A calorie is defined as the amount of heat needed to raise the temperature of a quantity of water by one degree. That sounds a bit strange but put more simply, a calorie is just a unit of energy. In the context of nutrition, the more calories that a certain food contains, the more energy it provides to our bodies. Likewise, the fewer calories that a certain food contains, the less energy it provides to our bodies. 

There are three major ways our body uses up energy (calories) throughout the day:

  • Through basic functions required to survive e.g. pumping blood around the body, breathing, and keeping our organs functioning. 
  • Through physical activity. This could be something as minor as fidgeting in your seat or walking around your home, or more rigorous exercise such as running or lifting weights. 
  • We also use up energy when we digest our food and absorb the nutrition from it. Some foods require more energy than others to be digested. 

There are numerous other factors that can also influence how much energy each individual requires including age, sex, environmental temperature, pregnancy, traumatic injuries, and severe illness. This is why dietitians avoid prescribing a ‘one-size-fits-all’ calorie target. Hopefully, you can see that despite what the mainstream diet culture says about calories, they are not inherently bad! 

However, the thing to know about calories is that if we end up eating or drinking more energy than our body needs, our body will store that excess energy. We store extra energy in our muscles and in our liver, and we also store extra energy in our adipose tissue (AKA body fat). There is a multitude of reasons why someone would put on weight, but calories are certainly a big part of the equation. To maintain a stable weight, the energy we put into our bodies needs to roughly be the same as the energy we use up. 

Read more: A guide to healthy portion control

So, what is a calorie deficit?

A calorie deficit is when you eat and drink fewer calories than your body uses up. Doing this for extended lengths of time results in a loss of body fat. You could also put your body into a calorie deficit by increasing energy output through increased physical activity. 

How do you know if you’re in a calorie deficit?

Is your weight increasing, decreasing, or staying the same? You can also utilise tools such as an estimated energy requirements calculator. This uses your age, sex, weight and physical activity level to provide an estimate of your calorie requirements. You can then compare your actual intake to your estimated requirements. However, in practice, this is often easier said than done. There are often underlying contributors that may influence someone’s weight and these need to be addressed for lasting (and healthy) weight loss: 

  • Physical activity
  • Stress 
  • Sleep habits
  • Medical conditions 
  • Medications 
  • Mental health
  • Social and economic factors. 

If you’re going to embark on a calorie deficit, it’s important not to compromise on overall wellbeing. Here’s how to do it healthily: 

  • Cut down on processed foods and drinks first that may contain a lot of added sugar or salt. Avoid an unnecessary reduction in nutritious foods that provide important macro and micronutrients. 
  • Liquids count! Reduce alcohol intake, as well as fizzy drinks, fruit juices, and coffees with added flavourings or syrups. 
  • Increase your protein intake.  
  • Boost your fibre intake through plant foods including fruits, vegetables, nuts and seeds, wholegrains and legumes.  
  • Get to know what healthy portion sizes actually are. A good starting point is to have ½ your plate filled with colour (i.e. fruits and veg), ¼ of your plate filled with protein, and ¼ of your plate filled with healthy carbohydrates. Add a sprinkle of healthy fats and you’ve got yourself a balanced meal that will keep you feeling satisfied. 
  • Prepare meals at home so that you can decide what ingredients are going in, as well as your portion sizes. If you do have takeaway, you don’t have to eat it all in one go, save some leftovers for the next day. 
  • Slow down. When we inhale our food mindlessly, we usually end up eating more than we need. 
  • Drink enough water. We can sometimes mistake the feelings of dehydration for hunger. Aim for at least 2L. 
  • If you’re sedentary, add some movement into your day. 

Read more: How many calories should you eat per day?


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