Entire walls of books at Barnes and Noble.
Really, really stupid article titles like, “Eggs are as Bad as Smoking”.
These are the things that come to mind whenever someone brings up the topic of dietary fat and heart disease.
I think the biggest issue with this whole discussion is people take a side, entrench themselves, and then can’t get out of it. If you ever find someone so entrenched on a given topic that they appear unreasonable, it is because they know enough to be dangerous but not enough to really know what they are talking about.
I am going to follow the advice of my 7th grade speech coach for this article and follow a 3 step process:
- I am going to tell you what I am going to tell you
- I am going to tell you those things
- I am going to tell you what I told you.
Ok, here we go. Here is what I am going to tell you in this article: diet plays a big role in chronic disease but I REALLY doubt that the exact type of fat you eat (trans-fats withstanding) and in the exact ratio you eat them is what is going to determine whether you die at 40 of a heart attack or have a healthy ticker to age 100.
Now that you know what I am going to tell you, let me tell you those things.
What does big data tell us?
My formal training to be a certified nerd was in exercise, metabolism, heart disease, and biostatistics, which oddly makes me a great person to tell you about what we know about large sets of nutrition data and what it tells us about heart disease.
Science almost always begins with making an observation and going, “hmmmm, that is interesting” and then repeated that observation until you can formulate a very specific question, also known as a hypothesis. Let’s start there, with observation.
Most of the “saturated fat causes heart disease” story relies on observation*. When we take all the observations we have made about dietary fat and heart disease, here is what we really know. When you look at the observational data in its entirety it is a total crap shoot.
Depending on which population you look at, how you define saturated fats (not all studies define it the same way), how you measure intake, what type of analysis you do, the time period of the population you are examining, and how well you control for confounding variables you can almost cook up any association you want.
There are a lot of papers showing saturated fat is associated with an increased risk of cardiovascular disease1,2,3. There other papers showing that saturated fat is associated with a decreased risk of cardiovascular disease4,5. And there are other papers showing no association what so ever.
I would personally argue that the observations might support a small increased risk from saturated intake over time but my confidence in that is about the equivalent of my post-college days of winning beer pong games (~56%).
This presents a substantial problem with saying anything concrete. Sure, you can dig REALLY deeply into the methods and redo studies and try and answer some questions and get a little bit better picture.
But the real story is that the relationship does not appear very clear and that heart disease is much more complicated than just saying, saturated fat is associated with heart disease in a few papers so we should remove it from our diets. We probably need to dig a little deeper.
Feed People Fat, Watch What Happens
Observational data from larger numbers of people is a great place to start asking questions. What you really need are experiments that you can interpret and establish some level of confidence about cause and effect.
That means you need to fiddle with things to see if you can make your observation come true. Meaning, if you hypothesize that saturated fat does cause heart disease than giving people saturated fat, or taking it away, will cause or prevent heart disease.
Thanks to a huge funding push from the NIH between the 1980s through the mid 2000s there are thousands of studies available to look at that have manipulated dietary fat and examined the effect on rates of heart disease (Figure 1).
I will spare you the gory details and a 500,000 word tome discussing these studies and summarize what we can learn. Similar to the observational research, modifying the diet with either saturated fat or unsaturated fat also has a fairly mixed effect on heart disease with a lot of studies showing unsaturated fats decrease risk, while others show an increased risk.
Looking at the data in aggregate it appears that swapping out some of your saturated fat with unsaturated fat lowers your risk of heart disease, but does not robustly “prevent” it. On this topic, I would argue that the observations might support a small decrease in the risk of cardiovascular disease by replacing some of your saturated fat intake with unsaturated fats.
My confidence on this is on par with the grade I got in my first college chemistry exam (76%, boy was that a rude awakening, I guess you have to study in college).
Saturated Fat and Atom Bombs
Here is where things start to get really, really interesting. It is also the last thing I am going to tell you about.
For something to cause something, like saturated fat causes heart disease, you have to show how it works; there has to be an underlying mechanism. For example, you can’t just say an atomic bomb explodes, you have to know how it works at an atomic physics level to make it work**.
The same thing applies to heart disease and there are some really big problems with the dietary saturated fat is a major cause of heart disease idea.
First, we have used animal models to support most of this work, which presents a major problem.*** So taking a study done in mice and citing, “Aha, see saturated fat does/does not cause heart disease”, is highly problematic.
Second, we have identified dozens of things that can lead to heart disease (e.g. inflammation, hypertension, smoking, lack of exercise, etc.) which means that there isn’t one singular cause but an accumulation of things that cause heart disease.
Conclusion (AKA is bacon a health food or will it kill me?)
Even as a scientist the massive amounts of data on this topic make it difficult to parse through. What we can conclude from a huge body of evidence is that any potential role saturated fat plays in heart disease has be to taken in the context that it is but one potential risk factor among dozens that also play a substantial role.
On the whole it appears that the evidence favors controlling, and in some cases lowering, saturated fat intake if you want to minimize your overall risk for heart disease. This means that bacon is neither health food, nor a death sentence.
Consider your overall saturated fat intake in the context of the rest of your overall diet, exercise, and overall health metrics. For a very in-depth analysis of other factors I direct you to a very nice review published in Trends in Cardiovascular Medicine written by yours truly6.
*Meaning you just observe, you don’t directly do an experiment so you can’t actually prove something causes something. You can only say “look these two things appear related”.
**Atomic physics is easily one of the most fascinating topics on the planet. You should YouTube this stuff and bone up on your physics because nuclear physics is what holds the universe together.
*** This is very strange in that mice don’t get human like heart disease and this has presented a BIG problem in research. I have more thoughts on this but this is a much different, far nerdier discussion than necessary here. But for your perusal here are a few interesting papers on the topic7,8. As someone who works with animal models in research and did their dissertation in cardiovascular work I would love to talk to anyone interested, email me.
- Meta-analysis of prospective cohort studies evaluating the association of saturated fat with cardiovascular disease
- Dietary Fat Intake and the Risk of Coronary Heart Disease in Women
- Meta-analysis of prospective cohort studies evaluating the association of saturated fat with cardiovascular disease.
- Dietary fats, carbohydrate, and progression of coronary atherosclerosis in postmenopausal women
- Saturated fat prevents coronary artery disease? An American paradox
- Dietary strategies for cardiovascular health.
- Small animal models of cardiovascular disease: tools for the study of the roles of metabolic syndrome, dyslipidemia, and atherosclerosis
- Small mammalian animal models of heart disease