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How many calories do I really need?

Are you eating the right amount of calories?

Ever wondered why he can eat the cupboard bare and never put on weight, while you just have to look at a pizza and your trousers get tighter?

It's just not fair is it? Unfortunately nature isn't very 'woke' and doesn't give a hoot about your equal rights. Not only are bodies all different - our build, our genes, but the jobs we do, whether we have kids or dogs, or even the amount of housework we do can make a tremendous difference.

Working out your personal 'caloric need' is key to managing your weight and live a healthy life. And it isn’t quite as simple as you might think.

According to the NHS website…

“As a guide, an average man needs around 2,500kcal (10,500kJ) a day to maintain a healthy body weight. For an average woman, that figure is around 2,000kcal (8,400kJ) a day.
These values can vary depending on age, size and levels of physical activity, among other factors.”

Yippee!! 2000 calories every day. I can cook up a few feasts with that allowance.

Just one problem. If know that if I eat 2000 calories a day, I’ll be as big as a house in just a few months. Yes, I can exercise more to burn off those extra calories, but how much? And are there enough hours in the day?

It really doesn't work for me, and let's face it it can't possibly work for anyone. A man who drives to work at the office, goes for a short walk at lunchtime and slumps in front of the TV in the evening must have very different energy needs from a guy who cycles to work and spends all day on his feet in a warehouse. And my friend who is six inches taller and weighs 10kg more than me must need more calories surely? Unless, of course, I'm much more active than her. It's a minefield and nowhere near as simple as these guidelines suggest.

Let's see how we got here.

Where do calorie recommendations come from?

So why do the NHS suggest these numbers? In fact, you’ll see these numbers almost everywhere. They first came about when the US Food & Drug Administration (FDA) wanted to give advice on nutrient intake. They based the numbers on self-assessed surveys – and we all know how accurate they can be. They averaged out the numbers and then rounded them to a nice number they thought people would accept.

The idea that all women should eat around 2000 calories every day is, quite frankly, ridiculous and potentially dangerous. Did you know that consuming 100 excess calories per day could result in an additional 5kg each year. That's just an extra slice of bread, a small bag of crisps or finishing off the pasta the kids left on their plates.

Whilst today we know so much more about how our bodies work and why ‘calories in / calories out’ is not a great way to assess a healthy diet, it can be useful to get a clearer idea about your personal needs. If you rely on these generalised, and rather arbitrary numbers you may well be eating far more, or far less, than you really need.

Why everything you thought you knew about calories is wrong.

The first thing we need to know is that everything we have been taught about calories is either wrong or extremely imprecise. The amount you need, the amount shown on food labels, the amount you burn. It’s barely more accurate than guesswork.

A surplus of just 100 calories per day could result in an additional 5kg each year.

What exactly is a calorie?

When we use the term 'calorie' what we are actually talking about is 'kilocalorie', which is 1,000 calories. That's why you'll see '1200kcal per 100g' on your food label. This is just for convenience and easier reading. Kilocalories are also known as 'large calories'.

The simple way to think of it is that one kilocalorie is the amount of energy required to heat one litre of water by one degree. We ingest calories in the form of food and we obtain the energy contained in the food to live and do all the things we do. The amount of energy we use doing those activities is the amount of calories we 'burn'. Now you know why you get hot when you run up the stairs; you are literally burning the energy contained in your body.

One kilocalorie is the amount of energy required to heat one litre of water by one degree Celsius.

What about kilojoules?

Don't worry about kilojoules? That’s just a metric version of kilocalories used mostly in Europe and Australia.

Can you trust the calories on food labels?

The short answer is no. Food labelling is allowed by law to be incorrect by up to 20%. Yes, that’s right. 20%. In fact for certain vitamins it can be as much as 35%. Bet you don’t take that into account you’re deciding which yoghurt to buy!

How do we use and store calories?

All food is a warehouse full of stored chemical energy. When we eat a tasty sandwich, the food is digested, our body does wonderful things with the nutrients and expels what it doesn’t need. The energy in the food is broken down and stored in our cells. When we have just enough energy circulating to allow us to do all our basic functions like breathing, digestion, blood circulation, cell regeneration, growing etc., and to carry out our daily activities, everything is hunky dory.

Energy is a very valuable resource for our bodies and it doesn't like to waste it so when we have too much energy, our bodies cleverly store it in our fat cells. And next week, when we have too little, hey presto, our fat cells release the energy and we can carry on with our day.

If we have a very large excess the body resorts to storing the energy in fat cells around the liver and other vital organs and even in our arteries. This is not good news and can lead to life-threatening conditions.

Thinking is a real calorie consumer – around 20% of all your calories are used by your brain. Unfortunately nobody has yet proved we can think ourselves slim!

How to measure your calorie needs

There are many formulas to measure your caloric need, but I’m going to give you the one that is deemed to be most accurate. It has the catchy name of the Mifflin-St Jeor equation. This allows you to work out your Basal Metabolic Rate or BMR. This is how many calories you require just to live. Then you add on calories to take account of your lifestyle i.e. how active you are. (Unfortunately, you can’t just think harder, you have to actually move.)

Mifflin-St Jeor equation

To do this you need your weight in kgs, your height in cms and you age (in real years!). Oh, and a calculator. Here is the formula.

Females: (10 x weight [kg]) + (6.25 x height [cm]) – (5 x age [years]) – 161

Males: (10 x weight [kg]) + (6.25 x height [cm]) – (5 x age [years]) + 5

Let’s take a 50 year old woman who is 160cms and weighs 58 kgs.

  1. 10 x 58kg = 580

  2. 6.25 x 160cms = 1000

  3. 5 x 50 yrs = 250

  4. 580 + 1000 = 1580 – 250 = 1330 – 161 – 1169.

This woman needs around 1169 calories just to carry out all her essential bodily functions. If she were bed-bound she might not need much more but, obviously most of us are living relatively active lives. Just walking, talking, eating, getting up to make a cuppa – it all takes energy. That's why we need to work out TEE - see below.

Why your BMR might be different

As always there are provisos and exceptions.

  • Age: BMR usually decreases with age, which means many people may need to adjust their diet as they get older to avoid weight gain.

  • Weight: Heavier individuals have a higher BMR.

  • Height: The taller you are, the more mass you are likely to have, influencing BMR. Height compared to weight also helps determine how much fat-free vs. fat mass you have, which also affects BMR.

  • Sex: Men typically have a higher BMR than women due to higher muscle mass and bone density.

  • Genetics: You can always blame your parents. Your genes could influence your BMR. This is a factor that formulas cannot determine or account for.

  • Body composition: Muscle uses more energy than fat so the more muscle you have, the higher your BMR can be, but this only accounts for a small amount of your energy expenditure.

  • Menopause: Reduced oestrogen during and after menopause may lower metabolic rate.

What is Total Energy Expenditure (TEE)?

Our 55 year old woman needs around 1170 calories just to stay alive so we need to add on extra calories to take into account her lifestyle.

To calculate your Total Energy Expenditure (TEE) and therefore your caloric needs, you multiply your BMR by the following amount:

  • Sedentary (little or no exercise) x 1.2

  • Lightly active (light exercise 1-2 times per week) x 1.375

  • Moderately active (light to moderate exercise 4-5 times a week) x 1.55

  • Active (moderate 6-7 times or intense exercise 3-4 times per week) x 1.725

  • Very active (intense activity every day / physical job) x 1.9

The formula says if she has sedentary lifestyle, she needs around 1400 kcals per day and if she goes to the gym two or three times a week she needs nearer to 1800. That's what's known as Total Energy Expenditure (TEE).

Have you worked out your TEE? Want an easier option? You can cheat and pop over here to get your own calculation done for you!

What does this mean for you?

Knowing your personal calorie needs gives you a reasonable starting point for weight management.

As we all now know, things are not as simple as managing the number of calories you consume because there are so many variables which affect how many calories we actually absorb. That's the topic of another article but just be aware that this science is pretty sketchy.

Nevertheless knowing your approximate personal calorie needs puts you more in control and can help you understand that whilst two people sharing a delicious pizza can consume the same calories, they may have very different outcomes.


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