It is the first question anybody asks, and it is almost always asked the wrong way round.
The question is not which plants have protein in them. All of them do.
The question worth answering is how much you actually need, and what happens if you go looking for a great deal more than that.
The short answer: The official requirement is 0.8 grams per kilogram of body weight a day, which works out at roughly 56 grams for an average man and 46 for an average woman. Every whole plant food contains all twenty amino acids. Beans and lentils run 20 to 30 per cent of their calories as protein, and leafy greens are higher still. If you eat enough food and most of it is unprocessed, the protein arrives without being chased.
How Much Protein Do You Actually Need?
The recommended intake is 0.8 grams per kilogram of body weight per day for adults.
For most people that lands somewhere between 45 and 60 grams a day.
Two things about that number are worth knowing, and neither gets mentioned often.
First, it is deliberately generous. A recommended intake is not an average requirement. It is set high enough to cover almost everybody in the population, including the people at the far end of the range. Most people need less than the number they are told to aim for.
Second, a single six-ounce steak carries about 50 grams. That is more than a day’s requirement in one item, which tells you something about how the typical Western diet is arranged.
The comparison that settles it
Human beings grow faster in the first months of life than at any other point.
The food designed for exactly that stage, by nothing more clever than evolution, is breast milk.
Breast milk is under 1 per cent protein by weight, and about 5 per cent of its calories.
If 5 per cent is enough to double a human being’s size, the idea that an adult sitting at a desk needs a third of their plate to be protein deserves rather more scrutiny than it usually gets.
The Best Vegan Protein Sources, by Percentage of Calories
Grams per serving is a misleading way to compare foods, because servings are different sizes and nobody eats a hundred grams of anything on purpose.
The honest comparison is what share of a food’s calories arrive as protein, because that is what you actually get when you eat enough of it to be full.
| Food | Protein, as a share of calories |
|---|---|
| Leafy green vegetables | close to 50% |
| Soybeans and edamame | over 40% |
| Lentils | 31% |
| Beans and chickpeas | 20 to 30% |
| Brown rice | 9% |
| White potatoes | 8% |
| Bananas | 5% |
Look at the bottom of that table rather than the top.
A potato is 8 per cent protein by calories. Breast milk is 5.
A diet built on potatoes alone would clear the requirement, which is not a recommendation, only an illustration of how much room there is.
Why every plant has all the amino acids
There is a reason for this, and it is rather elegant.
Animals can eat, so an animal can obtain amino acids it cannot make. Plants cannot eat.
A plant has to synthesise all twenty amino acids itself, because there is nowhere else for them to come from.
Which means every whole plant food you eat contains every one of them. The proportions differ. The presence does not.
The foods we actually keep in the house
We do not shop for protein and never have. We shop for beans, grains and greens, and it takes care of itself.
- Red lentils: no soaking, twenty minutes, and the gentlest legume for anyone whose digestion is not used to beans yet.
- Chickpeas: the most useful can in the cupboard. Salad, spread, or baked into balls.
- Beans of any kind: two tablespoons a day is associated with a 7 to 8 per cent lower death rate across five separate populations, which is the best return on a cheap food we know of.
- Leafy greens, which nobody thinks of as protein and which are close to half protein by calories.
- Tofu and tempeh, in ordinary amounts rather than as a meat substitute at every meal.
Do You Need to Combine Vegan Protein Sources?
No. And the story of where that idea came from is worth two minutes.
Protein combining, the rule that beans must be eaten with rice at the same meal, was popularised in the 1950s and spread widely in the 1970s.
The author who popularised it later retracted it in print. It was an idea about how nutrition might work, not a finding about how it does.
Your body keeps a circulating pool of amino acids and draws on it across the day. Nothing has to arrive in the same bowl.
Eat a variety of plants across a week and the arithmetic looks after itself.
The only two ways to end up short of protein are to eat too few calories overall, or to eat mostly refined and processed food. Both of those are worth fixing for other reasons anyway. Neither is caused by leaving meat off the plate.
What Happens When You Eat Too Much Protein
This is the half of the subject that almost never gets written about, and it is the half that matters more.
Bones
Most arguments about bone health are about how much calcium a person takes in.
They are on the wrong side of the equation. For most people the useful question is not how much calcium arrives but how much leaves, and a high animal protein intake increases the calcium you lose in urine.
Be aware that this one is genuinely argued over: higher protein also raises how much calcium you absorb, and the largest review of the bone evidence found no net harm above the recommended intake. What is not argued over is that hip fracture rates track with dairy intake across countries rather than against it, and that resistance exercise does more for bone than any of it.
Kidneys
Protein breaks down into amino acids and then into urea. Both oblige the kidneys to excrete more water, which raises the fluid pressure inside them.
Over a few days that is nothing. The type matters more than the quantity: a tuna meal raises kidney filtration rate by about a third within three hours, and the same amount of protein from tofu does not.
Where this becomes a real concern is in people who have already lost some kidney function, and Harvard’s work in the Nurses’ Health Study found that among those women, the more animal protein they ate the more function they lost. In healthy kidneys the evidence is much weaker than it is usually made to sound.
The growth signal
This is the part that is worth reading slowly.
IGF-1 is a growth hormone. In infancy and childhood it does exactly what you want it to. In an adult, more of it is not better, because what it promotes is growth in tissue that has finished growing.
The main dietary determinant of circulating IGF-1 is animal protein. In women, after adjusting for calories, neither fat nor carbohydrate intake tracked with IGF-1 levels. Animal protein and milk did.
What that is associated with, across several large studies:
- In the European Prospective Investigation into Cancer and Nutrition, higher IGF-1 was associated with a 40 per cent higher breast cancer risk in women over 50.
- In the Nurses’ Health Study, high IGF-1 was associated with roughly double the risk in premenopausal women.
- In the Physicians’ Health Study, which followed 21,660 men for 28 years, the men who went on to develop prostate cancer were about twice as likely to die of it if they drank whole milk daily. That is a finding about how the disease progresses in men already diagnosed, not about the odds of getting it.
Venny here. These are observational studies, which means they show association rather than proof of cause, and I would not want anybody to read them as a diagnosis or a promise. But there are several of them, they run in the same direction, they have a plausible mechanism behind them, and four separate meta-analyses have found the same link between IGF-1 and breast cancer. That is a stronger position than most nutrition claims occupy, and it is the reason I do not treat animal protein as a neutral ingredient.
And the number that puts it together
One study followed more than six thousand people for eighteen years and sorted them by protein intake.
In the 50 to 65 age group, the higher animal protein group had four times the cancer death risk and 75 per cent higher overall mortality than the lowest group.
The effect was specific to animal protein. Higher-protein plant foods did not carry it.
The high group was eating 20 per cent of calories as protein, against a US average of about 16. Above average, then, but nowhere near bodybuilder territory. This was not a study of extremists.
The One Group Who Should Eat More Protein, Not Less
We are including this because leaving it out would be dishonest, and because it is the part of the research that most plant-based writing quietly skips.
In the same study, the pattern reversed in the oldest group.
Among people aged 66 and over, the lowest-protein group had a higher cancer death rate over the following years, not a lower one.
The researchers’ explanation is that absorption declines with age. From around 65 onward, involuntary weight loss and frailty become the larger risk, and the calculation changes.
The floor usually suggested for that group is about 10 per cent of calories from protein.
Higher-protein plant foods are the first place to go for that: beans, lentils, hemp seeds, sunflower seeds, tofu.
Which is a useful reminder that almost nothing in nutrition is one rule for all adults, and that anyone who tells you otherwise is simplifying.
Vegan Protein Sources for Athletes
Training changes the answer less than people expect.
Sports nutrition bodies put the figure at 1.4 to 2.0 grams per kilogram of body weight a day, which for a 70 kilo athlete eating 3,000 calories works out at roughly 13 to 19 per cent of calories. That is higher than we would suggest for a sedentary person and we are not going to pretend otherwise.
The point is that it still arrives on its own: beans and lentils are 20 to 30 per cent protein, soy is over 40, and an athlete eating enough to fuel the training is eating enough protein by arithmetic.
An athlete eats more food than a non-athlete, so an athlete eats more protein without doing anything deliberate about it.
What genuinely changes with training is glycogen, not protein.
Your liver holds roughly 400 to 600 calories of glycogen and spends it keeping your blood sugar steady. Your muscles hold 1,200 to 1,500 and spend it on movement. The two stores are separate and both need replenishing daily, which is a job for starchy food, not for protein.
Muscle is built in training and repaired by ordinary food. It is not assembled out of powder.
On protein powder
One fact is worth knowing before spending money on any of it.
Supplements are not regulated the way food and medicines are. Nobody has to prove that the claims on the tub are true before printing them, and nobody has to demonstrate long-term safety.
If a product were as effective as its packaging suggests, that would be a strange thing to leave untested.
What a Day of Vegan Protein Looks Like
This is roughly our own week, and none of it is arranged around the question.
- Morning: oats, a banana, a spoon of seeds. Around 10 to 12 grams before anybody has thought about it.
- Midday: a grain and a bean in a box, or a thick soup. Another 15 to 20.
- Evening: lentils or beans with something starchy and a large pile of greens. Another 20 or so.
That clears the requirement comfortably, and we have never weighed anything.
If you are hungry between meals or fading in the afternoon, the problem is far more likely to be not enough food overall than not enough protein. That is the mistake we made ourselves for months.
What to Say When Somebody Asks
The honest version is short.
Beans, lentils, grains and greens. It adds up faster than people think, and I have never had a blood test suggest otherwise.
That is usually the end of it. We spent our first year with a great deal more to say and persuaded nobody, which is a lesson we wrote about separately.
Venny is a medical doctor and a dietitian; Andy is a psychologist. This is general information rather than medical advice. If you have kidney disease, are pregnant, are recovering from surgery or illness, or are over 75, your protein needs are genuinely different from the general case and are worth discussing with your own doctor.
And, always, seek health consciously.
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