Nutrition is the specialty that learned what we eat can act like medicine.

In July 1991, The Lancet published a trial about preventing birth defects of the brain and spine. Women who had already had a pregnancy with one of these defects were at high risk of another. The trial asked whether vitamins taken around conception could prevent them. It gave 1,817 of these women folic acid, a mix of seven other vitamins, both, or neither. Neither the women nor their doctors knew which. Six defects occurred in the groups given folic acid. Twenty-one occurred in the groups without it. That is a 72% lower risk. The other vitamins gave no clear protection. No harm from folic acid was found. One B vitamin, taken before pregnancy, had prevented most of these defects.

Almost three years later, in April 1994, the New England Journal of Medicine published a trial about vitamins and lung cancer. People who ate plenty of fruit and vegetables, and had high levels of beta carotene and vitamin E in the blood, got less lung cancer. The trial asked whether vitamin pills could prevent it. It gave 29,133 male smokers in Finland vitamin E, beta carotene, both, or a placebo, every day for five to eight years. Vitamin E did not reduce lung cancer. Beta carotene made it more common, by 18%. Deaths were 8% higher in the men given beta carotene, mostly from lung cancer and heart disease. A vitamin pill meant to prevent lung cancer had increased it instead.

Three years later, in April 1997, the same journal published a trial about diet and blood pressure. Weight, salt and alcohol were known to affect blood pressure. The trial asked whether a whole pattern of eating could lower it. It fed 459 adults a typical American diet for three weeks. Then it gave them, at random, one of three diets for eight weeks. The researchers kept salt and body weight the same, so only the pattern of food changed. The best diet was rich in fruit, vegetables and low-fat dairy foods, with less fat. It lowered systolic blood pressure by 11.4 mm Hg more than the typical diet in people with high blood pressure. It lowered it by 3.5 mm Hg in people without high blood pressure. A way of eating had lowered blood pressure without a single pill.

These are three of the thousands of studies that shaped modern nutrition. They taught nutrition that folic acid before pregnancy could prevent most birth defects of the brain and spine, that a vitamin pill meant to prevent cancer could increase it, and that a way of eating could lower blood pressure without a pill, and each time the answer was in a paper years before it was in a textbook.

It is still happening. Recently, in January 2026, the New England Journal of Medicine published a trial of fish oil for people on dialysis. Heart disease is the leading cause of death in patients on dialysis, and few treatments prevent it. Fish oil might protect the heart in the general population, but nobody knew whether it helped these patients. The trial gave 1,228 patients on dialysis a daily dose of fish oil or a corn-oil placebo. Neither the patients nor their doctors knew which. The patients were followed for three and a half years. Serious heart and blood-vessel events happened about half as often on fish oil as on placebo. Strokes fell by 63%. Side effects were no more common than with placebo. A daily fish-oil capsule had protected the hearts of patients on dialysis. Practice follows the literature as it goes. It is a good culture. It has exactly one cost.