You may have seen the recent “Presidential Advisory” from the American Heart Association making some strong and definite claims about saturated fat and heart disease. Two years ago I’d have found their assertions pretty compelling. Nowadays I don’t blindly trust any organization’s nutrition advice. If history tells us anything, it’s that closer looks must always be taken.

I’m going to need time to figure out what I think about this report (yes, I’ve seen Gary Taubes’s rebuttal), and maybe write a follow-up post later. For now, here are a few things to know that might not be clear from the headlines that have been circulating:

• The “Presidential” in the title refers to the president of the AHA, not the United States. This is not like the Presidential Fitness Challenge. Don’t be influenced either way by the presence of that word.

• The report doesn’t merely advise that we reduce saturated fats. The specific recommendation is to replace saturated fats with other kinds of fats, and not with carbohydrates as one might have guessed. The report says the data currently available on replacing saturated fats with carbohydrates shows no significant benefit.

• The report has nothing to do with any new research, at least in the sense you might assume. They didn’t conduct any new experiments or gather any new data. Rather, they took a fresh look at existing research, and thought hard about which studies to consider “core studies”. There’s nothing inherently wrong with this — it’s done all the time — but it’s worth understanding that this is what they’re doing. It means the report has to be very much judged on the criteria they used for deciding what’s “core”. Some very large studies were excluded from their core list, and a lot depends on the reasons for that exclusion.

Note that I don’t like distrusting health and nutrition authorities. I don’t wake up every day looking for some institution to be paranoid about. But the historical evidence has me feeling betrayed.

Compare this to other sciences. NASA has never given me a reason to doubt them if they say star X is distance Y from Earth and contains gases A, B, and C — and heck, those would be claims about a ball of fire billions of miles away. I’d love to have that same automatic trust in the American Heart Association, the American Diabetes Association, the US Dietary Guidelines, and so on, when they say “food X will do thing Y”. But as things stand, I can’t.