2. NUTRITIONAL VALUE - TREE NUTS AND HEALTH
PRESENTATION "TREE NUTS AND HEALTH"

There have been various studies over the last few years which have shown the beneficial effects that nuts have on health. From these, the negative connotations that these foods had have developed to the present state, when all specialists in nutrition and food recognise the useful properties which nuts have.

Nutritive composition of nuts

Nuts are, in general, fatty foods: between 51 and 73% of their weight is fat. Owing to this and to their low water content, their energy content is high; they have between 5.6 and 6.4 Kcal per gram of food.
In spite of their high lipid content, the nutritional profile of nuts is exceptional because the majority of the lipid compounds are unsaturated fatty acids. They have a large amount of oleic (C18:1) and linoleic (C18:2) acids which provide more than 75% of the fat content, although each variety has its own characteristics.
Therefore nuts could be classified into 2 groups: Those which are mainly rich in MONOUNSATURATED FATTY ACIDS, above all oleic acid, such as hazelnuts, almonds, macadamia nuts, and pistachios, and those rich in POLYUNSATURATED FATTY ACIDS, such as walnuts. Walnuts also have significant quantities of linolenic acid (C18:3 n-3), and given that other nuts show much lower quantities of this fatty acid, the walnut is considered to be an excellent dietetic source of omega 3 fatty acids.
As well as this peculiar lipids profile, nuts also have other very healthy nutritive components.
Their concentration in PROTEINS is high if they are compared with other foods of vegetable origin: they have between 13 and 26g of proteins per 100g of food. Moreover, this is a protein relatively low in lysine and also rich in arginine, an amino acid from which nitric oxide is derived to which various effects on cardiovascular health are also attributed.
With the exception of the chestnut, the carbohydrate content of nuts is relatively low. These have a carbohydrate content of 36g/100g while other nuts vary between 3.7 and 20g of carbohydrates /100g of food.
Nuts are also an excellent dietetic source of FIBRE, their content being 6 to 15g/100g of nut, varying according to the various types of nut. Finally, the high content of different micronutrients in nuts must be emphasised. They are extremely important dietetic sources of various MINERAL ELEMENTS such as calcium, magnesium, copper, manganese, phosphorus, selenium, and zinc, and of vitamins such as thiamine, vitamin E, niacin and riboflavin.
In addition to this, nuts contain a large quantity of PHYTOCHEMICAL compounds, amongst which mention should be made of various compounds with antioxidant activity such as vitamin E, ß-carotenes, lycopene and others.

THE EFFECT OF NUTS ON HEALTH: EPIDEMIOLOGICAL EVIDENCE

Prospective observational studies

The first evidence on the favourable effect of nuts on health were prospective observational studies such as the Adventist Health Study (1992), undertaken in a population of Adventists in California. In this, it was observed that a greater frequency of nut consumption was associated with a reduction in the risk of cardiovascular disease. Therefore, in those individuals who regularly ate nuts 5 or more times a week, it was observed that they showed a reduction in the risk of myocardial infarction of 51% in comparison with those who did not eat nuts. Other prospective observational studies undertaken more recently such as the Iowa Women's Health Study (1996), the Harvard Nurse's Health Study (1998) or the Physician's Health Study (2002) also showed that in those individuals with a greater frequency of nut consumption there was a lower risk of cardiovascular illness and of death through those causes.

Dietetic intervention studies

As well as the observational studies, various dietetic intervention studies have been undertaken with nuts in order to be able to demonstrate that the incorporation of nuts into the diet produces a reduction in cardiovascular risk factors such as cholesterol levels: all these have produced positive results. Thus for example, some of the most recent have been done by Zambón and collaborators (2000), who by means of a cross-study comparing a Mediterranean diet and a Mediterranean diet enriched with walnuts observed a reduction in the total cholesterol and LDL cholesterol figures (of 9 and of 11.2% respectively) significantly higher in those individuals with a diet enriched with walnuts. Almario and collaborators (2001) also obtained a reduction in the total cholesterol and LDL cholesterol figures in dyslipaemic individuals when these were subjected to a low-fat diet supplemented by nuts. Iwamoto and collaborators, in articles published in 2000 and 2002 also showed a reduction in of total cholesterol levels in those individuals who followed the diet rich in walnuts.

Effects on cardiovascular health

By all this, the beneficial effect that nuts have on cardiovascular health seems to be demonstrated: they reduce total cholesterol and LDL cholesterol levels, therefore very probably contributing to a reduction in the incidence and mortality of cardiovascular disease.
The protective mechanisms that nuts seem to have on cardiovascular health derive from their peculiar nutritive composition. Thus, their lipids profile, rich in mono- and polyunsaturated fatty acids and poor in saturated fatty acids, is the main cause of the reduction in total cholesterol and LDL cholesterol levels produced by eating them and therefore in the reduction of the risk of coronary disease. However, in the majority of studies, this reduction in risk goes further than expected, so that it seems evident that there are also other nutritive components in nuts which would have an effect on the level of the reduction of risk. Thus for example, their antioxidant content would protect the LDL particles from the oxidation which would be produced by the atherogenic process; arginine, by the production of nitric oxide, would be capable of reducing the adhesion and aggregation of the platelets; the omega 3 fatty acids would also reduce platelet aggregation; the dietetic fibre would contribute to the reduction in the levels of LDL cholesterol; and the folic acid content would favour good levels of homocisteine which also plays a preventive role in cardiovascular disease.

Other effects on health

As well as their protective effect against cardiovascular diseases, nuts possess a wide variety of nutrients which are beneficial for health.
They are one of the richest foods in antioxidants such as vitamin E, ß-carotenes, ellagic acid, flavonoids and tocotrienols. This antioxidant potential of nuts seems to give them a protective character against diseases such as certain types of cancer, especially intestinal cancers, and other chronic diseases cause by the cellular oxidation of the body.
Their dietetic fibre content also gives nuts certain functional properties, as an adequate ingestion of dietetic fibre is related to a lower risk of coronary disease, a lower incidence of cancers, better control of diabetes and better control of body weight.
Finally, various recently-published studies show that nut consumption of does not alter sensitivity to insulin in healthy adult individuals, or glycaemia in type 2 diabetic individuals, and that they produce beneficial effects on the lipids profile, in such a way that their incorporation into the diet of these groups of people would be totally justified.

Therefore it seems to be amply demonstrated that nuts are an excellent diet complement for this to be the instrument which helps to achieve an optimum state of health.

May 2005

Source:

Nucis (Health & Tree Nuts) Foundation www.nucis.org