Thursday, June 4, 2009

The Lyon Diet-Heart Study: Background

To appreciate the full significance of the Lyon diet-heart study, we have to go back in time a bit. We're off to 1982, the year the U.S. National Heart, Lung and Blood Institute published the results of their massive study, the Multiple Risk Factor Intervention Trail (MRFIT).

By 1982, the idea of the "prudent diet" was well ingrained in American medicine, despite a lack of direct evidence to support it, and even a certain amount of evidence at odds with it (such as the ill-fated Anti-Coronary Club trial). The prudent diet was designed to reduce the risk of heart attack, and suggests reducing total fat, saturated fat and cholesterol intake, while increasing consumption of vegetables, whole grains, fruit and fiber. Some versions of the diet replace saturated fat with polyunsaturated vegetable oils.

MRFIT involved 12,866 men at high risk of heart attack, making it one of the largest controlled trials of all time. Half of the group were told to keep doing what they were doing, under medical supervision, and the other half were given intense diet and lifestyle counseling. The intervention group was counseled to quit smoking and reduce their consumption of saturated fat and cholesterol, and increase polyunsaturated vegetable oil consumption.

After 6 years, 46% of the intervention group had quit smoking, compared to 29% in the control group. The intervention group reduced their cholesterol intake by 40% and their saturated fat intake by more than one-fourth, and increased their consumption of polyunsaturated fat (omega-6) by one third relative to the control group (source).

The results? After seven years, total mortality was 41.2 per 1,000 in the intervention group and 40.4 in the control group, a difference that was not even close to statistically significant. There were also no significant differences in heart attack rate or heart attack death rate. The authors and their apologists tried to wiggle out of the obvious conclusion through an avalanche of slippery math and editorials.

The results were mirrored by a later intervention trial published in 2006, the Women's Health Initiative dietary modification trial. This one was even larger, involving 48,835 postmenopausal women! This was another test of the prudent diet, in which participants were intensively counseled to
reduce total fat intake to 20% of calories and increase intakes of vegetables/fruits to 5 servings/d and grains to at least 6 servings/d.
After 6 years, the intervention group was eating 22% less fat, 23% less saturated fat, 20% less cholesterol, 15% more carbohydrate, 22% more fruits and vegetables, and slightly more fiber and whole grains than the control group. LDL dropped a bit in the intervention group.

I think you know what's coming...
Over a mean of 8.1 years, a dietary intervention that reduced total fat intake and increased intakes of vegetables, fruits, and grains did not significantly reduce the risk of CHD, stroke, or CVD in postmenopausal women...
Oh and you forgot to mention, 4.9% of women died in the intervention group as opposed to 5.0% in the control group. A "minor detail" that I couldn't find in the paper so I had to look up elsewhere. The study also showed that the diet modifications didn't reduce the incidence of breast or colorectal cancer, two of the most common cancers. RIP, prudent diet. Although it still seems to be struggling along, despite the beating. Another set of editorials appeared claiming that the diet didn't work because it wasn't extreme enough. How far do we have to move the goalposts before we give up?

There was one interesting finding that came out of MRFIT, which foreshadowed the result of the Lyon trial. MRFIT participants eating the most omega-3 from fish were at a 40% lower risk of coronary heart disease and a 22% lower risk of dying of any cause. This was not part of the intervention, so it doesn't necessarily reflect cause and effect. For that, we'll have to look at the Lyon trial.

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