Ancel Keys and John Yudkin Were Both Right about Meat and Sugar


In the 1950s, Ancel Keys had a theory that dietary saturated fats and cholesterol in animal products raise blood cholesterol and blood pressure to increase risk for heart attacks, a leading killer of North Americans. Also in the 1950s, John Yudkin was the leading spokesman for the theory that sugar and other refined carbohydrates were the main culprits. Yudkin and Keys argued continuously, in journals and at medical meetings, about whether sugar or saturated fats were the prime cause of heart attacks. Today, both are heroes. Ancel Keys was given much credit and praise during his lifetime for his work on the causes of heart attacks, but only recently has Dr. Yudkin’s theory that excessive amounts of sugar can cause heart attacks become accepted, so he did not receive this richly-deserved credit while he was still alive.

Keys recognized correctly that red meat is associated with increased risk for heart attacks and diabetes, and he spent many years trying to prove that the culprit was saturated fat, but more recent research shows that other components that come from meat, such as Neu5Gc or TMAO, may be responsible for the association with heart attacks. Even though some of his theories have been discredited, Keys showed that:
• smoking increases risk for heart attacks
• high blood pressure and high cholesterol increase risk for heart attacks
• eating less meat and taking in fewer calories help to prevent heart attacks,
• traditional Mediterranean diets help to prevent heart attacks, and
• most heart attacks are preventable

Why Yudkin and Keys Were Both Correct
It is established beyond question that having high blood cholesterol levels is associated with increased risk for heart attacks. It is also established that both high-sugar and high-saturated fat-and-cholesterol diets can markedly raise blood cholesterol levels, so now it appears that a diet to help prevent heart attacks should restrict both sugar-added foods and drinks AND meats.
• Eating foods such as meat that are rich in cholesterol, saturated fats and other components will raise blood cholesterol levels
• Eating foods and drinks that contain a lot of sugar will raise blood sugar levels. A high rise in blood sugar can damage cells throughout your body, so your pancreas releases insulin that lowers blood sugar levels by driving sugar from the bloodstream into your liver, muscles and fat cells, the only places that can store significant amounts of sugar. However, these sources for sugar-storage are small, so much of the extra sugar is immediately converted to fatty triglycerides to cause a high rise in blood triglyceride levels. Then your liver takes more than 1500 triglyceride molecules and a lesser number of cholesterol molecules and packages them into a lipoprotein ball that is eventually converted to the harmful small particle lipoprotein ball LDL cholesterol that is associated with increased risk for heart attacks, high blood pressure and strokes.

Early Life and Work
Ancel Keys was born in Colorado Springs on January 26, 1904. He hated high school, so he ran away from his home in California to Arizona, where he found work shoveling bat guano out of caves and putting it in bags to be sold as fertilizer. He decided that school was better than shoveling bat manure, so he enrolled at the University of California at Berkeley. He went on to receive a PhD in biology from UC at the Scripps Institute in La Jolla CA. In 1935, he organized an expedition to the Andes mountains to study how living in the oxygen sparse air at 20,000 feet affects humans.

In 1941, he went to work for the United States War Department to design lightweight and nutritious rations for paratroopers, even though he had no training in nutrition. He went to a grocery store in Minneapolis and bought hard biscuits, dry sausages, hard candy and chocolate bars. He mixed them together to form a hard, gummy food that had lots of calories and would keep for a long time. His first food packs for the troops were called C- and D-rations, with 3200 calories in a 28-ounce packet. The most popular formula was called K-rations, which tasted so bad that Dr. Keys spent the rest of his life denying that K-rations were named after him.

After the war, Dr. Keys set out to explain why the wealthiest North Americans, the businessmen and professionals, were the ones most likely to die from heart attacks. At the University of Minnesota, he conducted his “Twin Cities Study” and found that high blood pressure, high cholesterol and smoking were major risk factors for heart attacks. Heart attacks occurred most commonly in those who were the fattest, ate the most meat, exercised the least and smoked. His research showed that dietary cholesterol may not be responsible for the increased risk for the observed association between eating meat and heart attacks. More than 80 percent of the cholesterol in your body is made by your liver, while less than 20 percent comes from the food that you eat. When you take in more cholesterol, your liver makes less. When you take in less cholesterol, your liver makes more. However, most of the scientific community ignored Keys’ work on cholesterol and decided incorrectly that dietary cholesterol was an important factor in raising blood cholesterol.

The Flaw in Keys’ Saturated Fat Theory
Keys measured blood saturated fat levels and found that people who had the highest blood levels of saturated fats were at increased risk for developing heart attacks. However, he did not recognize that saturated fats that you make in your own body are different from the saturated fats that you eat. Your body contains two types of saturated fats: even-chain and odd-chain. The largest study of its kind, from the University of Cambridge in the UK, shows that the even-chain saturated fats, which are associated with increased risk for diabetes and heart attacks, are made primarily by the human liver from the sugar and alcohol that you take in. The odd-chain saturated fats in your bloodstream come primarily from the saturated fats that you eat, and they may not be associated with increased risk for heart attacks (Lancet Diabetes & Endocrinology, published online August 6, 2014). In this study, researchers followed 340,234 adults from eight European countries. Using high-speed blood analysis, they measured the types of saturated fats in the bloodstream and found that they could predict who would become diabetic by their high levels of even-chain saturated fats.  Recent studies confirm this association (Proc of the Nat Acad of Sci, Mar 15, 2022), and odd-chain saturated fats have been associated with protection from developing diabetes (Nutrients, May 1, 2019;11(5):998).

Good Foods and Bad Foods
In 1957, Keys started his “Seven Countries Study” that showed that the Greeks, Japanese and Italians had the lowest rate of heart attacks, while the Finns had the highest rate with North Americans not far behind. He theorized that the people who ate the most calories and saturated fat and had the highest blood cholesterol levels (Finns and North Americans) were the ones with the highest rates of heart attacks. He went on to explain that the Greeks and Italians who ate lots of vegetables, seafood, olives and olive oil were protected from heart attacks, and so were the Japanese who ate a lot of fish. He concluded that fruits, vegetables and fish help to prevent heart attacks and proposed that the most healthful way to eat was the traditional Mediterranean diet.

Lessons from Their Long and Productive Lives
In 1939, Keys married Margaret Haney, a medical technologist who worked for him at the Mayo Foundation, and they had three children. They traveled widely and lived in Italy for nearly 30 years. They co-authored three popular books, including How to Eat Well and Stay Well the Mediterranean Way (1975). The Mediterranean diet studies are perhaps Keys’ most lasting contribution to nutrition, although opinions vary widely on exactly what the diet is and why it is healthful (lack of meat? lots of vegetables? olive oil? seafood?). Keys’s healthful lifestyle worked for him; he died just two months short of his 101st birthday in 2004. Yudkin had died in 1995, at age 84.

Ancel Keys was one of the first researchers to show that the saturated fats in meat were associated with increased risk for heart attacks, strokes and premature death. John Yudkin was the lead researcher to show that sugar was a cause. They both were correct. Taking in large amounts of sugar and mammal meat are associated with increased risk for heart attacks, strokes and premature death. Eating lots of vegetables, whole grains, beans, nuts and other seeds is associated with reduced heart attack risk.

Ancel Benjamin Keys
January 26, 1904 – November 20, 2004

John Yudkin
August 8, 1910 – July 12, 1995