Mushroom protein.

The numbers

Fresh gourmet mushrooms contain roughly two to three grams of protein per 100 grams. A generous portion — a quarter pound of mushrooms, which is a lot on a plate — gets you somewhere around two to four grams.

For comparison, an egg is about six grams, a cup of cooked lentils around eighteen, a chicken breast around thirty. Mushrooms are a protein contributor, not a protein source, and any article implying otherwise is doing arithmetic on dried weight without saying so.

The dried-weight trick

This is where the confusion comes from. Dried mushrooms are 20–30% protein by weight, which sounds impressive — and it is the number that gets quoted. But drying removes about 90% of the mass, so 100 grams of dried mushroom is roughly a kilogram of fresh mushroom. Nobody eats that.

Whenever you see a high protein figure for mushrooms, check whether it is dry weight. It almost always is.

Both numbers are true. Only one of them describes a dinner.

Species differences

Real but small. Broadly:

• King trumpet and shiitake are at the higher end of the fresh range.
• Oyster species sit in the middle.
• Species with very high water content — pink oyster, golden oyster — come in lower per 100g fresh.

None of these differences should drive a purchase. Buy on flavour and shelf life from the species guide.

Protein quality

Here the news is better than the quantity suggests. Mushroom protein contains all nine essential amino acids, which is unusual for a non-animal food, and the digestibility of cooked mushroom protein is reasonable. It is lower in some amino acids than an animal source, but it is not a poor-quality protein.

So the modest amount you get is useful protein. There just is not much of it.

Where mushrooms genuinely help a plant-based diet

Not by supplying protein, but by making protein-rich food taste better. The practical role of mushrooms in a vegetarian or vegan diet is umami and texture — they are what makes a lentil ragù taste like it has been cooked with meat, and what gives a bean dish the savoury depth it otherwise lacks.

That is a real nutritional contribution, just an indirect one: people eat more pulses, grains and vegetables when those things taste good. Recipes that do exactly this: mushroom ragù, duxelles, shiitake dashi.

The meat-substitute question

Mushrooms substitute for meat in texture and role, not in nutrition. A king trumpet scallop or a lion’s mane steak occupies the centre of a plate convincingly — but it is not nutritionally equivalent to what it replaced, and a meal built on it needs its protein from somewhere else. Pulses, dairy, eggs, tofu or grains alongside, and the plate is complete.

Common questions