Science Time: How Calories and Food Work

By now I’m sure it’s safe to say everyone knows what calories are.
They’re those pesky little critters that sneak into your closet at night while you’re asleep and sew your clothes tighter.
You think that sounds absurd, but it’s not too far fetched for how most people associate calories with their lives.  
The truth is, everyone keeps hearing about how you should count calories and how that they’re important, but nobody can even explain what they are or how they work.
So that’s what I’m here to do, and I promise I’ll keep it simple, short, and sweet as humanly possible. 

​First off, What is a Calorie?
A calorie is a unit of energy.  Calories are typically associated with food in the United States, but they apply to any physical system that contains or uses physical energy.  For example, a gallon of gasoline contains 31,000,000 calories.  That sounds odd, right? Using calorie units of energy when not referring to foods, but it’s just as interchangeable as using Joules (units of energy) that most mechanical systems use.
Some background info on calories for those who may be truly interested, a calorie (or any unit of energy) is the amount of energy or heat required to produce physical work.  Calories are measured by how much heat it takes to raise the temperature of 1 gram of water by 1 degree Celsius.  One calorie is equal to 4.184 Joules, if you’re keeping score at home. 
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​What Exactly do Calories Do?
Now you’re probably thinking, “Okay Craven, enough of the physics lesson, just tell me what calories actually do to your body.”
You got it, slim.
We’re humans, which means we’re dynamic mechanical organisms, and like all mechanical systems, we need energy to work, and because we’re organisms, this means survive.  Survival as in breathe, move, pump blood, think, and overall just not die. 
So where do we get this energy needed to survive? I hope you guessed food because if you didn’t you’re not paying attention and probably need to start over.
The amount of calories in foods is the measurement of how much potential energy the food has.
Foods are comprised of only THREE MACRONUTRIENTS, and have a caloric load associated with them.  

These are not some made up values, but if you remember, they’re derived from how much energy each macronutrient requires to heat 1 gram of water by 1 degree Celsius; which means food is an actual physical fuel source.
If you know how many carbohydrates, fats, and proteins are in any given food (this is stupid easy to do) you know how many calories, or how much energy, that food contains.
You’ve probably noticed nutritional labels on the back of food packaging and thought of it as some cryptic code that you’ll never decipher, but let me hit you with some knowledge.
Below is a nutrition label for a slice of banana bread. The total calories, fat, carbohydrates, and protein values are all highlighted.  This is the ONLY information that is truly important on these nutrition labels, so don’t pay any attention to the % values or anything else as they are not relevant to what we need. 

This particular slice of banana bread has 190 calories.  What this means is if we were to light a slice on fire and get it to burn completely (which is actually very difficult to accomplish) the physical reaction would produce 190 calories. 
If we consider the macronutrients, fats, carbs, proteins, you’ll notice the bread has 4.5 grams, 35 grams, and 2 grams, respectively.  Of the 190 calories, 41 come from fat (4.5 cal x 9g), 140 come from carbs (35 cal x 4g), and 8 come from protein (2cal x 4g).
Our bodies “burn” the calories in the slice of bread through digestion and the metabolic process to break the carbohydrates into glucose and other sugars, the fats into glycerol and fatty acids, and the proteins into amino acids.  These broken down particles are then transported through the bloodstream to the body’s cells where they are either absorbed from immediate use or sent to the last state of the metabolic process where they are reactied with oxygen to release their stored energy. 

​So How Many Calories are Needed to Function?
This answer varies for every person due to individual height, weight, gender, age, current body composition, and activity levels.  There are three main factors that are involved when calculating the amount of calories your body needs.
-Basal Metabolic Rate
-Physical Activity Level
-Thermic Effect of Food
Your basal metabolic rate (BMR) is the amount of energy your body needs to function in a resting state. Not exercising, not working, but just sitting there.  Staying alive requires between 60 and 70 percent of calories burned in a day which includes keeping your heart beating, lungs breathing, and kidneys functioning.  Men will almost always have a higher BMR than women due to higher levels of muscle and body mass.  If you’d like to calculate your own BMR, here’s one of the simplest and most effective methods to do so using the Harris Benedict formula:

After your resting metabolic rate, physical activity uses the second most amount of calories.  Physical activity is anything and everything you do throughout the day, from brushing your teeth to doing your laundry.  People with higher amount of body mass will have a higher energy expenditure than people who are slimmer or have less body mass.  This may seem backwards, but bigger bodies consume more energy and have more stored potential energy. 
Lastly, the thermic effect of food is another way your body consumes calories.  This thermic effect of food is the amount of energy your body uses to digest and metabolize the food you eat.  The more food you eat in a given day, the higher your TEF will be.  This doesn’t mean the TEF of eating more food offsets the increased calories you’re consuming, but when coupled with increased physical activity and an improved body composition, it can be very beneficial towards allowing you to eat more food and increase your maintenance calorie level, which is never a bad thing. 

Energy Balance
Here’s where this talk about energy gets important, so make sure you’re paying attention as I do my best to explain this as clearly and concisely as possible.
If you take in MORE calories than your body burns, this will create an energy surplus which means an increased store of energy in the body, which will almost always lead to an INCREASE IN BODY FAT.  The rate of fat increase is dependent on how large this calorie surplus is, so don’t expect to get fat overnight after a few large meals, but over a long enough period in a large enough surplus, this can lead to a lot of fat gain.
Conversely, if you take in FEWER calories than your body burns, this will create an energy deficit which means a decrease in stored energy in the body, resulting in fat loss.  Once again, don’t expect to become super lean after a few days of restricting calories. Dramatic fat loss is a result of a good sized calorie deficit over time.
A surplus of 3500 calories stored in the body is manifested as 1 pound of body fat, and you guess it, a deficit of 3500 calories results in a loss of 1 pound of body fat.
There’s no simpler way to explain energy balance, and I hope it makes sense because it’s so incredibly important to grasp.  With this information you can change your body composition essentially on demand. 
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​Does it Matter where the Calories Come From?
Yes. And No. A surplus or deficit of calories will create fat gain or fat loss respectively, period.  In regards to nutrition and aiming to create an improved body composition, it actually does matter where these calories are coming from.  And when I say “where they come from” I mean either from protein, fat, or carbs, not some mystical type of nutrient that has yet to be discovered or something like that.
To achieve an improved body composition, meaning a slimmer, more toned physique, it’s imperative to consume adequate amounts of protein from meat.  Yes, I know you have a friend who has a cousin whos vegan and swears it’s improved her life and she’s all healthy and all that jazz, but I promise you it’s not just from eliminating animal proteins. Especially if you’re working out and training with weights, protein should be your go-to nutrient at every meal.
Followed by protein are carbohydrates, which come in all types of shapes, forms, and foods. Carbs are an excellent energy source and have a more difficult time being converted and stored as fat when in a calorie surplus, as opposed to dietary fat.  Vegetables are excellent carb sources for most people as they are extremely low in calories for the amount of volume they provide, so be sure to include veggies, especially green veggies, in most of your meals. 
Fats are often villainized because it’s always thought that “eating fat makes you fat”, but as you should know by now, that’s only the case when you’re consuming fat in a calorie surplus.  Fats are an essential macronutrient that the body needs to function optimally.  The caveat of dietary fat is the amount of calories packed in such a small amount of volume.  If you’ll remember, there’s 9 calories per gram of dietary fat, which means it’s exceptionally easy to over eat fat.  Do this for a long enough time and you’ll see a spike in your weight on the bathroom scale.