A Calorie is a Calorie?? Not exactly...

We here in America always talk about calories this, calories that, 100 calories in these cookies, 200 calories in that smoothie, 3500 calories in a pound of fat. But can you tell me what that even means?? The way we talk about calories is almost like the word itself refers to something tangible, that you could actually put in your hand and look at. But it's not necessarily the case. When we say a certain substance, let's just go with something pure like table sugar, has a certain number of calories, say 100, what we're actually saying is that substance has the ability to produce 100 calories of heat energy. The word Calorie is a metric measurement of heat, and is only somewhat relevant in the human body.

The way scientists determine the number of calories in a certain substance, food for our purposes, is to put it into an instrument called a Blast Calorimeter, which is for all intents and purposes an incinerator. Inside its sealed chamber a measurable amount of heat is applied until the substance has been reduced to ash. Whatever extra heat produced is the amount of caloric energy contained in that substance. In this case a calorie of fat is the same as a calorie of sugar, protein, fiber, etc.

However, your body isn't a blast furnace, it's a very complex biochemical system. One in which different types of substances act very differently. And in this system, no substance acts exactly the same as others, even from person to person. Ideally, and in a blast calorimeter, 1 gram of Carbohydrate material contains 4 calories of energy, Protein has 4 also, and Fat has 9. Oh by the way, Alcohol counts too, and contains 7 calories per gram. If only it were this simple. Each of these macronutrients have different classes and categories that all act a bit differently in the body, and may act differently when being taken in and spent as well.

As far as carbohydrates are concerned there are a few things to remember when checking out that food label. First off, because Fibers are technically a carbohydrate in structure, they're counted on food labels and will add to the total calorie count. But as we've discussed before these fibers are not digestible, so you're not going to be able to take in and/or expend or "burn" those calories. So don't go counting them toward your calories for the day. As far as the ones that Do count, we have complex and simple categories. Unfortunately this isn't enough of a distinction to give us all the info we need. Complex carbs, or starches, such as breads, pastas, or potatoes and the like quickly break down into glucose in the body, just like if you were to eat pure glucose or dextrose. Once your intestines get a hold of either starch or pure glucose it releases it straight into the blood which raises your insulin levels and generally all this energy is either quickly burned, or more likely stored. And except in certain cases this storage will be into fat cells. Other types of carbs, like fructose or galactose, don't have the same effect on insulin levels, so they may be utilized differently and may or may not be stored. Fructose is converted by the liver into triglyceride, which will circulate in the blood for a bit before being stored, making it available for a longer period of time to be used for energy. Galactose is converted into glucose, but not fast enough to raise insulin levels very fast, so similarly it allows a higher available level of energy to circulate in the bloodstream before being stored. Aside from how it's stored, glucose that circulates in the blood is much more easily used by your body to produce energy, either throughout the day or during exercise. So if you can hold off the storage of these carbs, through different methods, you may be able to convert them into energy a bit easier than if they're gobbled up by those fat cells. So here is one example where 100 calories may be either quickly stored, or slowly and steadily burned off before it creates a problem.

Fats are next, and aren't quite as tricky. All fats, from saturated to poly-unsaturated, have 9 calories per gram. Some different types are more easily used for energy, such as MCTs, or Medium Chain Triglycerides. One common source of these is Coconut Oil, which is technically a saturated fat, although it's melting point is in the 70's, meaning it can be a bit smoother for the body to work with since it's generally a liquid in the body. Most fats, however, form Long Chain Triglycerides. Obviously the body stores fats, at least the ones it doesn't immediately use. Since mono and poly unsaturated fatty acids tend to flow a bit more freely in the bloodstream, since they're not all globbed together, your body may be able to utilize these fats for more productive means more easily than saturated fats. One more reason to start incorporating more oils into your diet. One more bugger about those carbs from the last section: that insulin spike that causes the body to store that glucose, causes the body to store much more fat also. So once again, that insulin spike may be robbing you of a few calories that your body would otherwise expend. The final interesting thing about taking in fats is that you may not have to burn them to get rid of the calories. Since the body utilizes fats for many structural and biochemical processes, many of those calories may also be absorbed and converted by the body, meaning they're taken out of the whole Calories In/Calories Out equation.

Similarly to that last scenario is how the body treats Proteins. Proteins contain 4 calories of energy per gram. But the crazy thing about proteins, is that if you're leading a good active lifestyle you're not going to be using the protein you take in for energy. Instead you'll be using it to build/repair/replace all the structures in your body. You see, almost all structures in the body (meaning the ones that aren't specifically formed by phospholipids or fatty acids) are made up of proteins. Proteins are just chains of individual Amino Acids linked together in varying lengths. Through all the different activities we go through during the day, and even just breathing and pumping blood, these proteins break down or need to be replaced with a different protein.  The protein you take in from food will be broken down and used for this purpose, ideally. In fact, if you don't get enough of whichever Amino Acids you need for this maintenance and rebuilding process through your diet, your body can and Will break down existing muscle in order to find them. This fact alone can make things tough for vegetarians, who have to vary their food sources in order to ensure they're getting all the necessary aminos. Now assuming your body gets all the aminos it needs from the diet, any extra proteins can be converted for storage as fats, or can be used for energy as well, but the oxidation (burning for energy) of amino acids is a bit of a rough process, and your body would much rather use sugars or fats.

So that's the big three, and how calories of each are used/stored by the body. As you can see, those 2500 calories per day you're taking in can cause very different things to happen in your body depending on what they consist of. Carbs are different than Fats, which are different from Proteins. So please don't go thinking you can replace that 500 calories of fruit, veggies and lean meat you were going to eat for lunch with 8 Twinkies without some pretty hefty consequences, storage wise. Hopefully this sheds at least a little light on what all those numbers on your food labels might end up meaning once you get your grub on.

All in all: You're not a blast furnace. Don't eat like one!!