May 9, 2024 – In the 1970s, researchers first noticed an interesting trend in cancer data. This means that countries around the world have very different rates of disease, even when biological differences between populations are taken into account. One hypothesis was that differences in cancer incidence were caused by environmental factors, particularly changes in diet. In fact, when researchers compared population-level data on food intake, they found that intake of fats and oils was associated with the development of cancer.
“Based on this evidence, dietary guidelines across the United States and around the world emphasize reducing fat in the diet,” Walter Willett, professor of epidemiology and nutrition at Harvard's T.H. Chan School of Public Health, said on May 3. ” he said. At the 8th Cutter Symposium.
But since then, Willett says, study after study has found that the link between dietary fat and cancer incidence does not hold up. One rigorous study conducted in the 1990s and early 2000s involved tens of thousands of people and directly compared those who reduced the amount of fat in their diets with those who did not. After collecting data from individuals over several years, the researchers found no significant reduction in breast cancer in the low-fat diet group.
“When we summarize the data, it is clear that [the link] It’s very, very slimy,” Willett said. He pointed out that later studies looked at specific types of dietary fats, rather than classifying all dietary fats into one category. In general, studies have found that trans fats and saturated fats increase the risk of disease, while unsaturated fats do not. Importantly, the results relied on data analysis that controlled for hidden so-called confounders other than diet that caused the disease, which were not addressed in the 1970s studies.
This symposium focused on the role of confounders when studying the effects of diet on disease, one of the major challenges in obtaining accurate results in nutritional research.
The Cutter Lectures on Preventive Medicine, sponsored by the Department of Epidemiology and funded by a bequest from Harvard Medical School alumnus John Clarence Cutter, are held once or twice a year.
Careful data analysis required
Symposium speakers include Donna Spiegelman and Susan Dwight Bliss Professor of Biostatistics. If sex is found, it is necessary to account for confounding factors that could be the cause instead. Richard Peto, professor of public health at Yale University and professor emeritus of medical statistics and epidemiology at the University of Oxford;
Spiegelman said people who eat a healthy diet generally practice a healthy lifestyle, including aspects such as exercising, refraining from smoking and drinking alcohol, and seeing their doctor regularly. I explained that there might be. She said that if confounding factors like these are not accurately measured and analyzed during her research, the results may not show the true impact of diet. She has developed statistical methods and software that help address confounding issues.
Still, Spiegelman said, despite the challenges of determining exactly how different diets affect disease risk, a body of research in the field of nutrition suggests that diet does indeed have an impact. It was concluded that this shows that.
“For me, the link between diet and health is so strong that I moved into practical research to apply the knowledge already in place to improve public health,” she said.
– Jay Lau
Photo: Kent Dayton