Healthy Living Update: Cardiovascular Disease and Fat
At the latest Nutrition Congress in South Africa, held in Johannesburg during 16-19 September 2014, international guest speaker, Dr Jacques Rossouw, set the record straight on conflicting messages regarding fats and cardiovascular disease. Dr Jacques Rossouw is chief of the Women’s Health Initiative (WHI) Branch in the Division of Cardiovascular Sciences at the National Heart, Lung, and Blood Institute (NHLBI), part of the National Institutes of Health (NIH) in the United States of America.
Which dietary factors increase the risk of developing heart disease?
Dr Rossouw started off by explaining that low density lipoprotein cholesterol (LDL cholesterol, which is otherwise known as ‘bad’ cholesterol) has been proven to be the most important lipid risk factor for heart disease. Genetic studies and clinical trials proved that an increase in LDL increases the risk of developing heart disease. Additionally, individuals that are genetically predisposed to low LDL have a proportional decreased risk of heart disease (1 mmol reduction leads to a 24% reduction in risk). Clinical trials focussing on lowering triglycerides or raising HDL cholesterol levels have not shown risk reduction to the same degree. When looking at the combined effect of many small feeding trials in a meta-analysis, data showed that trans fatty acids and saturated fatty acids increased LDL when 10% of carbohydrates were removed from the diet and replaced with these fats. Monounsaturated fatty acids and polyunsaturated fatty acids, on the other hand, decreased the levels of LDL cholesterol in the body. Recently controversial meta-analyses have reported that saturated fatty acids do not increase cholesterol. These studies, however, had design flaws. Additionally, many studies have proved that substituting saturated fat for polyunsaturated and monounsaturated fat, reduces one’s risk of cardiovascular disease.
The ratio of total cholesterol (of which LDL cholesterol is a major part) to high density lipoprotein cholesterol (total cholesterol to HDL cholesterol) is predicted to increase with the intake of carbohydrates, saturated and trans fats. One should always keep in mind though, that many of these studies used a glucose (sugary) drink as a source of carbohydrates, while high fibre carbohydrate foods have not proven to increase risk of cardiovascular disease - quite the opposite, in fact. For every 5% increase in energy from high GI carbohydrates (usually refined sugars, sugary drinks, sweets, etc.) risk has been shown to increase by 30%, while low GI carbohydrates (found mostly in high fibre products) tended to decrease the risk of developing coronary heart disease.
Why is the world becoming bigger?
When specific foods were eaten in larger quantities, it was found that many of them contributed to weight gain and poor nutrition. These foods included potato chips and fries, processed meats, unprocessed red meats, butter, sweets and desserts, refined carbohydrates (low in fibre), sugar- sweetened beverages and fruit juices. It is important to keep in mind that reduced physical activity also played a role in the exacerbating worldwide problem that is obesity. Statistics from Sweden clearly showed that the Body Mass Index of the population continued to increase gradually regardless of fat and carbohydrate intake, even after high-fat low-carbohydrate diets became popular in Sweden between 2004 and 2010 all this, while serum cholesterol started increasing and the number of people who reported using lipid lowering medication also increased drastically.
Which dietary changes have been shown to work?
When investigating changing trends in nutrition and diet, and how these trends affect a population (population-intervention studies and secular trends), Finland is an excellent example. Up until the late 1960s, they had the highest rate of coronary heart disease in the world, and have since showed an 80% reduction in risk, which was attributed to risk factor reduction and diet. At the start of the project, no plant oils were available in Finland, which had a heavy dairy driven industry. After plant oil factories were initiated, men reduced their saturated fat intake by 41%, while polyunsaturated fat intake (plant fat) increased. Total fat was still reduced by 13%, which is usually replaced with carbohydrates in a diet. Despite this, death rate from type 2 diabetes in Finland has declined significantly.
The USA reported a similar reduction in deaths caused as a result of cardiovascular disease, which became visible after the promotion of a prudent diet by the American Heart Association, which advised the public to eat less fat, particularly less saturated fat, and rather include polyunsaturated fat for a healthy diet. The guidelines recommended reducing one’s sugar intake and increasing one’s daily consumption of fruit, vegetables and whole.
During his talk, Dr Rossouw reminded the audience that the diet heart hypothesis - which states that dietary saturated fat raises blood cholesterol in humans and therefore contributes to the risk of heart disease - has years of iron clad science behind it as proof. Dr Rossouw emphasised that this area is very well researched and that we can even go as far as to say that it is medical fact.
Written by Marilize Richter (MSc Dietetics, BSc Dietetics)
- Increased saturated fat intake leads to increased LDL cholesterol, which results in an increased risk for developing heart disease. The alternatives, namely polyunsaturated and monounsaturated fat, have been proven to lower the risk of cardiovascular disease when consumed in the place of saturated fat.
- High GI refined sugary carbohydrates increase the risk of cardiovascular disease and diabetes, while low GI, high fibre foods do not.
- Excessive weight gain/obesity continues to be a problem worldwide, regardless of carbohydrate or fat intake.