Raven spreads a printed table across the Windowsill. Three rows, three nutrients, and a column of numbers.
"Four, four, nine," Rocket reads. "Why is fat the odd one?"
"Good question," Raven says. "What do you notice about the column heading?"
Rocket squints. "Calories per gram. So one gram of fat holds more than twice the energy of one gram of sugar."
Nova hovers over the protein row. "Look at what each one becomes," she says. "Only one row is mostly about building, not fuel."
"Protein," Rocket says. "Amino acids. Building blocks." Raven nods. "Now read the whole table."
The free textbook Concepts of Biology has a section on nutrition. This table gathers what it says about the three main nutrients.
A calorie is a unit of food energy. The table gives calories for one gram of each nutrient.
Read the fat row first. Then compare the other rows to it.
| Nutrient | Digestion breaks it into | Main use in the body | Energy in one gram |
|---|---|---|---|
| Carbohydrates | glucose | energy for cells; extra is stored as glycogen in the liver and muscles | 4 calories |
| Proteins | amino acids | building every protein in the body; none come straight from food | 4 calories |
| Fats | fatty acids | building cell membranes; stored under the skin for insulation and energy reserves | 9 calories |
The National Library of Medicine says carbohydrates are one of the main nutrients in our diet, and they help provide energy.
There are three main types of carbohydrates in food: sugars, starches and fiber. Sugars and most starches are broken down into glucose.
Fiber is the part of food that is not broken down by the body. It passes through the system instead.
Proteins are the building blocks of life, the same library says. Every cell in the human body contains protein.
You need protein in your diet to help your body repair cells and make new ones. That is growth, built from rearranged food molecules.
Fats add energy and build membranes, the outer layer of every cell you learned about in week 3.
| Statement | True or false? |
|---|---|
| One gram of protein holds the same energy as one gram of carbohydrate. | ? |
| The body gets its proteins straight from food without taking them apart. | ? |
| Fiber is broken down into glucose. | ? |
| Fat is stored under the skin for insulation and energy reserves. | ? |
Excellent data reading. Tomorrow you follow the energy: how glucose, oxygen and your breath fit together.