Free mini-lesson About 4 minutes, plus a 4-question quiz
Understanding Protein: What It Does and Common Food Sources
Protein helps build, repair and maintain your body, and it comes from many everyday foods, both plant and animal. This short beginner lesson explains the basics, then a quick quiz checks what you've learned.
What is protein?
Protein is a macronutrient: one of the three nutrients we need in larger amounts, alongside carbohydrate and fat. It provides about 4 kcal of energy per gram, the same as carbohydrate.
Every protein is a chain of smaller units called amino acids. When you eat protein, digestion breaks it down into amino acids, and your body then uses them to build the proteins it needs.
Essential amino acids
For adults, 9 amino acids are essential. The body cannot make enough of them, so they must come from food. The body can make the others itself.
What protein does in the body
- Builds and repairs: protein is needed for growth, repair and maintenance of the body.
- Forms structure: it is part of every cell, including muscle, skin, hair and bone.
- Keeps processes running: enzymes (which help chemical reactions happen), some hormones and parts of the immune system are proteins.
- Provides energy: protein can also be used for energy, although that isn't its main job.
Common food sources of protein
Protein isn't only found in meat. Many everyday foods contain it, though the amount varies a lot from food to food.
| From animals | From plants |
|---|---|
| Meat and poultry | Beans, lentils, chickpeas and peas |
| Fish and seafood | Tofu, tempeh and other soya foods |
| Eggs | Nuts, peanuts and seeds |
| Milk, yoghurt and cheese | Grains such as wheat, oats and rice |
Protein foods bring other nutrients with them too, such as iron, fibre (in plant foods) or calcium (in dairy). Some processed meats can also be high in salt or saturated fat.
UK guidance (NHS Eatwell Guide)
The UK's Eatwell Guide groups beans, pulses, fish, eggs, meat and other proteins together. It suggests eating more beans and pulses, two portions of fish a week (one of them oily), and less red and processed meat.
This is UK guidance. Other countries publish their own healthy eating advice.
Why variety helps
Individual plant foods often contain less of one or more essential amino acids than animal foods do. Eating a variety of plant proteins across the day, such as beans, grains, nuts and seeds, helps provide all of them. You don't need to combine them at the same meal.
How much protein someone needs depends on things like age, body size, life stage and activity. This lesson doesn't set personal targets. Most people can get enough from a varied diet of everyday foods. For individual advice, speak to a doctor or registered dietitian.
Key points
- Protein is a macronutrient made of amino acids, providing about 4 kcal per gram.
- It helps build, repair and maintain the body, and forms enzymes, some hormones and parts of the immune system.
- Both animal and plant foods provide protein.
- A variety of plant proteins across the day provides all the essential amino acids.
Check your understanding
4 quick questions. Choose an answer to see the explanation straight away.
1. Which of these is one of protein's main jobs in the body?
2. Proteins are made from smaller building blocks called…
3. Which list contains only plant sources of protein?
4. Someone eats only plant foods. What helps them get all the essential amino acids?