Not all “bad” cholesterol is equally bad

Cholesterol is essential for all animal life with a typical adult human body containing about 35 g. It is an essential structural component of animal cell membranes and a precursor molecule for all steroid hormones and vitamin D. About one gram is synthesised by the cells of the body per day, while some is excreted through the liver.

Cholesterol is transported in blood bound to proteins called lipoproteins. There are two types of lipoproteins – low-density lipoproteins or LDL and high-density lipoproteins or HDL. Cholesterol bound to LDLs is often called the bad cholesterol and when bound to HDLs the good cholesterol.

Most of us know that high levels of LDL cholesterol can narrow the insides of blood vessels by forming plaques on their walls, thus restricting blood flow. This increases the risk of heart disease and stroke. HDL on the other hand carries the cholesterol to the liver. The liver then flushes it from the body, thus decreasing the risk for heart disease and stroke.

Sounds simple enough? Sorry, time to think again as it is more complicated than that.

Different subclasses of LDL

Contrary to normal wisdom, it has been shown that about 75 percent of patients who suffer heart attacks have total LDL levels that give no indication of cardiovascular risk. What’s going on?

Well, let’s complicate things a little bit.

It has been known since the early 1950s that LDLs comprise of three major subclasses, with particles of different sizes and densities. Subclass A contains more of the larger and less dense LDL particles; subclass I comprises an intermediate group; and finally, subclass B with smaller and denser LDL particles.

It has previously been shown that small and dense LDL is strongly associated with increased cardiovascular risk.

Now new research studying the molecular effect of the different LDL subclasses on blood vessel endothelium has confirmed that of the three subclasses that comprise LDL, only one causes significant damage. LDL subclass B was found to be the most damaging to endothelial function and contributed the most to the development of plaques. Therefore, it’s not the total amount of LDL cholesterol, but rather the concentration of subclass B to the other two, subclass A and subclass I, that should be used to diagnose the risk of heart attack.

However, don’t worry too much about the LDL subclasses as they are more of a diagnostic tool at this time.

Reasons for high levels of bad cholesterol

Let’s make clear from the beginning that most of our circulating cholesterol is actually formed by our own body and genetically determined. So we can blame our parents. However, environmental factors, in particular diet and exercise, appear to also be able to influence the expression of LDL subclasses. 

It was once thought that eating too much of cholesterol-rich foods (such as eggs) was the main cause of high cholesterol. Sure, some foods are high in cholesterol, but indulging in such foods has little influence on our blood levels of cholesterol as such.

Although typical daily cholesterol dietary intake might be around 300 mg, most ingested cholesterol is esterified and poorly absorbed by the gut. The body also compensates for absorption of ingested cholesterol by reducing its own cholesterol synthesis. For these reasons, cholesterol in food has little, if any, effect on long-term concentrations of cholesterol in the blood.

On the other hand, eating too much of foods high in saturated fats is more of a problem, and this has more impact on blood cholesterol levels. The principle mechanism by which saturated fat intake can influence LDL cholesterol is via decreased LDL receptor activity, which in turn decreases liver clearance and excretion of LDL cholesterol.

Mono- or poly-unsaturated fats have the opposite effect, increasing LDL receptor activity and turn-over of LDL cholesterol.

So what can you do?

People with high levels of LDL cholesterol may thus be able to reduce their cholesterol levels by:

  • Limiting foods that have a high saturated fat content (such as many biscuits, cakes and fatty take-away foods)
  • Replacing saturated fats in the diet with mono- or poly-unsaturated fats found in nuts, avocados and oily fish

It is also useful to include more fibre-rich foods in the diet such as fruit, vegetables and wholegrain bread and cereals.

Remember to keep active as it is also an important part of keeping cholesterol levels healthy.

Eating foods enriched with plant sterols has been proven to lower cholesterol levels by up to 10 percent.

Equally, cholesterol-lowering medication has a similar effect and might be necessary if lifestyle changes are not sufficient to reach a desirable cholesterol level. Statin drugs targets the first 18 steps of a complex 37-step process in the formation of cholesterol.

Healthy fat in avocados

Low-fat food on supermarket shelves (photo: Barry Ennor)

Low-fat food on supermarket shelves (Photo: Barry Ennor)

Look, I am the first to admit that I am getting a little confused here. It used to be simple. Fat was bad and should be avoided. It clogged your arteries, increased your LDL (or bad) cholesterol, and led to cardiovascular disaster. Saturated fats, specifically, have been targeted as being especially detrimental to good health. Low-fat products appeared on the shelves and are now abundant in every supermarket. The World Health Organization recommended that fat should constitute no more than 30% of our energy intake, and to restrict the intake of saturated fatty acids to less than 10% of daily energy intake. Given that fat provides about double the energy on a weight basis compared to other macro nutrients, products with more than 15g of fat per 100g should be avoided (alright, a bit oversimplified, if you have your calculator with you in the supermarket you can calculate the average fat content across the foods in your trolley and, given that you know your consumption amounts of each, you can get your daily fat consumption right – good luck with that).

Fat the good guy?

Now fat is suddenly the good guy and carbohydrates should be avoided. My fellow blogger at Tuit Nutrition, citing published research, says:

  • that there is a lack of any clear evidence that saturated fats are promoting any of the conditions that can be attributed to polyunsaturated fatty acids making one wonder how saturated fats got such a bad reputation in the health literature;
  • that the influence of dietary fats on serum cholesterol has been overstated, and a physiological mechanism for saturated fats causing heart disease is still missing;
  • that there is no reason to believe that replacing fat in the diet with carbohydrate at a constant caloric intake will improve the serum lipid profile significantly;
  • that indeed, a low-fat, high-carbohydrate diet causes an increase in serum triglycerides and small, dense LDL particles, which are more strongly associated with coronary artery disease than serum total cholesterol or the amount of actual LDL cholesterol bound to particles;
  • and that replacement of saturated fat with a higher carbohydrate intake, particularly refined carbohydrate, can exacerbate the atherogenic dyslipidemia associated with insulin resistance and obesity that includes increased triglycerides and small LDL particles, as well as reduced HDL cholesterol.

Translated, the now espoused view says that saturated fat might not be that dangerous after all and when we cut back on saturated fat and eat more carbohydrates instead, as we have been told to do for some fifty years, markers for heart disease get worse. That is really turning everything on its head.

Healthy fat in avocados

An avocado a day to protect the heart (Photo: Olle Svensson)

An avocado a day to protect the heart (Photo: Olle Svensson)

So how do I now justify writing this blog on the beneficial effects of unsaturated fatty acids from avocados replacing some saturated fat in the diet? You have to be the judge of that.

Anyway, according to new research published in the Journal of the American Heart Association, eating one avocado a day as part of a heart healthy, cholesterol-lowering moderate-fat diet can help reduce LDL cholesterol levels in overweight and obese individuals. The researchers evaluated the effect of avocados on cardiovascular risk factors by replacing saturated fatty acids from an average American diet with unsaturated fatty acids from avocados. Some 45 healthy, overweight or obese patients between the ages of 21 and 70 were put on three different cholesterol-lowering diets. They consumed an average American diet (consisting of 34 percent of calories from fat, 51 percent carbohydrates, and 16 percent protein) for two weeks prior to being randomly sequenced between each of three test diets for five weeks comprising a lower fat diet without avocado, a moderate-fat diet without avocado, and a moderate-fat diet with one avocado per day.

The lower fat diet, that provided 24% of calories as fat (11% from monounsaturated fatty acids), lowered the LDL cholesterol by 7.4 mg/dL, while the two moderate fat diets that both provided 34% of calories as fat (17% of calories from monounsaturated fatty acids) lowered the LDL cholesterol by 8.3 mg/dL (no avocado) and 13.5 mg/dL (with avocado), respectively. Several additional blood measurements were also more favourable after the avocado diet versus the other two cholesterol-lowering diets including total cholesterol, triglycerides, small dense LDL, non-HDL cholesterol, and others.

The researchers claimed that the results demonstrate that avocados have beneficial effects on cardio‐metabolic risk factors that extend beyond their heart‐healthy fatty acid profile that could be due to other micronutrients and bioactive components in avocados that may play an important role in reducing the risk of heart disease.

What to eat

So should you now start eating an avocado a day? And add to that a cup of blueberries a day as I will point out in a future blog, and on top of that increase your intake of wholegrain foods that will also be covered in a future blog? Your call, I am only providing the facts.

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The magical kale

Healthy kale (Photo: Lodigs)

Healthy kale (Photo: Lauren)

I have long known that kale is supposed to be one of the healthiest vegetables around. I didn’t think I had tried it, but I was so wrong. The other day I looked up a translation to Swedish and for my Swedish friends in case you don’t know it is what we call grönkål. I haven’t had it often but as a southern Swedish tradition it is served as a side-dish to the Christmas ham. We have tried to find it here in Australia for Christmas but failed so we replaced it with spinach. Now I am going to renew my efforts to find kale because it is so highly spoken of.

Kale is a leafy green vegetable that belongs to the Brassica family, a group of vegetables including cabbage, cauliflower, and Brussels sprouts. Curly kale has ruffled leaves and a fibrous stalk and is usually deep green in color. It has a lively pungent flavour with delicious bitter peppery qualities. It carries more nutritional value for fewer calories than almost any other food around. Although it can be found in markets throughout the year, it is in season from the middle of winter through the beginning of spring when it has a sweeter taste and is more widely available. If you are to believe the literature it has remarkable properties.

The good side

In a previous blog we covered cholesterol and the minimal impact cholesterol-containing foods have on cholesterol blood levels. But there is more. Without going into too much detail, our own cholesterol is metabolised in the liver to bile acids, which are released into the intestine. But here most of it is reabsorbed in an essential process for the digestion and absorption of dietary fats. Now kale has been found to contain a group of resins known as bile acid sequestrants, which have been shown to lower cholesterol and decrease absorption of dietary fat. The cholesterol-lowering components do a better job of binding together with bile acids in the digestive tract when kale has been steamed. Although cholesterol is essential to the body, too much is no good as we all know.

Stir fried kale retains beneficial compounds (Photo: Mike)

Stir fried kale retains beneficial compounds (Photo: Mike)

And there are anti-cancer compounds. Kale, as with broccoli and other brassicas, contains sulforaphane (particularly when chopped or minced), a chemical with potent anti-cancer properties. Sulforaphane is an antioxidant and stimulator of natural detoxifying enzymes and, together with indole-3-carbinol, a chemical also found in kale which boosts DNA repair in cells, may reduce the risk of breast, bladder and prostate cancer. Epidemiological studies show that people who eat a lot of cruciferous vegetables have reduced incidences of cancer. In-vitro and animal studies have confirmed the anti-cancer effects and have demonstrated a reduction in frequency, size, and number of tumours. However, since boiling destroys much of the sulforaphane, steaming, microwaving, or stir frying is preferred to retain the activity of the compound.

Kale is very high in beta carotene, vitamin K, vitamin C, and rich in calcium. It is also a source of two carotenoids, lutein and zeaxanthin and a large number of flavonoids. Many of the flavonoids in kale are also now known to function not only as antioxidants, but also as anti-inflammatory compounds. It might sound too good to be true so I better stop there before I go overboard.

The bad side

There is another side of kale you should know about before rushing head on. It is among a small number of vegetables, including rhubarbs that is the most well-known, that contain measurable amounts of oxalates. When oxalates become too concentrated in body fluids, they can crystallize and cause health problems. For this reason, individuals with already existing and untreated kidney or gallbladder problems may want to avoid eating kale.

It might also pay off to buy organic kale since conventionally grown kale has been found to carry fairly high pesticide levels in some countries. However, finding organically grown kale should not be that difficult since it is a popular crop with organic farmers.

Enjoy your kale and live a long and healthy life.

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The low fat and no cholesterol diet myths

Have you been a follower of the low fat and no cholesterol diet recommendations? Have you reduced your consumption of eggs because of their high cholesterol levels? Do you always buy low fat products but you never check the total energy content? And all in the name of heart health. Well, do I have news for you. It’s all been a con! Or close to.

Our body controls cholesterol levels

Free to eat bacon and eggs again (Photo: Sean Munson)

Free to eat bacon and eggs again (Photo: Sean Munson)

Many of us have been told repeatedly that foods like red meat, eggs and bacon raise our cholesterol levels. An idea we no longer questioned since it had been ingrained in our belief system over a long time. The theory that diets high in cholesterol and saturated fat raise cholesterol blood levels came from studies in animals and humans conducted more than half a century ago. Although the results were rather dubious, persuasive argumentation helped making it a truth and a basis for diet recommendations in many countries. However, more recent results from high quality studies do not support this theory.

It is now clear that we fine-tune our own blood cholesterol levels irrespective of diet intake. The body tightly regulates the amount of cholesterol in the blood by controlling internal production. When we eat less cholesterol, the body makes more, and when we eat more cholesterol the body makes less. As a matter of fact only 25% of the cholesterol in our body comes directly from the diet while 75% is produced by our own liver on demand. Much of the cholesterol that can be found in food can’t even be absorbed by our bodies. So the theory that eating cholesterol will give you a heart attack is clearly a myth for most of us. This is also true for a few hyper-responders in which dietary cholesterol does moderately increase total cholesterol, but not the risk of heart disease.

Low-fat fad

With that out of the way we then come to the low-fat diet. In a way it makes sense to lower fat intake since fat contains about twice as much energy on a food weight basis compared to carbohydrates and proteins. But when food manufacturers lower the fat content they often replace it by sugar to improve the all important taste of their products. If you read the food label you will see that the total energy content is the same or even higher in low-fat compared to conventional products. So there is no real net gain from a weight loss point of view.

But the fat profile might be important. It’s true that some studies have shown that saturated fat intake raises blood cholesterol levels in the short term. This might not be true in the long term and some scientists even claim that the link between saturated fat and heart disease is poorly supported by scientific evidence. There is still too much controversy around this point so it might still be prudent to limit saturated fat intake if not total fat intake. Even though total fat intake varied widely, population and intervention studies have indicated that the risk of atherosclerosis can remain quite low as long as the balance between unsaturated and saturated fatty acids is favourable.  As a matter of fact new Nordic nutrition guidelines just released recommend that consumption of saturated fatty acids should be limited to 10% of total energy intake while monounsaturated fat should be 10-20% and polyunsaturated fat 5-10% of total energy intake.

New focus for diet recommendations

Added sugar in low-fat food the real culprit (Photo: jude)

Added sugar in low-fat food the real culprit (Photo: judy)

The low-fat, high-carbohydrate diet supported by medical authorities for so long might actually be an unintended culprit in the current epidemics of obesity and cardiovascular disease. Studies on low-carbohydrate diets which in turn tend to be higher in total fat suggest that they not only don’t raise blood cholesterol, but have several beneficial effects on cardiovascular disease risk markers. Low-fat diets can even be worse than low carbohydrate diets with the food industry replacing saturated fats with added sugar. There is growing evidence that added sugar may be an independent risk factor for metabolic syndrome which increases the risk of diabetes and should be the focus of new dietary recommendations.

But in reducing carbohydrate consumption do you really need to go for a high fat diet as some proponents suggest? Well, maybe not just yet. It is true that short term you might reduce your weight but long term consequences aren’t yet all that clear particularly if you include a lot of saturated fat in the diet. It will take some effort for me to drop the entrenched view that saturated fat is bad for you.

Confused by the conflicting science? Stick to the balanced diet concept and plenty of exercise and you will not go wrong.