First of all, there’s no going around the law of conservation of energy. Take in more calories than you expend and you will gain weight. Take in fewer calories than you expend and you will lose weight. But the thing is, finding out the exact numbers of calories you took in or expended is not as easy as it seems. The first article in this series will be all about counting calories in.
Food labels are imprecise
The calorie counts on food labels and in online databases are just averages. Research shows that the actual calorie content of foods varies a lot. The FDA knows that calorie measuring methods are not precise and that’s why they allow inaccuracies on food labels of up to 20 %. So, a Snickers bar that contains 242 kcal according to the label actually contains anywhere between 200 and 290 kcal.
You don’t absorb all calories you take in
Scientists have used a formula to better estimate how many calories we get from various macronutrients. It looks like this: 1 g of protein contains 5,65 kcal but we absorb 4 kcal; 1 g of fat contains 9,45 kcal but we absorb 9 kcal; 1 g of carbs contains 4,1 kcal but we absorb 4 kcal. This formula works for some foods, but not all. For example we get much less energy from nuts and seeds, only 68 % in case of almonds and 79 % in case of walnuts. The opposite is true for foods high in fibre like fruits and vegetables, we get 28 % more calories from kale, 17 % more from tomatoes, and 15 % more from cooked black beans. On average across all foods, this leads to a 10% error.
Food preparation changes calorie content
Cooking, chopping, blending, and other food preparation methods generally increase the calories available for absorption. For example, a large raw egg contains 72 kcal, hard-boiled 78 kcal, scrambled 84 kcal, and fried 98 kcal which is a 35% increase. This is often not considered in calorie counting accurately and can result in significant errors far beyond 35 %.
Gut bacteria can make a big difference
Studies also show that people, who have a higher proportion of butyrate-producing colon bacterial species, like Firmicutes bacteria, absorb up to 150 kcal more than others every day.
It’s also important to note that all of these errors are a problem when we know what and how much we are eating. How about when you eat out in a restaurant or a cinema? The next article will be all about problems with calorie counting when you don’t have perfect information about the food in front of you.