Are you counting your calories and limiting your energy intake from food and drink for a slimmer you? Or maybe just talking about calories in general terms as many of us do. Then you might like to know what you are talking about or counting so I thought a brief explanation would be useful. It is actually a little bit complicated as it has evolved over time.
Let’s start from scratch
It is self evident that food and drink provide the energy we need to stay alive and active. However, the standard measure of energy in the International System of Units or SI system is joules (although a derived unit from the seven defined SI base units) and not calories. The joule is named after James Prescott Joule. It is clearly defined as a unit of work or energy equal to the work done by a force of one newton acting through a distance of one meter.
So why do many of us still think in calories (or Calories as you will see below)?
It might be historical as the term calorie has been in use since the early 19th century when Nicholas Clément-Desormes in 1825 defined it as the amount of heat required to raise the temperature of a kilogram of water from 0°C to 1°C. However, scientists were not happy with this definition so changed it to the amount of heat required to raise the temperature of a gram (not kilogram) of water from 0°C to 1°C. So the initial calorie (now often expressed as the capitalised Calorie) is now equal to 1,000 new calories or 1 kilocalorie (abbreviated kcal). The concept entered the food world when W.O. Atwater used it in 1887 to describe food energy.
After that the Calorie became the preferred unit of potential energy in nutrition science and dietetics for a while.
But it didn’t stop there as in the early 20th century the calorie started to be defined in terms of joules. Thus the Committee on Nomenclature of the International Union of Nutritional Sciences changed the definition of the “small calorie” to the amount of heat required to raise the temperature of 1 g of water from 14.5 to 15.5°C, a 1% change from the previous definition. And the Calorie followed. This way a Calorie could be defined as equal to 4.184 kJ.
To avoid further confusion most countries have officially adopted the joule as a measure of food energy, expressed as kilojoule (kJ) for convenience on food labels. However, a few countries (and maybe you and me) stick to Calories and the final say goes to the current US Dietary Reference Intakes that define 1 kcal (or Calorie) as 4.186 kJ, again slightly different to previous definitions.
So after all that feel free to think in Calories as long as you know that you can multiply your Calories by 4.2 to get to kJ or divide your kJ by 4.2 to get to Calories. Or for the lazy you can even use a simple 4 for the calculations to get to a close enough approximation.
Energy intake in practice
With that out of the way let’s get back to practical considerations in looking at energy intake. It is assumed that an average adult needs about 8,700 kJ (2,100 kcal) a day to maintain a healthy weight. But it varies quite a bit – some people need more and others less. It depends on age, gender, height and weight as well as how active we are. If consuming more energy than we use, the extra energy is stored as fat. To lose excess fat means you need to take in less energy (fewer kJ) or use more through exercise, or preferably both.
The energy is provided by the protein, carbohydrate and fat in the foods we eat and in drinks. These nutrients deliver energy in varying amounts. Fat is the most concentrated source of energy (37.7kJ/g), followed by protein and carbohydrate (both at 16.7kJ/g). Alcohol also provides energy (29.3kJ/g) while also increasing the amount of vitamins and minerals that the body requires.
Although every person’s daily energy intake is highly variable, based on their personal goals and needs, the typical daily energy intake of 8,700kJ is often split with 1,800kJ for breakfast, 450kJ for a morning snack, 2,500kJ for lunch, 450kJ for an afternoon snack and 3,500kJ for dinner.
Spending the daily energy intake
Preferably we should balance our energy intake with our energy expenditure. Metabolism is the process by which the body changes food and drink into energy. During this process, nutrients in food and drinks mix with oxygen to liberate the energy the body needs. Digesting, absorbing, moving and storing food burn energy. About 10% of daily energy consumed are used for digesting food and taking in nutrients. This can’t be changed much.
Then we have the basal metabolism. Even at rest, a body needs energy for all it does. This includes breathing, sending blood through the body, maintaining body temperature, keeping hormone levels even, and growing and repairing cells. The amount of energy a body at rest uses to do these things is known as basal metabolic rate. Our basal metabolism makes up about 60-70% of the energy we burn and again can’t be changed much although it is partly related to muscle mass. That is:
- people who are larger or have more muscle burn more energy, even at rest;
- men usually have less body fat and more muscle than do women of the same age and weight and thus burn more energy;
- with aging, people tend to lose muscle and more of the body’s weight consists of fat slowing energy burning.
Adding all this up we have already spent 6,000 to 7,000kJ and we haven’t accounted for all of our incidental activities that can be changed a lot. These include things such as housework, walking around the house, gardening, walking to a shop, hanging out the washing or even fidgeting. These activities are collectively called non-exercise activity thermogenesis and accounts for about 500 to 3,000 kJ used daily.
We are now hopefully in energy balance.
But how well do we stick to the average energy intake of 8,700kJ? Not so sure about that!
We have the morning break and go for a coffee and order a large flat white (this is Australia) and an apple danish without considering the energy content. The apple danish will actually contribute 1,100kJ and the coffee 670kJ, well above our indicated average of 450kJ for the morning snack.
We might feel a bit tired in the afternoon and go for another coffee. This time we pick a cappuccino (only Italians limit a cappuccino to before 11am) and a blueberry muffin. Now we have added another 1,600kJ to our energy intake. On second thought we could replace the large blueberry muffin with a mini muffin to limit the energy intake to 850kJ for the afternoon snack, still above the suggested 450kJ.
After a long day we sit down for dinner. As we had a really successful day we share a bottle of red wine with our partner. If you share it equally you’ve had 1,260kJ even before you start to consider the energy content of the first bite of food. That’s the equivalent of a cup of chunky vegetable soup, a slice of wholemeal bread with a teaspoon of butter, and two slices of prosciutto. You skip the wine and instead go for a 375mL bottle of 4.5% strength beer. That way you limit the extra energy intake to 400kJ as long as you stick to only one beer.
We could go on with many other examples. Adding a chocolate croissant to our normal breakfast would contribute about 1,000kJ. A gin and tonic to relax in the evening provide 715kJ. A medium sized glass of a cola soft drink would add a further 750kJ. If you want to get more bad news you can search for the energy content of many other food and drinks on the excellent fatsecret Australia website.
Spending the extra energy
But even with the extra energy intake all is not lost as we can become more physically active. This is the form of energy expenditure that we have real control over. This is the energy used by physical movement and it varies the most depending on how much energy you use each day. Physical activity includes planned exercise like walking the dog, going for a run or playing sport.
Just standing for an hour working at your desk and your muscles have spent 600kJ to keep you upright. A walk with the dog for an hour would consume 1,000kJ or if you are power walking it could be close to 2,000kJ per hour. During strenuous or vigorous physical activity, our muscles may burn through as much as 3,000kJ per hour. If you are the one mowing the lawn (if you have one) you would spend 1,500kJ for an hour’s work. Fast step dancing, shovelling snow (not needed here in Sydney), using an exercise machine, or playing basketball all four half an hour and you have spent close to 1,000kJ.
As you can see there are many ways to spend excess energy intake so a little indulgence now and then wouldn’t go astray while still keeping your energy intake and expenditure in balance. Keep your brain working by reading a captivating book for an hour and you have spent 600kJ.
A matter of balance
Of course there is much more to consider when consuming food and drink. Empty calories (see there I can’t get myself to stick to kJ) are the worst, that is food and drink which mainly provide energy and few nutrients. Candy, pastries, chips, bacon, and sugar-sweetened beverages are less nutrient dense. These foods contain added sugar, solid fats, and refined starch, and they provide few essential nutrients.
On the other hand there should also be pleasure in eating. Food can nourish our body in a lot of different ways. In fact, experts often indicate that eating for pleasure not only fuels the body but the mind as well. When people feel satiated, they are less likely to feel deprived or restricted.
So we are back to the balanced diet concept with the last word going to the Verywell Fit website. The best you can do is to find a balance between enjoying food and life, feeling good, and enjoying the best health we can.
What more can we ask for?