Wednesday, January 11, 2012

Why You Don't Need to Worry About Saturated Fat

Ohh saturated fat, where do I even begin?  You've been vilified for decades by the likes of the USDA, the American Heart Association, and the Academy of Nutrition and Dietetics (formerly the American Dietetic Association... new name, same haters).  Foods high in saturated fat will clog our arteries and kill us, they say.  In fact, in the newest version of the Dietary Guidelines for Americans, the USDA has taken the war on saturated fats to a new level with the creation of a new category known as "SoFAS".  While that may look like it was typed by a 14-year-old girl on Twitter, it is in fact an acronym for "solid fats and added sugars", and the guidelines recommend we avoid them like the plague.  With the creation of this new category, traditional sources of saturated fat like grass-fed butter and coconut oil are now considered equal to processed junk like Crisco and candy corn.  Seriously.  This is what our government is telling us.

But why?  Why do they think saturated fat is going to clog our arteries and kill us?  There are three parts to this hypothesis, and they go like this...
  1. Saturated fat in the diet increases the cholesterol levels in your blood
  2. High cholesterol in the blood is associated with heart disease
  3. So, high saturated fat intake leads to heart disease
Sounds good right?  Not quite.  This is the circa-1990, total-cholesterol-is-everything, eat-more-low-fat-cookies-and-throw-out-the-yolk theory of heart disease.  I hate that theory of heart disease.  In this article, I'll attempt to disprove the first and third parts of this:  whether or not saturated fat leads to high cholesterol and/or heart disease.  I'll ignore the second part, because it's a little off-topic and it becomes irrelevant with the collapse of the first part.  Plus I've covered the cholesterol thing in the past (1, 2, 3).  Here we go...


Does eating saturated fat give you high cholesterol?
Most clinical trials are in agreement on this one.  When participants are asked to eat more saturated fat, their cholesterol typically goes up.  But these studies have one key limitation:  their short duration.  The typical clinical trial showing the saturated fat and blood cholesterol connection is only 2-13 weeks long (4).  What happens in the long-term?  While we don't have any controlled, clinical trials of this length, there has been plenty of prospective, observational research conducted.  And even though research of this type usually takes a backseat to the more controlled trials, it comes in particularly handy here.  Dr. Stephen Guyenet recently conducted a review of this type of research on his blog, Whole Health Source, citing eight such prospective studies (5).  Of the eight, only one showed a connection between saturated fat intake and blood cholesterol, and that one connection was a weak one.  In other words, people in the real world who eat a high saturated fat diet generally have the same cholesterol levels as those who eat a low saturated fat diet.  This is clearly at odds with the clinical evidence showing that saturated fat causes a spike in blood cholesterol.

The likely truth is that saturated fat intake does increase blood cholesterol in the short term, but that this effect fades over time.  Long term research indicates a minor increase at best, and quite possibly no relationship at all.  This is consistent with what has been observed in several other animal species as well; why would humans be any different (6)?  Yet the idea that saturated fat increases cholesterol is so engrained in the scientific community and the media that you're likely to get some weird looks at the very suggestion that it's not true.  I know I have.  But that doesn't make me wrong.  I'm sticking to my guns.  I do believe, however, that even though saturated fat doesn't ultimately affect total cholesterol, it alters the balance of HDL and LDL, as well as modulates LDL particle size.  But that's more detail than I care to go into right now.  Perhaps another time.

Does eating saturated fat increase your risk for heart disease?
Proponents of the aforementioned hypothesis will tell you that since saturated fat increases blood cholesterol, and high cholesterol leads to heart disease, then saturated fat obviously leads to heart disease.  As we've seen already, the first part of that statement isn't true.  And if you've read my past articles on cholesterol, then you know that the second part isn't quite right either.  So that brings us to the third and final part (which ends up being sort of redundant since it crumbles by default along with the first two, but I will ask the question anyway; perhaps you're not fully convinced).  Does saturated fat consumption increase your risk for heart disease?

No it does not.  As my proof, I offer you a pair of well-done meta-analyses.  A meta-analysis, for those of you who don't know, is a type of scientific study.  Essentially, it is a study of studies.  In other words, it looks at the data from several existing papers and pools them together to find the bigger picture.  It is significantly more informative than any single study because it takes an (ideally) unbiased look at the data as a whole.  My first meta-analysis was performed by Dr. Ronald Krauss and company.  They took a look at 21 prospective epidemiological studies that had looked at this saturated fat and heart disease thing before (7).  Out of the 347,747 subjects in all 21 studies combined, 11,006 of them developed coronary heart disease (CHD) or stroke.  And I quote, "Intake of saturated fat was not associated with an increased risk of CHD, stroke, or CVD (cardiovascular disease)."  I think that speaks for itself.  On to my second meta-analysis.  This one, which I think I've mentioned like ten times on this blog, was done by Dr. Dariush Mozaffarian and colleagues at Harvard (8).  Although their study specifically targeted red meat and its relation to heart disease, stroke, and diabetes, it also has key implications for saturated fat consumption.  Out of the 20 studies they chose to look at, consisting of 1,218,380 participants, they found a very significant link between processed red meats and chronic disease.  There was no link, however, between unprocessed red meat and chronic disease, and this was irrespective of saturated fat content of the meat.  So, to clarify my point, processed meats like the low-in-fat deli turkey were associated with higher rates of heart disease, stroke, and diabetes.  But unprocessed meats like a not-low-in-fat rib-eye steak showed no connection. So then, the summation of a combined 41 studies, and 1,566,127 participants (FYI: that's more than the population of eleven U.S. states), shows no connection between saturated fat intake and heart disease. 

Oh, and there's another piece of evidence that I've written about in the past.  It's a completely observational look at saturated fat and heart disease in countries across Europe (9).  It turns out, the seven European countries that eat the most saturated fat all have lower rates of heart disease than all seven of the countries that eat the least saturated fat.  Sounds ass-backwards right?  But it's real.  Check it out.

Of course, no blog post of mine would ever be complete without the evolutionary biology view.  The most up-to-date research on the diets of our hunter-gatherer ancestors, which constituted our diet as humans for over 99% of our existence, shows that we consumed 10-15% of our calories from saturated fat (10).  Anything outside of that range would be considered to be the exception rather than the rule, and is likely to be discordant with the human genome.  In contrast, the current USDA recommendations say to keep our intake of saturated fat below 10% of total calories.  So I'm not saying you should base your diet on lard, but should you make a conscious effort to avoid saturated fat?  Absolutely not.  Incidentally, if you choose to eat real foods, like meat, fish, eggs, fruits, veggies, dairy, and potatoes, you'll likely end up with a saturated fat intake right around that 10-15% range.


And after all that, I must admit... I don't really like discussing saturated fat like this, as if it's all the same stuff.  There are all different kinds:  you've got beef fat, grass-fed beef fat, pork fat, chicken fat, milk fat, grass-fed milk fat, egg fat, coconut fat... hell, there's even saturated fat in vegetables, albeit in very small amounts.  There are at least eight important saturated fatty acids found in food, and each of these food sources offers them in a varying proportions.  It's almost useless, in my opinion, to assess saturated fat as a whole like I did in this article; I'd much rather look at one type at a time in a food-based fashion.  We eat foods.  We don't eat all saturated fats equally, and we don't eat individual fatty acids either.  It only makes sense to study them the way we eat them.  Next time on the blog, I'll do exactly that and focus on dairy fat.  I know you're looking for a reason to spoon-feed yourself butter, so stay tuned!

1 comment:

  1. Great post Burn! Can't wait to read the next on dairy fat! Keep up the great work.

    ReplyDelete