Calories In vs. Calories Out
In Part One of this series, we discussed how your body uses calories from specific macronutrients as fuel. The calories you consume are referred to as your caloric intake. In this installment, we will elaborate a bit on the amount of calories your body uses daily, also known as caloric expenditure. Although on the surface this "calories in/calories out" system sounds very simple, the opposite is true. This energy balance involves so much more than simply looking at total calories consumed versus calories burned.
A few years ago, I had a very well educated client whose goal was to lose body fat. So based on his estimated daily caloric expenditure, I designed an eating and exercise program to help him reach his goal. A few days later, I noticed him exercising vigorously on the Stair Master. Two hours later, he was still sweating away on the gym's cardio deck, only now he had switched to jogging on the treadmill. My recommendation for his cardio had been for only 20 minutes per session, so I knew something was amiss.
Gremlin vs Leptin
After his workout, we sat down in the office to discuss his program. As I mentioned before, he was a knowledgeable and had read several studies on gremlin and leptin, two hormones that have an effect on appetite and fat loss. In a case of missing the forest from the trees, he felt that these hormones were the key to losing body fat and that if he only consumed 1000 calories per day and burned the same amount or more during his workouts, he would lose weight. With all due respect, this is a case of having knowledge, but not be able to properly apply it.
Thermo Effect of Food
Your body burns calories 24 hours per day. Significant portions of those calories are used for basic physiological functions such as breathing, circulation, regulating temperature, etc. - in other words, life support. Smaller portions of calories are expended in the digestive processes once food has been consumed. This is called the thermo effect of food. The remaining calories can be used o fuel your body during physical activity - working, walking the dog, cleaning the house, exercising, etc. And while in your mind, getting into peak physical condition is a priority, your body is more concerned with keeping you alive. This is where the confusion about energy balance begins.
Body's Survival Instinct
Since life support is your body's main concern, it will do whatever it needs to do to survive. Should you not provide it with enough nutrients (protein, fats, carbohydrates, vitamins & minerals) or energy (calories in general), your body would make adjustments to survive as best as it can by burning fewer calories. If you have heard of the expression, "slowing your metabolism", this is how and why it happens.
Your body will be able to use stored body fat as fuel for only so long before it searches for a more nutrient-dense tissue to sustain itself, aka muscle tissue. Muscle is a much more metabolically-active tissue than body fat, meaning it requires more calories to maintain your body's muscle mass as opposed to body fat. If you begin to lose muscle tissue, your body will burn fewer calories per day, which is counterproductive to fat loss. And, if your calorie consumption is significantly below your caloric expenditure, your body will respond by slowing your heart rate and lowering your body temperature in an effort to burn fewer calories. This "slowing of metabolism" phenomenon dates back centuries as a way of surviving a famine.
This explains how both underrating and over-training will prevent you from reaching your fat loss goals. In many cases, the same can be said for a lack of proper nutrients in your diet. The easiest way to illustrate this is with your protein needs. Let's say you just finished a great workout and you are ready to head home with your protein shake in hand. As you leave the gym, you accidentally bump your pumped-up biceps on the metal door frame and cut yourself. Your body now has a greater need to use that protein shake to help heal your wound and ward off a possible infection. This decision is a matter of priorities - survival instinct versus muscle growth. And, if you are not meeting your daily protein requirements, or you are just barely getting enough, your wound may be slower to heal and you will not be able to reach your goal of a leaner, muscular physique.
This is an example of why you need to make sure you are aware of where you are getting your calories from every day. Other analogies can be used with carbohydrate and fat consumption, as well as vitamin and mineral deficiencies. They are all part of a bigger picture.