The science of weight loss: How we gain and lose weight

Almost everything in the food we eat has some impact on our health. Food sustains the normal function of your body, promotes growth or creates energy

Food is made up of a combination of the three macronutrients - carbohydrates, proteins and fats – which are needed in large amounts every day to keep your body healthy. You use each macronutrient in a different way.

Almost all food contains some carbohydrate, protein and fat, but in different proportions. For example, pasta is highest in carbohydrates so we consider pasta to be a carbohydrate food.

This section of the website explains the role of these three macronutrients and how we derive energy from them for digestion, growth and normal everyday functioning. When we eat too many macronutrients and do not use all the energy they produce, we store the excess as body fat.

A word about energy

The word ‘energy’ can mean different things to different people. We know how it feels to be ‘low on energy’ or to have ‘lots of energy’, but this is usually related to our physical and mental health. In nutrition, the word ‘energy’ is measured by the number of kilo- joules (or calories) in a food type. The more kilojoules, the more fuel (or energy) is available to run the body. Unfortunately, most of us eat more kilojoules than our body needs and the unused ones end up as stored fat.

Each macronutrient offers a different amount of energy:

• 1 gram of carbohydrates = 16 kJ (4 Calories)
• 1 gram of protein = 17 kJ (4 Calories)
• 1 gram of fat = 39 kJ (9 Calories)

How do the following impact our bodies and our weight?