There are seemingly a million different diet options but only one basic diet formula: weight gain = calories in – calories out. In other words, diet X may proclaim to better satiate cravings and diet Y may proclaim to boost metabolism, but when it comes down to it, as long as you’re burning more calories than you’re consuming, you’ll lose weight. Theoretically, this logic is incontrovertible. The law of conservation of energy is a law after all. Practically, however, the question is not so simple.
The biggest assumption we make when we apply the weight gain = calories in – calories out formula is that we can accurately count the calories we consume. But can we? Even if you measure every portion size to the gram, the FDA allows for a 20% error on nutrition labels! This means that something labeled 100 Calories per serving may legally contain 120 Calories. On the scale of a 2,000 Calorie diet, that equates to a difference of 400 Calories per day, 2,800 Calories per week, and 145,600 Calories per year!
What’s more, the method we use to measure the Calories in the foods we eat does not accurately represent how our body breakdown food into energy. For example, let’s say a banana contains 100 Calories. This number was determined by putting the banana into a closed chamber, blowing it up like a bomb, and measuring how much heat was released. This technique, called bomb calorimetry, differs enormously from cellular metabolism in terms of both mechanism and efficiency. Simply put, there is little reason to believe that the way we measure the Calories in food accurately represents the Calories we actually extract from food.
Combining nutrition labels’ 20% margin of error with the erroneousness of bomb calorimetry, not to mention accounting for the ways in which our bodies adjust to conserve energy when we are in a Calorie deficit, we need to ask ourselves: Is counting calories an exercise in futility? And, if so, how can we be smarter about weight control?