It's all to do with a special class of amino acids, known as sulfurs, that are primarily found in protein-rich foods, such as meat, dairy, nuts and soy products.
A diet low in the amino acids increases longevity and health, at least according to animal studies—and the average American eats nearly three times the amount of sulfurs that the body actually needs.
Researchers from Penn State College of Medicine wanted to discover the impact of the amino acids on people, and so tracked the diets and biomarkers of more than 11,000 healthy participants. The average consumption of the amino acids was two-and-a-half times higher than the recommended daily allowance of just 15mg per kilo of body weight—and those eating the largest amounts also had the most biomarkers for heart disease.
Conversely, those who ate less of the amino acids had fewer biological markers for heart and also other chronic diseases.
Foods that are low in the acids include grains, vegetables and fruits. A diet for someone who weighs 132 pounds (60 kilos)—which means they could safely eat 900mg of the amino acids every day—could include a slice of bread, half an avocado, an egg, a half-cup of raw cabbage, six cherry tomatoes, two ounces of chicken breast, a cup of brown rice, three-quarters of a cup of zucchini (courgette), three tablespoons of butter, a cup of spinach, an apple, an eight-inch pizza and a tablespoon of almonds.