Why A Calorie Is Not Just A Calorie With Respect To Weight Change

So, if you burn more calories than you consume you will lose weight. Its simple isn’t it? You’ve worked out through a complex formula, a simple multiplication or perhaps even trial and error that you need to consume ‘x’ amount of calories to maintain your weight. These calories will come from protein and carbohydrates, each providing 4 calories per gram, and fats providing 9 calories per gram. So irrespective of the balance of these macronutrients, as long as the total number of calories consumed hits your maintenance level, you will maintain your weight. If it is below your maintenance level you will lose weight and if it is above it you will gain weight. Right? Well not exactly…

Whilst it is a basic scientific principle that all energy must be accounted for, how the energy is accounted for means there is a considerable difference in relation to the effects on body composition between consuming 200 calories from a piece of cake and 200 calories from a piece of chicken. Whilst the maintenance level you have calculated may account for activity levels and your basal metabolic rate the energy expenditure through the choice of foods you eat is often mistakenly overlooked. Research indicates that with a typical western diet approximately 10% of all calories consumed will be lost through the digestion of the food you eat. The formula you have used to calculate your maintenance calories may well have accounted for this however, this percentage, known as the Thermic Effect of Food (TEF), can vary considerably with the choices of food we consume. Let’s look at the approximate percentages of energy utilised in digesting the food we eat for the different macro nutrient groups:

Protein = approximately 30% of the calories consumed are used to digest the food itself

Carbohydrates = 5-10% (20% for fibre)

Fats = 3%

Let’s see how this can affect the maintenance calorie intake:

Take a standard western diet of 15% protein, 60% carbohydrate and 25% fat. A 2000 calorie diet would be broken down into its macronutrient constituents as 300cal from protein, 1200cal from carbohydrates and 500cal from fat. Let’s take a look at the thermal effect of food in this diet using the above energy expenditure percentages:

Protein = 30% of 300cal = 90cal

Carbohydrate = 7.5% of 1200cal = 90cal

Fat = 3% of 500cal = 15cal

So the total energy spent on digesting the food is going to be approximately 195 calories (90+90+15). Therefore, 9.75% of the calories consumed will be used just in the digestion process. But what happens when we consume the same total number of calories but on a high protein diet? Let’s take a look at the energy expended during digestion for this same 2000 calorie diet but with a macronutrient content of 50% protein (1000cal), 25% carbohydrates (500cal) and 25% fat (500cal).  The thermal effect of the food would look like this:

Protein = 30% of 1000cal = 300cal

Carbohydrate = 7.5% of 500cal = 38cal

Fat = 3% of 500cal = 15cal

The energy spent digesting the food would now be approximately 353 calories or 17.7% of the total caloric intake. So an additional 158 calories will be burnt every day just by altering the macronutrient content of the diet, without adjusting the total number of calories! So to a degree, it is possible to adjust a diet to gain, maintain or lose weight without changing the total number of calories or altering the activity levels! Still think it takes 3,500 calories to burn a pound of fat?

What’s more, a study by Barr and Wright published in 2010 showed that whole foods have a greater energy requirement during digestion than processed foods even when the macronutrient content is similar. Fibre is generally lower in processed foods and as fibre requires more energy to digest than glycogenic carbohydrates, this is likely to be the leading cause.

There is also a great deal of research that suggests spices such as cayenne pepper, chilli powder and ginger can further increase the thermal effect of food and hence the frequent recommendations of these types of spices in weight-loss diets as well as their use in thermogenic fat burners. So, next time you’re counting calories, consider the thermogenic effect of the food you are about to eat and that a calorie is not just a calorie when it comes to your bodyweight!