Heart disease debate - carbohydrates vs fats
Reacting to last month's controversial UCT centenary debate between Professor Tim Noakes and Dr Jacques Rossouw, which saw argument over the most fundamental causes of heart disease, Professor Bongani Mayosi, head of UCT's Department of Medicine said that there would be no change in how students at UCT are taught about the risk factors for heart disease.
"It is clear to me that the diet-heart hypothesis is alive and well and we do not see any reason to change what we teach our students about the link between an unhealthy diet, high blood cholesterol and heart disease," he said.
Noakes, whose controversial ideas on the diet-heart hypothesis have been widely publicised in the last year, proposed during the debate, that high blood cholesterol is not a risk factor for heart disease, as it has been billed for more than three decades and that conventional dietary recommendations do more harm than good. Rossouw, a Washington-based epidemiologist and former director of the Medical Research Council's Institute for Nutritional Diseases, presented research to contradict this theory and warned of the dangers of the medical profession turning its back on the more widely accepted causes of heart disease.
"Noakes' theory has the potential to divert people from diets and treatments that are known to do good," said Rossouw.
Carb-resistance - fact or fallacy
Noakes believes that human health began deteriorating about 12 000 years ago with the introduction of agriculture, but dipped severely in the last 35 years following introduction of the 1977 US Department of Agriculture Dietary Guidelines, based on a 1953 idea proposed by Ancel Keys (PhD) that dietary fat increases the blood cholesterol concentration, which clogs major arteries causing heart disease and stroke.
Contrary to this widely accepted finding, Noakes believes that not everyone metabolises carbohydrates safely and a large population has genetic carbohydrate resistance, which becomes worse with age. Obesity, he proposes, is the result of a carbohydrate-intolerant individual eating a high carbohydrate diet.
Rossouw agrees that certain people are carbohydrate intolerant before becoming diabetic, but believes obesity causes carbohydrate intolerance, not the other way around. He argues that the proportion of truly carbohydrate-intolerant people runs to about 6% while Noakes claims this figure is at least 10 times higher.
Dr Rossouw was in Cape Town as a guest of the Chronic Diseases Initiative in Africa (CDIA). A respected medical professional, he has worked with the National Heart, Lung, and Blood Institute (NHLBI) of the National Institutes of Health in the USA since 1989 and served on the NHLBI National Cholesterol Education Program.
Good cholesterol, bad cholesterol
At the UCT debate, Rossouw presented extensive data collected over many decades that supports the current consensus that blood cholesterol occurs as 'good' HDL cholesterol, which protects arteries by removing cholesterol from artery walls, and 'bad' LDL cholesterol that carries cholesterol molecules into the artery walls.
"This is true for men and women, people of all ages and those with diabetes and after suffering a heart attack. High levels of 'bad' cholesterol can be treated with a group of drugs called Statins, which reduce heart attacks in people using them.
"The science is clear that if one follows an unhealthy diet high in fat, one increases one's 'bad' cholesterol levels causing heart attacks and angina," said Rossouw. He also showed that people who had inherited high 'bad' cholesterol levels had heart attacks at an early age while those lucky people who were born with very low levels of 'bad' cholesterol lived to a ripe old age without any heart disease.
Not all fats are equal
The data presented by Rossouw supports current dietary guidelines and he emphasised that since these were shown to improve health, they should not be altered.
The dietary recommendation for a healthy heart is to eat a varied diet while reducing fat intake, particularly saturated fats from animal products and giving preference to fish, chicken, low-fat dairy products and legumes. Eating unrefined carbohydrates, such as whole grain products and focusing on more fruits and vegetables for sufficient vitamins and minerals, such as potassium. Fibre is also recommended. Salt and alcohol intake should be moderate.
Rossouw explained that the trend of increasing obesity could be attributed to factors like poor diet, lack of physical activity and the environment in which people live. "The association between overweight and diabetes," he said, "is clearly illustrated, as is the benefit of losing weight to prevent diabetes. The data shows that reduced calorie diets result in clinically meaningful weight loss, regardless of which foods are present in low calorie diets."
Rossouw agrees with Noakes that fast foods and sugar pose a danger to a healthy heart, but differs on the value of unrefined carbohydrates. "Noakes' definition of refined is anything above a glycaemic index of 40, which excludes most carbohydrates except leafy vegetables. He asserts that they produce a large glycaemic load, which in time causes problems and wears out the pancreas, producing diabetes and obesity. Therefore bread, pasta, rice and bananas should be avoided."
Rossouw warns, "Noakes maintains that diabetics do not have higher blood cholesterol levels than other people, that half of all heart attacks occur in people with normal blood cholesterol, that glucose is the single most important predictor of risk and a high-fat diet reverses almost all coronary risk factors. Except for a very few close followers, the scientific evidence is clear and he's flying against it. There is now absolute proof that high blood cholesterol is causal in heart disease."
Debate convenor and Associate Director of the CDIA, Professor Krisela Steyn, agrees. "Noakes' diet is particularly dangerous for a certain part of the population at high risk for kidney failure, with high cholesterol or ischaemic heart disease. The public will also be at increased risk if this diet is followed for a long time. Damage is being done by radically oversimplifying things and not basing public statements on the best available data."
Dr Vash Mungal, CEO of the Heart and Stroke Foundation South Africa points out, "Any diet that is calorie and energy restricted will reduce weight. But caution should be used when generalising and saying that everyone should eat fats, no sugar and no carbs, especially when there is no long-term data on this, while there is extensive data on the conventional diet."
According to Professor Steyn, the Cochrane Collaboration at the Medical Research Council will release a formal review of all existing data on the subject in the near future.