Weight loss is more complicated than simply being a mathematical equation. We’ve all heard that there are 3,500 calories in a pound, and that if you want to lose one pound a week, you need to create a calorie deficit of 500 calories a day, either by eating fewer calories or burning more calories through exercise or some combination of the two. This recommendation is based on the calories in – calories-in-calories-out concept as if losing weight is purely a mathematical endeavor.
But does calories in – calories out work? Well, if it did, there would be fewer overweight people in this country than we have, because nearly everyone who has ever attempted to lose weight has restricted their calorie consumption, and some have even tried to burn more calories. Some weight loss is possible initially, but over 90% eventually regain the weight.
Why Calories In – Calories Out Doesn’t Work
Certainly, if you eat more calories than you burn, you will gain weight, and you must create a calorie deficit to lose weight, but the concept doesn’t always work. Here’s why. There are three reasons why calories in – calories out doesn’t always work when it comes to losing weight.
You cannot Accurately Measure Calories Consumed and Calories Burned. Reality Trumps Theory.
First, there’s a practical problem. It’s not possible to accurately determine how many calories you consume each day, and how many calories you truly actually burn each day. Do you know how many calories you eat in a day and how many you burn? If you don’t, then how can you determine if you are creating a calorie deficit
There can be up to a 20% variance on food labels, too. What looks like 100 calories per serving on a food label may be 120 calories.
There’s another problem. There probably are not 3,500 calories in a pound of fat in most of us. See our article How Many Calories in a Pound? [Maybe not 3,500]. Calories in a pound of fat can range from roughly 2,800 to 3,700 per pound.
You don’t have to be off much in your calculations to realize the limit of making weight loss a simple mathematical equation. If you consume 10 calories more each day than you calculate, and you burn 10 fewer calories each day than you calculate, you are off 20 calories a day. Multiply that by 365 days and you are off 7,300 calories, or nearly 2 pounds. Over one decade of life, say from 40 to 50, you will have been off the equivalent of 20 pounds. How’s that for a weight loss plan?
In theory, calories in – calories out makes sense, but not in practice.
Calories Consumed and Calories Burned Are Dependent Variables – One Affects the Other
Secondly, how many calories you consume and how many calories you burn are not independent variables. They are dependent variables. The minute you try to change one, the other one changes, offsetting some of what you were hoping to achieve. For instance, if you restrict your caloric intake each day, eventually your metabolism slows down, limiting the number of calories burned.
The body senses it’s being short-changed on calories, so it conserves energy, therefore conserving calories by reducing metabolism. This puts you in a situation of having to restrict calories even further to create that 500-calorie-a-day deficit. Conversely, if you start to exercise or if you already exercise and kick it up a notch, you will stimulate a greater appetite and start to consume more calories.
Try these experiments on yourself. Keep your exercise program the same, but reduce your calorie intake. You will find that you will struggle with your exercise program, or find that you’re less active during other parts of the day, from a lack of energy. Then, keep your calorie intake the same and increase your activity level. You will find that you are hungrier. You might be able to resist at first, but sooner or later, you will increase your intake of calories.
But burning more calories makes it easier to create a calorie deficit. The real reason to exercise for weight loss is to bring about hormonal effects that persist long after the exercise is over, enabling you to burn more calories while at rest.
When it comes to consuming and burning calories, it’s difficult to change one without changing the other.
Not All Calories Are the Same
Thirdly, not all calories are the same. The source of the calories is important. The source of the calories (fat, protein, carbohydrate) and the glycemic index of the carbohydrates greatly influence the secretion of hormones, which determine if calories are stored as fat or are burned for energy. See Not All Calories Are the Same When It Comes to Weight Loss.
Fewer calories are burned when a low-fat diet is consumed (another name for a low-fat diet is a high-carbohydrate diet) compared to low-glycemic diets and very low-carbohydrate diets with more emphasis on protein. High glycemic foods and diets that are high in carbohydrates produce more insulin, which is a fattening hormone, and prevent the burning of calories from fat stores.
A calorie is not a calorie; some are better than others.
Increase your activity level, consume a balanced low-glycemic diet, and optimize your hormones, and you will greatly increase the odds that you will achieve a healthy weight that you can maintain as you age. In the end, this is the best and safest way to lose weight.
Article updated 06/30/25. Originally published on 8/11/12.
References:
Good Calories, Bad Calories: by Gary Taubes
Why We Get Fat: And What To Do About It, by Gary Taubes
See related articles.
“High-Intensity Interval Training: Short and Sweet”
“Achieve Weight Loss With These Hormones”
