Massive study of heart healthy diets exhonorates salt
Separating fact from opinion, researchers from McMaster University in Hamilton, ON, released in this week's Archives of Internal Medicine "A Systematic Review of the Evidence Supporting a Causal Link Between Dietary Factors and Coronary Heart Disease ." Using meticulous, pre-determined methodology, the researchers sifted through 5,705 medical journal articles on diet and heart disease, applied the rigorous Bradford Hill Criteria for Assessing Causation, and analyzed 146 prospective cohort studies and 94 randomized controlled trials to answer the question: what does medical science tell us about diet and heart disease? As USA Today commented: "What we know for sure about diet and what protects the heart is a relatively short list." And entirely missing from that list, much to the chagrin of political nutritionists who have been beating the drum for salt reduction is, no surprise to us, salt.
The results of the study, in the authors' words:
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 -3 fatty acids, folate, whole grains, dietary vitamins E and C, beta carotene, alcohol, fruit, and fiber. Insufficient evidence (2 criteria) of association is present for intake of supplementary vitamin E and ascorbic acid (vitamin C); saturated and polyunsaturated fatty acids; total fat; -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.
No evidence implicated salt as a cause of coronary heart disease
This is the first systematic review examining diet and heart disease using the rigorous Bradford Hill guidelines. Applying a predefined algorithm found
strong evidence of a causal relationship for protective factors including intake of vegetables, nutes and monounsaturated fatty acides and Mediterranean, prudent and high quality dietary patterns, and harmful factors, including intake of trans-tatty acides and foods with a high glycemic index or load and a western dietary pattern. Among these dietary exposures, however, only a Mediterranean dietary pattern has been studied in RCTs and significantly associated with CHD.
Note: the Meditteranean diet contains about 30% more salt than the western diet.
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