What are calories?

What are calories?

Defining the term calorie isn't hard: according to the majority of science textbooks, that's how much energy needed to raise one gram of water 1-degree Celsius. But how does that relate and relate to caloriecounts you see on everything from menus for fast food to snack bar nutrition labels

If we take a look at caloriecounts in the context of calorie count, we're generally looking to know how much energy we're putting to our bodies. But a nutrition label cannot give you at least precisely. There are too many elements involved, some of that are influenced by the physiology of an individual, as well as others we're just in the process of determining.

Take a look at this: Beginning in the year 2020 nuts suddenly appeared to contain around 30 percent fewer calories than they had in the year before. The walnuts and cashews experienced a similar drop of energy density. Nuts didn't suffer, however, the method employed to calculate calories changed.

This is because the FDA and USDA frequently use a century-old method for measuring calories. This method was created in the 19th century (though exceptions can be made when there's more recent research available, for instance, for these nuts). In the latter half of the 18th century Wilbur Atwater, who was a researcher, wanted to quantify the energy content in food items through burning the ingredients by calculating the amount of energy was present in it before feeding similar food to individuals and determining how much energy was contained in their urine and pee. The distinction between energy in and energy out, or so was the basis for the calorie-calculating figures that we have today for macronutrients: nine calories in a gram of fat, and four each in grams of carbohydrate and protein.

For the 19th century, this was a huge leap in our understanding of energy density of food. However, for the 21st century this doesn't seem to be quite right.

[Related: The truth about measuring caloriesThe truth about counting calories

An calorie of fat from a nut for instance, does not appear to be the same as the calorie made from fats from animals. Although it's not clear the reason for this and why, it's likely that our bodies aren't able to break down all food items equally, so some calories remain in the food and go to our feces, but haven't affected our waistlines in any way. (We should be aware that the research on calories-in-nuts was funded in part by various nuts boards, but these parties did not design or conduct the research).

The concept of bioavailability has just recently become a subject of research, so there's a lack of data on what other types of foods we may be improperly measuring. We've learned, for example, that cooking food seems to make the nutrients in the food more readily available. We are also aware that our unique microbes in our gut help determine how much energy we extract from our food for example, by dissolving cell walls within certain vegetables. The Atwater system does not account at all for the cooking process, regardless of how you cook it neither does it take into account differences in bioavailability between different types of food items. It's just the amount of protein, fat or carbohydrate are in the food.

The new studies on nuts don't even employ a more advanced technique as Atwater used. In essence, they fed almonds (or walnuts or cashews) to participants, and the study measured their poop in order to determine the amount of energy absorption. It's only that the USDA scientists took the time to study one food specifically.

As long as we don't find a better method for quantifying the energy in any one food group or food group, the term calorie actually, is a number we've given to food. It's best not to think about it too much.