Calories and Kilojoules Explained

Calories & Kilojoules are two different ways to measure the amount of energy in foods. Most importantly, it’s the amount of energy which determines whether someone will gain weight, lose weight or maintain.

All people have a baseline amount of calories that they expend which is based on their age, activity level, sex and size. Some foods can influence how many calories are expended too. For instance, certain fruits and vegetables may actually boost how many calories the body naturally expends, because they take energy to be broken down or absorbed or they provide nutrients which boost metabolic rate.

Exercising uses up calories as well of course and can play a small to moderate role in our ability to influence weight gain or weight loss. Largely though, the amount of calories eaten (the diet) is the biggest factor with changing one’s weight.

So what amount is right to shoot for? This all depends on a person’s individual factors and using a simple online calculator which takes into account activity along with the other details can help determine the right amount. Then, a person will want to make sure it comes from the right macronutrients. Each macronutrient supplies a different amount of calories per gram and is listed in the table below. The densest sources of calories come from fat and alcohol, which is why it’s particularly important to keep these in check.

Macronutrients & Calories per Gram
SourceCalories / Gram
Fat9 calories / gram
Carbohydrates4 calories / gram
Protein4 calories / gram
Alcohol7 calories / gram


Using the above chart along with reading food labels helps to determine if a food’s calories come mainly from fat, carbs or protein (alcohol is not usually listed). In most cases, sticking to a low amount of around 1500 calories (about 6200 kilojoules) will lead a person to lose weight slowly over time, while a higher amount of calories, say around 2500 (104600 kilojoules) is often enough to cause gradual weight gain.

The easiest way to estimate how many calories a person is eating is to do a 24 hour recall of all food eaten and to input this into an online calculator like the ones on or This can provide a close enough reference, as well as show what meals or food sources provide the largest amount of calories for a person’s day. This can be a vital tool for someone who is struggling to lose or gain weight and needs some guidance.


Are Calories & Kilojoules the MOST Important Measurement?

While finding out how many calories or kilojoules are coming from foods is helpful, it’s not the only tool one should use and it’s far from being the most helpful. Many foods which may be lean in the calorie department may not be healthy or help a person progress in their goals. Sugar free soda, low fat cookies or white flour products may all be low calorie, but they’re not good foods to add into the diet.

More than looking at calories, a person will want to make sure they’re eating a mostly whole food diet with minimally processed items. It helps to do this by preparing most of foods from home and limiting restaurants to a small portion of the overall intake. Some research shows that having more foods in a whole and unprocessed state will naturally boost a person’s metabolism as well and thus may help with a weight loss or fat loss goal.

With information on your intake of calories or kilojoules you’ll be better primed to balance your activity with the proper diet. For more information on adjusting calories or kilojoules, reach out to a nutritionist or health professional that can help provide advice relevant to your goals.