Protein
See what protein does, roughly how much an adult needs, and how to get enough from animal and plant foods.
THE BUILDER
What protein does
Protein builds and repairs you: muscle, skin, hair, the enzymes that run digestion, some hormones, and the antibodies that fight infection. Each protein is a long chain of smaller units called amino acids. Human proteins use 20 of them, and your body links them in different orders, like letters making different words.
When you eat a lentil or an egg, your body breaks its protein back into amino acids, then uses them to build its own proteins.
Essential amino acid
One of the 9 amino acids your body can't make for itself, so it has to come from food. The other 11 it can build from what it already has. "Essential" here means essential in your diet, not more important inside the body.
Eggs, milk, fish and meat contain all 9 in useful amounts. Most single plant foods run low in one or two, which is why variety matters.
Check yourself
What makes an amino acid "essential"?
- It's found only in meat
- The body can't make it, so it must come from food
- The body needs more of it than of the others
- It has to come from a supplement
Show the answer
The body can't make it, so it must come from food
Right. Nine amino acids can't be made by the body, so food has to supply them. Plenty of plant and animal foods contain them.
Common reference for healthy adults:
about 0.8 g of protein per kg of body weight, per day
Reza weighs 70 kg
70 x 0.8 = 56About 56 g of protein a day.WHO and FAO give a very similar figure (about 0.83 g/kg). Needs rise in pregnancy and breastfeeding, older adults may benefit from a little more, and very active people need a bit more too. It's a guide, not a line you must hit to the gram.
Check yourself
Leila is a healthy adult who weighs 60 kg. Using about 0.8 g per kilogram, roughly how much protein does she need a day?
- About 8 g
- About 48 g
- About 120 g
- About 600 g
Show the answer
About 48 g
Yes. 60 × 0.8 = 48, so about 48 g a day.
Roughly how much protein is in everyday foods
| Food | Protein (about) |
|---|---|
| 1 egg | 6 g |
| 200 g plain yoghurt | 7–10 g |
| 30 g nuts (a small handful) | 5–7 g |
| 100 g cooked lentils | 9 g |
| 100 g cooked chickpeas | 8–9 g |
| 100 g cooked chicken | 25–30 g |
An egg at breakfast, a bowl of yoghurt, a lentil stew and a piece of chicken at dinner already comes to well over 50 g.
Animal and plant protein
Animal foods
Meat, fish, eggs, milk, yoghurt, cheese. Each contains all 9 essential amino acids in useful amounts. Some, like fish and eggs, are easy wins; others, like processed meat, come with baggage.
Plant foods
Lentils, beans, chickpeas, grains, nuts, seeds. Most are low in one essential amino acid, but not the same one, so eating a variety across the day covers the gaps. Soy is complete on its own. They bring fibre too.
Two half-finished puzzles make one whole
Grains tend to run short of one amino acid (lysine) that legumes have plenty of, and legumes run a little short of others that grains supply. On their own, each is a puzzle with a few pieces missing. Together, the missing pieces fill in. That's why so many traditional dishes pair them: rice with lentils (adas polo), bread with hummus, rice and beans. They don't even have to be in the same meal; across the day is enough.
Check yourself
Which of these meals pairs a grain with a legume, so the two plant proteins cover each other's gaps?
- Plain white rice
- Rice with lentils
- Bread with butter
- A fruit salad
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Rice with lentils
Right. Rice is a grain and lentils are a legume. Together, as in adas polo, they cover each other's missing amino acids.
Which protein foods to lean on
- WHO and national guidelines favour legumes, fish, poultry, eggs and nuts.
- They suggest limiting red meat and especially processed meat: sausages, cold cuts, salami, hot dogs.
- Processed meat is linked to a higher risk of bowel cancer, which is why it's the one to limit most.
- Aim for a protein food at each meal rather than a lot at one sitting: it helps you stay full.
Check yourself
Sort these protein foods by what mainstream guidelines suggest.
- A bowl of lentil soup
- Sausages
- Grilled fish
- Sliced cold cuts in a sandwich
- Two boiled eggs
- Salami
- A handful of unsalted walnuts
Show the answer
Lean on these: A bowl of lentil soup, Grilled fish, Two boiled eggs, A handful of unsalted walnuts
Limit these most: Sausages, Sliced cold cuts in a sandwich, Salami
Check yourself
Eating extra protein, on its own, builds extra muscle.
Show the answer
False
False. Muscle grows in response to training, such as lifting, carrying or climbing, with enough protein and energy to support it. Protein beyond your needs without that training is simply used for energy or stored. Very high intakes aren't recommended for people with kidney disease.
Lesson recap
- Protein builds and repairs the body. It's made of 20 amino acids, 9 of which are essential: they must come from food.
- A common reference for healthy adults is about 0.8 g per kilogram a day: about 56 g for someone weighing 70 kg.
- Most people with enough food already get enough; powders are rarely needed.
- Animal foods have all 9 essential amino acids; plant foods cover each other when you eat a variety, like rice with lentils.
- Lean on legumes, fish, poultry, eggs and nuts, and limit processed meat most.