The Real Math Behind Calories and Exercise

“You can’t outwork a bad diet.” Words that are repeated so often as to become cliché, and yet so rarely are they followed. So often people tell themselves, “Oh, I’ll just hit the treadmill later,” or “I’ll just work out extra hard tomorrow” to make up for overindulging. But beyond people simply not following up on those empty promises, there is an even more fundamental reason why that mindset doesn’t work.

Increasing Activity

 To burn off a pound of fat, you have to burn 3500 Calories (kcals) more than you consume. So, for someone aiming to lose a pound per week, that amounts to 500 kcals per day. Sounds doable, until you think about how much activity that is.

A study by Syracuse University of 12 men and 12 women showed that, on average, men burn 124 Calories per mile while women burn 105. The difference is due primarily to the weight difference between the men and women, so if you are heavier than “average”, you’ll burn a marginally greater amount.

So if a mile of running burns a little over 100 calories, and you need to reach 500 to lose a pound a week, the numbers are already looking daunting. But in fact, the reality is even worse. The problem is that your body burns calories naturally even when you’re sitting still, doing nothing. So if you look at the net Calories burned (by subtracting out the Calories your body would have burned anyway), those numbers drop to 105 and 91, respectively. In other words, you’re looking at having to run 5 miles every day of the week to lose just one pound. Furthermore, if you had been gaining weight before, you have even more to overcome, which means even more daily activity.

Basal Metabolic Rate

The problem here is that exercise really makes up a small portion of your daily Calorie expenditures. Most of your daily burn comes from your basal metabolic rate (BMR), which is the energy your body uses just to keep you alive. Human beings are “warm-blooded” animals (as you may remember from grade school), which means we regulate our body temperature. In our case, that means keeping our bodies at a toasty 98.6°F (37.0°C). Since our bodies are mostly water, that’s a lot like keeping a human-sized pot of water warm 24/7. Any other cellular processes, etc., all factor into the BMR as well.

Your BMR isn’t really under your control, unfortunately. People who weigh more have more to keep warm and more cells to keep alive, so they have a higher BMR. But if your goal is to lose weight, each step in the right direction is decreasing your BMR. Now, the change isn’t drastic, especially if you’re only losing a few pounds, but the point is that a big chunk of your Calorie expenditure is a relatively fixed number.

The reason that exercise counts for a small proportion of your daily needs is that we exercise by moving around. And it turns out that moving around doesn’t take that much energy. Let’s consider the 105 net Calories that an average man burns while running a mile. Calories were defined in physics as the amount of energy required to raise the temperature of one liter of water by one degree Celsius, so that a mile is equivalent to taking a liter of water from ice cold to boiling.

I don’t think any of us would be very happy if we had to run a mile just to boil some water for pasta.

Calories in Food

But now let’s think about how many Calories are in the foods we eat. That same 105 kcals is around the same as half a bagel (without cream cheese). A McDonald’s double cheeseburger off the dollar menu weighs in at 430 kcals, so you’d better be putting those savings toward a treadmill.

It is easy to overeat without realizing it, and then to find yourself in a hole that is unrealistic to exercise your way out of. Thanksgiving feasts alone can pack over 1,000 Calories, so keep moderation in mind when your eyes are working up an appetite at the dinner table.

So, Does Exercise Not Matter?

The purpose of this article is to explain the importance of a structured diet with an appropriate Calorie intake. But if you got the sense that this means exercise is unimportant, you’re just making things harder on yourself. And while we all want to look better, getting in shape is about improvingourr health as well. Cardiovascular exercise is a great way to reduce your risk of cardiac disease and stroke. Plus, it’s hard to experience everything life has to offer from your couch, so being fit enough to go out and enjoy the world should be another great motivator.

Try This

There are loads of online calculators available for determining your theoretical daily maintenance Calorie intake, but the pitfall is that these are all theoretical, and a steadfast adherence to them will likely lead you astray. Whether or not you choose to use one, logging your daily meals is critical to effectively controlling your diet. MyFitnessPal is a terrific option with both a website and an app to make logging easy.

Once you’ve got a sense of how many Calories you eat in a day (be honest with logging!), try cutting 500 Calories per day, right off the bat. Resist the temptation to eat back the Calories from your workouts as well. Workout machines are notoriously inaccurate at estimating your Calorie burn, so you’re likely to just be shooting yourself in the foot. Plus, it’s so easy to underestimate what we eat (a food weighing scale is a great way to counteract this), that the double effect of eating less and moving more just helps improve your odds of steady success.