"In an ideal world, I would take the next 1,000 children born, randomize them into two different groups, and have half of them eat nothing but fresh fruit and vegetables for the rest of their lives"
It's too difficult to randomly assign different diets to different groups of people and have them stick with those diets for enough time to find clues about whether certain foods caused certain diseases. The problem is that it's just not practical to run these sorts of rigorous trials for most important nutrition questions. (This was how James Lind figured out that citrus fruits seemed to have an effect on scurvy.) So if there's a difference in outcomes, it's fair to say that the treatment was the cause. The idea is that because people were randomly assigned, the only real difference between the two groups (on average) was the treatment. One group gets a treatment the other gets a placebo. Researchers will take test subjects and randomly assign them to one of two groups. In many areas of medicine, the randomized controlled trial is considered the gold standard for evidence. 1) It's not practical to run randomized trials for most big nutrition questions To get a sense for how difficult it is to study nutrition, I spoke to eight health researchers over the past several months. It's also part of why researchers can't seem to agree on whether tomatoes cause or protect against cancer, or whether alcohol is good for you or not, and so on, and why journalists so badly muck up reporting on food and health. The messiness of this field is a big reason why nutrition advice can be confusing.
It's filled with contradictory studies that are each rife with flaws and limitations. Nutrition science has to be a lot more imprecise. It involves looking holistically at diets and other lifestyle behaviors, trying to tease out the risk factors that lead to illness. And fixing them isn't just a question of adding an occasional orange to someone's diet. They don't appear overnight they develop over a lifetime. Unlike scurvy, these illnesses are much harder to get a handle on. People are consuming too many calories and too much low-quality food, bringing on chronic diseases like cancer, obesity, diabetes, and heart disease. Today, our greatest health problems relate to overeating. In developed countries, these scourges are no longer an issue for most people. By the 20th century, medicine had mostly fixed scurvy and goiter and other diseases of deficiency. Unfortunately, studying nutrition is no longer that simple. Doctors could develop hypotheses and run experiments until they figured out what was missing in people's foods. Many of troubling diseases of the day, such as scurvy, pellagra, anemia, and goiter, were due to some sort of deficiency in the diet. This sort of nutritional puzzle solving was common in the pre-industrial era. The men who ate oranges and lemons eventually recovered - a striking result that pointed to vitamin C deficiency as the culprit. The sailors were divided into six groups, each given a different treatment. So Lind took 12 scurvy patients and ran the first modern clinical trial. In 1747, a Scottish doctor named James Lind wanted to figure out why so many sailors got scurvy, a disease that leaves sufferers exhausted and anemic, with bloody gums and missing teeth. There was a time, in the distant past, when studying nutrition was a relatively simple science.
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