Is exercise necessary for weight loss?

You’ll be surprised, but the answer is no. Weight loss can be achieved through diet only, without exercise. We definitely don’t recommend that approach though, and here is why.

Losing weight does not necessarily mean getting leaner. For example, if we lose muscle mass and maintain fat mass, our body weight goes down, but our percentage of body fat goes up. We become lighter yet fattier.

On the other hand, if we lose fat but build muscle at the same time, our weight on the scale may not change (or it may go up), but we’d definitely be leaner.

That’s when exercise comes into place, being a key factor to increase or preserve muscle mass. Strengthening exercises, especially.

In a study that exemplifies this well (1), the authors divided overweight men in 3 groups: group 1 did hypocaloric diet and no exercise, group 2 hypocaloric diet + aerobic exercise, and group 3 hypocaloric diet + aerobic + strength exercises. After 3 months, all the participants lost weight, about 20lbs, but how they lost the weight changed quite a bit.

Group 3 (diet+aerobic+strength) almost fully preserved lean mass. They lost an average of 21lbs of fat and 1lb of muscle mass.

Groups 1 and 2, on the other hand, lost a significant amount of muscle mass: 6.5lbs and 4.4lbs, respectively.

Similar results were found with obese older adults (2). After 6 months of intervention, all the participants, except the control group, lost about 20lbs of weight. The group who did aerobic exercise lost an average of 14lbs of fat and 6lbs of muscle. The group who did strengthening exercises lost more fat (~16lbs) and less muscle (~2lbs).

So although we can lose weight without exercising, it’s not a good deal. Losing muscle leads to weakness, loss of functionality in daily tasks and a slower metabolism. For older adults, sarcopenia can lead to falls and the loss of physical independence.

By exercising, we preserve muscle mass and lose what we really need: fat. Plus, as we burn more calories, it’s easier to sustain a hypocaloric diet. As we move more, we get to eat more, and still get leaner.

Willian Alba

1. PMID: 10487375

2. PMID: 28514618