The Three Groups of Energy-Giving Nutrients
Before a Liga MX match, a player eats pasta or rice, not fatty carnitas. And at your house, a tortilla leaves you feeling "full" in a different way than a handful of walnuts does. What do foods have that gives us energy, and why don't they all do it the same way? By the end of the page, you will answer the player's question.
Foods are mixtures of substances
A food is not a single substance: it is a mixture of water, nutrients, and other substances. Nutrients are the substances your body takes from food to build its tissues, to function, and to get energy.
Three groups provide most of the chemical energy you use when you walk, study, or play soccer:
Classify the following foods from Mexican cuisine according to the nutrient group they mainly provide (carbohydrates, proteins, or lipids): corn tortilla, cooked beans,…
Classify the following foods from Mexican cuisine according to the nutrient group they mainly provide (carbohydrates, proteins, or lipids): corn tortilla, cooked beans, avocado, chicken breast, nuts, and rice. Briefly justify each choice.
Carbohydrates: the quick-use fuel
Carbohydrates (sugars and starches) are made of carbon, hydrogen, and oxygen. They are found in corn tortillas, rice, bread, potatoes, oatmeal, fruit, and sugar.
The starch in a tortilla is a long chain of glucose molecules. When it is digested, the body breaks it down into glucose, which travels through the blood and is used in cells to release energy. That is why carbohydrates are the fastest fuel to use, the favorite of the brain and the muscles.
They provide about 4 kcal per gram.
Proteins: building and repair
Proteins are chains of molecules called amino acids. Besides C, H, and O, they contain nitrogen. They are found in chicken, eggs, fish, milk, beans, and lentils.
Their main function is not to give energy but to build and repair: muscles, skin, hair, enzymes, and defenses. But if other nutrients are lacking, the body can also use them as a source of energy: they provide about 4 kcal per gram.
A traditional combination in Mexican cooking, corn with beans, provides amino acids that complement each other. It is knowledge from the peoples of Mesoamerica that modern nutrition science confirms.
Lipids: the concentrated reserve
Lipids (fats and oils) are found in avocados, walnuts, peanuts, oil, butter, and fatty meat. They do not dissolve in water.
They provide about 9 kcal per gram, more than double the other two groups. In addition, the body stores them in adipose tissue as an energy reserve, they protect organs, and they help absorb some vitamins.
This explains why a food with a lot of lipids is energy-dense in a small volume: an avocado provides much more per 100 g than a cucumber, which is almost all water and fiber, substances that give almost no energy.
Both the avocado and the cucumber are plant-based foods, but their energy content is very different. Explain, in terms of which nutrient each one contains more of…
Both the avocado and the cucumber are plant-based foods, but their energy content is very different. Explain, in terms of which nutrient each one contains more of (lipids or water and fiber), why the avocado provides much more energy per 100 g.
Carbohydrates provide about $4 \text{ kcal}$ per gram, proteins about $4 \text{ kcal}$ per gram, and lipids about $9 \text{ kcal}$ per gram. Order these 10 g portions of…
Carbohydrates provide about $4 \text{ kcal}$ per gram, proteins about $4 \text{ kcal}$ per gram, and lipids about $9 \text{ kcal}$ per gram. Order these 10 g portions of pure nutrient from lowest to highest energy content: 10 g of fat from butter, 10 g of protein from tuna, and 10 g of sugar (carbohydrate). Show the calculation for each one.
How the body gets energy
The energy in food is chemical energy, stored in the bonds of its molecules. The general process is:
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Digestion: the body breaks large molecules into small ones (starch → glucose; proteins → amino acids; fats → fatty acids).
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Transport: the blood carries them to the cells.
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Cellular respiration: in the cells, glucose reacts with the oxygen you breathe and releases energy:
It is a chemical reaction, similar to combustion but slow and controlled: the energy is released little by little (part of it as body heat) and not all at once like a flame.
Energy is measured in kilocalories (kcal) or in kilojoules (kJ), with $1\ \text{kcal} = 4.184\ \text{kJ}$. On food labels, the kilocalorie appears as "Calories."
Before a race, many athletes eat pasta or rice for dinner instead of a high-fat meal. Using what you know about nutrient groups and their function in the body, explain…
Before a race, many athletes eat pasta or rice for dinner instead of a high-fat meal. Using what you know about nutrient groups and their function in the body, explain two chemical and biological reasons why this choice makes sense.
Vitamins, minerals, and water
Besides the three energy-giving groups, the body needs other substances that do not provide energy but are indispensable:
| Substance | What it is for | If it is lacking | Examples |
|---|---|---|---|
| Vitamins | Regulate reactions in the body and defenses | For example, lack of vitamin C: weakness and bleeding gums | Orange, guava, chile, tomato |
| Minerals | Bones, blood, nerves | Iron: anemia; calcium: fragile bones; iodine: thyroid problems | Nixtamalized corn tortilla (calcium), beans (iron), milk |
| Plain drinking water | Dissolves and transports substances, regulates temperature | Dehydration, dizziness, tiredness | Purified or boiled water |
The fact that they don't give energy does not mean they don't matter: without them, the reactions that release the energy from the other nutrients don't work well. And plain water is a better choice than soft drinks, which provide sugar without other nutrients.
Go back to the beginning: the player chooses pasta or rice because their carbohydrates quickly turn into glucose for the muscles, while a greasy meal is digested slowly and feels heavy.