Low-fat diets for decades have been touted as the solution to leading a healthy, long life. At some point, you’ve no doubt had someone extol the virtues of cutting fat out of your diet; you’ve probably also been told that all saturated fat is dangerous, as it causes heart disease. In the book, The Big Fat Surprise: Why Butter, Meat and Cheese Belong in a Healthy by Nina Teicholz, she tackles these questions.
This sort of thinking started in the 1950s, largely because of the efforts of a nutritionist named Ancel Keys. Despite the widespread acceptance of fat as our nutritional enemy since then, recent studies have shown that fat just isn’t as evil as we’ve come to believe.
To best understand the two main types of fats and how they affect your body, it’s important to grasp the chemical composition of each. In general, fat is made up of chains of carbon atoms, surrounded by hydrogen atoms. These carbon and hydrogen atoms are connected by bonds. There are two kinds of bonds: single and double.
Imagine a bond as a sort of handshake between a carbon and hydrogen atom. In a single bond, the atoms are connected by one hand each. In a double bond, the atoms hold both hands together.
If a chain of fat is connected by single bonds, it’s called a saturated fat. If the chain has at least one double bond, it’s called an unsaturated fat. Animal fats, such as butter, cheese or meat, are saturated fats. Olive oil or other vegetable oils are unsaturated fats. Importantly, the differences in the bonds of saturated and unsaturated fat explain some of their characteristics.
A saturated fat is called thus as it is saturated with hydrogen; its single bond can’t grab any other molecules to add to its chain, which makes it stable. These single bonds pack molecules together densely, which is why saturated fats – like butter – are solid at room temperature.
Unsaturated fats, with their double bonds, are essentially “looser” as the extra “hand” can grab other molecules, such as oxygen in the air. When unsaturated fats are exposed to air, they oxidize, or go rancid, quickly. These type of fats are usually liquid – like cooking oil – at room temperature.
Saturated and unsaturated fats are the two most important kinds of fat. Understanding how they are chemically composed is important in understanding how they affect your body.
Your local supermarket probably carries a range of milk with different fat contents: nonfat, skim, 2 percent and so on. Why do we make these distinctions? A nutritionist named Ancel Keys played an early role in the debate over dietary fat. One of his prime fields of study was food and starvation. During World War II, he developed what was known as the “K-ration,” a ready-to-eat meal for soldiers of hard biscuits and sausages, among other items.
Keys also had a passion for physiology, and began researching heart disease. He combined this with his work in nutrition, and discovered an interesting link: that a person’s fat intake played a crucial role in the development of heart disease.
The reason for this is straightforward: the fat you eat affects your level of cholesterol. If you have high levels of cholesterol, that can increase your chance of getting heart disease.
Though having high levels of cholesterol can be dangerous, our bodies regardless do need a certain amount of cholesterol to function. Cholesterol is present in the membrane of every cell in your body, helping to control what goes in and out of your cells.
However, cholesterol is also a primary element in the plaque that can build in your arteries. Plaque thickens the walls of your arteries, restricting blood flow, and thus increasing your blood pressure. This eventually can lead to serious heart disease.
In 1958, Keys conducted an experiment in which he fed participants meals with either saturated or unsaturated fats, and then measured the participants’ cholesterol levels. He found that the cholesterol levels of participants who ate saturated fats went up, while the cholesterol levels of those on an unsaturated fat diet went down.
He thus concluded that saturated fats were unhealthy while unsaturated fats in contrast were healthy, as they lowered cholesterol levels and in turn, the risk of heart disease. Keys’s hypothesis – that saturated fats cause heart disease – quickly spread through society as he worked tirelessly to convince influential institutions to embrace his ideas.
The first major supporter was the American Heart Association (AHA). The AHA was founded with the goal of gaining more understanding about heart disease, and it quickly became the leading source of information on the topic. In 1961, Keys became part of the AHA’s nutrition committee.
Shortly after Keys joined the organization and largely because of his influence, the AHA released a report linking fat and heart disease. Just two weeks after that report was published, the weekly magazine Time published a cover story on Keys and his work. The magazine’s reach (at the time it was one of the most influential news magazines in the world) generated serious publicity for Keys’s ideas.
Another study cemented Keys’s hypothesis. Called the Framingham Study, it monitored a group of some 5,000 people over the span of six years. Researchers analyzed how different factors, such as what participants ate or whether they smoked, affected their chances of developing heart disease.
The Framingham researchers concluded that participants were more likely to develop heart disease when they had high levels of cholesterol. This result, combined with media coverage and AHA reports, led to the widespread acceptance of Keys’s ideas.
Keys’s hypothesis – that saturated fat causes heart disease by increasing cholesterol levels – became known as the diet-heart hypothesis. After it became widely accepted that consuming saturated fats could lead to heart disease, food manufacturers had to start looking for fat alternatives.
Keys’s diet-heart hypothesis was so influential that even the American government started pushing the food industry to find a replacement for saturated fats. Unsaturated vegetable oils were a first choice; however, as unsaturated vegetable oil is liquid at room temperature, it wasn’t ideal, as a solid fat was preferred.
Yet unsaturated vegetable oil can be treated through a process called partial hydrogenation, which “saturates” oils with just enough hydrogen to make the oil more solid. By the late 1980s, partial hydrogenation was a very common process. You’d find partially hydrogenated oils in margarines, potato chips, cookies and other baked goods. The problem of saturated fats solved, hydrogenated vegetable oil quickly become the backbone of the processed food industry.
Unfortunately, partially hydrogenated oils presented some serious problems, too. The process of hydrogenation produces trans-fatty acids, which are dangerous for human health. Trans fats rarely occur naturally but are usually the result of artificial processing.
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