55)—but behind it all lies basic math. Even if you choose not to count calories, it’s worth understanding a few key points about them.It’s not as sexy as the latest diet craze sweeping through Hollywood, but in the search for a slimmer figure, slow and steady weight loss (one or two pounds a week) really does win the race. Whether you want to lose five pounds to fit into your clothes better or need to lose fifty to protect your health as you get older, losing weight boils down to a simple equation: The number of calories you take in must be less than calories out. In fact, diet plans that claim you don’t need to count calories usually reduce your calorie intake anyway because you eat smaller portions or cut out certain foods (or in some cases, entire food groups). Some of those plans have helpful principles—reducing your refined-carb intake is almost always a healthy move, for instance (55)—but behind it all lies basic math. Even if you choose not to count calories, it’s worth understanding a few key points about them.
Everyone has a baseline number of calories they need to maintain their current weight, but the number differs according to your gender, weight, activity level—and your age. It isn’t just your imagination; your calorie needs do decline as you get older. Your metabolism slows about 5 percent each decade, so at age forty, women burn about 100 calories fewer per day and men burn about 50 calories fewer than they did at age thirty. That may not seem like much, but over a year it can translate to an extra five or ten pounds. The dip in your metabolism is mostly due to a decrease in muscle mass and a corresponding increase in body fat (21), but your organs also use fewer calories as you age.
The best way to determine your calorie quota is by measuring your resting metabolic rate (RMR), the number of calories your body requires for the daily tasks of living, such as breathing, blood circulation, and forming and repairing cells. Your gym may have a handheld device called a calorimeter that can measure your RMR pretty precisely. If you don’t have access to a calorimeter, a 2005 review of studies in the Journal of the American Dietetic Association discovered that a tool called the Mifflin-St Jeor equation is the next most reliable way to estimate a person’s RMR. You’ll need to translate your weight from pounds to kilograms and height to centimeters; the formulas are as follows: 1 pound = 0.45 kg; 1 inch = 2.54 cm
For men: (10 × weight in kg) + (6.25 × height in cm) – (5 × age in years) + 5
For women: (10 × weight in kg) + (6.25 × height in cm) – (5 × age in years) – 161
Once you have that number, you can add in your physical activity: Multiply your RMR by 1.3 if you’re sedentary, 1.4 if you’re moderately active, and 1.5 if you’re very active. Although this number is just an estimate, it should give you a feel for how many calories you need to maintain your weight at your current activity level and fight the dreaded middle-age spread. To lose one pound a week, you’ll have to create a deficit of 3,500 calories, or an average of 500 calories per day, from your RMR. It’s easiest to reach that goal by both eating a little less and moving a bit more, but remember that it takes less time and effort to avoid eating 300 calories (a homemade cupcake) than it does to burn off the same amount through exercise (walking three miles at a 4-mph pace).
Now that you know how many calories you need to burn to lose weight, it might be tempting to drastically limit your food intake to peel off pounds faster. But that strategy can backfire, say experts. Eating less than 900 calories a day sends your body into starvation mode and slows your metabolism by up to 20 percent. At that low intake, you’ll also start burning precious muscle for energy, which makes your metabolism even more sluggish. Not to mention that it’s nearly impossible to get the nutrition you need in that few calories. Don’t go below 1,200 to 1,500 calories a day to keep your metabolism humming, ensure good nutrition, and burn fat instead of muscle.
