energy balance

The Energy Balance Equation – Do Calories Matter?

You might have been told in the past that all you need to do to lose weight is eat less and exercise more. It sounded so simple, but unfortunately things are never easy when it comes to weight loss.

What is the energy balance equation?

The energy balance equation is simple. According to this if you want to lose weight then your calories in must be less than calories out. The math seems simple and that is why people are drawn to it. Here is an example to make it a little easier to understand:

Jane is trying to lose weight so she faithfully tracks everything she does and eats with a tracker like MyFitnessPal. She eats 1200 calories per day. She has calculated her total daily energy expenditure as 1700 calories. She is eating 500 calories per day, or 3500 calories per week less than what she is using.  Here is the math:

1200 – 1700 = – 500 calories per day 
In a week:
– 500 x 7 = – 3500 calories which is equivalent to 1 lb lost.

It sounds so easy, so what is the problem? The energy balance equation relies on two things being accurate – calories in and calories out. It also relies on your ability to control these variables.

Calories In

This part is not as simple as it sounds. You eat a banana and it has 105 calories. Right? Actually it depends on the size of the banana. But, the problems don’t stop there. We need to understand what a calorie actually is to understand where things go wrong.

Calorie is a unit of energy. It is supposed to indicate how much energy we get from foods. We actually usually use kcal or kilocalorie but call it big C Calorie. A kcal is the amount of energy needed to raise 1 kg (2.2 lb) of water by 1 degree Celsius.

Scientists have measured the number of calories that each macronutrients contains in the laboratory. A food is broken up into its macronutrients and then the calorie count for that food is calculated. Unfortunately, the method used was developed about a 100 years ago and is not precise. The US FDA allows for up to a 20% error in the calorie count reported so the calorie count shown on a food might not be accurate, so Jane could actually be consuming 1440 calories.

The next problem is that we don’t absorb all the calories available in a food and it is dependent on the food, not on the macronutrient. This means that a gram of protein is not always 4 calories. It depends on the source. How the food is processed and cooked also changes the calorie content. For example a boiled egg has 35% more calories absorbed than a raw egg. Making it worse is that individuals absorb calories at different rates. Maybe the app Jane used uses the calorie count of a raw egg and she absorbs more calories than average from her food because of her gut bacteria.

Another problem is estimating how much you have actually consumed. You spoon some sour cream out, using a soup spoon and assume that it is a tablespoon, or you splash some salad dressing on your salad. Or you eat out and have no idea what the portion size is. If you have used an app like MyFitnessPal you understand how difficult it is to be exact with portion sizes. 

Calories Out

There are several components to calories out. These are your basal metabolic rate (how many calories you burn at rest), the calories burned during activity and the calories used to digest foods. I will look at how each of these is hard to estimate.

You can have your basal metabolic rate or your resting metabolic rate measured, but this is expensive and most people will use and estimate for this. There are many things that effect that estimate:

  • How much muscle vs fat you have on your body
  • Hormone levels
  • How much sleep you get
  • Genetics
  • How much you eat
  • Your gut bacteria

It is also difficult to estimate calories during activity. Laboratory tests can be conducted to determine the calories expended during an activity, but the most accurate tests are very expensive to perform and are rarely used. If you use the calories burned on fitness equipment or on fitness trackers, these are generally not very accurate. Making sure your information such as age, weight and height are entered will increase the accuracy.

If you use standard tables then it becomes even less accurate because most standards use an average weight and height person. Intensity needs to be taken into account as well and usually this is difficult to know exactly.

You also have to account for all the time where you are not resting and not exercising. For example when you are making dinner, doing laundry or buying groceries. This can account for between 15 and 50% of your daily calorie expenditure. Fitness trackers attempt to estimate this, but are even less accurate than with exercise. On your own this is almost impossible to estimate. How much do you walk around the office or the house, do you fidget, etc.

People who have dieted in the past may also use fewer calories when moving around than people who haven’t. This seems to be caused by the body becoming more efficient with its use of calories. 

You can see where Jane’s estimate of 1700 calories expended may not be accurate.


One of the first things I was taught when I started learning about fitness was how to determine how much someone should eat and how much they needed to exercise to lose weight. Unfortunately there are so many variables that we can’t measure properly that calorie counting becomes difficult at best. You may be drawn to the numbers, but keep in mind that calories are just a guide and counting calories is probably not the best way to lose weight.

Join my 5 Steps To Weight Loss Challenge to discover 5 changes you can make to start losing weight without counting calories.


Similar Posts

Leave a Reply

Your email address will not be published. Required fields are marked *