Dig more than skin deep and the human body is a very confusing thing. At any given moment, an uncountable number of interlinked biophysical processes are happening inside you, from electrical signals flashing along nerves to chemicals shuttling between cells, which control everything from the movement of your muscles to whether you can remember where you left your house keys. It's a complex system and it needs a lot of fuel to run.
To power the human body (and this is a gross oversimplification of how it actually works) we need to eat. If we eat too much, we end up with a bunch of leftover energy, which gets stored for later as fat. If we don't eat enough, then the system doesn't have enough energy to function properly and taps those stores to make sure it keeps ticking over.
Which brings us onto calorie counting. It’s a way to monitor how much energy goes in so you can balance it against how much gets burned up, the idea being that with a bit of basic math you can keep to either a deficit (in which case you'll lose weight) or a surplus (which means you'll put weight on).
Although this concept has been around for years, it’s still easy to be sceptical – does counting calories actually make fat loss or weight gain easier? The following article will explore why calories are important, explain how you can count calories safely, and most importantly, take a critical look at whether calorie counting actually works long-term.
What is a calorie?
Strap in, because things are about to get technical.
A calorie is a unit of energy. Specifically, the amount of energy needed to raise the temperature of 1g of water by 1°C. In that context, it's very rarely used by scientists these days, having been replaced by the joule.
In food, of course, it's very commonly used. But technically, we're not talking calories – we're talking kilocalories (kcal).
1kcal = 1000 calories.
A kilocalorie can also be written as Calorie, capitalising the 'C'. We know – it can be super confusing
1000 calorie (cal) = 1 Calorie/kilocalorie (kcal)
Our bodies need energy to do what they do, that’s why calories are so important. However, keeping track of calorie intake is not always easy. If you want more on the science behind calories, check out our article How to Calculate the Energy Value of Food, written by one of our expert nutritionists, Rebecca Williams SENr, RNutr.
The history of calorie counting
Over 100 years ago, a guy called Wilbur Olin Atwater developed a way to measure the calorie content of foods. It’s called the Atwater system (who’d have thought?) and it’s still used today. Full disclosure: it’s not 100% accurate. But it’s still pretty good.
According to the Atwater system:
1g of fat = 9kcal
1g of alcohol = 7kcal
1g of carbohydrate = 4kcal
1g of protein = 4kcal
So 100g of butter (which is mostly fat) will contain more calories than 100g of oats (which is mostly carbohydrate). Fibre is not accounted for in this system, but because it’s not digested as well as other carbohydrates, it’s usually assumed 1g of fibre = 2kcal.
Although the Atwater system helps us understand calorie counting mathematically, it's not the most practical if you actually want to know how much energy there is in what you're eating.
Why count calories?
Just as you can figure out how many calories are going into your body, you can also calculate how many you 'burn'. Again, we're actually talking kilocalories here. And unlike food, where you can use scales and nutrient types to get to a decent estimate, figuring out energy burn is trickier.
If you were just to lie in bed all day and not move, you'd still burn a lot of calories just keeping yourself breathing, blood pumping, nerves firing, cells growing, and everything else your body does to keep you alive. This is known as your basal metabolic rate (BMR) – the amount of energy required for you to do nothing at all. In most people, BMR accounts for up to 75 per cent of your total calorie burn. The rest is based on how much you move around.
The more you move, the more calories you need to fire your muscles. But also, the more muscle you have, the more calories you burn doing nothing. That's because muscle is 'active', whereas fat just sits there and requires no energy to maintain. Then again, the bigger you are, the more energy you need to move around. That means you need to eat more, which also means you burn more energy digesting the food you eat...and so on. Like we said, it's complicated.
Helpfully, there are tonnes of apps and calculators out there now which can help you to estimate your calorie needs. This is one of our favourites. If you want a more accurate read, then fitness trackers monitor things like heart rate, blood oxygen levels and how much distance you're covering to give a more personal picture of your daily calorie burn. Bear in mind, though, that they're still estimates.
This is why the entire concept of calorie counting exists, because calorie intake is person-specific. Calorie ‘needs’ vary from person to person. ‘Needs’ is defined roughly as the number of calories someone needs to maintain their weight. If someone is eating fewer calories than they need, they’re in what’s called a calorie deficit and will lose weight. If someone is eating more calories than they need, they’re in a calorie surplus and will gain weight.
So why count calories? Well, it is likely a person is counting calories because they’re trying to eliminate weight gain, as excess calories are normally stored in the body as fat. Alternatively, someone very active like an athlete might want to count calories to track progress of muscle growth, as excess calories can be converted by the body into muscle with exercise.
Calorie needs vary based on height, weight, age, gender and a whole host of other factors. Here are a few examples:
The bigger the body, the more calories it needs.
The higher your level of physical activity the higher your calorie needs because you need more energy to do all that running, hopping and jumping.
Muscle burns more calories than fat, so if you have a higher muscle percentage compared to someone of the same height and weight, your calorie needs will be higher.
