If you are a serial dieter, counting calories might have become second nature to you.
But have you ever asked yourself what a calorie actually tells you about your food?
Spoiler: It is not a good indicator of the quality of food.
Mathematically, a calorie is the amount of energy required to heat up a liter of water by
one degree Celsius. Calories became especially popular in 1887 when experiments on
college students have shown that a gram of protein, as well as a gram of carbohydrates, contains four calories, and a gram of fat nine calories.
In other words: a calorie tells us how much energy we get out of our food. In that logic, calories in vs. calories out sounds like a valid method for weight management. And yes, it works. But it's not as easy as wearing a fitness tracker, logging your meals or following a ready-made meal plan.
That is because we all digest and store calories a little differently, based on many factors that we can't always control.
Factors that affect your calorie absorption and hunger
How many hours of sleep you're getting
Your (chronic) stress levels
The time of day at which you eat
Your gut microbiome (bacteria that lives in your gut and affects nutrient absorption, appetite, metabolism, mood and much more)
How your food is prepared. Example: cooking makes calories more readily availabe (means your body gets more calories out of cooked veggies than raw veggies, whereas re-heating starchy food like potatos and rice can lower their calorie content
What you eat. Not all calories are digested equally. Protein takes the most energy to digest: 20-30% of total calories in protein go to digesting it. Next is carbohydrates (5-10%) and then fats (0-3%)
Your metabolism and body composition (fat mass vs. muscle mass)
Things I am forgetting right now...
Inacurracte calorie trackers
Studies from Standford University show that even the most accurate activity trackers were off by an average of 27 percent. And the least accurate ones were off by 93 percent! Outexercising your diet is much harder than these gadgets suggest.
Misleading labels packaged food
Calorie content stated on labels of packaged foods can be up to 20% off. That's how much inaccuracy the FDA allows. A 220 calorie protein bar is actually a 176 - 264 calorie bar. Remember that when you choose your least favorite snack because it contains marginally fewer calories.