• Do we know anything about nutrition at all?!?!?

    A friend pointed me to this study, almost two months old now, “Association of Dietary, Circulating, and Supplement Fatty Acids With Coronary Risk: A Systematic Review and Meta-analysis“:

    Background: Guidelines advocate changes in fatty acid consumption to promote cardiovascular health.

    Purpose: To summarize evidence about associations between fatty acids and coronary disease.

    Data Sources: MEDLINE, Science Citation Index, and Cochrane Central Register of Controlled Trials through July 2013.

    Study Selection: Prospective, observational studies and randomized, controlled trials.

    Data Extraction: Investigators extracted data about study characteristics and assessed study biases

    Researchers wanted to summarize the collected evidence linking fatty acids to coronary disease. Cause we all know they’re terrible, right? They wanted high-quality studies, so they restricted them to prospective observational studies and RCTs.

    They found 32 of the former that examined dietary consumption of fatty acids, with more than 500,000 participants, and 17 that looked at fatty acid biomarkers, with more than 25,000 participants. They also found 27 randomized controlled trials, with more than 100,000 participants.

    Those are some fairly large numbers. So if there’s an association, we should see it. For each outcome, they compared the third of people who had the highest levels/amount the most with the third who had the lowest.

    There was no statistically significant relationship between total saturated fats, monounsaturated fats, ω-6 polyunsaturated fats, and coronary disease. Long-chain ω-3 polyunsaturated had a small protective effect (relative risk 0.87, 95% CI 0.78-0.97), and trans fatty acids had a small damaging effect (relative risk 1.16, 95% CI 1.06-1.27).

    But remember that these studies are on “reported” diet. It’s possible that people could be over- or under-reporting what they eat. So a more precise measure would be to see what’s actually in their body. When they looked at studies that measured circulating fatty acids (the levels in your blood), they found that there was no statistically significant difference between total saturated fatty acids, total monounsaturated fatty acids, α-linolenic acid, total long-chain ω-3 polyunsaturated fatty acids, total ω-6 polyunsaturated fatty acids, total trans fatty acids, and coronary disease. No relationships at all.

    In randomized controlled trials of supplementation, there was no statistically significant protection from α-linolenic, long-chain ω-3 polyunsaturated, or ω-6 polyunsaturated fatty acid.

    What do guidelines say? That you should reduce your consumption of total saturated fatty acids and increase your consumption of ω-6 polyunsaturated fatty acids. What does this meta-analysis say?

    In conclusion, the pattern of findings from this analysis did not yield clearly supportive evidence for current cardiovascular guidelines that encourage high consumption of polyunsaturated fatty acids and low consumption of saturated fats.

    There are days when I feel like we’re nowhere. Luckily, my consistent advice of “moderation in all things” seems to be relatively safe.

    @aaronecarroll

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