass than those who took it slow. The moderate group would likely have continued losing muscle mass as well, during the time it would take them to lose the same amount of total weight.

The results were not all positive. While the severe energy restriction very effectively made the subjects lose weight and fat quickly, the negative effects on bone mineral density were also more prominent. However, one thing to keep in mind is that the subjects in this study didn’t weight train. We already know that pumping some heavy iron keeps the skeleton in shape and prevents bone mineral loss. Adding regular strength training to a low calorie diet should prevent the loss of bone mineral. In addition, if weight training had been part of the program, chances are high that the loss of muscle mass could have been eliminated in both groups, regardless of energy intake. That is also something that we know from earlier research.

In summary, this study suggests that you if want to lose a certain amount of weight, you can do so fast or slow, whichever you prefer. You don’t have to worry about losing more muscle if you do it quickly, certainly not if you add strength training to the mix. Your own preferences, and whether or not hunger and eventual stress from not eating a lot trumps dieting for a long time, can be your guidelines.


Effect of Weight Loss via Severe vs Moderate Energy Restriction on Lean Mass and Body Composition Among Postmenopausal Women With Obesity. Nutrition, Obesity, and Exercise
October 30, 2019.

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Andreas Abelsson

Andreas is a certified nutrition coach with over three decades of training experience. He has followed and reported on the research fields of exercise, nutrition, and health for almost as long and is a specialist in metabolic health and nutrition coaching for athletes. Read more about Andreas and StrengthLog by clicking here.