National Geographic : 2017 Jun
Ancel Keys and the McGovern committee had been wrong about dietary fats because they had assumed that all fats were the same. They hadn’t accounted for the different types of fats, specifically, saturated fats, unsaturated fats, cis fats, and—most important—trans fats. In the years that followed, Americans would pay a high price for their ignorance. To undersTand where Keys and McGovern had gone wrong, we’re going to need a brief refresher course in high school chemistry for the few people who might have forgotten it. Just kidding. Everyone’s forgotten it. But to understand what words like “sat- urated” and “unsaturated” and “trans fats” mean, we need to understand some of the chemistry behind them. It’s really not that hard. So hang in there. Fats are composed of three types of atoms: carbon (C), hydrogen (H), and oxygen (O). Carbon atoms, the backbone of fats, have four binding sites (areas where one atom attaches to another). If all four sites are bound, then the carbon atom’s binding sites are said to be saturated. The fat shown to the right is a saturated fat. Foods rich in saturated fats include butter, lard, coconut oil, palm oil, mayonnaise, and fish oils; dairy products like cream, cheeses, milk, sour cream, and ice cream; and processed meats like bacon, sausage, salami, steak, ham, ground beef, and luncheon meats. Sometimes, however, a carbon atom will share two binding sites with another carbon atom (such as in the carbon atoms pictured in bold in the example to the right). Because these carbon atoms can still share one of their binding sites with another atom (like a hydrogen atom), the fat is said to be unsaturated. The fat shown here is an unsaturated fat. Foods rich in unsaturated fats include salmon and other fatty fish, almonds, walnuts, pistachios, avocados, olives and olive oil, margarine, natural peanut butter, and pumpkin, sunflower, flax, and chia seeds. By the early 1980s, when the relative quantities of these two different types of fats were clear, several studies had shown that saturated fats increased the risk of heart disease. These studies gave birth to the notion that unsaturated fats were good and saturated fats were evil. In response, two groups made it their mission to eliminate saturated fats from the American diet. It wasn’t until much later that Americans realized what they’d done wrong. In 1984 the Center for Science in the Public Interest (CSPI) launched its “saturated fat attack,” targeting companies that fried or baked foods using animal fats and tropical oils rich in saturated fats. A year later Phil Sokolof launched the National Heart Savers Association (NHSA), spending $15 million to force companies to eliminate saturated fats from fast foods. In 1988 he sent thousands of letters to companies urging them to stop using saturated fats. When his letters were ignored, he took out full-page ads in newspapers. “Who is poi- soning America?” his advertisements blared. “Food processors are by using saturated fats!” The text that followed was no less subtle. “ We have contacted all of the major food processors beseeching them to stop using these potentially dangerous ingredients ... Our pleas have gone unanswered. Obviously these compa- nies have more pressing priorities than your health. SOMETHING MUST BE DONE ... We implore you. Do not buy products containing coconut or palm oil. YOUR LIFE MAY BE AT STAKE.” CSPI’s “saturated fat attack” and NHSA’s letter- writing campaign targeted every major company Unsaturated fat H-C–C–C–C–C–C=C–C–C=C–C–C–C–C–C–C–C-COOH HHHHHHHHHHHHHHHHH HHHHHHHHHHHHHHHHH Saturated fat H-C–C–C–C–C–C–C–C–C–C–C–C–C–C–C–C–C-COOH HHHHHHHHHHHHHHHHH HHHHHHHHHHHHHHHHH 144 national geographic • June 2017 that prepared foods using shortenings or oils high in saturated fats. By the late 1980s virtually every major cookbook and reputable dietitian promoted diets low in saturated fats, efforts that were supported by the FDA, the World Health Organization, the USDA, and the National Institutes of Health. The solution to the prob- lem of heart disease appeared to be obvious: Replace saturated fats with unsaturated fats. Americans were told to eat margarine instead of butter. Unfortunately, margarine contained a type of fat (trans fats) that was far more dangerous than anyone could have imagined. To undersTand whaT trans fats are, let’s go back to our description of an unsaturated fat. In the diagram on the next page, look at the carbon atoms in bold. The hydrogen atoms connected to those two carbon atoms are both on the same side. This is called being in the “cis configuration.” Cis, in Latin, means “on this side of.” When both hydrogen atoms are on the same side, they repel each other, causing a bend in the molecule.