Calories And The Energy Balance

We use the term all the time without giving it much thought but what is a Calorie? A calorie is a measure of energy just like a meter is a measure of distance. A calorie is the amount of energy it takes to raise the temperature of 1 g water with 1 degree Celcius. Which isn’t much. Therefore we tend to speak in kilocalories or Calories with a capital C, so times 1000. These are the values you find on the back packaged foods and say something about the energy value of food.
We eat food for energy and nutrients and our energy expenditure (EE): how many calories we need, depends on three main factors:
Your BMR (Basal Metabolic Rate): this is the amount of calories you need at rest, not digesting any food and not moving. The energy you need to just keep your heart beating, your lungs breathing and fuelling your cells. This makes up about 60% of your energy expenditure in most people. BMR is affected by body size and composition: bigger bodies have more cells and need more energy. It also matters what your body is made of. Muscle tissue burns more calories than fat tissue which is another reason why it’s beneficial to lift weights, even if your goal is fat loss.
TEF (Thermic Effect of Food): This is the energy you need to digest and absorb nutrients from the food you eat. This makes up about 10-25% of your calorie requirement depending on the type of foods you eat. Eating lots of processed foods means you’ll be at the lower end of this spectrum and you won’t lose much calories digesting and absorbing food. The clue is in the name here: processing food does the digesting for you. If you eat a diet based on whole foods your body needs to do all the work. Therefore TEF will be higher, which means you’re effectively absorbing less calories from your food. Great if you’re on a fat loss diet.
The final 30-40% is made up of your PAL: physical activity level. The more active you are, the more calories you need. This is made up of EAT Exercise Activity Thermogenesis and Non-Exercise Activity Thermogenesis, basically the exercise you do in and outside of the gym. The impact of EAT is often overestimated and the impact of NEAT underestimated. People tend to think that if they exercise every day they can eat as much as they like. However, exercise doesn’t always burn as much calories as we like/hope. Even if your spin class burns 400 calories you need to take into account the calories you’d have burned regardless without doing anything. If you hadn’t done the class you may still have burned 100 calories, so this class really only adds 300 calories to your Energy Expenditure. That’s only a little more than the average chocolate bar people down mindlessly with their coffee. If you spend the rest of the day sat at a desk and travel by tube like many people in London working in an office job do, your NEAT is going to be low. So if this is you, when you’re making an estimation of your activity level and train every day, be conservative if you don’t do much else. On the other hand, someone who is on their feet all day and works as a waiter for example, but never set foot in a gym, this person can have a higher EE because his EAT may be zero, but his NEAT is high. Because we spend more time outside of the gym than inside, the effect of NEAT is often stronger. So if your goal is fat loss, you may want to consider getting off the tube a few stops early and walk an hour every day or consider ditching the tube all together and take the bike.
The energy balance
There are a few ways to take all these details and put a number on it. Several formulas have been developed to make an estimation of calories, some are more accurate than others. Here’s a handy website that I often use to make an estimation of calories. At FFF we use the Mifflin St. Jeor Equation. The formulas are below:
10 x weight (kg) + 6.25 x height (cm) – 5 x age (y) + 5
10 x weight (kg) + 6.25 x height (cm) – 5 x age (y) – 161
The number that comes out of this equation is how many calories you need to sustain your body at its current weight and composition: maintenance calories. Whether you should eat this amount of calories is depending on your goal. To describe the relationship between calories burned and eaten we use the term energy balance. If you burn as much as you eat the balance is 0 or neutral. You’re not gaining or losing any weight.
If you are trying to lose weight you’ll need to eat less calories than maintenance. Your body will then have a shortage and rely mainly on your body’s reserves: body fat, but also muscle tissue for energy. The energy balance is negative and you’d be in an energy deficit. A positive energy balance means you’re eating more than you burn and you’ll be putting on weight. Depending on if you’re doing any training this weight gain will be a combination of muscle and/or fat. Gaining muscle generally goes best in an energy surplus but because muscle growth is a slow process you only need to be in a slight surplus. Eating well above maintenance may only gain you body fat, which isn’t usually desired.