You're correct that my thinking on saturated fat has evolved. One catalyst was a scientific analysis of 21 earlier studies, which showed "no significant evidence" that saturated fat in the diet is associated with an increased risk of coronary heart disease. The 21 studies analyzed included nearly 348,000 participants, most of whom were healthy when they were enrolled. They were followed for five to 23 years, during which 11,000 developed heart disease or had a stroke. Looking back at the dietary information collected from these thousands of participants, the investigators found no difference in the risk of coronary heart disease, stroke, or coronary vascular disease between those individuals with the lowest and highest intakes of saturated fat. This goes completely against the conventional medical wisdom of the past 40 years. It now appears that many studies used to support the low-fat recommendation had serious flaws.
In the meantime, as nutritionists have been recommending low-fat foods, consumption of added sweeteners, especially high-fructose corn syrup, has been steadily rising. This may be at least partially due to the fact that low-fat prepared foods are often highly sweetened. A study from Emory University and the U.S. Centers for Disease Control and Prevention published in April, 2010, showed that sweeteners appear to lower levels of HDL ("good") cholesterol and raise triglycerides. Both of these effects increase the risk of heart disease. What's more, through their direct effects on insulin and blood sugar, refined starches and sugars are more likely than saturated fat to be the main dietary cause of coronary heart disease and type-2 diabetes.
Another study, published in the Dec. 21, 2010 issue of the Annals of Internal Medicine, showed that a natural substance in dairy fat, trans-palmitoleic acid, may substantially reduce the risk of type 2 diabetes (and, as result, of heart disease). The research team from the Harvard School of Public Health looked at more than 3,700 men and women age 65 or older in a National Institutes of Health funded Cardiovascular Health Study who had been followed for 20 years to evaluate risk factors for cardiovascular diseases in older adults. The investigators found that participants who reported eating more whole-fat dairy products had higher levels of trans-palmitoleic acid in their blood. Over the following years those men and women who had the higher levels of trans-palmitoleic acid were about 60 percent less likely to develop diabetes than those whose blood levels of trans-palmitoleic were lowest.
In addition, the findings from two other studies conducted by the Harvard School of Public Health on the health effects of dairy products are intriguing. One found that consumption of low-fat dairy foods contributed to infertility caused by failure to ovulate, while consumption of full-fat dairy foods may help the problem. The second showed that drinking skim milk was associated with a higher incidence of acne in teenage boys.
Given the results of these studies, I no longer recommend choosing low-fat dairy products. I believe the healthier choice is high-quality, organic dairy foods in moderation. My personal choice would be high-quality, natural cheese a few times a week. I don't advise eating saturated fat with abandon, because the foods that are full of it (salty bacon, conventionally raised beef, processed cheese) are often not the best for our health. Try to limit it to about ten percent of daily calories. You may choose to use your "budget" of saturated fat calories on ice cream, butter or high-quality natural cheese, or even an occasional steak (from organic, grass-fed, grass-finished cattle, please). I still recommended skinless chicken and turkey because poultry fat (concentrated just beneath the skin) contains arachidonic acid, which promotes inflammation. I also still recommend strictly avoiding foods that contain chemically altered fats (such as hydrogenated vegetable oils found in many prepared foods), as these do appear to raise cardiovascular disease risk.
Continue to emphasize fruits, vegetables and whole grains, and limit sweeteners and other high-glycemic-load carbs.
Andrew Weil, M.D.