Heartfelt warning

The Banting diet, the subject of much discussion at dinner parties and in the media after Tim Noakes' recommendation of it, demands a reasoned response from the medical community. Banting advises eliminating virtually all carbohydrate from one's diet and replacing it with saturated (animal) fat as our main source of energy. While people following this diet may experience significant weight loss and an increased feeling of wellbeing, its effects on blood cholesterol could be harmful.

So far, the Banting diet has not been shown to be safe or beneficial in the longer-term. Countless studies have shown that cholesterol-induced hardening of the arteries, also known as atherosclerosis, is responsible for most heart attacks, strokes and narrowing of the leg arteries, and is the most frequent cause of illness and premature death.

The emergence of atherosclerotic cardiovascular disease (ASCVD) in developed and developing countries is a crisis that is engaging the medical profession and national governments around the world. Any physician familiar with the nature of heart attacks and strokes finds it impossible to accept that they could be caused by a single element in the diet and that the risk could be reduced by eating saturated fat.

The medical profession's understanding is that there are many factors that may cause these diseases. They include environmental aspects such as air pollution, living conditions and the emotional stresses to which we are subjected. Lifestyle factors such as smoking, a lack of physical exercise, excessive body weight and bad eating patterns increase the risk. High blood pressure, diabetes and raised blood cholesterol, often caused by our lifestyle, raise the risk even further.

Yet even this is not the whole story. All these factors are influenced by age, gender and as yet undefined genetic tendencies. Given this complexity, it seems clear that the risk of heart attack and stroke needs to be combated by a multipronged approach, not simply by diet alone. For many years the "lipid" theory has been central to our understanding of ASCVD. Experiments showed that rabbits fed on cholesterol developed fatty deposits (plaque) in their arterial walls. In humans, people who have inherited high levels of cholesterol develop ASCVD prematurely.

Those with a double dose of a certain gene - the FH gene - experience heart attacks in their teens; those with a single dose are generally affected in their fifties. In 1963, research found that communities eating a high-fat diet had a higher incidence of heart attack and stroke. More recent research has demonstrated that the presence of low-density lipoprotein cholesterol (LDL-c), the so-called "bad cholesterol", in the arterial lining can set up inflammation that promotes the development of plaque. Meticulously conducted imaging from inside heart arteries shows that reducing LDL-c in turn reduces the growth of plaque.

The case for lipid theory was advanced further when statins were introduced to medicine by the 4S study in the late 1980s. Simvastatin, in common with other statins, reduces the production of LDL-c in the liver, in some cases lowering cholesterol by up to 47 percent. This fall in cholesterol was associated with a 30 percent reduction in the risk of dying, when compared with those on placebo treatment. The 4S study was followed by many trials involving various statins used on different patient groups: people without symptoms, high-risk patients with high blood pressure or diabetes, and patients who had already had a heart attack or stroke.

To date, almost 200 000 patients have been involved in trials that typically lasted four to five years. Combining all these results, a collaborative analysis by groups of scientists who conducted trials confirmed the benefit of statin treatment in a very broad spectrum of patients. One remarkable result of these trials is the close relationship that exists between the reduction in cholesterol achieved and the amount by which heart attacks and strokes are decreased. Even after all these trials, we still do not know exactly how low cholesterol should be reduced to obtain the maximum benefit. In a recent authoritative study, when statin treatment was combined with good control of other risk factors, it was found that in patients with diabetes, the risk could be reduced by 50 percent in the long-term. In developed countries, the risk of ASCVD has declined significantly in the past two decades by managing these risks effectively.

The lipid hypothesis has not been "discredited", as Noakes alleges. Indeed, it remains one of the mainstays of our understanding of how to combat heart attacks and strokes, and is the subject of active, ongoing research. Noakes has criticised the pharmaceutical industry for exerting undue influence on guideline development and alleges that the authors of guidelines present biased views, He dismisses the value of clinical practice guidelines, a view that is hard to support given the number of instances in which following the guidelines has led to improved clinical outcomes. Broadly speaking, two methods are used in dietary research.

Either the short-term effect of adding, removing or substituting a single item in the diet is measured, or a population-based observational study is performed on a large number of patients who follow a reasonably uniform diet. Dietary research is beset by difficulties inherent in keeping participants on fixed eating patterns over a number of years.  There remain deficiencies in our knowledge about the ideal eating pattern, but towards the end of 2013 the expert committee of the American Heart Association and the American College of Cardiology issued updated guidelines on lifestyle and diet, which largely confirmed the earlier advice.

They weighed all recent scientific evidence and came to the conclusion that, on the best information available, the Mediterranean diet or the Dash (dietary approaches to stop hypertension) diet, which share a number of similarities, should be favoured. The evidence showed that LDL-c and blood pressure are reduced by substituting saturated fat with, in order of preference, Pufas (polyunsaturated fats, such as extra virgin olive oil), Mufas (monounsaturated fats, such as sunflower seed oil) or carbohydrates (starches). However, trans fats (such as those found in margarine) had undesirable effects. In summary, the recommendations encourage the consumption of vegetables and fruit, whole grains and legumes, low-fat dairy products, poultry and fish, and non-tropical oils and nuts.

The consumption of salt, sweets and sugar-containing beverages and red meat should be limited. Additional support for the Mediterranean diet comes from the Spanish Predimed diet study, which shows that the Mediterranean diet, supplemented by either extra virgin olive oil or nuts, when compared with the usual diet, is associated with 30 percent fewer deaths, heart attacks and strokes. A second trial suggested that eating nuts may be preferable to using extra virgin olive oil. Maintaining an ideal body weight is an important goal when preventing heart disease. However, it is vital that weight control is achieved by safe means.

Though the Banting diet results in significant weight loss, accompanied by a reduction in new occurrences of diabetes and a modest fall in blood pressure, many medical practitioners are noting that their patients' blood cholesterol levels have risen sharply on the Banting diet. In one instance, a patient's cholesterol rose 77 percent. These rises in cholesterol levels suggest that the Banting diet may increase the risk of heart attack and stroke later in life. Worse still, patients who have already had a heart attack or stroke may have inferred from Noakes' pronouncements that they could safely stop taking their statin treatment.

Noakes defends his position by labelling the rise in blood cholesterol as unimportant. He supports the theory of insulin resistance with raised blood triglycerides and low high-density cholesterol (called atherogenic dyslipidemia) as the only causative factor in ASCVD, stating that LDL-c is not implicated in causing heart attacks or strokes. He holds that the Banting diet will benefit all the known risk factors for ASCVD. In his words, "high-fat diets have the unique ability to reverse all known coronary risk factors. Insulin resistance, the metabolic syndrome and atherogenic dyslipidemia are neither new concepts nor can they be summarily dismissed as not contributing to heart attacks and strokes. As many as one in six heart attack or stroke victims may have these changes in their blood fats.

However, we simply do not have enough information about how to manage these problems, and none that indicates what the clinical outcome of an intervention may be. Noakes is well aware that a long-term clinical trial needs to be done to prove the safety and benefit of what he is proposing. Until such time, his theories must remain just theories, his results on weight loss and improved energy simply road signs that do not necessarily point to the desired destination. In deciding on the best eating pattern, we may need to keep an open mind, but not so open that our brains fall out! We already have reassuring evidence that the Mediterranean diet reduces the risk of heart attack and stroke. We do not have comparable evidence for the Banting diet. Potentially, we place ourselves and our families at risk by adopting a diet that has not been proved to produce a long-term benefit and is known to be associated with a rise in cholesterol. Until more is known about its long-term effects, the Banting diet should not be promoted

Richard Steyn: The Financial Mail, 12 September 2014