Energy, Excretion and Exertion

Yesterday’s post focused on how we can use nutrition labels to gauge what we eat. It briefly mentioned that calories are units of energy – but today I’ll explain what calories actually do.

Just like cars, our bodies need fuel. Cars combine refined oils with oxygen into combustible gases, which expand in the piston cylinders and make the wheels turn. You probably know that energy can neither be created nor destroyed. It can only be stored or transferred. So what is actually happens to the energy we obtain from food?

After being broken down in our stomachs, our intestines absorb food nutrients into the blood. As blood is pumped through our bodies, so too are the nutrients which are taken into our cells. Here, glucose is converted into ATP (Adenosine triphosphate) through a series of processes referred to as cellular respiration. The ATP is further broken down into usable biochemical energy, thereby creating water, carbon dioxide and heat as byproducts.

This video brings back memories of high school freshman biology, but it’s detailed, short and not too complex:

So then what? Of the usable energy,

• 65-75% goes to fueling our bodies core needs. The speed with which your body burns energy at rest is called basal metabolic rate (BMR) and it varies depending on how big you are, your gender, how much you eat, and your activity level. The climate is also a factor.
• 12.5-25% goes to fueling your muscles, such as exercising or walking up a flight of stairs.
• %10 goes to the actual processing of food. In other words, it takes some energy to breakdown food to release more energy – just like drills used to find oil use gasoline engines.

These percentages assume you’re only eating as much as you need to balance your BMR, physical exertion, and digestive requirements. If you consume more calories than you expend, the extra energy is stored in your body as fat. This is critical to understand. Though fat is the most calorie-dense nutrient, the fat that we see around our waists is fat created by calories. That means it could be from carbohydrates, alcohols, fats, or even proteins. Though eating a lot of fat will yield a lot of calories (as well as other potential issues such as high cholesterol), most people gain weight because they consume excessive carbohydrates, which are the cheapest and most readily available food source.

Carbohydrates aren’t bad—and neither are fats. In fact, they are necessary. But eat too much of anything and you won’t need to buy an exercise ball for Christmas. You’ll be the size of one. I’ll make this more tangible in the next post – weightloss basics explained.