Calories are essentially units of energy that you get from the carbohydrate, protein, and fat content of foods you eat and are used by the body to perform basic function of living such as breathing, digesting, walking, talking, etc.
Simply put, calories become a problem when you absorb more calories than you need because they will be stored as fat for later use. This may have been great during the caveman years when food was scarce, however that is not the case today.
A very common misconception is that all calories are created equal, and that 100 calories of say potato chips are absorbed the same way as 100 calories of say chicken. Here are some reasons why calorie counting doesn't always add up and some incentives to eat more natural foods:
1. Your body does not absorb all calories from some foods.
For example, almonds. Recent studies have found that about 20% of the calories from almonds are not absorbed by the body. This means if a package advertises a serving of almonds to be 160-170 calories, you are actually only absorbing about 120-130 calories. Read more about this here.
2. Your body absorbs more calories from cooked foods compared to raw foods.
Cooking breaks down the bonds in food that hold it together, which makes it easier for your digestive system to break down the food. In effect, your body doesn’t have to work as hard to break down the food and less energy and calories are lost to digestion. When foods are raw, all of the bonds are intact making your digestive system work harder to break down the food. Think about when you bite into a raw carrot compared to a cooked one, which is easier? Read more about this here.
3. Your body burns more calories with protein.
Up to 30% of calories from protein are lost to digestion, meaning if you eat 100 calories of protein you are only really absorbing 70 of them. This is because proteins are built up of several amino acids, which very have strong bonds holding them together. It takes a lot of effort by your digestive system to break these bonds down, in effect causing you to take in less calories.
4. Your body absorbs less calories with fiber.
There are a couple main reasons you will take in less calories with fiber rich foods. First of all, the human body cannot absorb the calories from fiber. This means the calories listed in your food that are attributable to fiber are not actually used (fiber is listed as a carbohydrate in nutrition labels with 4 calories per gram). Secondly, our digestive systems work extra hard attempting to break down fiber leading to more calories being lost in the digestion process. This means your net calorie intake from fiber rich foods is a fraction of what the nutrition label might say.
5. Your body absorbs less calories from whole foods compared to processed foods.
The reasons behind this are similar to cooked versus raw food in that bonds have been broken down during the manufacturing process to make foods easier for you to eat. A good example of this was a study done that had individuals eat one of two sandwiches. The sandwiches had exactly the same number of calories, differing only in the amount of processing they had undergone. One was white bread with processed cheese and the other was a multi-grain bread and cheddar cheese. Researchers found that it took about 50% more energy digesting the multi-grain sandwich with cheddar cheese and this resulted in about 10% less calories absorbed. Read more about this here.
Another way to think about this is comparing biting into a chip to biting into an apple, which do you think takes more work to break down just starting with the mouth? Food companies are smart, they know the easier a food is eat, the more you will eat, and the faster the food will be absorbed. Unfortunately this leads to not only overeating and absorbing every single calorie ingested, but will also be unlikely to keep you full for long considering virtually all nutrients have been stripped from your food in the manufacturing process.
6. Gut bacteria can influence how many calories are absorbed.
Gut bacteria help with the breakdown of food and effect the amount of calories you absorb from food. Research shows that there are two main types of gut bacteria that regulate calorie absorption, the firmicutes and the bacteroidetes. Obese individuals tend to have more firmicutes in their gut while lean individuals tend to have more bacteroidetes. Researchers attribute this to firmicutes being able to extract more calories from food and store it, leading to weight gain.
A sedentary lifestyle and a diet high in fat and sugar has been found to increase the firmicutes in the gut, while physical activity and a diet high in plants and low in sugar and fat is associated with more bacteroidetes in the gut. This is a relatively new research area, and more research is currently being done to better understand the role of bacteria in our gut.