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Dietary Fat Consumption and Risk of Endometriosis
Abstract & Commentary
By Jeffrey T. Jensen, MD, MPH, Editor, Leon Speroff Professor of Obstetrics and Gynecology, Vice Chair for Research, Oregon Health and Science University, Portland, is Editor for OB/GYN Clinical Alert.
Synopsis: Consumption of trans fats increases the risk of endometriosis, while long-chain omega-3 fats are protective.
Source: Missmer SA, et al. A prospective study of dietary fat consumption and endometriosis risk. Hum Reprod 2010 March 23; Epub ahead of print.
To investigate the relation between dietary fat intake and the risk of endometriosis, these authors analyzed 12 years of prospective data from the Nurses' Health Study II that began in 1989. Dietary fat was assessed via validated food-frequency questionnaire in 1991, 1995, and 1999 and averaged over the three diet questionnaires. The risk of a new diagnosis of laparoscopically confirmed endometriosis was assessed using a Cox proportional hazards models after adjustment for total energy intake, parity, race, and body mass index at age 18. The cohort included 586,153 woman-years of follow-up and 1199 cases of laparoscopically confirmed endometriosis. While there was no association with total fat consumption and endometriosis risk, those women in the highest fifth of long-chain omega-3 fatty acid consumption were 22% less likely (risk rate [RR], 0.78; 95% confidence interval [CI], 0.62-0.99) to be diagnosed with endometriosis compared with those consuming at the lowest fifth. In contrast, those consuming at the highest quintile of trans unsaturated fat intake were 48% more likely (RR, 1.48; 95% CI, 1.17-1.88) to be diagnosed with endometriosis compared with those consuming at the lowest fifth. The tests for trends were positive for increasing consumption in both groups. These data support findings from other animal and observational studies that trans fat is associated with an increased risk or progression of confirmed endometriosis.
This large prospective study of diet and endometriosis demonstrates once again the impact of diet on overall health. If there were not enough reasons to avoid trans fats already (associated with increased risks of obesity, cardiovascular disease, stroke, Parkinson's), we can now add endometriosis. Endometriosis is a highly prevalent condition that is the third leading cause of gynecologic hospitalization. Endometriosis is also associated with pelvic pain and infertility, two important health concerns of women. Therefore, identification of a modifiable risk factor that could reduce the risk of operative intervention for endometriosis represents an important contribution that warrants careful scrutiny.
The Nurses' Health Study (NHS) was established in 1976 with funding from the National Institutes of Health to investigate the potential long-term consequences of the use of oral contraceptives, but has yielded important health information in many other areas. The selection of nurses for this long-term prospective cohort study was a deliberate design feature; their nursing education would motivate them to participate in a long-term study and yield high-quality responses to technically worded questionnaires. The initial cohort consisted of approximately 122,000 married registered nurses ages 30-55. This group has received follow-up questionnaires every 2 years with an impressive 90% response rate. To address the interaction of diet and disease, food-frequency and diet questions were added in 1980. Question related to quality of life were added in 1992. The Nurses' Health Study II cohort was established in 1989 to study these same associations in a younger (ages 25-42) population. A total of 116,686 women were enrolled in NHS II, and response rates have been the same (90%) as the original cohort. The data from the current report come from this younger population of nurses that would be expected to develop gynecologic problems. While a cohort study always suffers from potential bias, the large number of participants, excellent follow-up, multivariant adjustment of confounders, and careful independent validation of self-reported outcomes renders data of extremely high quality. Furthermore, only those women with laparoscopically diagnosed endometriosis were included as cases. Since asymptomatic endometriosis may have been discovered incidentally in women with infertility undergoing laparoscopy, this group was considered separately.
The consumption of trans fats correlates with high plasma lipid levels, inflammation, and arterial calcification, known risk factors for coronary heart disease (CHD).1 They also inhibit cyclooxygenase, an enzyme required for the conversion of arachidonic acid to prostacyclin, necessary for the regulation of blood flow. Epidemiological data suggest that when trans fat percentages go up, death rates rise, and when trans fats go down, death rates go down.1 (Just as governments justify increasing taxes on cigarettes and alcohol to recover health care costs, perhaps we should consider taxes on trans fat-containing food to finance our new expansion of health insurance.)
Although the FDA ruled that the amount of trans fat in a food item must be stated on the label after Jan. 1, 2006, the exact wording contains loopholes that permit many trans fat-containing foods to be sold without this warning. In contrast, omega-3 fatty acids (derived from fish oil) reduce inflammation and cardiovascular risk. Dietary supplementation with omega-3 fatty acids should be considered in the secondary prevention of cardiovascular events.2 Even more importantly, substitution of omega-3 and polyunsaturated fats tends to reduce the overall consumption of trans fat.
It is important to point out that there was no association with overall fat consumption and endometriosis. This reduced the confounding influence of proportion of fat calories. What emerged was a consistent story: As trans fat consumption increased, so did the risk of endometriosis, and as omega-3 fat consumption increased, the risk diminished. In other words, as women shifted their diet away from pro-inflammatory trans fats to anti-inflammatory omega-3 fats, their risk of endometriosis decreased.
Clinicians have previously had little information to offer guidance to women who present with a significant family history of endometriosis. Compared with other modifiable risks, diet is an attractive lifestyle intervention to stress during general counseling. "You are what you eat" is more than a cliché. More than 20% of women in the cohort that reported consuming total dietary fat at the highest quintile were overweight and 18% obese, compared to only 14.8% overweight and 7.2% obese in the group reporting the lowest total fat consumption.
So we can feel even more comfortable encouraging a healthy diet in our general counseling of young women (that Big Mac might lead to a laparoscopy for endometriosis). With the HPV vaccine and new schedules for less frequent pap tests, we need to rethink the annual exam. Get back to the basics and focus on preventive measures: A healthy diet low in trans fat and high in omega-3 fat, avoiding smoking, regular exercise, safe sexual practices, and effective contraception are all low-cost interventions with great benefits to patients.