Calories In, Calories Out
Your body’s recipe for weight loss is deceptively simple: calories in (what you consume) and calories out (what you burn and metabolize) equal your total energy. What does this really mean, though? To break down the mechanism of weight loss, let’s review the basics of how the body uses calories. Before that, let’s review what a calorie even is.
What Are Calories?
A calorie isn’t a vague idea; it’s a scientific unit of energy. This is important to know; in order to understand how to create a caloric deficit for weight loss, you’ll want to take a moment and think about what a calorie means.
One calorie constitutes the energy it takes to raise the temperature of one gram of water by one degree. But what does heating water have to do with our bodies and our weight? Our bodies need energy to power everything from cellular processes and regeneration, organ function, breathing, digestion, and our thoughts and nervous systems. In the context of our bodies, calories have everything to do with, well, everything we do. A calorie simply represents a measurable amount of energy. And at every moment of every day and every night, your body is “using” energy, whether you know it or not.
An adult body uses between 1,000 and 1,500 calories per day to maintain all its key functions. The amount of calories a body requires to maintain its functions at rest is called the resting metabolic rate; this depends on age, weight, sex, and muscle composition. Bodies need additional calories each day according to activity and exercise. All this, taken together, constitutes calories out, or the calories your body “uses” every day.
Calories in is pretty simple; though there all kinds of foods, drinks, and nutrients, all food contains calories (energy); how much you consume in a day constitutes calories in.
Weight Loss: A Deficit
When you compare your calories in (how much you consume) to your calories out (how much your body burns), and see a deficit (you have consumed fewer calories than you have burned), you’re on the way to losing weight. All types of weight loss require you to maintain a caloric deficit.
A caloric deficit can be achieved through diet alone, exercise alone, or a combination of both. How? Let’s look at an example. Mary, a thirty-year-old woman, has a resting metabolic rate of 1,400 calories per day. If she does little to no exercise, and rests all day, her body will burn an amount of energy equal to 1,400 calories, plus those calories she uses up from walking around at home and at work, grocery shopping, and getting in and out of her car. Let’s call her daily energy use on such a day 1,600 calories. If Mary eats exactly 1,600 calories over the course of the day, she’ll have a net caloric balance; she will neither gain nor lose any energy.
However, if Mary eats a snack, bringing her up to 1,800 calories, she has a net caloric gain. She has consumed more calories than she burned. But what if Mary goes for a walk? If she walks for two hours, and burns 400 calories, she will now be in a caloric deficit; at the end of the day, her calories consumed equaled 1,800, and her calories burned equaled 2,000. She had a deficit of 200 calories for that day.
To lose a pound, you must have an overall deficit of 3,000 calories; with Mary’s example in mind, she would have to continue that pattern for 15 days to lose one pound. You can see how, if Mary at less and exercised more every day, she would lose weight faster. The opposite would be true if she ate more and exercised less.
How to sustain a caloric deficit
It isn’t always easy to do something as simple as burning more energy than you consume. That’s because easy, to begin with, to forget, and to slip into old habits. The key to maintaining a caloric deficit for a long period of time—and to losing weight—is managing your hunger. If you feel hungry, no diet in the world will succeed in putting you on the path to weight loss. But if you feel full, you’re on your way to success. Learning to eat responsibly, avoiding insulin spikes and cravings, and training the body to maintain its resting metabolic rate more easily is the key.