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What are calories?

‘Calorie’ is the term we use when we’re describing the energy we get from the food and drink we consume, as well as the energy we expend in our day to day activities. A calorie is a measurement, just like a gram or an ounce – it’s a measure of energy units (calories).

The term, calorie, is shorthand for kilocalorie, although you may also see the term kilojoules (KJ) used – this is the metric measure of a calorie and to convert a kilojoule to calories you simply divide the kilojoule figure by 4.2.

Discover our low-calorie meals, how many calories to lose weight and 10 weight loss myths busted.

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How will I see calories listed?

You’ll see the calorie content of shop-bought foods listed on the packaging as part of the nutrition panel. Look for the “energy” heading – this will show you the number of calories in 100 grams/100 millilitres of the product depending on whether the item is food or drink. This information allows you to compare the calorie contents of different brands. Many labels also show the number of calories in a portion, you can use this information to see how the food fits into your overall daily intake.

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At the nutritional information for our recipes is presented on a per serving (portion) basis – check the nutrition bar at the top of each recipe for the full nutritional information.

Why are calories important?

Our bodies need energy, even at rest, to maintain good health for growth, to keep us warm and to fuel our activity. When we eat food, it is broken down to release energy (calories), this is either used by the body straightaway or stored for later use depending on our needs at the time. The calories we eat will be used for everything from pumping blood around our body and fuelling our lungs so we can breathe, to powering us as we run for the bus if we’re late for work!

How many calories should I eat?

The number of calories each of us needs varies and depends on our unique requirements, factors that influence this include our age, gender, build including height and weight, activity levels as well as our general state of health and our genetics.

Your GP or health professional may have given you a calorie goal. If not, the following guide is relevant for an average, moderately active, healthy person. Be aware that these are estimates and not recommendations – they are average figures so some of us will need more and some, especially those who are sedentary, will need less:


  • Infant (under 12 months): 502-646kcal
  • Toddler (1-3 years): 717-1076kcal
  • School age child (5-12 years): 1362-2103kcal
  • Teenager (18 years and under): 2223-2462kcal
  • Adult (over 18 years): 2000kcal
  • Pregnancy (1st & 2nd trimester): 2000kcal
  • Pregnancy (3rd trimester): 2200kcal*
  • Senior adult (75 years +): 1840kcal

*Note: Your additional calorie needs during pregnancy will depend on your age, pre-pregnancy weight and activity levels.


  • Infant (under 12 months): 574-718kcal
  • Toddler (1-3 years): 765-1171kcal
  • School age child (5-12 years): 1482-2247kcal
  • Teenager (18 years and under): 2414-3155kcal
  • Adult (over 18 years): 2500kcal
  • Senior adult (75 years +): 2294kcal

When might I need more calories?

One of the most effective ways to find out if you’re meeting your calorie needs is to establish whether your weight is stable.

There are times when our calorie needs increase, pregnancy is a classic example, but illness can also increase demand. Conditions like chronic obstructive pulmonary disease (COPD) require a greater effort and energy expenditure to breathe, similarly those with Parkinson’s disease perform involuntary movements that expend extra energy. If you’re in bed with a fever you can expect your calorie demands to climb too, this is because your body uses up calories as it increases your body temperature.

What's the problem with calories?

Simply counting calories ignores other nutritional needs, this may be especially relevant as our energy needs change over our lifetime. For example, as we age we lose muscle mass and tend to do less physical activity. This means our calorie needs fall but our need for other nutrients, like protein, vitamins and minerals, remains unchanged or even increases. Choosing a food purely on its calorie contribution ignores the many other nutritional benefits that may or may not be on offer. Numerous studies support this and show that obtaining your calories from nutrient-dense fruit, vegetables and wholegrains decreases the risk of certain health conditions and improves overall diet quality.

As research progresses, we’re beginning to understand that the theory of ‘calories in and calories out’ is an over-simplification of the way our body uses energy. There are many other factors at play including the type of foods we eat and how we prepare them, our basal metabolic rate and even the type of bacteria that live in our gut.

Is counting calories safe for everyone?

Although some people find counting calories useful for managing their energy needs, it may not be appropriate for all of us, especially those with a history of disordered eating or an obsessive or unhealthy attitude towards food.

Pregnant and breastfeeding women as well as diabetics and those on medication should seek medical advice before considering any significant change to their calorie intake. This is also relevant for teenagers, children and the elderly, who may be at risk of missing out on crucial nutrients for growth and repair.

Last words

Calories are essential for health. Managing your calorie intake can be an effective way to quantify your energy needs but it does ignore the wider contribution food makes to our health and well-being.

Many weight loss programmes focus on calorie intake but for some this detracts from the pleasure of eating and turns it into a weighing and tallying exercise, it may also lead to the avoidance of nutritious, healthy but high-calorie foods. In the end, it's important to follow what works for you.


All health content on is provided for general information only, and should not be treated as a substitute for the medical advice of your own doctor or any other health care professional. If you have any concerns about your general health, you should contact your local health care provider. See our website terms and conditions for more information.

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