How Many Calories Do You Need to Eat To Lose Weight?

The weight-loss mantra has typically been to burn more calories than you take in. Move more, eat less, lose weight. Simple, right?

The shortfall of this classic advice is its lack of precision. Yes, you moved more — maybe a lot more — in your effort to lose weight, but how far did all of that movement really get you? And sure you ate less — maybe a lot less, or maybe not enough less, and maybe that was the problem. The point is that despite your dietary diligence and fitness fervor, you still fell short of your target while others following the same general guidelines can now fit back into the tuxedos and gowns they wore to prom.

And therein lies the problem: “We vary greatly in our [metabolic] efficiency,” says Bob Forster, P.T., founder and CEO of Phase IV Health and Performance Center, in Santa Monica. “Which is why your wife or girlfriend can eat a pint of Haagen Dazs every night and never get fat while you can’t touch it.”

The fast and easy (and free) way to figure out whether binging on butter pecan will pad your love handles or burn off in your metabolic furnace is to determine whether doing so will cause you to exceed your “maintenance calories” (i.e., the number you need to eat per day to maintain your current weight). You can do that using one of the following quick-and-dirty formulas, which are based on activity level:

• Sedentary lifestyle (desk job, no exercise): Current weight in pounds x 12
• Moderately active lifestyle (waiter, nurse, or desk job with moderate daily exercise): Current weight in pounds x 13
• Highly active lifestyle (construction worker, wildland firefighter, or desk job with intense daily exercise): Current weight in pounds x 14

From there, you can subtract 500 calories if you’re trying to lose weight, but make sure that number stays above 1,200 — anything lower can be dangerous in the long term. (For a more detailed discussion of estimating metabolic rates, click here.)

Those formulas will give you a ballpark number that will help most people see results. But if you’re one of the unfortunate few for whom ballpark numbers don’t work, or if you’re an athlete trying to fine-tune your training and nutrition plans, you’ll need a more accurate method for determining daily caloric needs. “And the two ‘gold standards’ in this regard are resting metabolic rate (RMR) and VO2 Max testing,” says Forster.

The RMR Test

You don’t only burn calories when you work out. The calories you torch while cycling, running, lifting, or otherwise being active are just icing on the metabolic cake. The vast majority of the calories you burn each day are torched by the myriad bodily processes that keep you alive and engaged with the world. Even at rest (sleeping, watching TV, sitting in traffic, filling out TPS reports) your heart is pumping, your lungs are billowing, your kidneys are filtering, your muscles are contracting, your intestines are digesting, your brain is processing — honestly, you have no idea how exhausting it is being you, even when you’re doing nothing at all. Resting metabolic rate (or RMR) refers to the amount of energy (in the form of calories) that you body needs to function in a sedentary state. This number is individual, identifiable, and the basis for figuring out how many total calories you burn each day.

“We need to know if you are high burning or low burning, because weight loss comes from how many calories you are burning per minute at rest — not how many you are burning during a workout,” says Forster.

Medical offices can perform an RMR test, but most people take them at a place that specializes in diet and human performance, such as Forster’s Phase IV Health and Performance Center. In preparation for the test, you will be asked to fast for at least four hours, and overnight if possible (yes, that includes coffee and anything else that isn’t water). Strenuous physical activity is also a no-no in the hours preceding the test, and you may be asked to “chill” for 10 minutes once you arrive to establish a resting heart rate. A technician will then place a mask on your face or a tube in your mouth, and ask you to breathe. That will be your sole job for the next 10 to 15 minutes. The machine will do the rest, and you will be charged $60 to $125 for its efforts and that of its human handler.

That machine is monitoring two things: Exhaled oxygen and carbon dioxide. Each calorie requires a specific amount of oxygen to burn, and by measuring the amount of oxygen you exhale, the machine can calculate the number of calories you burned while sitting there. Analyzing carbon dioxide, meanwhile, tells it how many of those burned calories came from fat and how many came from carbohydrate. Since you’re sitting (i.e., at rest), the majority should come from fat.

At the end of the test, the numbers are crunched and a couple of things are revealed, the most important of which is how many calories you burn at rest per day. The average woman burns about 1,500, and the average man burns about 1,700, but if life has led you to this level of testing, odds are that you’re not average. To this value, the tech will then add the number of calories you typically burn during exercise, and the number of calories you burn throughout the day while active but not exercising (e.g., walking to your car, running to a meeting, making dinner, etc.). The resulting number of calories is your total energy expenditure (TEE), and to lose weight, you must consume fewer than that.

The VO2 Max Test

VO2 max refers to the maximum amount of oxygen your body can utilize during high-intensity exercise, and it’s expressed in milliliters per kilogram per minute. As you can imagine, your “aerobic capacity” (as it’s also known) has some serious implications for athletic performance, especially where stamina and endurance are concerned.

VO2 max is influenced by such variables as gender (it’s generally higher in men than women), age (the younger you are, the greater it is), size (the bigger your body, the higher it is), and genetics, and can be effected by external factors such as temperature and altitude. The average for men is around 35 ml/kg/min, and the average for women is around 30 ml/kg/min. Anything above 50 is excellent. Lance Armstrong’s is 84.

In addition to gauging your VO2 max, the test reveals other key values, including your aerobic threshold (i.e., the intensity at which you body begins to shift from aerobic [oxygen dependent] to anaerobic [oxygen independent] metabolism) and your anaerobic threshold (i.e., the intensity at which your body begins producing metabolic waste faster than it can clear it). Such information can help athletes optimize their training to maximize athletic potential.

But there’s another result that’s particularly useful to those trying to lose weight: How much oxygen (and thus calories) you burn at specific intensities/heart rate zones, and whether those calories come from fat, carbohydrates, or a combination of the two. In short, it tells you exactly how hard to push yourself to burn the most fat. What’s more, since you know exactly how many calories you burn per minute in each zone, you can calculate how many total calories you burn during a workout far more precisely than a fitness tracker.

Like the RMR test, there are a couple of VO2 max test do’s and don’ts. Number one: Do come to the test rested (no hard activity for two days prior). Number two: Do not have caffeine in your system (it’s a performance enhancer). You’ll be allowed to choose your method of torture (treadmill, stationary bike, elliptical machine, or rowing ergometer), and you will wear both a heart rate monitor and a mask (to measure exhaled oxygen and carbon dioxide). Then you will be asked to gradually hit the accelerator, ramping up workout intensity until you top out. It’s best to have this test performed at a university lab or a place that specializes in athletic performance. The cost is typically $180 to $225.

Additional Considerations
What most people don’t understand about these tests is that they only provide a snapshot of your metabolism at a specific point and time. “The numbers are good for about eight weeks, maybe a little more,” says Forster, adding that the fitter you are, the hotter your metabolism will burn. Follow up tests will establish newer (and hopefully higher) metabolic rates. By testing again, training and nutrition plans can be tweaked to keep your metabolism healthy.

That usually means eating more; after all, the more metabolically active tissue (i.e., muscle) you have, the more calories you need to consume to fuel it. “Most people we work with are eating too few calories, and that’s why their metabolisms stall,” says Forster. By using RMR and VO2 Max as a road map, athletes and non-athletes can come up with the “right” combination of training and feeding for success. “The right amount of exercise at the right intensity with the right amount of recovery combined with the right amount of calories from carbs, proteins, and fats will create a healthy metabolism,” he says. And a healthy metabolism is one of the keys to achieving any fitness goal — regardless of whether its athletic or every day in nature.