Dietary Cholesterol impact on Blood Cholesterol

This has been a back and forth subject for some time, with much confusion in the air; this has been especially true as the dietary guidelines committee was called upon to change their guidelines on dietary cholesterol from a set mark to, well, erasing it. With several review papers expressing the body of literature as swaying toward dietary cholesterol not being as big a factor, the dietary guidelines have now gotten rid of their cholesterol limitations – should they have? Let’s find out.

Dietary Cholesterol on Serum

Dietary recommendations were set at “below 300mg” a day with the last dietary guidelines, and yet have now removed these recommendations, so cholesterol is “free game” [1]?

The dietary guidelines still caution to keep an eye on cholesterol, but for a good portion of the population, it may just be okay to consume higher levels of cholesterol – within reason.

It comes down to this: dietary cholesterol does increase total cholesterol, but by a much smaller margin than initially thought [2][3][4]. The initial thought process was based on a “in and out” model; meaning, high levels of cholesterol in leads to a rapid upswing in serum (aka, blood) cholesterol. However, a closer look at the body of research indicates that the body is more resilient than we gave it credit, as low and high values of cholesterol have a modest impact on serum cholesterol [2][3][4].

The recommended serum cholesterol (not to be confused with dietary – what you eat) is set at below 200 mg/dL (11.1 mmol/L) – let us take that as our bench mark [5].

The confusion mostly comes from the fact that dietary cholesterol impact is highly variable from person to person, so pinpointing recommendations can be difficult, but assuming a person is hypercholesteremic (meaning, they innately have high cholesterol), per consumption of 100mg of dietary cholesterol, there has been a 3.2 mg/dL (0.18 mmol/L) increase in serum cholesterol [2]. So, assuming you consume 1000 mg of dietary cholesterol (5-6 eggs worth), the higher end increase in serum would be a 32 mg/dL (1.8 mmol/L) increase. However, that is in people with already high cholesterol levels, so what about most people without cholesterol issues?

In that case, people might expect around an increase of 1.5 mg/dL (0.08 mmol/L) increase in total serum cholesterol per 100mg of dietary cholesterol, so around 15 mg/dL (0.8 mmol/L) per 1000mg (5-6 eggs) [2]. That is a lot of cholesterol intake for a modest bump in serum cholesterol.

That, however, is not the end of the story…

Increases in total cholesterol can be further broken down into their constituent parts, primarily High Density Lipoprotein (HDL – “good cholesterol”) and Low Density Lipoprotein (LDL – “bad cholesterol”), as well as others – we will focus on these two extremes.

While there is a modest total increase in cholesterol, there is, predictably, an increase in LDL cholesterol, and yet there is also a proportional increase in HDL cholesterol [2]. This means that although total cholesterol may increase due to increases in LDL cholesterol, there is a compensation through an increase in HDL cholesterol to regulate cholesterol in the body.

So, all in all, dietary cholesterol does impact serum cholesterol, but the changes are mild when contextualized with a standard diet, and the occasional high intake of cholesterol will have no real-world impact. Not only that, what increases there are in cholesterol are also attenuated by proportional increases in HDL cholesterol. So, healthy populations with cholesterol levels below the serum recommendations do not need to worry over their cholesterol intake, and those with moderate to high cholesterol can ease off the paranoia by being mindful, but not obsessive.

Understanding the
Physiology

While I have an entire article describing the physiology of cholesterol, it is important to point out why dietary cholesterol may not have as dramatic an impact on serum cholesterol as we initially thought. To do this, we must delve into some of the physiological modifications our body undergoes.

As free cholesterol (as seen in diet) is absorbed by the intestine, it is packaged to the liver, as well as released in HDL packages to the blood stream (eventually, also making its way to the liver). The liver then repackages free cholesterol into various LDL iterations to eventually end up as LDL particles. If consumption of cholesterol is low, the liver will synthesize more, as cholesterol is necessary for varying key cellular functions (hormones, cell walls, etc.). If cholesterol in the diet is high, there are a variety of feedback mechanisms that prevent serum cholesterol from increasing equally – this is why serum cholesterol increases modestly.

The first of these mechanisms is a reduced absorption by facilitated diffusion into the epithelial cells of the intestine. Yet, even at this level, we absorb cholesterol continuously, so as LDL particles increase in number due to increased intake and/or synthesis, they are eventually also rejected from peripheral tissues that would normally use this cholesterol for varying cellular processes. So, cholesterol is being released from the liver, dietary intake is allowing cholesterol in, and the periphery (muscles, heart, kidneys, other organs) is not clearing said cholesterol – this leads to large amounts circulating in serum. So, what does the body do – other than reduce absorption?

It has a cellular feedback mechanism based on receptors on the cell walls, so the hepatocyte (aka, liver cell) receptors for LDL cholesterol get saturated, leading to the hepatocytes to knock down synthesis of cholesterol – this eliminates another source of contribution. However, there may still be high levels of LDL, possibly from dietary, so the liver begins excreting cholesterol in bile, which is then excreted in our stool. Not only that, it may produce HDL particles, along with the intestine, to help regulate the extra-hepatic cholesterol found in LDL, tissues, and generally across the body, and these HDL particles will pick up unwanted free cholesterol and return them to the liver to be excreted.

So, you can see, through feedback and transport mechanisms, the body takes into account dietary cholesterol by knocking down its own synthesis of cholesterol and the opposite is seen when no dietary cholesterol is incoming.

SUMMARY

All things considered, dietary cholesterol does play a role in serum cholesterol numbers, but the numbers ingested are far more lenient than previously imagined. A person would need to consume a rather large amount of cholesterol, every day, to see a noticeable increase in blood cholesterol numbers – this does not even take into consideration if this rise in cholesterol would increase HDL (“good”) cholesterol, as well – which it tends to do. So, aside from consuming grams of cholesterol or being cholesterol sensitive, dropping the recommendation to consume under 300mg a day is likely an educated move.

Author: Nicolas Verhoeven
References

[1] New Dietary Guidelines remove restriction on total fat and set limit for added sugars but censor conclusions of the scientific advisory committee. (2017, November 20). Retrieved from https://www.hsph.harvard.edu/nutritionsource/2016/01/07/new-dietary-guidelines-remove-restriction-on-total-fat-and-set-limit-for-added-sugars-but-censor-conclusions/

[2] McNamara, D. J. (2013). Cholesterol intake and plasma cholesterol: an update. Journal of the American College of Nutrition. Retrieved from https://www.ncbi.nlm.nih.gov/pubmed/9430080

 

[3] Griffin, J. D., & Lichtenstein, A. H. (2013). Dietary Cholesterol and Plasma Lipoprotein Profiles: Randomized Controlled Trials. Current Nutrition Reports, 2(4), 274-282. doi:10.1007/s13668-013-0064-0
 

[4] Hopkins, P. N. (1992). Effects of dietary cholesterol on serum cholesterol: a meta-analysis and review. American Journal of Clinical Nutrition, 55(6), 1060-1070. Retrieved from https://www.ncbi.nlm.nih.gov/pubmed/1534437
 

[5] Cholesterol test - About - Mayo Clinic. (2016, January 12). Retrieved from https://www.mayoclinic.org/tests-procedures/cholesterol-test/about/pac-20384601
 

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