Although a wealth of literature links dietary factors and coronary heart disease (CHD),
the strength of the evidence supporting valid associations has not been evaluated
systematically in a single investigation.
We conducted a systematic search of MEDLINE for prospective cohort studies or randomized
trials investigating dietary exposures in relation to CHD. We used the Bradford Hill
guidelines to derive a causation score based on 4 criteria (strength, consistency,
temporality, and coherence) for each dietary exposure in cohort studies and examined
for consistency with the findings of randomized trials.
Strong evidence supports valid associations (4 criteria satisfied) of protective factors,
including intake of vegetables, nuts, and "Mediterranean" and high-quality dietary
patterns with CHD, and associations of harmful factors, including intake of trans-fatty
acids and foods with a high glycemic index or load. Among studies of higher methodologic
quality, there was also strong evidence for monounsaturated fatty acids and "prudent"
and "western" dietary patterns. Moderate evidence (3 criteria) of associations exists
for intake of fish, marine omega-3 fatty acids, folate, whole grains, dietary vitamins
E and C, beta carotene, alcohol, fruit, and fiber. Insufficient evidence (< or =2
criteria) of association is present for intake of supplementary vitamin E and ascorbic
acid (vitamin C); saturated and polyunsaturated fatty acids; total fat; alpha-linolenic
acid; meat; eggs; and milk. Among the dietary exposures with strong evidence of causation
from cohort studies, only a Mediterranean dietary pattern is related to CHD in randomized
trials.
The evidence supports a valid association of a limited number of dietary factors and
dietary patterns with CHD. Future evaluation of dietary patterns, including their
nutrient and food components, in cohort studies and randomized trials is recommended.