Cholesterol sounds taboo for some because it is thought as something abnormal. Nevertheless, it is something that keeps us alive and allows us to keep cell membranes in check through the transportation of molecules and by creating hormones which are important biological components that regulate our body’s needs. Cholesterol is a waxy substance found in our blood that binds to protein. The combination of proteins and cholesterol forms what we call “lipoproteins.”[1] The importance of cholesterol in our diets is essential, but what happens when there are high levels of it in the bloodstream? Two things can happen in the body depending on genetics and diet; however, before expanding on this, let us examine how cholesterol is processed in the body.
Figure 1. General Overview of Fat Metabolism[2]
The CDC daily intake recommends for adults to consume the following macronutrients: 45-65% carbohydrates, 20-35% fat, 10-35% protein.[3] These macronutrients are broken down with the help of enzymes, which are molecules that allow us to synthesize a substrate or material being absorbed into the bloodstream. These molecules that are being absorbed provide the body with energy and the necessary biochemical components to function and survive. As we shift into the discussion of fats, the only macronutrient discussed in this article will be about exogenous fat; however, the USDA explains in great depth about the other macronutrients, such as proteins and carbohydrates breakdown, which can be examined further independently.[4] So, when we eat a meal that contains fat or exogenous lipids, the stomach, and particularly the small intestines, have fat signal molecules, called chemoreceptors, and submucosa cells that detect fat content and release cholecystokinin, or CCK. CCK is a hormone produced by I-cells in the lining of the duodenum that contracts the gallbladder to release bile salts into the duodenum. Pancreatic enzymes released in the duodenum are responsible for the hydrolysis of fats by forming them into a globule. The globule is called micelle which encloses triglycerides and cholesterol. This micelle can then pass through the intestines into bloodstream. The polar heads or water loving side of the phospholipid will be facing inwards and the nonpolar tails will face outwards, allowing the micelle to cross the barrier between the epithelium of the intestines and the bloodstream as shown in Figure 2.
Figure 2. Micelle Formation [5]
Before fats can enter the bloodstream, there is a crucial step that allows them to be carried to their destination – this is the addition of apolipoprotein-B48, or Apo B-48. This lipoprotein allows for chylomicrons, which are previously broken pieces of fat made for ease of transport, to be carried into the bloodstream. The chylomicron-Apo B48 complex then begins attracting other lipoproteins. Apolipoprotein-E and apolipoprotein-CII, or Apo-E and Apo-CII, respectively, are the two lipoproteins that attach to the chylomicron-Apo B48 complex. As shown on Figure 3, Apo-E is the molecule responsible for binding to the surface receptors on endothelial cells, called lipoprotein lipase, that are responsible for the break down into the components fatty acids and triglycerides which form cholesterol-ester. These components are easier to transport into tissues. But we cannot forget our friend Apo-CII, which is responsible for the activation of fat metabolism and maintaining a lipid balance. Apo-CII is secreted by the liver into the bloodstream to enhance the triglyceride hydrolysis of VLDL and energy delivery to organs.
All of these sophisticated processes designed to deliver fat to tissues is what keeps us alive and allows for the proper transportation of other nutrients to the correct locations.
Figure 3. Lipoprotein Overview[6]
We know that consuming high cholesterol-rich foods is a significant risk for health complications from chest pain and heart attacks to strokes. [7] Nowadays, it is hard to manage cholesterol since many foods are rich with nutrients, with some being “good” and others “bad”. With our busy, fast-paced lives, some do not look at the nutritional facts of the food they purchase, missing the importance of eating the proper amount of daily nutrient recommendations. The recommended consumption of total cholesterol a day is 200 mg a day.[8] That is mind-blowing because from personal experience, eating two whole eggs is about 300 mg according to the nutritional values of most eggs, depending on their size. It is hard to imagine including all the other foods that contain cholesterol in daily cholesterol consumption calculations. The Table below provided by the Cleveland Clinic shows the target cholesterol levels by age and sex.
The key to controlling cholesterol is by tracking how much cholesterol we consume in our diet. This may seem challenging, but with most people owning a smartphone, tracking food consumption has become easier than ever. For example, there is an app called MyFitnessPal that can be used to track diet and exercise. One of the app’s features gives the ability to track nutrients by the product barcode. For example, the camera can scan the egg product/bar code shown in Figure 4 and display the screen shown in Figure 5.
Figure 4. Egg Bar Code
Figure 5. MyFitnessPal App Screen Shot of Egg Macronutrient and Mineral Distribution
The image in Figure 5 shows that consuming one egg is 185 mg of daily cholesterol recommendation, which is almost the full amount recommended. Below is a list of commonly consumed foods high in cholesterol shown in Figure 6.
Figure 6. Contraindicated Foods to Avoid High Cholesterol[10]
It is important to understand cholesterol is necessary for many processes in our bodies, but limiting cholesterol can have detrimental effects, as well. Controlling the amount of cholesterol we consume is key to a more fruitful life and the chance for higher survival. [11]
It is important to emphasize that controlling the risk of high cholesterol can reduce the likelihood of developing cardiovascular diseases. This can easily be prevented by consuming the recommended nutritional values. What you put in your body is what it will turn out to be.
[1] “High Cholesterol – Symptoms and Causes,” Mayo Clinic, accessed September 19, 2021, https://www.mayoclinic.org/diseases-conditions/high-blood-cholesterol/symptoms-causes/syc-20350800.
[2] Bonnie C. H. Kwan et al., “Lipoprotein Metabolism and Lipid Management in Chronic Kidney Disease,” Journal of the American Society of Nephrology 18, no. 4 (April 1, 2007): 1246–61, https://doi.org/10.1681/ASN.2006091006.
[3] “2020-2025 Dietary Guidelines for Americans: We Want to Hear from You,” accessed September 19, 2021, https://www.usda.gov/media/blog/2018/03/01/2020-2025-dietary-guidelines-americans-we-want-hear-you.
[4] “2020-2025 Dietary Guidelines for Americans.”
[5] Aditi M. Jhaveri and Vladimir P. Torchilin, “Multifunctional Polymeric Micelles for Delivery of Drugs and SiRNA,” Frontiers in Pharmacology 5 (2014): 77, https://doi.org/10.3389/fphar.2014.00077.
[6] J. P. D. Reckless and J. M. Lawrence, “HYPERLIPIDEMIA (HYPERLIPIDAEMIA),” in Encyclopedia of Food Sciences and Nutrition (Second Edition), ed. Benjamin Caballero (Oxford: Academic Press, 2003), 3183–92, https://doi.org/10.1016/B0-12-227055-X/00613-1.
[7] “Patient Education: High Cholesterol and Lipid Treatment Options (Beyond the Basics) – UpToDate,” accessed October 15, 2021, https://www.uptodate.com/contents/high-cholesterol-and-lipid-treatment-options-beyond-the-basics.
[8] “Cholesterol: Types, Tests, Treatments, Prevention,” Cleveland Clinic, accessed October 15, 2021, https://my.clevelandclinic.org/health/articles/11920-cholesterol-numbers-what-do-they-mean.
[9] “Cholesterol.”
[10] “Top 10 Foods Highest in Cholesterol,” myfooddata, accessed October 15, 2021, https://www.myfooddata.com/articles/foods-highest-in-cholesterol.php.
[11] John B. Warren, Simon B. Dimmitt, and Hans G. Stampfer, “Cholesterol Trials and Mortality,” British Journal of Clinical Pharmacology 82, no. 1 (July 2016): 168–77, https://doi.org/10.1111/bcp.12945.
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