This morning, you might have had an egg white omelet cooked in canola oil with two pieces of whole wheat toast, lightly ‘buttered’ with margarine.
I had a lard-greased pan of bacon and eggs.
Who had the healthier breakfast? The answer might surprise you!
Behold: a brief history of saturated fat, cholesterol, and heart disease (and how rabbits are not humans).
The 20th century witnessed the appearance of a new ferocious killer: heart disease. In 1900, it was the fourth most common cause of death and since 1940, it’s been the number one killer. The scientific community took notice and began frantically looking for the cause.
In 1953, a researcher named Dr. Ancel Keys published a study examining animal fat consumption (i.e. saturated fat) and heart disease in 6 countries. This was an observational study and lead to many more publications on the same topic (notably the famous Seven Countries study).
The results were compelling! When plotted on a graph, the points lined up neatly, showing a near-perfect correlation between saturated fat intake and heart disease. This was interpreted as meaning that eating saturated fat = clogging of arteries = development of cardio-vascular disease (CVD).
With that, the low-saturated-fat-craze was off to the races. Do you have hypertension, high cholesterol, or high tryglycerides?
No more bacon for you.
Since animal fats looked like the bad guy, scientists started targeting cholesterol, which is found hand-in-hand with saturated fat in animal foods. Enter: studies looking at dietary cholesterol and heart disease.
In a famous experiment, researchers fed rabbits cholesterol.
Shortly thereafter, the rabbits developed atherosclerotic lesions, and CVD.
This idea is wrapped-up into the Lipid Hypothesis (also called the diet-heart hypothesis): The cholesterol you eat becomes the cholesterol in your blood, and the cholesterol in your blood blocks your arteries and is the source of heart attacks.
Time to throw your red meat, eggs, butter, and bacon away.
Of course not, silly!
Time for the fun part.
Let’s start with the rabbits.
In the rabbit experiment, the problem was, of course, that rabbits are herbivores. No wonder they got sick when fed cholesterol, something found solely in animal foods, which herbivores are never supposed to eat in the first place. The effect of dietary cholesterol on herbivores cannot be extrapolated to indicate our human ability to deal with it.
In fact, the way we respond to ingesting cholesterol is quite simple: dietary cholesterol is poorly absorbed and rapidly excreted, and has zero influence on the levels of cholesterol in our bloodstream. Our cholesterol levels are tightly regulated by our liver, and we actually make as much as we need to create cell membranes, and synthesise vitamins (among other awesome body things).
Again: no matter how much cholesterol you eat, it will not have any effect on your blood cholesterol.
Despite the mountain of evidence disproving both the Ancel and rabbit studies, the notion that eating cholesterol raises blood cholesterol has stuck around for a long time. Finally, today, after decades of throwing egg yolks into the sink, cholesterol is being absolved and the scientific community is accepting its innocence. In fact, The Dietary Guidelines Advisory Committee has lifted their limit on cholesterol intake, and we hope that the new USDA Nutritional Guidelines for Americans (to be published later this year) will also reflect this. In the DGAC’s own words, “cholesterol is no longer a nutrient of concern”.
Remember Dr. Keys, the scientist who published the 7 Countries Study? Even he stated that dietary cholesterol has no impact on the cholesterol in your arteries.
“From these animal experiments only, the most reasonable conclusion would be that the cholesterol content of human diets is unimportant in human atherosclerosis.”
What about saturated fat? For starters, we know that on a molecular basis, saturated fat directly stimulates cholesterol synthesis and increases circulating blood levels of it.
– However, saturated fat does increases blood levels of cholesterol.
So this means we should stop eating saturated fat, right?! Because if we eat saturated fat, we will have increased blood levels of cholesterol, and this will clog our arteries and give us heart attacks.
PLOT TWIST ALERT!
I know, shocking.
The idea that high blood cholesterol causes heart disease is accepted as gospel by the general public- but we are realising it may not be the case.
Let’s look at some evidence:
– More than 40 trials have been performed to determine whether lowering cholesterol levels can prevent heart disease. In some trials heart disease rates went down, in others they went up. But when the results of all of the trials were taken together, just as many people died in the treatment groups (who had their cholesterol levels lowered by drugs) as in the control groups (who had no treatment).
– Women suffer 300% less heart disease than men, in spite of having higher average cholesterol levels. At the Conference on Low Blood Cholesterol, which reviewed 11 major studies including 125,000 women, it was determined that there was absolutely no relationship between total cholesterol levels and mortality from cardiovascular or any other causes.
– A recent study in the Journal of American Medical Association indicated that high LDL cholesterol is not a risk factor for from coronary heart disease (CHD) mortality or total mortality (death from any cause).
– In patients who have already had a heart attack, low serum cholesterol is associated with a marked increase in mortality.
– Among 136,000 patients hospitalised for a heart attack between 2000 and 2006 in the US, 50% of them had normal levels of cholesterol.
There is a lot of data, and all in all, sound and reliable medical research has not proven that lowering (or low) cholesterol in and of itself reduces risk of death from heart disease across a population.
It seems that the real culprits are inflammation and oxidative stress, not high blood cholesterol. Inflammation in our arteries is caused by eating refined carbohydrates and trans fats. This inflammation leads to the oxidation of LDL particles, plaque buildup, and CVD. Looking at total cholesterol doesn’t matter- what is of greater importance is the degree to which your arteries are inflamed and your cholesterol is oxidised.
Have you heard of ‘The French Paradox’? (I’m feeling very patriotic right now).
This is the ‘confusing’ observation that has always startled researchers, which is that the French eat diets high in saturated fats, but have lower incidences of Coronary Heart Disease than most other developed nations.
So what about Dr. Keys and his seven countries study?
Since you, my dear readers, know all about the pitfalls of observational studies, you know that correlation does not mean causation (I explained this here). So sure, countries with higher animal fat intake have higher heart disease rates, but what Keys’ graph does not show is any indication that eating saturated fat will give you heart disease (nor indeed, that it doesn’t).
Here’s what his graph would’ve looked like taking into account La France.
[If you’d like to know more about all the confounding factors in Dr. Keys’ analysis, please head over to this post by the incredible Denise Minger.]
So what are we left with?
Dietary cholesterol has no influence on blood cholesterol. Saturated fat increases blood cholesterol, but blood levels of cholesterol alone are not a good indicator of heart disease. There are some better markers, such as oxidation and inflammation levels (which can be measured by your doctor), as a predictor for heart disease.
As I’ve mentioned before here, reducing saturated fat intake is much less of a concern than staying away from refined carbohydrates, sugar, trans fats, smoking, stress, and insufficient physical activity. Maintaining heart health is about keeping inflammation at bay, not about having low levels of blood cholesterol.
And who ever said food blogs just make you feel depressed about eating? Throw away your margarine and go fry up some bacon – your heart will thank you for it.