Are all calories equal?
A nutritional topic that has stood the test of time and currently builds the foundation for many heated online debates is the question of whether all calories are in fact equal? Are the calories in mars bars, apples, protein shakes, and pizzas all the same? Is how much you eat more important than what you eat? Before answering this question, it helps to understand a little more about what we are talking about.
Put simply, a calorie is just a unit of energy. When talking about food, calorie is often used in place of kilocalorie, where 1 calorie (or kilocalorie) refers to the amount of energy needed to increase water temperature by one degree (1). This means that all calories are in fact equal, given we are simply talking about a unit of energy. As with all things in nutrition however, the nuance is in the detail…
When used in the context of a person's diet, it helps to pay attention to more than just calories. The calories of a food do not tell us the macronutrient distribution, micronutrient content, and other helpful information such as fibre content. For example, 2000 calories from mars bars will contain vastly different quantities of protein, fibre, and other vitamins and minerals than 2000 calories from a combination of lean meats, fruit, whole grains and salads.
To add more complication however, there is evidence to suggest that equal proportions of calories in different macronutrient combinations may impact the body differently. For example, protein is widely reported to be the most satiating macronutrient, and it is reported that high protein meals may make individuals feel more full and satisfied than high fat meals (2). This effect has been shown repeatedly (3). Similarly, fibre has been shown to increase satiety and fullness between meals - It makes total sense, given carbohydrates containing fibre are less energy dense than high-fat foods, and a higher volume or quantity of carbohydrate rich food can be eaten providing the same or less energy content than high fat foods (4).
In addition, the Thermic Effect of Food (TEF) is the energy required to digest, transport and store food, and is responsible for approximately 10% of total energy expenditure (5). Research suggests TEF of protein is highest by 20-30%, followed by carbohydrates (5-10%) and fat (0-3%) (6). Put simply, higher protein and carbohydrate meals will have a higher thermic effect of food, increasing the energy your body uses to process and store this food.
Ultimately, this means eating a higher protein and fibre meal may result in more feelings of fullness, and greater energy expenditure, than high fat meals, when energy content is matched. If you're a constant snacker, ensuring your meals have a good hit of protein and fibre may reduce your craving to snack!
In summary, all calories are technically equal, as a calorie is simply a unit of energy. However as we can see, calories do not tell us the quality of a diet, or the nuance of how this may be impacting your physiology or eating habits.
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