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How Many Calories Should You Eat Per Day?

Many people are familiar with calories, the measurement of energy in food. Calorie counting is often used in diets for weight loss, but how do we know how many calories each individual needs in a day? There are a lot of diets out there recommending the same number of calories for every single person, but everybody is unique in the same way our calorie requirements are unique to each individual.

Understanding what determines our individual energy requirements and how you can calculate these can be very helpful for reaching your goals, whether it is to maintain your weight, lose weight or gain muscle mass.

What are calories and kilojoules?

Nearly everything we eat and drink provides our body with energy. The energy is used to fuel the body for its daily activities and processes.

Calories are a measurement of potential energy contained in food. A single calorie is the amount of energy, or heat, required to heat a gram of water by 1 degree Celsius. The calorie system for measuring the energy in food was first put together in the early 1990s by Edward atwater.

In Australia, kilojoules replaced calories around 40 years ago. A kilojoule is a unit of measure of energy, in the same way that kilometres measure distance. Kilojoules are the metric term for calories, however, calories are still popularly used by many in the general population. On food packaging in Australia, the kilojoule content of foods must be listed on the packaging, while calorie content is often listed but is not mandatory. One calorie is approximately equal to 4 kilojoules.

What is a caloric deficit?

Different foods and drinks contain different amounts of energy, or calories depending on the ingredients, serving sizes and how the food is prepared. When we consume food and drink, they provide energy for the body to use for daily activities and keeping internal systems functioning. Every person’s daily energy requirements are unique and are based on their age, body size, gender, genetics, daily movement/activity levels and exercise. If we eat more calories than our body uses, the spare energy is stored away in muscle, liver and as body fat. Over time, consistently consuming excess energy results in weight gain. On the other hand, a caloric deficit occurs when a person consumes less energy than their daily energy requirements. Over time, a consistent caloric deficit results in weight loss as the body needs to convert stored energy to support the body’s daily needs.

How to calculate your requirements

There are multiple equations that exist to estimate daily calorie requirements, as well as plenty of online calculators, however calculating calorie requirements is always an estimate and should be interpreted with a degree of awareness.

The below is an energy requirements equation known as The Mifflin Equation, which provides an estimate of a person’s energy requirements based on their estimated BMR (basal metabolic rate), age, height, weight and activity levels. It’s important to remember that this provides only an estimate. An individuals energy requirements will vary each day depending on changes to activity levels.

Step 1: Calculate BMR (basal metabolic rate)

  • Males:
    Bmr (metric) = (10 × weight in kg) + (6.25 × height in cm) – (5 × age in years) + 5
  • Females:
    Bmr (metric) = (10 × weight in kg) + (6.25 × height in cm) – (5 × age in years) – 161

Step 2: Calculate daily energy requirements by multiplying BMR from the equation above with one of the following activity levels:

  • 1.2: if sedentary, little or no exercise and sedentary job
  • 1.375: if lightly active, light exercise, or sports 1-3 days a week
  • 1.55: if moderately active, moderate exercise, or sports 3-5 days a week
  • 1.725: if very active, hard exercise, or sports 6-7 days a week
  • 1.9: if extremely active, hard daily exercise of sports and physical job

Note: The equation above provides an estimate only, and is a similar equation to what is often used in free online calculators. To understand how to interpret this and put nutrition plans into action, as well as achieve your goals safely, seeking advice from an accredited dietitian is recommended.

How many calories do I need if my goal is to lose weight, gain weight or maintain weight?

Step 1 and 2 of the equation above outline how to calculate your daily calorie requirements to maintain your current body weight. If you were to consume that amount of calories every day on average, your body weight would stay roughly the same.

Many people look at calories for the purpose of understanding their food intake for weight loss. A caloric deficit is required for weight loss, where less energy is consumed than is expended through daily activity and exercise.

Between 250g – 500g is considered a healthy and safe amount of weight loss per week, which will depend on the individual and what is realistic and achievable for their body without causing negative side effects. Creating a caloric deficit to achieve this weight loss goal can be done by subtracting 250 – 500 calories from daily maintenance requirements.

Simply take your daily energy requirement, and subtract 250 – 500 calories (1050kj – 2100kj) for a moderate weight loss of 0.25 – 0.5kg / week.

Similarly, to gain weight, a moderate amount of weight gain of 250 – 500g per week can be achieved by creating a calorie surplus. Simply take your daily energy requirement, and add 250 – 500 calories (1050kj – 2100kj) for moderate weight gain of 0.25 – 0.5kg / week.

Are there any downsides to calorie counting?

Yes, calorie counting is a logical way of understanding your individual energy requirements, however, calorie counting has frequently been seen to lead to obsessive behaviours around food. Individual requirements change daily based on energy output and other factors such as illness, so calorie counting should always be used as an estimate and in consultation with an accredited dietitian who can support you in achieving your goals in a healthy and sustainable way.

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