Diet, Heart Health, Cholesterol and Macadamia






Reprint From CMS Yearbook 1993





Dr. David Colquhoun2


Address to the media, Coolum 19 August 1992


Pain in his arm, in his breast and in one side of his cardia… it is death that threatens him. Ebers Payrus, 1600 B.C. (Cyril Bryan translation, 1930)


Coronary heart Disease (CHD) has plagued Homo sapiens since the dawn of civilization approximately 12,000 years ago. CHD is largely a lifestyle disease and 12,000 years ago at the end of the last Ice Age, humans made a monumental change in lifestyle changing from hunter-gathering to become herders and pastoralists. This led to a major change in the way humans behaved and what they ate. For the first time, food was in abundance and saturated fat was consumed in high quantities, particularly amongst the privileged in society. Paleopathological studies of Egyptian mummies have demonstrated that the underlying pathology causing CHD, Atherosclerosis was common in ancient Egypt. Pliny the Elder described angina pectoris (due to narrow coronary arteries) among ancient Roman nobility and Hippocrates described sudden death amongst the ancient Greeks.


It is only in this century that the diet of the rich was available to all classes and associated with this has been the global pandemic of CHD. In the 1960s, Australia was in the top five for death rates from CHD. Fortunately, since the peak in the death rate from coronary disease in Australia, there has been a greater than 60% decrease in the death rates from CHD in males and females. Australia now ranks around fifteenth. Australia has had the greatest decline in death rate from CHD of any nation of the world. The United States is close behind. The National Heart Foundation of Australia has played a significant role in this decline with its relentless campaign in urging Australians to cut down on saturated fat, to cut down smoking, to exercise more and to have their blood pressure checked and treated.


In the polemics that surround the role of cholesterol and heart disease, it is frequently forgotten that the atheromatous plaque, which is the underlying lesion in the coronary arteries, is predominantly a fatty lesion and in particular is cholesterol rich. Approximately 50% of the dry weight of the plaque are fat. There are numerous cells and other molecules such as fibrinogen, collagen, tissue factor and calcium. However a sine qua non for the development of coronary heart disease is fat infiltration of the blood vessel wall. When a plaque ruptures, a blood clot rapidly forms inside the artery, which results in a heart attack or sudden death. The plaques with the greatest amount of cholesterol in them are the ones more susceptible to rupture.


It has been known for over 40 years that the higher the cholesterol, the greater the risk of developing coronary heart disease. There have now been over 20 prospective studies showing that as cholesterol increases from around 3 mmol/liter, there is a progressive increase in the risk of developing a heart attack. As cholesterol increases from 4 mmol/liter to 7 mmol/liter, the risk quadruples. If there is smoking present, the risk doubles yet again. In-patients with the genetic order of familial hypercholesterolemia where the cholesterol level is around 8-12 mmol/liter, 50% have a heart attack by 40 and 50% are dead by 50.


The average serum cholesterol in Australians is far too high though there fortunately has been a decrease over the last few years. A "desirable" total cholesterol level is less than 5.5 mmol/liter according to the National Heart Foundation. This is a minimal desirable level. It is important to know the HDL cholesterol level. The HDL or high-density lipoprotein cholesterol is involved in getting cholesterol out of the blood vessel wall. The higher the level, the more the benefit. For asymptomatic individuals, it is desirable to have the total cholesterol to HDL ratio less than 4.5.


Over the last two decades, there have been 25 well-designed cholesterol lowering trials involving 43,000 patients. Treatment in these trials varies from various dietary regimes, diet plus drugs and also a surgical procedure on the gut to lower cholesterol. The cholesterol reduction in these trials varied from only 2% to around 10%. These trials were conducted in the era before the new powerful cholesterol-lowering drugs, which lower cholesterol, by an average 30%. However, despite the modest reductions in cholesterol, these trials clearly demonstrate that lowering cholesterol prevents heart attacks and the development of angina (P < 0.001). The analysis of these trials shows that the greater benefit is seen with longer treatment and with greater cholesterol reduction. Most of these trials were less than 3 years’ duration.


More impressive are the coronary regression trials where x-ray pictures are taken of the coronary arteries at the beginning of the study and then one or two years after vigorous cholesterol reduction. There have now been 10 studies published over the last 8 years. In these trials, cholesterol reduction was generally of the order of 25%. Again the results are clear. With vigorous cholesterol reduction, progression of the disease is halved and the regression rate trebled. Up to 30% of patients achieve regression. The narrowing of the artery opens more blood flows down the artery and often angina improves within a few months of vigorous cholesterol reduction. This translates into fewer heart attacks and, in the largest trials, improved survival. Interestingly, in three trials this dramatic benefit was seen with the diet and other lifestyle measures without drug therapy.


The Lord said to Moses, "Say to the people of Israel, you shall eat no fat of ox, or sheep, or goat. The fat of an animal that dies of itself, and the fat of one that is torn by beasts, may be put to other use but on no account shall you eat it. "Leviticus 7:22-24



The first step in lowering blood cholesterol is dietary modification. The first study demonstrating that manipulation of diet can change blood cholesterol levels was in 1950. Since then there have been over 30 dietary studies published showing that manipulation of diet can affect blood cholesterol levels. The most important component of diet, which affects blood cholesterol levels, is saturated fat. Next in importance is cholesterol content of the food itself, then the balance between the monounsaturated fat, polyunsaturated fat, fiber content and amount of calories. Saturated fat is found as the visible fat on meat, in high fat dairy products and it is "invisible" in processed foods often under the title of vegetable oils. Often these vegetable oils are tropical oils, which are cheap and have been demonstrated to be cholesterol raising. They are usually from palm oil, palm kernel or coconut oil.


Over the last few decades, a blood cholesterol-lowering diet has been thought to be synonymous with a low total fat diet. However, low fat diets are associated with low compliance rates with less than 25% of individuals adhering to a diet of 20% of the calories as fat or less. The average Australian eats around 35 % of their calories as fat. It has been clear for the last few decades, however, that a high fat diet is compatible with low blood cholesterol levels and a low incidence of heart disease if the right type of fat is eaten.


Data from the famous Seven Countries Study, involving study of 16 different population groups in 7 countries, showed clearly that a high fat diet might be associated with very low incidence of heart disease. In Crete, 40% of the calories came from fat and they had the lowest incidence of CHD of all the population groups in the study. The Cretins have a lower incidence of heart disease than the Japanese groups, which had 8% of the calories as fat. In East Finland, where the fat content was high and equal to that of the Cretins, they have a 30 times greater incidence of CHD. The reason being is that most of their fat came from saturated fat. In Crete, the fat content was almost entirely from olive oil a rich source of monounsaturated fat.


In the Seven Countries Study, there was an inverse correlation between the incidence of coronary disease and monounsaturated fat consumption. There was a direct relationship with saturated fat intake and serum cholesterol and the incidence of coronary heart disease. Recently, in The Lancet, the death rate from CHD and the relationship of dairy fat consumption showed a very close association. However, the death rate in France was far lower than predicted. However, the dairy fat the French eat is different to what Anglo-Celtics consume. In France, butterfat is only a small proportion of the dairy intake with highly fermented cheeses being high on the French list. Also, when alcohol consummations is taken into the overall context, then the death rate from coronary heart disease in relationship to fat and wine consumption is as predicted. The French lifestyle is associated with one of the lowest incidences of CHD in the world as is seen in other Mediterranean countries.


The food sources for a high intake of monounsaturated fat are olive oil, canola oil, avocado and certain nuts including almonds, pecans, walnuts, macadamias, pistachios and cashews.


Over the last few years at the Wesley Hospital, we conducted two trials investigating the effects of a high monounsaturated fat diet compared to the classic low fat cholesterol-lowering diet (American heart Association Phase 3 Diet). In the first study, avocados were used, and the second study, Macadamia nuts. Avocados and Macadamia nuts are similar to olive oil in that they are foods high in fat, which is predominantly monounsaturated fat. In the first study, 15 staff members from the Wesley Hospital were assigned to either a low fat diet first then an avocado-enriched diet for 3 weeks. After 3 weeks, subjects switched over to the alternative diet. On the avocado-enriched diet, the cholesterol level dropped by 8%, better than on the low fat diet. Also the HDL level remained unchanged whereas the HDL dropped by 13% on the low fat diet. Compliance was much better with the avocado-enriched diet.


In the Macadamia nut study, 14 individuals were randomized to either a low fat diet or a Macadamia-enriched diet for one month. After one month, subjects switched over to the alternative diet. In this study, the low fat diet and the Macadamia-enriched diet were equally effective in lowering cholesterol with no significant change in the HDL. The blood triglycerides were lower on the Macadamia diet.


Both these high fat diets (38-40% of the calories as fat) were at least as effective as low total fat diet (20% of the calories as fat). No weight gain was seen during the high fat phases of the studies, as the calorie content was not increased. A diet rich in monounsaturated may have other benefits by decreasing the tendency of cholesterol in the blood to oxidize a necessary prerequisite for causing cholesterol buildup in the coronary arteries. Also, monounsaturated tend to thin the blood, lower blood pressure and have no effect on sugar metabolism. There is no evidence to suggest at all any increased risk of cancer or gallstones. Most importantly, a diet rich in monounsaturated tastes good. There is nothing better than a modified Greek salad with avocado slices, Macadamia nuts, a dash of olive oil, vinegar and lemon.


The low risk coronary male is no longer "the effeminate municipal worker or embalmer, completely lacking in physical and mental alertness and without drive or ambition or competitive spirit who is taking nicotinic acid, pyridoxine and long term anticoagulants since his prophylactic castration". The true, low risk coronary male is a "shepherd or a farmer or a beekeeper or fisherman. He walks to work in the soft light of his Greek Isle." He enjoys life, a glass of wine and good food and now he also eats avocado and Macadamia nuts to his heart’s content.


We can now appreciate better the axiom of Hippocrates, the grandfather of medicine, Let food be thy medicine. Circa. 400 B.C.


  1. Australian Macadamia Society Limited News Bulletin, Volume 19, Number 6, March 1993


  3. Consultant cardiologist, Wesley Medial Centre, Auchenflower, Queensland, Australia