What are calories and how do you spend them?

What are calories and how do you spend them?

When summer arrives, many have already started an arms race against the calories: light foods, diets, training, cosmetic surgery … Perhaps a good way to defeat the “enemy” is to know him better. So, let’s explain how they are consumed and why those calories are needed.

First, a calorie is defined as “the amount of heat energy that is necessary to increase the temperature of one gram of water by one degree centigrade”. That is, it is a tiny amount of energy that is the same regardless of whether it comes from a sponge cake or a lettuce leaf.

Typically, food labels are expressed in kilocalories: so, for example, one type of bun has 223 kilocalories (ie, 223,000 calories). Or put another way: the bun has enough energy to raise the temperature of 223 liters of water by a degree centigrade (at least in theory, since the same energy of burning is not extracted than of digesting a bun).

What is energy and what is it needed for?

The concept of energy seems basic and intuitive but has several definitions. In a simple way, energy is the ability to perform a work, ie a change, for example in speed or temperature. In fact, each and every one of the functions on which life depends requires energy, from walking to dreaming, and in the process of performing them, the heat that keeps the human body at about 37 ° C is released.

All this energy is basically used for two processes: the production of new “bricks” or molecules for the building that is the human body (anabolism), and to keep the whole machinery functioning (catabolism).

How do calories burn?

When the nutrients enter the cells, a process known as cellular respiration occurs and has nothing to do with lung breathing. It consists of oxidation (degradation to smaller units) of food molecules to produce carbon dioxide, which is then exhaled in respiration. In the process, oxygen is used and ATP is produced, a molecule that serves as an “energy currency” that serves as an “energy store” and that cells can use to afford their processes.

This process occurs in mitochondria, a small “organ” that looks like a croquette inside the cells and functions as power plants. Inside there are “electron transport chains”, which in the way of a human chain pass energy and electrons from the food molecules to oxygen to one another. Thanks to these leaps, the cell gets ATP, to use it where it needs it.

Depending on the origin of the calories, whether fat, protein or sugar, cells have a different way of working. Generally, sugars are degraded by the first glycolysis and the Krebs cycle then, the fatty acids (fats) by the so-called beta-oxidation and the amino acids (proteins) through several routes that later reach the Krebs cycle.

What are they used for?

The production of new “bricks” and the maintenance of functions (anabolism and catabolism, respectively) translate into three fundamental processes. The first is the basal metabolism, which is the set of processes that keep the body alive, and whose intensity depends on age, sex, weight and height. But not all tissues consume the same energy. For example, the lean part (muscles and viscera) has a higher metabolic expenditure than the fat part. This is one of the reasons why men spend more energy in their basal metabolism since women have a higher proportion of fat in the body.

The second is the digestion of food itself. Energy is spent digesting and assimilating food, and some require more than others. For example, proteins require more energy to be digested.

The third is physical activity. Beyond sport, “every time we use our body we are burning energy”, so that the more physical activity we do, the greater the expense.

How many are in the food?

Finding out how many calories in a product requires several laboratory tests “to calculate the amount in grams of each of the macronutrients: carbohydrates (sugars), fats and proteins”. Then, these amounts are converted into kilocalories: one gram of carbohydrates provides 3.75 kilocalories, one gram of fat 9, and one gram of protein 4 kilocalories. Or put another way, the number of calories is theoretical and is obtained indirectly.

Does everyone enjoy them the same?

No. Although the routes of food use are the same, there are people who are able to extract more energy from food than they have in theory. Possible reasons include the composition of intestinal bacteria (intestinal flora).

In fact, several studies speak of patterns of slimming flora. Future research on this subject could be of interest for the treatment of overweight and obesity in people who have traditionally been “resistant” to traditional dietary treatments.

How long does it take to use them?

This can be measured by the time it takes to appear the feeling of hunger since we stopped eating, which is usually 3 or 4 hours. That is, “every 3-4 hours we can say that we have used food”. At that time, the energy will have been consumed or stored.

Simple sugars, present in soft drinks, ice cream or fruit, are absorbed very fast in the stomach. Polysaccharides, more complex sugars such as starch, take longer to take advantage of, which is why they are known as slowly absorbed sugars.

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