Calories – we are all familiar with it. We here about them all the time. You cut them; you burn them. You see them on the food product labels and on the menu at your favourite restaurants. But do you know what a calorie is?

What is a Calorie?

In simple terms, a calorie is a unit of energy. Calories are a way of keeping track of the body’s energy budget. When we put in as much energy as we lose, we strike a healthy balance. If we continually put more energy into our bodies than we can burn, the excess will gradually be stored as fat in our cells, and we will end up gaining weight. Similarly, if we burn off more energy than we replenish, we will lose weight. Calorie is the unit that allows us to measure the energy we consume and use.

A calorie is a unit of measure that determines the amount of energy it would take to raise the temperature of one kilogram of water by one degree Celsius. One thousand of these calories are called kilocalories. Calories or kilocalories are what we use to define energy from food.

Where do calories come from?

Everything we consume has a calorie count, a measure of how much energy the items store in its chemical bonds. Calories in a food comes from macronutrients – carbohydrates, proteins, and fats. Each macronutrient has a standard number of calories:

  • 1 gram of protein = 4 calories
  • 1 gram of carbohydrate = 4 calories
  • 1 gram of fat = 9 calories

How is energy from food used in the body?

Our body uses this energy from food to carry out various functions. The amount of energy used by the body in carrying out all of its activities is called the metabolic rate. When we consume food the energy from it is released during digestion and stored in other molecules

that can be broken down to provide energy when the body needs it. It’s used in 3 ways: about 8% enables digestion, about 32% fuels physical activity and the biggest chunk, around 60% supports the basic functions of our organs and tissues. This 60% of energy use corresponds to our resting metabolic rate – a number of calories you would need to survive if you weren’t eating or moving around (link).

Generally, the recommended daily calorie intake is 2000 calories per day for women and 2,500 for men (link). These estimates are based on factors like average weight, levels of physical activity, muscle mass and age. If you are very active your body could use more than the recommended daily calories intake. Pregnancy requires slightly more calories than usual and elderly people typically have slower metabolic rate so less is needed.

Now, before you start counting calories it is important to take few things into account. The calorie counts on nutritional information labels measure how much energy the food contains and not how much energy you can get out of it. Fibre-rich foods like carrot, broccoli and whole wheat for instance takes more energy to digest, so you would actually extract less energy from a 100 calories serving of carrot than a 100 calories serving of potato chips. Also, there are two categories of calories when referring to nutrition:

  • Empty calories: that contain few to no nutrients (carbohydrates, protein, fat, vitamins and minerals). Ultra-processed foods like candy, chips, white bread, cookies and soda tend to be high in refined carbohydrates and/or saturated fats are good examples of empty calories. These foods do provide energy but far less nutritional value. Eating too many of these foods could leave you overweight and malnourished.
  •  Nutrient-dense calories: contain energy, plus fibre, vitamins and minerals that support maintenance of multiple systems of the body. Fruits, vegetables, whole grains, lean meats, dairy, seeds, and legumes are foods that provide nutrient-dense calories. These foods promote optimal health.

Lastly, it is also important to appreciate that different people might not get the same number of calories even with the exact same food. Variations in things like enzyme levels, gut bacteria, and even intestinal length, means every individual’s ability to extract energy from food is a little different. So, calorie is a useful energy measure, but to work out exactly how many of them each of us requires we need to factor in things like exercise, food type, and our body’s ability to process energy.

More important than counting calories is to eat a healthy and well-balanced diet that you can sustain long-term. Equally important is to be physically active and to balance the calories consumed with the energy used each day.

By Dr. Tanvi Shinde, PhD