“The whole point of being in a calorie deficit is providing your body fewer calories than it needs to support the components of calorie expenditure,” says Morello. “And doing this over a longer period of time results in weight loss, allowing you to tone up.” On the flip side, you gain weight when you regularly provide your body more calories than it needs to support these functions. According to the Academy of Nutrition and Dietetics (PDF), a calorie deficit of 500 calories per day is sufficient for weight loss (between a pound or two a week) and won't really affect your hunger or energy levels.

Morello says the first thing he teaches clients is how many calories they should be eating in a day. “This is called your maintenance calories.” A simple equation is to multiply your weight by 10. So if you're a 185 pound man, you'll need around 1,850 calories a day to maintain your weight (without any exercise). If you're moderately active, say with two to four workouts a week, you should up that to 14 times your weight. “Just because a little calorie deficit is good for weight loss does not mean that eating as little as possible to lose weight is a good idea,” says registered dietitian and sports nutritionist Amy Goodson. “The key is making sure that you're fueling your body appropriately for the amount of activity being done.”

To make sure you're hitting your deficit, you want to start by calculating your Basal Metabolic Rate (BMR), the calories required to keep your body functioning normally. An online calculator will give you this number, taking your height, weight and age into account. Then you'll add that with calories expelled during physical activity. Again, this is where a tracker can come in handy. The MyPlate app syncs with fitness trackers like your AppleWatch, so it pulls in the calories burned during workouts, making it easy to see where you are in terms of calories for the day. Because once you're regularly hitting your deficit, that's when your body burns your fat stores for the necessary energy.

All workouts will burn calories, helping you to reach a deficit. But intervals and high-intensity training is a proven way to kickstart your metabolism and shed some pounds in the process. Kurt Hester, head strength and conditioning coach at Louisiana Tech, says HIIT is more time efficient in caloric expenditure than a traditional cardio workout. “Not only will your body burn more calories during HIIT workouts but you'll also continue to burn more calories and fat in the 24 hours after a HIIT workout,” he says. Especially when you're not overindulging in calories, you want to keep the workouts brief but effective.

“As the weeks go by, you may need to adjust those calories in order to continue to hit new goals and lose weight,” says Morello. He also says it's important to mix up meals so it doesn't get boring or feel too much like a diet. That's why he ended up writing a cookbook, Buon Appetito, full of easy-to-make but satisfying recipes that fill you up without overloading on calories. “The main thing I tell my clients is not to drink your calories and to eat as much whole, unprocessed foods as you can.” He says that's a whole lot easier to do when you cook your own meals at home. “That's the beauty of really learning more about your calories and body because then it gives you so much more freedom to branch out, adopting a healthy balanced lifestyle while still achieving your goals—which is one of the biggest things I try and teach all of my clients.”