Why beans and rice together beat either one alone

Rice and beans on one plate is treated as the food of people who cannot afford meat. It is also, by accident of chemistry, one of the best-constructed meals in ordinary cooking — and versions of it appear on every continent that grows both. Nigeria, Brazil, India, Mexico, the Caribbean. That is not coincidence, and it is not only about cost.

Here is what is actually happening.

Protein is not one thing

Protein is built from twenty amino acids. Your body makes most of them itself, but nine it cannot make at all — those have to come from food, which is why they are called essential. If a meal is short of even one of them, your body can only use the rest in proportion to the one that ran out. A wall stops going up at the height of the shortest brick.

Meat, fish and eggs contain all nine in useful amounts. That is what people mean by "complete protein".

Most plants do not. And — this is the useful part — plants tend to fall short in a predictable pattern.

Beans and grains fail in opposite directions

Beans are relatively short of the sulphur-containing amino acids, methionine and cysteine.

Grains — rice, maize, wheat — are relatively short of lysine.

Beans are rich in lysine. Grains are rich in methionine. Each one is strong exactly where the other is weak, so eaten together the shortfall disappears and the protein becomes effectively complete: comparable in usefulness to protein from meat, from two things that grow in the ground and cost very little.

This is why beans-and-rice cultures are not nutritionally poor cultures. They worked something out.

You do not have to eat them in the same mouthful

Older nutrition advice insisted the two had to be combined in a single meal, and that idea is still repeated. It is not right.

Your body keeps a working pool of amino acids and draws on it over hours. Beans at lunch and rice at supper does the same job as both on one plate. So does bread with your beans, or garri, or plantain — plantain is a bit different but the principle of eating your beans with something holds.

Combining them in one meal is convenient and it tastes good. It is not a rule you can break by mistake.

What else beans bring

The protein argument is the interesting one, but it is not the only reason to eat them.

• Fibre, a great deal of it — which is where the fullness comes from, and why a bean lunch does not leave you flat at three o'clock the way white rice can.
• Slow energy. Beans release their sugar gradually rather than all at once, so there is no spike and no crash.
• Iron, folate, magnesium and potassium, in real amounts.
• Almost no fat. Whatever fat is in your plate of ewa came out of the oil bottle, not out of the beans.

The gas

There is no clever solution and anyone who promises one is selling something.

Beans contain sugars called oligosaccharides that the small intestine cannot break down, so they travel on to the gut bacteria, which can. Gas is what those bacteria produce. It is a sign of a working digestive system, not a fault in it.

Soaking beans before cooking and throwing away the soaking water removes some of those sugars. Beyond that, the real answer is frequency: people who eat beans regularly react far less than people who eat them occasionally, because the gut population adjusts. Eating them more often is genuinely the cure.