Dietary measures involve more than lipids.

Pr. J.L. SCHLIENGER

A low fat diet is not sufficient to prevent the process of atheromatosis and its cardiovascular consequences. Qualitative aspects of lipids and food diversity, such as in the "Mediterranean diet", lead the way to a more efficient prevention.

Whereas many cardiovascular risk factors are fought with efficient molecules, the role of preventive and therapeutic nutrition remains necessary in the fight against the process of atheromatosis and its consequences. Since the simplistic concept of an anti-atheromatous diet proposed by the American Heart Association (severe hypolipidic regimen), research has led to define a nutritional policy both richer and better nuanced.

The so-called "7-country study" (United States, Finland, Greece, Italy, Japan, Netherlands and Yugoslavia), which begun at the end of the fifties and lasted 30 years, underlined the existence of a relationship between coronary mortality, cholesterolemia and saturated fat consumption. Thereafter, many studies confirmed the benefits of reducing dietary lipids to 30-35% of energy intake for subjects at risk, keeping the polyunsaturated-saturated fatty acids ratio (P/S) close to one. Finally, the preventive role of n-3 polyunsaturated fatty acids provided by fish has been identified through studies conducted with Eskimos.
In France, in spite a saturated fatty acid intake and a cholesterolemia comparable to those of Finland or the United States, cardiovascular mortality is 3 to 4 times less frequent: that is the "French paradox", compelling us to consider the role of non-lipidic nutrients.
The Lyon dietary intervention study showed the evident superiority of a Mediterranean diet model (see box) over a conventional hypolipidic diet, in presence of hardly different cholesterolemia indices.
From this data, two concepts of atheroma preventive or curative diet were developed successively.
The first one focussed on the quantitative role of dietary lipids and cholesterol. The second one revolved around the aspects of qualitative contribution of lipids and the necessity of a varied diet.

Atheromatosis is a complex process, implicating mostly lipids: any reduction in the LDL fraction of cholesterol or any elevation in the HDL/LDL ratio slows the atheromatous process and reduces coronary morbidity and mortality.

Lipids
In predisposed subjects, abundant lipid intake raises cholesterol and triglyceride levels above normal, inducing thrombosis, obesity and carbohydrate intolerance. Insufficient lipid intake decrease HDL cholesterol and lead to a lack of antioxidant vitamins E and A. It is therefore necessary to focus on the qualitative aspects of dietary fats rather than on the hypocholesterolemic effects of a low fat diet.

Dietary cholesterol
Reduction in dietary cholesterol intake brings a limited intrinsic effect in the absence of cholesterol absorption or excretion defects. Indeed, a reduction in dietary cholesterol is accompanied by a reduction in HDL cholesterol: in presence of hypercholesterolemia, it is therefore unnecessary to severely reduce cholesterol intake.

Saturated fatty acids
Saturated fatty acids increase total cholesterol levels, LDL cholesterol and also... HDL cholesterol.

Monounsaturated fatty acids
As their precursor, oleic acid, monounsaturated fatty acids are better absorbed when they are from plant origin. They reduce LDL while maintaining HDL levels constant.

Polyunsaturated fatty acids
Polyunsaturated fatty acids bring about their beneficial effects because of their great fluidity and the specific biologic properties of their chemical structure. Fatty acids of the n-6 family, including linoleic and arachidonic acids, decrease LDL and HDL concentrations and interfere with the process of thrombosis. When the P/S ratio is above one, excess lipoproteins are more prone to peroxydation, enhancing the synthesis of thromboxanes A2, causing vasoconstriction and platelet aggregation. A diet comprising only lipids rich in n-6 fatty acids is therefore not indicated.
Fatty acids of the n-3 family, including alpha-linolenic acid and its precursors (docohexaenoic acid or DEXA, eicosapentaenoic acid or EPA,…), are found mainly in fat fishes. They reduce triglyceridemia and have anti-thrombogenic and anti-atheromatous properties.

Trans fatty acids
The presence of trans fatty acids in the diet, from heated oils and margarines, is generally considered like an enhancing factor of cardiovascular risk.

Energy intake
Excess energy intake increases, in certain subjects, production of lipoproteins rich in triglycerides (VLDL) and the risk of LDL hyperproduction. On the other side, caloric restriction improves the lipid profile in obese subjects.

Carbohydrates
Simple carbohydrate intake can contribute to the development of hypertriglyceridemia, opposite to a diet rich in complex carbohydrates, often related to a fibre-rich and low saturated fat diet.

Fibres
A fibre-rich diet (20 to 30 g. per day of dietary fibre) decreases cholesterolemia by increasing faecal elimination of cholesterol. This effect is due to soluble fibres from fruits and plants: pectin, hemicellulose, soluble fibre from oat bran (but not from wheat...).

Alcohol
Alcohol per se induces a favourable effect on lipid profile by significantly increasing the concentration of HDL and the size of LDL, making them less oxidizable. Non alcoholic constituents of wine, and to a lesser degree of beer, possess interesting properties, namely antioxidant ones, as demonstrated in vitro.
Otherwise, alcohol decreases platelet aggregation. Consumption of one glass of an alcoholic beverage with meals insures cardiovascular protection without increasing other causes of mortality.

Fruits and vegetables
Antioxidant properties of fruits and vegetables are due to their content in soluble fibre but also and maybe especially to specific plant constituents such as phytosterols and polyphenols.
A daily intake of 10 to 15 g. of phytosterols decreases cholesterolemia by 10 to 20% in hypercholesterolemic subjects. Phytosterols act by inhibiting the intestinal absorption of cholesterol. Their anti-atheromatous effect has been demonstrated on various animal models but there is no direct evidence of their ability to reduce coronary mortality in human subjects. We may nevertheless already recommend the consumption of plant foods in considerable quantities.
Polyphenols are powerful chelators of free radicals involved in oxidation reactions and are found in abundance in wine, green tea, olive oil, onions and some fruits (grape, apple, lemon). These foods improve the antioxidant load and bring some favourable but inconsistent changes to the lipid profile.

Antioxidants
The protective role of antioxidants established in experimental models could not be clearly confirmed by intervention studies although oxidation increases the atherogenic potential of LDL and result in vascular endothelial damage. Dietary antioxidants are essentially the E, C and A vitamins and polyphenols. Diet insures an intake of antioxidant enzyme cofactors such as selenium and zinc.

Although the physiological process of atheromatosis is inherent to ageing, there is a large variation in cardiovascular risk because of the interaction between genetic predisposition and environmental factors. The ideal preventive measures would quantify individual cardiovascular risk and identify subjects responding to dietary intervention. At present, a family history of hypercholesterolemia or hypertriglyceridemia, or even a slight increase in LDL and/or triglycerides are as many formal indicators to follow a preventive diet from the age of 40.
However, dyslipidemia is not the only target. Cardiovascular disease prevention also comprises other aspects, such as measures against tobacco use, arterial hypertension and excess weight.

A low fat diet is not a panacea for the prevention of atheromatosis. Qualitative aspects of foods are at least as important as their quantitative aspects. To prevent atheroma formation, a moderately hypolipidic diet must preserve a considerable part of monounsaturated fatty acids and must provide a meaningful amount of alpha-linolenic acid and other n-3 polyunsaturated fatty acids, soluble fibre and antioxidants. To this day, a diet close to the Mediterranean type constitutes a model to recommend to populations exposed to a high cardiovascular risk.

Pr. J.L. SCHLIENGER
CHU Strasbourg

The Cretans have a very low cardiovascular morbidity and mortality. They consume olive oil, plant foods with antioxidant properties (fruits, vegetables, salads and walnuts) and fibre-rich foods. The highlights of this regimen are the considerable unsaturated fat and the low saturated fat intakes. Olive oil, particularly rich in the monounsaturated oleic acid, is the common denominator in diets from Mediterranean countries, as well as fishes rich in n-3 polyunsaturated fatty acids and low fat cheeses. Consumption of almonds provides mono and polyunsaturated fatty acids. In total, the contribution of lipids represents a little less than 30% of energy intake, comprising 7% saturated fatty acids, against 40% and 13%, respectively, in the western and northern countries.
Moderate alcohol consumption as wine during meals is another important feature of this diet style. The Mediterranean model is not the unique diet to recommend to populations with high cardiovascular morbidity and mortality. However, it certainly does provide indication to follow and integrate to diverse socio-cultural environments.

Nutritional recommendations			Foods to favour
	Lipids: < 30% of energy intake      < 10% saturated fat      = 15% monounsaturated fatty acids        = 6% polyunsaturated fatty acids      including:      10 g. linoleic acid      1.5 g. alphalinolenic acid Antioxidant vitamins Soluble fibre Carbohydrates: 55 to 60% of energy intake favouring unrefined complex carbohydrates. Proteins: equally from animal and plant origin.			Colza and olive oils Fishes Lean meats Fruits and vegetables, raw vegetables Bread and other cereals Dry vegetables