Nutritional Pearls: Not All Fats Are Created Equal
Jeanette is a 33-year-old overweight woman struggling to lose weight. She has recently begun exploring low-fat diets as an option for her weight loss efforts, and asks if you think cutting fat out of her diet is a good way to get healthier.
(Answer and discussion on next page)
Dr. Gourmet is the definitive health and nutrition web resource for both physicians and patients with evidence-based resources including special diets for coumadin users, patients with GERD/acid reflux, celiac disease, type 2 diabetes, low sodium diets (1500 mg/d), and lactose intolerance.
Timothy S. Harlan, MD, is a board-certified internist and professional chef who translates the Mediterranean diet for the American kitchen with familiar, healthy recipes. He is an assistant dean for clinical services, executive director of The Goldring Center for Culinary Medicine, and associate professor of medicine at Tulane University in New Orleans.
Answer: Not all fats are bad, and choosing the right types of fats can be extremely beneficial.
For a long time, low-fat diets were all the rage. They were supposed to help your patients lose weight, improve their cholesterol scores, and help them avoid heart disease. Fortunately, in the last few years there's been a wealth of well-designed research showing that not all fats are bad for you: Indeed, some are definitely good for you. Transfats? Definitely bad. Omega-3 fatty acids? Definitely good.
A team at Harvard's Medical School, School of Public Health, and the Brigham and Women's Hospital in Boston looked at the associations between intake of various types of dietary fats and mortality, not just from all causes but also from more-specific causes like heart disease, cancer, neurodegenerative disorders, and respiratory diseases.
For their analysis, they utilized data from the Nurses' Health Study (NHS) and the Health Professionals Follow-up Study (HPFS). The data used from the NHS included semiannual dietary questionnaires from over 83,000 women participating, starting in 1980 and continuing through 2012. The data from the HPFS included similar dietary questionnaires, also administered every 2 years, from over 42,000 men starting in 1986 and continuing through 2012. Those with diagnosed heart disease, cancer, or type 1 or type 2 diabetes at the start of the study were excluded from this analysis.
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 with those who did not. Those with the highest quintile of total fat intake had a 13% greater risk of all-cause mortality—but those with the highest quintile of polyunsaturated and monounsaturated fats were 19% and 11% less likely, respectively. Similarly, higher saturated fat intake meant a greater risk of death from cancer (about 7% higher), while higher total fat intake substantially increased the risk of death from respiratory diseases by a whopping 56%. Greater levels of polyunsaturated and monounsaturated fats, on the other hand, meant lower risk of death from neurodegenerative and respiratory disorders.
The researchers went a step further and modeled the outcomes 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 meant a 27% drop in all-cause mortality as well as a lower risk of death from heart disease, cancer, and neurodegenerative disorders, while switching to monounsaturated fats cut the risk of death from neurodegenerative disorders by 29%.
What’s the “Take-Home”?
This study's strengths include its large sample size, multiple measures of dietary intake, and its length, making its conclusions very strong indeed. That said, this is an observational study, so it does not show causality—just association. Still, it's consistent with research we've seen elsewhere. It's important for your patients to understand that not all fats are bad for them and that choosing the right types of fats can be extremely beneficial.
Wang DD, Li Y, Chiuve SE, et al. Association of specific dietary fats with total and cause-specific mortality. JAMA Intern Med. 2016;176(8):1134-1145.