Mediterranean Diet

Mediterranean Diet

MEDITERRANEAN DIET MAY ALSO KEEP CANCER AWAY
The traditional diet of the Mediterranean region is thought to protect against heart disease. Now, French researchers investigating that link think it may also help prevent cancer.

The Lyon Diet Heart Study followed 605 people who had had previous heart attacks. They put half of them on a Mediterranean-type diet rich in fruits, vegetables, whole grains, legumes, fish and olive oil, and moderate in red wine and a specially formulated omega-3rich margarine. The other half ate an American Heart Association-style diet--low in total fat, but lower in plant foods and higher in animal products.

After four years, those on the Mediterranean diet were less likely to develop cancer or die of any cause than those on the AHA diet. The researchers attribute the benefits to the fiber and antioxidants in fruits and vegetables, and to getting more omega-3 fats and fewer omega-6's.


Scientific basis of the healthy Mediterranean diet

Abstract It is now clear that the main problem with nutrition in industrialised countries, as well as in the more prosperous segments of developing countries, has shifted from nutritional adequacy to overnutrition--too much food in general, and a predominence of foods that are linked to cardiovascular disease or cancer. The incidence rates of cardiovascular disease and cancer, particularly those that are high in northern Europe, America, and Australia (colon, prostate and breast) are low in parts of Greece in which traditional dietary patterns are maintained. Favourable effects of Mediterrean diets on cholesterol and low density lipoprotein concentrations in the blood, as well as on blood pressure and hypertension, are likely to be one reason for the low coronary disease rates. The Lyon Heart Study used a traditional Mediterranean pattern to prevent death from coronary disease. The diet increased intake of vegetables, fruits, and fish which supplied vitamins such as folic acid, vitamin B6, carotenoids, and tocopherols, as well as oleic acid, alpha linolenic acid, and other n-3 fatty acids. Thus the Mediterranean diet may be considered beneficial not only because of the reduced amount of saturated fat and cholesterol and increased mono-unsaturated fats, but because of micronutrients that act by mechanisms other than reducing blood cholesterol. For this reason, a worldwide group of scientists, clinicians, and health educators developed a dietary pyramid, based on traditional eating patterns in the Mediterranean, that reflected current science, and that had a goat to prevent cardiovascular disease and cancer. [Aust J Nutr Diet 1998;55(4 Suppl)S4-S7].

Keywords: cancer; nutrition; dietary fats; cholesterol; coronary heart disease

For the last 20 years, guidelines to the public on healthy eating patterns emphasised a balance between groups of foods intended to meet the basic nutritional needs of the population. In the USA and Canada, the national nutritional guidelines are similar, and emphasise a high carbohydrate, low fat diet. It is now clear that the main problem with nutrition in industrialised countries, as well as in the more prosperous segments of developing countries has shifted from nutritional adequacy to overnutrition--too much food in general, and a predominence of foods that are linked to cardiovascular disease or cancer. The dietary prescriptions of health promotion groups have begun to reflect this shift but problems remain in shifting the guidelines to correlate with the newly established nutritional science. Recently, several groups are working towards a new consensus to preventing chronic disease.

In the standard dietary recommendations to the public in the USA, information is conveyed via a graphic in the form of a pyramid, whereas in Canada a multicolored banner is used with sections to represent the major food categories. The drawbacks of both include lumping together red meat, poultry and fish as 'meats', grouping beans and nuts together with the meats as high protein foods, making no distinction between vegetable oils and animal fats, and not favouring low fat dairy over full fat dairy products. For this reason, a worldwide group of scientists and clinicians, working with the Oldways Preservation and Exchange Trust, a foundation in Boston, developed an alternative dietary pyramid that reflected current science with a goal to prevent cardiovascular disease and cancer. The pyramids were also based on traditional eating patterns in various cultures. The first such pyramid was the Mediterranean dietary pyramid (Figure 1), and others were subsequently developed based on traditional Asian, Latin American and vegetarian diets. The base of the pyramid shows cereals, vegetables, nuts, beans, and fruits intended for daily eating. Olive oil, the traditional table and cooking oil of the Mediterranean, is included in the category of foods listed for daily consumption. Fish and poultry are recommended over red meats. Sugar and other refined carbohydrates are not recommended for regular use. In addition, recognising that alcoholic beverages are a traditional part of meals in the Mediterranean, and that moderate intake is associated with longevity, wine or other alcoholic beverages are recommended for moderate intake, according to personal preference. Regular physical activity is integral in any prescription for health, and this is included alongside the dietary pyramid.

I will now review the scientific basis for the Mediterranean diet pyramid. This has been described in detail in a supplement to the American Journal of Clinical Nutrition ( 1). The classic Seven Countries Study, led by Ancel Keys, demonstrated that countries or areas in which saturated fat intake was low (Japan and rural Mediterranean areas in southern Europe) had much lower rates of coronary disease than the USA and northern Europe where meats and dairy fats were eaten daily ( 2) (Figure 2). In contrast, there was no relationship between total fat intake and coronary disease (Figure 3). This is because Mediterranean diets are not only low in saturated fat but high in olive oil, rich in mono-unsaturated fat, which accounted for the high total fat intake. In addition, the plant-based diets of Mediterranean countries are rich in other potentially protective nutrients called phytochemicals. The lowest rate of coronary disease was in Crete which had the highest intake of total fat, nearly all from olive oil. Japan also had very low coronary rates coinciding with low total fat intake. Thus Japan and Crete could be considered as two cultural models of healthy eating--one based on rice, soy and fish, and low in all fat; the other based on cereals, vegetables, fish and olive oil. A 25-year follow-up of the seven countries cohorts continues to show very low coronary rates in Japan and rural areas of southern Europe ( 3). Cancer rates, particularly those that are high in northern Europe, America, and Australia (colon, prostate and breast) are low in Crete as well as in Japan ( 4).

A favourable effect of Mediterrean diets on cholesterol and low density lipoprotein (LDL) concentrations in the blood is likely to be one reason for the low coronary rates. Keys and his colleagues placed nutrition and blood cholesterol on firm scientific footing demonstrating the adverse effect of saturated fat and dietary cholesterol on blood cholesterol, and the benefits of replacing saturated fats with unsaturated fats or carbohydrate ( 5). In the 1980s, researchers began to re-investigate diet, extending Keys' work to the newly recognised lipoprotein risk factors, LDL, HDL (high density lipoprotein) and triglycerides. The results of many studies, summarised by Dutch nutritionists, Mensink and Katan, showed that reducing intake of saturated fat, replacing it with either carbohydrates or unsaturated oils, lowered blood concentrations of LDL cholesterol ( 6), a firmly established cause of atherosclerosis ( 7). However, replacing saturated fat with carbohydrate also lowered HDL cholesterol, a lipoprotein that protects against cholesterol accumulation in artery walls. Low HDL concentrations are associated with high coronary rates ( 8). Mono-unsaturated fat did not have this HDL-lowering action ( 6). Also, the high carbohydrate diet but not the mono-unsaturated fat increased blood triglyceride levels ( 6), another coronary risk factor ( 9, 10). Taken together, a high carbohydrate and low fat diet has a mixed effect on blood lipids whereas as high mono-unsaturated fat diet has beneficial effects on all established lipid risk factors.
Epidemiological studies of diet and coronary disease across populations suggest that reducing saturated fat is beneficial ( 2). Moreover, the US Nurses Health Study found that coronary incidence is lower when monounsaturated or polyunsaturated fat rather than carbohydrate replace saturated fat (II) (Figure 4). This potential advantage of mono-unsaturated or polyunsaturaturated fat compared to carbohydrate correlates with the previously mentioned effects on blood lipids and lipoproteins.

Clinical trials prove that dietary intervention prevents coronary events ( 12). The most convincing evidence comes from randomised controlled trials of four or more years duration. In the 1960s, a common cholesterol lowering diet was high in polyunsaturated vegetable oils such as corn, safflower or sunflower oils. Like Mediterranean diets, high in mono-unsaturated fats, these anti-coronary diets were not low in total fat but were low in saturated fat. The Finnish Mental Hospital study ( 13), the Oslo Heart Study ( 14), and the Los Angeles Veterans Administration Hospital study ( 15) all demonstrated significant reductions in coronary rates of 43%, 25% and 23%, respectively, with the polyunsaturated fat diets (Table 1). The British soy oil trial ( 16) showed reduction in coronary incidence of 15% which was not statistically significant. These diets were also effective in reducing blood cholesterol concentrations. In contrast, there has been no similar trial of a low fat diet, that is, a trial that was sufficiently Large and long in duration to determine effects on cardiovascular events. The results of two low fat trials, the British Medical Research Council trial ( 17) and the Diet and Reinfarction Trial ( 18), did not show reductions in coronary rates with low fat diets, although both were too short in duration (two to three years) to adequately address the question. However, since the low fat diets in these two trials did not reduce blood cholesterol, it is dubious whether coronary rates would have reduced. Since a low fat diet should reduce blood cholesterol ( 5, 6), adherence was suspect. Very small, short-term trials investigated low fat diets, usually in combination with other healthy interventions such as exercise, weight loss or smoking cessation, and found reduction in the progression of coronary atherosclerosis ( 19-n21). Although the results of these short-term lifestyle programs appear promising, it is unknown whether they would be effective in preventing coronary events. A definitive study would require 100-fold more patients, a more representative population, and long-term adherence. Successful coronary prevention trials have required five years of treatment. These facts form the basis for debate among nutritionists, dividing them into those that favour one dietary pattern over the other.

Another approach to preventing coronary disease tested a Mediterranean dietary pattern in survivors of myocardial infarction ( 22). The Lyon Heart Study, presented in detail in the conference by one of the lead investigators, increased intake of vegetables, fruits, and fish which supplied vitamins such as folic acid, vitamin B6, carotenoids, and tocopherols, as well as oleic acid, ?linolenic acid, and other n-3 fatty acids. Interestingly, saturated fat was not reduced, nor did blood cholesterol improve. Nonetheless, coronary rates were reduced by 70%. A similar trial in India, that used a vegetarian diet also found beneficial effects ( 23). Thus the Mediterranean diet may be considered beneficial not only because of the reduced amount of saturated fat and cholesterol and increased mono-unsaturated fats, but because of micronutrients that act by mechanisms other than reducing blood cholesterol. These mechanisms may include reduced serum homocysteine concentration and protection from adverse oxidative changes to blood lipids.

Blood pressure is a risk factor for hypertension and cardiovascular events including myocardial infarction and stroke. High intake of vegetable products are related to lower blood pressure levels and low stroke rates worldwide. For this reason, the US National Heart Lung and Blood Institute sponsored a multicentre clinical trial to determine whether dietary patterns based on these epidemiological findings could indeed reduce blood pressure. The DASH study (Dietary Approaches to Stop Hypertension) found that increased intake of fruits, vegetables and nuts reduced blood pressure ( 24). A more comprehensive approach that further increased vegetable intake, reduced intake of meat and sweets, and increased low fat dairy products approximately doubled the effects. The effects of the DASH diet on blood pressure in mildly hypertensive patients was astounding, -12 mmHg systolic, far exceeding the results of other non-pharmacological interventions, and similar to drug monotherapy. Previously, investigators in Italy found that such diets, formulated in the Mediterranean context, also lowered blood pressure ( 25). Thus, the low cardiovascular disease rates in the Mediterranean may be due to favourable dietary effects on blood pressure as well as the lipid risk factors.

In January 1998, I chaired a conference of nutrition and public health leaders, mainly from the USA and Europe, to consider the scientific evidence on the optimal level and type of fat in the diet. The organisers were concerned about the increasing schism in the nutrition and public health community between those who advocate a low fat diet and those who advocate a Mediterranean-type diet. This has led to much conflicting information to the public, and understandable confusion. Participants were known for views on one or another side of the debate. Dietary effects on cardiovascular disease, diabetes, cancer and obesity were considered. A consensus view was achieved that mainly took into account cardiovascular disease, diabetes and cancer. There was marked divergence in views on the optimal diet to promote weight loss, and, on balance, the information base is not sufficient at this time to definitively favour a low fat or a high unsaturated fat diet for this condition. The following statement was released to the public:

There is increasing scientific evidence that there are positive health effects from diets that are high in fruits, vegetables, legumes, and whole grains, and which include fish, nuts, and low-fat dairy products. Such diets need not be restricted in total fat as long as there is not an excess of calories and the diet is low in saturated and partially-hydrogenated oils. Diets that emphasize vegetable oils (predominantly monounsaturated), nuts, and fish are preferable to those high in animal products and partially-hydrogenated oils. Many individuals will have to limit their intake of fat or carbohydrate to avoid excess calories.

It may be appreciated that this statement implicitly recognises the potential benefits of traditional diets of the Mediterranean or of Asia. Judging from the very low incidence in the Mediterranean and in parts of Asia, of cardiovascular disease and the cancers that plague our society, these traditional dietary patterns have the potential to dramatically benefit the population. Challenges remain for public health leaders to educate the population on scientifically based dietary choices, and to improve the food supply to enhance the success of such efforts.
Table 1. Prevention of coronary heart disease with polyunsaturated fat diets
Legend for Chart:

A - N
B - Dietary fat (% of total energy)
C - Duration (years)
D - Change in serum cholesterol (%)
E - Coronary events(a) (%)

A B C D E F

Finnish Mental 676 34 6 -15(*) -43(*)
Hospital (13)

Oslo secondary 412 39 5 -14(*) -25(*)
(14)

British soy oil 393 46 4 -15(*) -14
06)

Los Angeles (15) 846 40 8 -13(*) -23(*)

(*) P < 0.05.

(a) Coronary events refers to the difference in coronary

event rates in the treatment compared to the control group.

DIAGRAM: Figure 1. The Mediterranean diet pyramid: a cultural model for healthy eating. Copyright 1994 Oldways

Preservation & Exchange Trust

GRAPH: Figure 2. Saturated fat intake and coronary heart disease incidence. Seven Countries Study ( 2)
GRAPH: Figure 3. Total fat intake and coronary heart disease incidence. Seven Countries Study ( 2)
GRAPH: Figure 4. Replacement saturated fat with carbohydrate, mono-unsaturated fat or polyunsaturated fat. Predicted effects on coronary heart disease (CHD) incidence ( 11)

References

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By Frank M. Sacks

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