If you are eating to lose weight, you will undoubtedly have heard of calories. You may well have decided that you need to eat a certain number of calories per day to continue losing weight and even weigh and measure your food to make sure you aren’t eating too many.
While this is a useful way to make you more mindful of what you eat, it’s important to understand that not all calories are the same and you need to think about more than just calories if you want to lose weight and be healthy.
What is a calorie ?
A calorie is a unit of heat energy – it’s the amount of energy required to raise the temperature of one gram of water by one degree centigrade. To estimate how many calories food contains, scientists burn it and measure the amount of heat it gives off. A calorie is equal to 4.2 kilojoules – the standard energy measure in countries that use the metric system.
Different types of food contain different amounts of calories:
- Protein – four calories per gram
- Carbohydrate – four calories per gram
- Alcohol – seven calories per gram
- Fat – nine calories per gram
It is estimated that one pound of body fat contains around 3,500 calories which is why most diets suggest you create a 500-calories per day deficit to lose one pound of fat per week (7 x 500 = 3,500).
There is more to food than calories
The thing is, while the number of calories in a food is worth knowing, your body uses the calories from different foods in different ways. Calories from protein are used differently to calories form fat for example.
For this reason, it is important to consider not only how many calories you consume but where they come from and how your body will use them…
The Good – Protein: is used for muscle growth and repair and is very rarely used for energy. Your body has a very hard time converting protein into fat so it’s a very “safe” food for dieters. Breaking down protein also uses a lot of energy – about 30% of the number of the calories the protein provides. This means that while protein DOES contain four calories per gram, only around three calories are usable and, really, it’s unlikely that they will be used for fuel anyway. More about protein at “Beginner’s Guide to Protein Powder” article.
Carbohydrates, on the other hand, are used for energy but, if you are inactive or eat more than you need, your body will quickly turn unused calories from carbohydrate into fat. Much less energy is needed to break down carbohydrate – 5 to 10% on average – and so you get more energy from carbs compared to protein. This helps explain why high protein/low carb diets often lead to weight loss even if you eat the same number of calories.
The Bad – Alcohol: contains seven calories per gram but it can only be used for energy. Alcohol is a priority fuel meaning it must be burnt before food calories can be used. If you drink alcohol with a meal, you are more likely to store the food calories as fat while your body burns alcohol. Alcohol can also increase your appetite and make it harder to make sensible food choices as it can inhibit your decision making process.
The Ugly – Fat: is the most calorically dense food and it takes very little energy to digest. This means that fat not only contains a lot of calories, all of those calories are useable within your body. Food fat calories are easily converted to fat on your body which, combined with its high calorie value, explains why low fat diets can be useful for weight loss.
Not all fat is ugly – But, not all fats are created equally and where your body does like to use saturated fats for energy, it uses unsaturated fats for important chemical reactions meaning that although all fats contain nine calories per gram, some fats will only be used for fuel if you eat too much of them.
If you count calories, it’s important to understand that doing so only gives you a rough idea of how much energy you are actually consuming. A high protein meal of 500 calories will affect your body very differently to a high carbohydrate meal of the same size. It’s not enough to count calories; you also need to think about where those calories have come from.
Also, people who count calories often get very good at substituting foods. For example, if, at the end of the day, you have 100 calories left to eat, you could eat an apple and some natural peanut butter OR a couple of cookies. Despite containing roughly the same number of calories, these two foods will behave very differently in your body with one (the cookies) being much more likely to cause weight gain.
Counting calories is only half the battle of losing weight – the source of those calories is equally important!