Nutrition cheat sheet

Macronutrients

Carbohydrates, proteins and fats supply energy and have different biological roles. Nutrient amounts and food portions are separate measurements.

Read grams per stated serving before comparing foods.

Energy calculation

Approximate energy factors are 4 kcal/g for carbohydrate, 4 kcal/g for protein and 9 kcal/g for fat.

10 g carbohydrate + 5 g protein + 2 g fat ≈ 78 kcal.

Micronutrients

Vitamins and minerals support physiological functions. They do not supply energy in the way macronutrients do.

Iron is a mineral; vitamin C is a vitamin.

Digestion and absorption

Digestion breaks food into smaller components. Absorption moves substances across the intestinal lining.

Breaking down a protein and absorbing amino acids are different stages.

Mechanical and chemical digestion

Mechanical processes break food into smaller pieces; enzymes catalyse chemical breakdown into absorbable components. Digestion and absorption are related but distinct processes.

Breaking starch into smaller carbohydrate units differs from moving nutrients across the intestinal lining.

Fibre and carbohydrate

Dietary fibre includes carbohydrate components resistant to digestion by human small-intestinal enzymes. Some are fermented by gut microbes, so fibre is not simply identical to digestible starch.

Compare the listed fibre amount separately from sugars when reading a nutrition label.

Energy units

A food kilocalorie is approximately 4.184 kilojoules. Use one unit consistently when adding values or comparing labels.

100 kcal ≈ 418.4 kJ.

Per serving and per 100 g

A per-serving value depends on the stated portion. Per-100-g values make equal-mass comparisons easier, but do not tell you the amount actually eaten.

A 40 g serving of a food containing 12 g protein per 100 g supplies 4.8 g protein.

Worked example: a label

A drink contains 8 g sugar per 100 mL. A 250 mL portion contains 8 × 2.5 = 20 g. The calculation uses the actual volume consumed, not the label’s suggested serving count.

Write the scaling factor as 250 mL ÷ 100 mL = 2.5 so the units cancel.

Common mistake: one nutrient decides quality

A nutrient quantity describes one part of a food. Overall dietary patterns, portions, context and individual requirements matter; a single label claim cannot evaluate the entire diet.

Compare like portions and read the full label rather than treating “low” or “high” as a complete assessment.

Check your understanding

How much protein is in 60 g of food labelled 10 g protein per 100 g?

6 g: 10 × 60/100.

Curriculum connections

Sources