Sep 14, 2016
A team at Harvard's Medical School, School of Public Health, and the Brigham and Women's Hospital in Boston has looked at the associations between intake of various types of dietary fats and one's risk of death, not just from all causes but also from more specific causes like heart disease, cancer, neurogenerative disorders like ALS or Alzheimer's, and respiratory diseases.
Data from two large-scale, long-term studies, the Nurses' Health Study (NHS) and the Health Professionals Follow-up Study (HPFS). The data used from the NHS included dietary questionnaires from the over 83,000 women participating responded to every 2 years starting in 1980 and continuing through 2012. The data from the HPFS included similar dietary questions, also administered every 2 years, from over 42,000 men starting in 1986 and continuing through 2012. The authors analyzed the participants' dietary records and determined the individuals' intake of total fat, trans-fats, saturated fat, polyunsaturated fat, and monounsaturated fat. They also broke out the poly- and mono-unsaturated fats into subtypes, including omega-3 and omega-6 fatty acids as well as specifying the source (from fish and shellfish or otherwise) of those omega-3 and -6 fatty acids.
The fat intake of those who died from various causes was then compared to those who did not. Those with the highest of five levels of total fat intake were 13% more likely to die of any cause - but those with the highest quintile of polyunsaturated and monounsaturated fats were 19% and 11% less likely. Higher saturated fat intake meant a greater risk of death from cancer (about 7% higher), while higher total fat intake substantially increase the risk of death from respiratory diseases (a whopping 56%). Greater levels of polyunsaturated and monounsaturated fats, on the other hand, meant lower risk of death from neurodegenerative and respiratory disorders.
Researchers used mathematical models to find out if the outcomes might change if the participants had replaced just 5% of the calories they consumed from saturated fats with the same number of calories from polyunsaturated or monounsaturated fats. Switching from a saturated fat to a polyunsaturated fat means a 27% drop in risk of death from all causes as well as a lower risk of death from heart disease, cancer, and neurodegenerative disorders, while switching to monounsatured fats cut the risk of death from neurodegenerative disorders like ALS or Alzheimer's by 29%.
This study involving thousands of people, multiple measures of dietary intake (not just one at the start of the study) and lasting at least 20 years, making its conclusions very strong. The authors were careful to excluding anyone who had been already diagnosed with heart disease, cancer, or type 1 or type 2 diabetes before the start of the study. This is an observational study, so it does not show causality - just association. It's consistent with research we've seen elsewhere. Fats are not bad for you - just choose the right types of fats.