The term “cholesterol” gets thrown around like a football at MetLife Stadium, being tossed between opposing ideas and theories. Once upon a time, research deemed cholesterol as the devil, shunning it from the health world and isolating it from its other dietary counterparts. A couple of decades later, new research emerges claiming it’s not so bad after all. Despite the confusion stemming from the debate, more and more studies are coming out of the woodwork on cholesterol and what its true role in the body entails.
What is cholesterol in the first place? It’s a waxy, fat-like substance that is found in all of our cells. The body needs cholesterol to produce certain hormones (i.e., testosterone and progesterone), help create Vitamin D, make up digestive bile acids in the intestines and contribute to the structure of our cell walls. The body actually doesn’t need external sources of cholesterol; it produces all the cholesterol it needs by itself.
Cholesterol travels through our bloodstreams in small packages called lipoproteins. There are two types of packaging that are used: low-density lipoproteins (LDL) and high-density lipoproteins (HDL). The amounts of these types of lipoproteins in our bodies can have a significant impact on our health. LDL cholesterol is known as the evil stepsister of lipoproteins, as too much of them can wreak havoc on your arteries. LDL cholesterol can form a thick and hard deposit in the arteries, making them narrower and harder for blood to pass through. Blood carries oxygen to the heart, so if the blood supply is blocked by cholesterol-infused arteries, a myocardial infarction (aka heart attack) can occur. High levels of LDL cholesterol can also increase risk of heart disease and stroke. LDL levels in the blood should not exceed 100 milligrams/deciliter (mg/dL).
HDL, on the other hand, is the fairy godmother of lipoproteins, ridding our bodies of excess and unwanted LDL cholesterol. It carries the cholesterol to the liver, where it’s then removed from our bodies. It also helps clean up clogged arteries, lowering our risk for any heart-related issues. Desirable blood levels for HDL should be at least 60 mg/dL.
What causes high LDL cholesterol levels? Is it the food we put in our bodies or the sheer misfortune of genetics? This has been a highly debated question for decades. It was initially hypothesized that diet was the main culprit behind high blood cholesterol. Dietary cholesterol can be found only in animal sources like egg yolks, dairy products, shellfish, meats and poultry. The Dietary Guidelines for Americans used to recommend limiting our cholesterol intake to about 300 mg/day. To give you an idea of what 300 mg of cholesterol looks like, picture four pieces of fried chicken or 14¼ slices of salami. However, due to the new research that has been burgeoning providing inconclusiveness on the matter, they have removed that recommendation, concluding with a general statement to just limit dietary cholesterol.
In a study done by Kratz (2005), he found that an increase in dietary cholesterol intake resulted in a minimal increase in total cholesterol and HDL levels. Griffin and Lichtenstein (2013) also concluded that dietary cholesterol has only a modest effect on plasma lipid concentrations.
In terms of cholesterol and cardiovascular disease (CVD), similar results were seen. A systematic review and meta-analysis done by Berger et al. (2015) on dietary cholesterol and cardiovascular disease deemed past and current research inconclusive. Shin et al. (2013) conducted a review/meta-analysis on egg consumption and CVD. Eggs were the quintessential example of foods once thought to cause high blood cholesterol. Results showed that individuals who ate an egg a day didn’t have a significantly higher risk of CVD than those who never consumed eggs daily.
Current research has found that our bodies tightly regulate blood cholesterol levels by controlling the amount it produces. When we eat more cholesterol, our bodies in turn produce less and vice versa. Therefore, what we eat may have little impact. However, in about 25 percent of the population, a high dietary cholesterol intake does impact blood cholesterol levels. These individuals are known as “hyperresponders” and their tendency towards high serum cholesterol is most likely genetic. There is currently blood test to find out whether someone is a hyperrresponder other than finding out the hard way, after the fact.
In conclusion, there is no concrete research that confirms dietary cholesterol’s impact on blood cholesterol levels. It is difficult to create a research study that can purely study the sole effect of dietary cholesterol on blood cholesterol. There are a number of potentially confounding factors that can affect research results. For example, there are foods that are both high in cholesterol and saturated fat. The saturated fat can affect the blood cholesterol level, skewing the results and hindering researchers’ ability to truly determine a relationship between these two factors. Another confounding factor can be the inverse relationship of dietary cholesterol intake and fiber, which can also skew results. In the meantime, consumers can follow a diet rich in moderation, full of fruits, vegetables, whole grains and legumes, sprinkled with animal sources if that is what your heart desires, until research has commanded otherwise!
By Melissa Papir Kolb, MS, RD