Saturday, April 9, 2011

The flip side of eating eggs

Apr 9, 2011
By Andy Ho

WHEN I brunched at Ya Kun Kaya Toast with a co-worker recently, I slurped down quite a few soft-boiled eggs.

She shook her head, saying: 'You have a death wish.'

Eggs do have lots of cholesterol, which is found only in animal-based food like offal and seafood, not plant-based foods like palm oil or coconut oil.

And raised blood cholesterol levels are indeed associated with heightened coronary heart disease (CHD) risks.

But studies show that cholesterol in food has just a small impact on blood cholesterol levels. The idea that dietary cholesterol (read: eggs) raises blood cholesterol levels is one first pushed vigorously in the 1970s. But many studies since show it is wrong. But the idea that 'eggs are bad for the heart' has become entrenched.

Scientists now say it is saturated fats in the diet that are turned into blood cholesterol. So it is reducing the intake of saturated fats that will help lower blood cholesterol levels - and thus CHD risk.

This is why nutritionists urge that we eat less of fatty cuts of red meat, shortening, hydrogenated margarine, processed foods and fried foods.

But how did this idea of dietary cholesterol (eggs) being bad for the heart come about? In the early part of the 20th century, scientists experimentally fed cholesterol-rich foods such as butter to animals. These lab animals then developed clogged coronary arteries. Chemical analysis of those clogs showed cholesterol to be their key component. So scientists concluded that dietary cholesterol had gone straight into the coronary arteries.

In fact, the very foods the lab animals were fed were also very high in saturated fats: Cholesterol and saturated fats tend to coexist in the same foods.

Scientists now say it was the dietary saturated fats - not the dietary cholesterol - that raised the levels of blood cholesterol, which clogged up the arteries.

Later, some large epidemiological studies showed the link between raised blood cholesterol and a heightened CHD risk. These studies also noted that increasing dietary cholesterol intake raised blood cholesterol levels too.

So just like the animal models, these early epidemiological studies were confounded by the presence of large amounts of saturated fats in diets that were high in cholesterol. Again, wrong conclusions were drawn about dietary cholesterol - and thus eggs - being bad for the heart.

We now know that dietary cholesterol (eggs) can indeed increase blood levels of cholesterol a bit - but of both 'bad' and 'good' cholesterol.

If 'bad' cholesterol is like a truck that goes around in the blood delivering cholesterol to tissues where it is used to make hormones, say, 'good' cholesterol is that which comes around to truck away unused 'bad' cholesterol.

If there is too much 'bad' cholesterol in the blood, it is deposited in artery walls to narrow them. Conversely, lots of good cholesterol in the blood means a lower likelihood of clogs forming.

Studies suggest that the negative impact of eggs raising the blood levels of 'bad' cholesterol may be offset by the positive impact of raising the blood levels of 'good' cholesterol at the same time.

Some studies have been done to address the question of how much egg consumption raises one's CHD risk.

A huge meta-analysis published in the Journal of the American Medical Association in 1999 found no difference in CHD or stroke risks whether someone had less than one egg per week or more than seven eggs a week. (In diabetics, however, eating more eggs did raise CHD risk.)

A Japanese study published in the Circulation Journal in 2001 found no link between CHD risk and egg intake of up to four or more a week.

Another Japanese study published in the American Journal of Clinical Nutrition in 2004 showed no increase in the risk of fatal heart attacks, strokes and cancer in men who ate two eggs or more daily. However, these risks were raised in women eating one egg or more daily.

Finally, a 2009 study published in Risk Analysis looked at how much egg consumption raised CHD risk in men and women compared to smoking, obesity, exercise and other lifestyle habits.

Overall, such habits accounted for under 40 per cent of CHD risk. Of these modifiable behaviours, consuming an egg a day accounted for under 1 per cent of that risk. This suggests that if you want to lower your CHD risk, it makes more sense to stop smoking, decrease your saturated fat intake and exercise regularly than to obsess over not eating eggs.

In recent years, the UK Food Standards Agency (FSA) and the National Health and Medical Research Council of Australia have stopped setting limits on how many eggs healthy people may take per week whose diets are not excessive in saturated fats.

But not so if you are diabetic. Or if you have the Apo E-4 gene, which leads to high blood cholesterol if you take eggs.

The rest who love their eggs may be comforted to know that a 2002 FSA report says it is 'a protein-rich, nutrient-dense food that is high in neither calories nor saturated fats'. But if in doubt, cutting down on eggs does make a small difference. For some, that is reason enough not to over-indulge.

No comments: