Calories, macro and micronutrients: review of the basics for a thoughtful weight loss process

When thinking about a weight loss process, the first things that usually come to most people’s mind is checking the internet for the last trendy diet or asking family or friends what has worked for them… However, one of the first steps should be to make sure to be well aware of all the basics: what are calories and macronutrients? How does the body process them? How does what we eat impact weight gain/ loss/ maintenance? Having the answers to those questions will give you a thorough knowledge of weight loss, and hence allow you to make informed choices!

Let’s start with the corner stones: the calories and macronutrients.

Calories: the energy provided by food as well as the energy that the body needs or spends is measured in kilocalories (abbr. kcal or Cal). This is the unit of energy.

Nutrients: the nutrients are provided by the diet. They are essential to the proper function and the growth of the body. There are 6 types of nutrients: protein, carbohydrates, lipids, vitamins, minerals and water.

Macronutrients: the macronutrients are the nutrients that the body needs in large amounts – in contrast to the micronutrients, that the body needs in small quantities. Protein, carbohydrates and lipids are macronutrients.

Now, let’s see how the body uses the different macronutrients.

When food arrives in the body, it is broken down into tiny pieces, from which are extracted the nutrients (macro and micronutrients) that it is made of.

Carbohydrates aka carbs are used in priority by the body to produce  energy (1g of carbs brings 4kcal). Carbs are present in food under 3 different forms: sugars, starches and fibers.

Sugars are small molecules that can be found in fruits, vegetables, milk, honey, syrups… Their small size allow them to be absorbed quickly by the body and hence be the fastest source of energy.

Starches are bigger molecules found in bread, pastas, rice, beans… They are called “complex carbs” and are slowly broken down and absorbed by the body. They are a slower but steadier source of energy.

Lastly, dietary fibers are even bigger molecules found in wholegrain food (bread, pasta, rice…), beans, seeds… They are also classified as complex, but they are so big that the body cannot digest/ absorb them. They are used to ensure a healthy transit.

Lipids are subdivided into two families: the fats, solid at room temperature (butter, cheese are rich in fats), and the oils (sunflower, olive, nuts, fish oils…), liquid at room temperature. Lipids are very slowly digested and therefore are the slowest source of energy but also the most efficient (1g of lipids brings 9kcal). They are as well used by the body to make the cells’ membrane.

Proteins are the main structural component of all the body’s cells. They are primarily used to maintain and replace tissue (such as the muscles, the skin…) and to regulate all the processes. They are the least favorite source of energy for the body – since it prefers to use mainly the carbs and the lipids. Animal sources such as beef, chicken, pork, eggs, fish, mil, cheese, and plant sources such as nuts and certain vegetables are source of protein. 1g of protein brings 4kcal.

But what’s the link with weight gain/ maintenance/ loss?

The body continuously needs energy to function. It uses it to perform all basic functions (breath, sleep, think…) but also to function during physical activity (walk, sports…). However, food is brought to the body only punctually. What happens then? The body uses the macronutrients to provide energy on the short term (simple carbs) and stores the part that it will need to use later. For instance, a part of the carbs that the body doesn’t use instantly is stored as glycogen, the rest is converted to fat. If the supply of lipids is higher than what the body needs it also stores is as fat at different places of the body (in the fat tissue, under the skin, in the abdomen…). It can be later conversed into energy. The excess intake of protein is also stored as fat.

The stores play an important role since they can be used later (during physical activity or fasting periods – while sleeping for instance) but also ensures key functions in the organism. For instance, the layer of fat under the skin provides insulation and thin layers of fat protect the vital organs.

Therefore, when the energy brought to the body through the diet matches what it needs to function, the weight is maintained.

However, when the energy brought to the body is higher that what it actually needs, it stores all the excess as fat, which hence leads to weight gain.

Do you see where we want to go? Based on the body’s function, we can deduce that weight loss happens when the energy brought to the body (calorie intake) is inferior to the energy it needs to function (energy expenditure). This is the definition of a caloric deficit. That implies that the body uses the energy he has previously stored and the one brought by the diet to sustain its energy level.

In conclusion, the key of a successful and sustainable weight loss is to manage the energy intakes. It is therefore mandatory to identify your energy needs to maintain your weight  and set up a slight caloric deficit. Providing your body with the right balance of all macronutrients, from healthy and varied food sources, will ultimately lead to weight loss.