Cholesterol: an about-face

A recent (February, 2015) report by the Advisory Panel to the US Departments of Health and Human Services (HHS) and Agriculture (USDA) has removed dietary cholesterol as “a nutrient of concern”, thereby overturning decades of stern and adamant advice. They did this unapologetically.

Nevertheless, the science has been around for a while now – dietary cholesterol does not have a significant impact on overall blood cholesterol. The important distinction here is between dietary cholesterol (that you eat) and blood cholesterol (that is in your bloodstream).

Consistent with their decision that dietary cholesterol is no longer a health concern, the Advisory Panel has removed any recommendation for limiting its daily intake.

2013-10-17 11.11.52The proclamation to limit dietary cholesterol to less than 300mg (about 1.5 eggs) a day appeared in the 1960’s and has been trumpeted ever since. It led to a 30% per capita reduction in egg consumption in the US (the advice was effective at a population level). The result? Egg producer’s livelihoods were affected (presumably artisan producers were the first to go, leaving mass-producers with cost-cutting methods in business); people who liked eggs but listened to the advice missed out; people who liked eggs and ignored the advice felt guilty, defiant or, (ideally) indifferent; a nutritious source of food was demonised and; it was all for nothing.

So, the total capitulation of the Advisory Panel requires a closer look.

1. What is cholesterol and what does it do?

Cholesterol_molecule_ballCholesterol is a kind of fat (a lipid to be correct). It is an essential component of nearly every cell in your body. It is used to form the cell walls (membranes) that makes cells into separate functioning compartments. Crucially, its presence allows cells to be distorted in shape. This means that tissues can lengthen or shorten and so it is possible for us to move (and for hearts to pump, lungs to expand, skin to stretch etc). Cholesterol also serves a multitude of other physiological purposes in systems as diverse as hormones, fat-soluble vitamins and cell signalling. There is a disproportionate amount of cholesterol in the brain for its size because it is an essential component of brain cells.

In contrast, there is no cholesterol in plant matter. Plants use carbohydrates (mainly) for their cell walls and structure and, apart from some flexibility, these cells cannot change shape – plants are fixed in place and in form.

If not for our cholesterol, the best we could hope to be is vegetation (or bacteria) – without a brain.

2. Where does the body get its cholesterol?

It is too important to take any chances with – the body manufactures it. In fact every cell manufactures cholesterol, but the main source (and sink) of blood cholesterol is the liver. The brain does not get its cholesterol from the bloodstream – it makes its own ‘in house’.

When we eat cholesterol, most of it is rendered ineffective by a series of processes. Some dietary cholesterol survives, however the liver compensates for this by reducing the amount of cholesterol it manufactures. Hence, there is little overall effect on blood cholesterol level.

3. What is ‘good’ and ‘bad’ cholesterol?

Because it is so important, the body regulates cholesterol carefully, partly by using other molecules to transport it to and from the liver. These molecules are lipoproteins. As the name suggests, they are a kind of fat-protein combination. Cholesterol is a lipid (fat) so it doesn’t dissolve in water (blood) and therefore cannot flow through the bloodstream. But, by attaching itself to the lipid end of a lipoprotein, cholesterol can be carried around because the protein end is water-soluble.

There are at least 5 lipoproteins that play a role in cholesterol transport, however the two that are usually reported in blood tests are low-density lipoprotein (LDL) and high-density lipoprotein (HDL). These are often called ‘bad’ and ‘good’ cholesterol respectively. However, this is just shorthand – neither HDL nor LDL are cholesterol, they just transport it around. Strictly speaking, there is no good or bad cholesterol – just cholesterol.

In simple terms, LDL carries cholesterol from the liver into the bloodstream to distribute it to cells in the body. HDL scavenges excess cholesterol and returns it to the liver. Hence LDL increases blood cholesterol and HDL reduces it – thus the ‘bad’ and the ‘good’ terminology.

There is a lot more involved in regulating cholesterol level, certainly more than I could ever understand. Research is currently directed at these regulatory mechanisms and, in time, we should be able to better manage cholesterol if need be.

4. What triggered this dietary revision and what happens next?

The responsible US organisations (HHS and USDA) are required by law to re-examine their advice every 5 years (2015 is such a year). They start with an independent scientific Advisory Panel (AP) that looks at the scientific evidence and makes recommendations (which are not binding). The AP report was finalised in February this year. The report then went through a public submission process that has just ended. The HHS and USDA are now formulating their final recommendations, which are due in August. So, assuming that their decision is evidence-based (there will be other pressures), it seems certain that dietary cholesterol will officially go off the radar this coming August.

In the meantime – perhaps a soft-cooked sous vide egg in a nest of deep fried corn silk?

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Then again, maybe not. The AP is still wagging its collective finger at saturated fat. The evidence is clear that this too doesn’t matter. Revisit this space in a decade or two…

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