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Personal trainer reveals whether diet or exercise is more important for losing weight

Both exercise and diet play a critical role when it comes to losing weight, as well as keeping that weight off. Easy to say, very hard to live by; I am now currently demolishing my third Big Mac of the week, and now hitting a two-week streak of evading the gym.

Anyway, I do want to believe I will change my ways soon, but you have to realize just how critical each of these components really are. It can be incredibly hard to know, especially if you're embarking on a health and fitness journey alone. Jillian Michaels knows this all too well.

Jillian, a health and fitness expert and creator of the Jillian Michaels app, said it really depends on whether your goal is weight loss or weight maintenance. Each regime has specific details you should follow if you truly to change your life and body. Michaels has recommendations for both.

If you're trying to lose weight, for example, Jillian says exercise matters more. According to Michaels, weight loss is 80 percent exercise and 20 percent diet. She says that you can't "starve the weight off", because that will shut down your metabolism down. Instead, she says you need to exercise it off by creating "an energy deficit."

What Michaels means by this is that you're burning more calories than you're taking in. Creating an energy deficit can be hard work. Jillian knows this, and gives a pretty good example. Let's say you're a 30-year old female who's five feet, four inches and has a metabolic rate of 1,600 calories per day without exercise. This means you burn around 1,600 calories per day as is.

From that, Michaels recommends at least 1,200 calories per day. According to her, a pound is roughly equivalent to 3,500 calories, though of course this depends on the individual. This means without working out, you'll have an energy deficit of 400 calories per day (the difference between the calories you're taking in, and the calories you're burning).

If we take a closer look at that energy deficit, 400 multiplied by seven is 2,800, which isn't even a pound a week. This is exactly why exercise is so vital when you're trying to shed pounds. "If you want to be efficient at weight loss, you have to exercise to boost the calories out," Michaels said.

When it comes to weight maintenance, Michaels says the formula is switched: for this you switch to 80 percent diet, 20 percent exercise. She says this because if you're not overeating, you won't gain weight.

Using the above example of the woman with a metabolic rate of 1,600 calories, if she takes in 1,600 calories per day and doesn't work out, she'll maintain the weight she's at because she'll be taking in the same number of calories she's burning.

Michaels does, however, make the point that this doesn't necessarily mean you'll be healthy or in good shape. "I know people that never overeat... Their body fat percentage might be higher, they might not have a ton of lean muscle, and they might not necessarily be healthy, but they won't gain weight," she says.

While it's not entirely in black and white, the basis of this theory is excellent to build on. Before you know it, you'll have just abs good if not better than Jillian's. And that's saying something.