Eating fat makes you fat! Fats drive up your cholesterol levels! Replace fats with carbs! There surely are a lot of rules when it comes to eating fats, but how many of them stem from evidence-based research? The common thought on fats has completely changed over the course of one century. With the publishing of new studies and production of promising technology, our knowledge of fats grows. Today, we know that fats are important components of the diet (for more information, view our post about the basics of lipids); however, the journey to where we are now was not easy. Let’s take a look at the past to see previous opinions of fats.
What They Ate - Paradoxes
Several societies thrived (and continue to do so) on a high-fat diet. This baffled researchers due to the popular belief that fats make you fat and gave you hear disease. For example, Aleš Hrdlička, observed the Native Americans inhabiting the American Southwest in 1898. Their diet mainly consisted of meat consumption, especially buffalo. During his time there, Hrdlička was baffled by how long they lived and how healthy the elderly appeared. Also, he was dumbfounded by the absence of malignant disease such as cancer as well as heart disease, varicose veins, appendicitis, atherosclerosis, or stomach ulcers.
In 1906, Icelandic anthropologist Vilhjalmur Stefansson traveled to the Canadian Arctic to live with the Inuit nation there. During his stay he adapted the Inuit diet that consisted primarily of caribou, salmon, and eggs. It was estimated that about 70 to 80% of the calories in their diets were were from fats. Stefansson observed no obesity or disease in his new friends and even thought that they were among of some of the healthiest individuals he had ever seen! This is was a surprising conclusion due to the diet they were consuming, so he and a friend formulated an experiment to be sure the health of those in the Arctic was due to their diet; they planned to only consume meat and water for an entire year. This was a scandalous idea but they did it anyway and after a year was up they were found in perfectly good health (aside from Stefansson being sick one time, which was quickly resolved). News of their well being struck scientists everywhere; the men were expected to fall ill to deficiencies because their diet was so restricted. Stefansson avoided this issue by eating the whole animal (organs included).
In the early 1960s another doctor traveled far to observe the eating habits of a healthy nation. George Mann ventured to Kenya in order to study the Masai people. Mann’s work was based off of another doctor, A. Gerald Shaper, who studied the Samburus people of Uganda. They drank 2 to 7 liters of milk a day and ate meat regularly. Mann discovered that the Masai would drink 3 to 5 liters of milk a day and eat lamb, goat, and beef often. The Masai and Samburus consumed 60% of their calories through fat; however, they had blood pressures about 50% lower than Americans at that time. In the Masai, Mann could not find a trace of heart disease, and considering the popular hypothesis in America at the time was that animal fat caused heart disease, this was an astounding find.
Demonizing Saturated Fats
Ancel Benjamin Keys pioneered the idea that fat causes heart disease. He theorized that cholesterol was linked to heart disease and caused heart attacks. Russian pathologist Nikolaj Anitschkow put together an experiment of his own in 1913 to test how animals metabolized cholesterol. Antischkow claimed that he could induce lesions from atherosclerosis by injecting these animals (rabbits mainly) with large amounts of cholesterol. His research aided Keys and promoted the theory about animal fats leading to heart disease. However, Antischkow’s experiment was inadequate, he neglected to test animals who are meat-eaters like humans are (ex: dogs). When these animals were used as subjects the results were that they had the ability to eliminate the excess cholesterol - meaning that cholesterol isn’t the monster Keys and Antischkow thought it was; however the damage was done and the fear of serum cholesterol spread across America. Keys himself found in one of his later studies that no matter how much cholesterol he fed to his human subjects their cholesterol levels did not change significantly. Even with this evidence he held onto his original hypothesis.
In 1952 the gas-liquid chromatography was invented. This device allowed researchers the capability to test different kinds of lipids and their effects on the body. This invention led to the discovery of the different types of fats (e.g. saturated, monounsaturated, polyunsaturated). E. H. “Pete” Ahrenz, a lipidologist, led the pack with research in this field. Also in 1952, Keys announced his diet-heart hypothesis: fat in the diet causes serum cholesterol in the blood that causes heart disease. Originally, he had thought that total consumption of fat led to an unhealthy life instead of the type of fat, but after a few more experiments he found the opposite to be true. Due to his new discovery, he claimed that saturated fats should be avoided for a healthy heart. This led to the Keys equation; a way to calculate how much serum cholesterol could be affected by the ingestion of saturated fat, polyunsaturated fat, and cholesterol.
Keys’s hypothesis had an overwhelming support from fellow scientists; although, some, like Mann and Jacob Yerushalmy, disagreed with his findings. Mann pointed out the paradoxes of the nations with a high-fat diet and low instances of heart disease and Yerushalmy mentioned that Keys had the tendency to find a population to fit his hypothesis and not a hypothesis to fit the real data. In response to his critics, Keys launched his seven countries study (1970) traveling to Italy, Greece, Yugoslavia, Finland, the Netherlands, Japan, and the United States. Unfortunately, Keys did not fix the errors of his past experiments and he continued to allow his bias to cloud his judgment; he did not collect his subjects through randomization and actively avoided countries (such as France and Switzerland) where data contradicting his own was found. Also, he ignored the impact cultural components, such as Lent and nations left in poverty from WWII, had on his study because their omission would not help support his theory. The conclusion of the study was that there is a direct correlation between saturated fat consumption and heart disease related deaths.
In 1999, a man by the name Alessandro Menotti, an Italian researcher looked back on the date from the seven countries study and found that sugars seemed to be the responsible food category for disease. Earlier, in 1992, it was revealed that saturated fats are not related to heart disease, although that fact was found in 1968. Keys rejected the idea as he had done since the early 1970s with his debates with John Yudkin, the leader of the sugar hypothesis: formed the sugar hypothesis: sugar products and refined carbohydrates had the highest correlation with deaths from heart disease, and led the nation to believe in the diet-heart hypothesis still.
The National Institutes of Health (NIH), American Heart Society (AHA), and the Dietary Guidelines for Americans (foundation for the food pyramid) were founded during Keys’ reign. The influence he had on these organizations still impacts the way we think about fats. For instance, food brands can advertise “cholesterol free!” implying that cholesterol is a negative component of the diet (the importance of cholesterol is discussed in a previous blog post). Thankfully, we are no longer taught to follow the food pyramid, now we are encouraged to eat according to “My Plate” guidelines.
ReferencesTeicholz, N. (2014). The Fat Paradox: Good Health on a High-Fat Diet, Why We Think Saturated Fat is Unhealthy, The Low-Fat Diet is Introduced to America, The Low-Fat Diet Goes to Washington. In The big fat surprise: Why butter, meat, and cheese belong in a healthy diet. New York, New York: Simon & Schuster Paperbacks