Chris Pratt went from 300 pounds while playing Andy Dwyer in "Parks and Recreation" to 172 pounds of muscled macho man in "Jurassic World: Fallen Kingdom." While a celebrity success like that may inspire you to shed excess pounds that are increasing your risk for heart diseases, diabetes, cancer, and more, it's important to understand what role calorie reduction and exercise play in achieving — and maintaining — such dramatic results.

You often hear that weight loss is all about eating less, and that exercise is helpful for keeping weight off but not losing it. That's not entirely true.

You can’t lose weight without taking in fewer calories. That's a fact. If you shave 500 calories a day off your regular intake, you may lose a pound a week, which is the perfect goal for success and maintenance of weight loss.

But exercise has a more challenging role in weight loss. First, because you may overestimate how many calories you've burned by exercising, and then overeat afterward. A half-hour of intense aerobics may burn 300 calories; you can undo that in a heartbeat with a slice of pizza.

Second, research shows that you may be more sedentary than usual after exercise.

For exercise to help you lose weight, you have to do more than the minimum recommendation of 150 minutes of moderate-intensity aerobics weekly; 300 minutes a week should be your minimum goal, along with strength training.

If you can avoid the pitfalls of dieting (over-deprivation and bounce back) and sustain an increased workout routine, you should see results that don't fade away.