What are calories?

Everyone these days are talking about calories. Low calories, high calories, macronutrients, healthy foods, diet foods, healthy fats, the list goes on and on.

But what does it all mean. Do many people actually know what a calorie is? Are calories all the same? How do different macronutrients affect our body? What are macronutrients in the first place?

It’s no wonder lots of people find it hard to eat healthily, because what is “eating healthily”?

Understanding what foods do to our body, what they contain and how this affects us is key to knowing what makes up a healthy diet. This in turn should mean we understand what we need to do to lose weight, maintain your current weight and tone up.

What is a calorie?

Well scientifically, 1 calorie (actually called kilocalories) contains the energy needed to raise 1kg of water 1OC.

But this doesn’t mean anything to us.

So, calories are energy. Our muscles, brains and all the other cells in our bodies require energy to work and we get this energy from eating calories.

This means if we don’t have enough calories it can have negative effects. Muscle wastage, being unable to concentration and lack of energy are all symptoms of not consuming enough calories. So, although many people need to eat less calories to start losing weight, we shouldn’t eat too little either.

To maintain weight, we consume the same number of calories that we expend. In simpler terms, we must eat as much as we use up. So, if you have a very active job, plus you walk to work and go to the gym, you will be able to eat more than someone with a sedentary job and not gain weight. If you usually maintain your weight anyway, if you start going to the gym and burning an extra 300 calories, you can eat 300 calories more per day (if you want to maintain your current weight).

Calories are the key to weight loss

To lose weight, you must be burning more calories than you eat.

Like in the example above, if you manage to maintain your weight all the time, you could start going to the gym and burn an extra 300 calories. Now if you don’t eat any more than usual, you are burning more calories than you eat. This is the key to weight loss.

This is the one main thing you should take away from this post, if you read nothing else.


Number of calories in foods

Here is a quick list of foods and the number of calories they contain per 100g:

  • Apple – 52 calories
  • Chicken – 132 calories
  • Beef – 170 calories
  • Chocolate Bar – 480 calories
  • 2% Milk – 50 calories
  • Cheese – 371 calories
  • Broccoli – 34 calories
  • Bread – 265 calories
  • Egg – 155 calories

These are just examples of calories in foods. 100g of eggs is 2.5 full eggs, which would be quite filling whereas I bet anyone could easily eat 100g of chocolate. This isn’t to say you can’t have chocolate but you must realise how having a small amount will quickly raise how many calories you are consuming. Having a general knowledge of roughly how many calories foods contain is going to help you make better decisions and not consume too much.

This information is shown on the back of the packaging. It will appear under the heading energy and is usually shown as “kcal”.

How many calories should we eat?

Your activity levels, age, whether you exercise regularly or not and what kind of job you have all affect how many calories you can consume without gaining weight.

The NHS recommends men need around 2500kcal per day and women need 2000kcal per day to maintain a healthy weight. (Check your calorie requirements here: http://www.bbc.co.uk/guides/zy7j2p3)

If you want to lose weight, then eating less than your recommended daily calories will help you achieve this.

But what should we eat? Technically an average man could eat 500g of chocolate a day and they will slowly lose weight. However, we all know this wouldn’t be a good way to lose weight. We hear about healthy, balanced diets but what are we trying to balance?

What are macronutrients?

When we consider the nutritional needs of the body, we can break these down into the three main categories…

Fat, Protein and Carbohydrates

These are what you may hear people calling their “Macros”.

What we eat is made up of a mixture of these three macronutrients. But the amount of fat, protein and carbohydrates in our food will vary a lot.

Foods such as butter and oil are mainly made up of fat. Fruits and vegetables are mainly carbohydrates. Milk and other dairy usually have a good mixture.

So what effects do these macros have on us (and our calories)?

How many calories do my macronutrients contain?

Macros provide different amounts of calories which then make up the calories in our foods.

Fat contains 9 calories per gram.

Protein contains 4 calories per gram.

Carbohydrates contain 4 calories per gram.

(And alcohol contains 7 calories per gram but this isn’t classed as a macronutrient)


So, this easily explains why we are told to avoid fatty foods. The more fat the food contains, the more calories we end up eating.

But don’t think that means fat is bad. We need fat as part of our diet, we just don’t need to eat too much of it.

However, this can be a difficult task as fat is very easy to over consume. Since it contains more than twice the calories per gram than that of protein or carbohydrates, even if you eat less fat than you do carbohydrates for example, you could still end up consuming more calories.

For example, if you had a big portion of chip shop chips (400g) this could contain over 900 calories. If you ate 900 calories worth of baked potatoes, you’d have eaten about twice as much (800g) but only had the same number of calories.

This is due to the fat content boosting up the number of calories, so we could be eating a lower volume of food, but eating more calories.

Good sources of fat to include in your diet would be:

  • Sunflower, rapeseed, olive and vegetable oil plus any spreads made from these
  • Avocados
  • Nuts and seeds
  • Oily fish (e.g. mackerel, salmon or trout)

So how much fat should we eat? Our diets should be made up of 20% - 35% of our calories coming from fats.

So that’s 500-875 calories of fat for men (55g-97g of fat) and 400-700 calories of fat for women (44g-77g) of fat.


Carbohydrates also get a bad reputation for making people fat. But usually it is the type of carbohydrate and the quantity that people eat of them that causes the weight gain.

Carbohydrates are the body’s main source of energy and is easily used by the body’s cells and tissue, since it isn’t as hard to break down as fat and protein.

However, this quick source of energy is why it has a bad reputation for making people gain weight. Simple carbohydrates are digested very quickly and enter raise the blood sugar level in the blood stream. These simple carbohydrates are also known as sugar. They cause insulin to be released which shuttles all the energy away for storage. In other words, it stores it as fat.

So here are some carbohydrates that we should eat:

  • Vegetables
  • Fruit
  • Grains
  • Legumes (beans, lentils, peas, etc.)

So how much carbohydrates should we eat? Our diets should be made up of 45% - 65% of our calories coming from carbohydrates.

That’s 1125-1625 calories of carbohydrates for men (281g-406g of fat) and 900-1300 calories of carbohydrates for women (225g-325g) of fat.


Protein makes up the building blocks of everything in our body. All cells contain protein so it is a major part of the skin, muscles, organs and glands.

Protein is also a very filling macronutrient. If we eat foods high in protein we are likely to stay fuller for longer, therefore reducing snacking. It also takes a long time to digest, unlike sugar, so gives us a slow release of energy which we can use, rather than it being stored as fat.

Great sources of protein are:

  • Beef
  • Pork
  • Poultry
  • Fish
  • Legumes (beans, lentils, peas, etc.)
  • Nuts and Seeds

So how much protein should we eat? Our diets should be made up of 10% - 35% of our calories coming from protein.

That’s 250-875 calories of protein for men (62g-219g of protein) and 200-700 calories of protein for women (50g-175g) of protein.

I would personally recommend trying to eat more protein so aim for around 30%-35% if you can. This will help you feel fuller, reduce the number of calories you consume and so help you lose weight.

Tracking our Calories and Macros

The best way of making sure that we stick within the number of calories we use every day is to track what we eat. This will help you learn, what foods could be having a negative effect on your diet, which foods you could eat more off and whether your diet contains the optimal ratio of macronutrients.

Apps offer us an easy of constantly tracking what we eat. MyFitnessPal is an app I have found very easy to use, as you can scan barcodes of foods and easily add in foods that you eat regularly.

This isn’t ideal as it does take time and can be quite a boring repetitive task, but if you are desperate to lose weight, it can be an invaluable tool.

You can try it for a while and see how it changes what you eat. Then eventually you will have a better idea of what you should be eating.

Calculating Claories