As we mentioned above, eating in a calorie deficit is key. Jim recommends eating 500 calories less than your total daily energy expenditure, or TDEE. This is the number of calories you burn in a day, which is based on factors like age, height, sex, and activity level. To calculate what this number is and what your calorie target should be to lose weight, use this formula. Just make sure you don't go below 1,200 calories a day for women; in a previous interview, Jim said eating any fewer calories than that can slow down your metabolism and result in negative side effects like low energy, loss of hair, hunger pangs, and a negative impact on your menstrual cycle.
Sure, you can lose weight quickly. There are plenty of fad diets that work to shed pounds rapidly -- while leaving you feeling hungry and deprived. But what good is losing weight only to regain it? To keep pounds off permanently, it's best to lose weight slowly. And many experts say you can do that without going on a "diet." Instead, the key is making simple tweaks to your lifestyle.