Does a reduction in dietary fat decrease the risk of heart disease?
A large clinical trial published on February 8 in the Journal of the American Medical Association showed that a low fat diet in postmenopausal women had no effect on the incidence of cardiovascular disease. There was no difference in the incidence of heart disease or strokes in the study group compared to the control group. This is not surprising given the repeated assertions from many dietary experts that inflammation, and not cholesterol levels or fat intake, is a primary contributing factor in heart disease.
This study (The Women’s Health Initiative) observed 49,000 women aged 50 to 79 years over a period of 8 years. Intensive behavior modification training in the study group sought to reduce total fat intake to 20 percent of calories and increase the intake of fruits, vegetables, and grains. The study group did manage to reduce total fat intake from 38 percent to 29 percent of energy. They increased servings of fruits and vegetables from 3.6 to 5 servings per day. Grain intake remained the same. Most participants in the study were overweight or obese (mean body mass index, 29). Not surprisingly, the reduction of fat intake in the study did not result in weight loss of the participants.
Many nutritional experts are pointing to excess carbohydrate intake as a major culprit in the production of inflammation, weight problems, and blood sugar disorders, all of which can increase the risk of heart disease. Interestingly, in this study the intake of grains remained the same before and after the study group’s dietary interventions (4.5 servings per day). If carbohydrate intake does constitute a significant factor in the likelihood of developing heart disease, then we would predict the exact results that this study revealed. Maintaining the same level of grain intake and reducing the level of fat intake will not alter the incidence of heart disease.
Howard BV, et al. Low-fat dietary pattern and risk of cardiovascular disease. JAMA Feb 8, 2006; 295(6):655-666.
What about breast cancer?
The same study population was observed for the incidence of invasive breast cancer. After 8 years of follow-up there was no significant reduction in the incidence of invasive breast cancer associated with a lower dietary fat intake. However, a decrease in fat intake did reduce the risk of breast cancer for disease that was positive for the estrogen receptor and negative for the progesterone receptor. There was also a reduction in the level of circulating estradiol (estrogen) in these women. Although the authors do not suggest it, I wonder if the positive estrogen receptor cancer incidence was reduced in this group because of a reduction in the intake of animal fats from animals treated with hormones and the intake of both animal fat and plant oils that concentrate pesticides (a potent xenoestrogen). Since hormones, including estrogen, are concentrated in the fat of animals, and since estrogen taken into the body does tend to increase the risk of breast cancer, a reduction in fats that may contain estrogen could reduce the incidence of estrogen receptor positive breast cancers.
Prentice RL, et al. Low-fat dietary pattern and risk of invasive breast cancer. JAMA Feb 8, 2006; 295(6):629-642.
Both of these studies lend credence to the concept that reduction of total dietary fat does not convey health benefits. The low fat diet fads in fact can cause fatty acid deficiencies. Saturated fats are necessary for calcium absorption into bones and a healthy immune system. I do recommend the elimination of trans fats (partially hydrogenated oils) from everyone’s diets, but saturated fats and cholesterol are excellent and necessary nutrients, especially from organic sources.