Small lifestyle changes can lead to big gains. If you’re looking to reshape your body by trimming the fat while building muscle, it probably won’t take as long as you think.

Stretching yourself to the limit, various health regimens claim you can lose several pounds per week through a combination of exercise, hydration and diet changes. But pushing weight loss that quickly could be detrimental to health — if, for example, the dietary changes rely on starving the body of nutrients it needs to function in the name of keeping off calories. And people who shed weight quickly tend to gain it back: Livestrong notes that only about 5 percent of people who lose weight on a crash diet manage to keep it off because the others revert to old eating and exercise habits.

Read More: 7 Things No One Tells You About Losing Weight

Also with crash diets, the pounds you’ve lost won’t necessarily be the fat you wanted to get rid of to begin with. Women’s Health explains, “Your body thinks you're starving when you lose too much too fast. So instead of burning calories, it conserves them in the form of fat.” When the scale is showing a decrease, those pounds were probably from water weight or even muscle. To compound the problem, losing muscle makes it harder to burn calories, that magazine says.

The Mayo Clinic recommends losing one to two pounds a week. That doesn’t sound like very much, but that could be 50 to 100 pounds in a single year, which is nothing to scoff at.

Read: Best Diets of 2016

As far as building muscle goes, while it is not necessarily sustainable over a long period of time, it is possible to gain a few pounds of muscle per week, according to Muscle & Fitness. Food can be as crucial as lifting weights during that time: “You can work out all you want, but if you don’t ingest adequate calories and macronutrients, you won’t build muscle,” the magazine says. “What and when you eat is paramount to your results.” Men’s Health suggests a good protein intake, and says that eggs are a better source than beef or fish. It is also important to pick a muscle fitness routine and stick with it.