A recent study in the New England Journal of Medicine looked at the benefits of a Mediterranean diet to prevent cardiovascular events (heart attack and stroke).
Patients at risk for heart disease (7,887 people in total) were randomized to a control (low fat) diet or a Mediterranean diet with either supplemental olive oil or with supplemental nut intake three groups in total). The baseline Mediterranean diet is considered to be high intake of fruits, vegetables, and fish, low red meat consumption, and occasional wine. Note that the control diet group was not only counseled on low fat intake, they were discouraged from eating nuts, fatty fish, and olive oil. In the end, the control group didn’t reduce their fat intake much at all, so the comparison was not the low-fat diet as intended but was essentially the baseline diet.
Both of the Mediterranean diet groups had a rate of cardiovascular events of about 0.8% per year vs the control diet group which had a rate of 1.1% per year. Interestingly, the biggest driver in terms of events was stroke, though there were also small differences seen for heart attack and death rates.
The absolute difference between the Mediterranean diet groups and the control (low fat) diet group is small . . . about 0.3% per year. Over time, this can become meaningful. Over ten years, this would mean that 3 people out of 100 would be better off. Further, it seems conceivable that the benefits could compound over longer periods (this is purely my own speculation and not a conclusion of the study).
It’s challenging to do a good, controlled study on diet/nutrition. This study was superbly done. Nuts and/or olive oil (and probably wine) do the body good. Probably better than vitamins (I’ve written about that topic here, making note of the lack of evidence of benefits for vitamins).
It’s important to keep in mind that diet/nutrition is a highly varied, multi-factorial, complex subject. To that point, the Women’s Health Initiative (sponsored by the National Heart, Lung and Blood Institute) monitored 48,835 women for a decade. Study participants either maintained their initial diet or were counseled to cut fat intake by 20% and replace those ‘fat calories’ with fruits and grains (total calorie consumption remained the same as before diet modification). Overall, a low fat diet did not produce benefit. In terms of weight, nine years later the women in the diet modification arm weighed on average about one pound less than the control group. There was also no difference in cancer, stroke, or heart attacks. (One caveat, the diet modification arm cut fat intake to 24% of calories from fat at year one and 29% of calories from fat at year six from baseline of 35-38%. This fell short of the goal set by the study of 20% of calories from fat. The diet modification group was successful at increasing consumption of vegetables and whole grains.) While generally negative, the study suggested that a low fat diet might reduce the risk of ovarian cancer.
In light of the Women’s Heath Initiative, simply reducing fat consumption does appear to be the key to improving health. Instead, the right fats (olive oil and nuts) in combination with wine, fish, and vegetables might make the difference. This is all simply food for thought (pun intended).