Sunday, 24 June 2012

Food Myths: High Cholesterol Foods Raise Serum Cholesterol

In a previous post, I recommended that people who want to lose weight should eat eggs for breakfast rather than toast or cereal.  Given the scare stories that were all over the media a while back, I can imagine the reaction in some reader's heads. 

Aren't eggs high in cholesterol? 
Won't they raise my cholesterol levels? 
Won't they increase my risk of heart disease?  

Well, the answers are yes, no, and no, respectively. 

In 1968 the American Heart Association recommended that people with high cholesterol limit their intake of dietary cholesterol.  The recommendation was later expanded to the general population.  This advice seems to have been based on an unproven assumption that cholesterol in the food we eat goes straight into our blood.   The best analogy I can think of is  Meat is muscle tissue so it will go straight to your muscles. Eating a lot of meat will make you look like a body builder - no exercise or weight lifting necessary. Our internal food processing systems just aren't that simple.

Cholesterol gets a bad rap, but it is actually fundamental to our existence.  Every cell in the human body requires cholesterol to form its protective waterproof membrane.  Cholesterol is also needed for the production of vitamin D and the sex hormones oestrogen and testosterone.  The brain has a higher concentration of cholesterol than any other organ.  Studies have found links between low cholesterol levels and the incidence of strokes, brain haemorrhages, dementia and depression.

The vast majority of  cholesterol in our bodies is manufactured internally.  Cells can produce their own cholesterol or import it from the bloodstream. About 75% of cholesterol in the body is made by the liver.  In normal, healthy people, the liver balances its cholesterol production.  It can manufacture around 1000 mg a day.  If it takes in extra cholesterol from food sources, it simply makes less. 

Research into human eating habits has been unable to demonstrate a relationship between high cholesterol foods such as eggs and dairy products and a harmful increase in serum cholesterol levels.  One US study examined the diets of 957 men  and 1,082 women in the town of Tecumseh, Michigan.  Their food intake over 24 hours was categorized into a wide range of nutritional components including specific types of fats, carbohydrates and protein as well as cholesterol.   The participants were divided into three groups according to their serum cholesterol and triglyceride levels. 

Analysis showed that the men and women with the highest serum cholesterol did not eat significantly more fat or cholesterol in their diets than the participants with the lowest serum cholesterol.  In fact, the study did not reveal any dietary factors that could account for the difference. 

Another study specifically set out to assess the nutritional significance of eggs in the American diet and to determine the degree of association between egg consumption and serum cholesterol.  The researchers analyzed data from 27,378 participants in a national health and nutritional survey.  They found that

Contrary to what might be expected, total serum cholesterol concentration was negatively related to frequency of egg consumption. Subjects who reported eating four or more eggs per week had a significantly lower mean serum cholesterol concentration than those who reported eating one or fewer eggs per week.
The researchers also compared the nutritional intake of people who reported eating an egg within the last 24 hours with those who didn't.  The egg eaters consumed  a significantly greater level of every nutrient except fiber and vitamin B6.  They conclude

Results of our study indicate that eggs make important nutritional contributions to the American diet, and frequent egg consumption does not associate adversely with serum cholesterol concentrations. Our work repudiates the hypothesis that increased egg consumption leads to increased serum cholesterol concentrations and also adds to the growing body of literature which supports the nutritional benefits of eggs.

Back in 1991, a news story was widely circulated about an 88-year-old man living in a retirement home who had consumed an average of 25 soft boiled eggs a day for over 15 years. He maintained normal levels of blood cholesterol.  When asked to comment on the case, a clinical dietician  said that the man's healthy cholesterol level was not surprising. "All of the studies we have done showed no effect of high egg consumption in a normal diet."

So go ahead and enjoy the nutritional benefits of an egg breakfast as often as you like.  Serve omlettes, frittatas, souffl├ęs and quiches for lunch and dinner too.  Eggs really are good food cheap.

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