Guidelines Dietary - Eat For Health

Most fruit, vegetables and legumes have a low energy (kilojoule) density and high dietary fibre and water content,providing a plausible mechanism for the association of consumption of these foods with reduced risk of weightgain. Any effect is likely to be mediated through potentially increasing satiety, and also through taking longer tochew, which leads to reducing total energy (kilojoule) intake. 8,9 High dietary fibre intakes have been linked to lowerrates of obesity, type 2 diabetes and cardiovascular disease, mainly through an effect on plasma cholesterol. 8The majority of vegetables are nutrient-dense and low in kilojoules – in particular, green, Brassica and other ‘salad’vegetables are relatively low in energy (kilojoules). 9 However, starchy vegetables are less nutrient-dense and arehigher in kilojoules, but provide a rich source of complex carbohydrates. 9Diets high in fibre and specific complex carbohydrates such as non-starch polysaccharides have been usedwith modest success by people with type 2 diabetes attempting to lose weight. The small effects seen inthese experimental situations might relate to a satiating effect due to the prolongation of food absorption and asmoothing of the blood glucose response after meals. 8In the prevention and dietary control of type 2 diabetes, some vegetables are likely to be of particular valuebecause of their low energy density and relatively high content of dietary fibre, although longer term studiesmay be required to demonstrate effects.Legumes are also believed to confer cardiovascular health benefits because they provide a valuable low saturatedfat source of protein as an alternative to meats, and because of their glycaemic properties and phytoestrogenand isoflavone content. 417,418 These reviews suggest the isoflavone in soy foods may have a role in cholesterolreduction, improved vascular health, preservation of bone-mineral density 417 and anti-oestrogenic, anti-proliferative,pro-apoptotic, anti-oxidative and anti-inflammatory processes. 418 However more research is needed to determinethe relative effect of legumes/beans and soy foods themselves as opposed to isoflavones specifically.Guideline 2Cancer mechanismsThere is no dominant mechanism to explain the protective effect of vegetables, legumes/beans and fruit forsome cancers, and this is complicated by the range of site-specific cancer mechanisms. Some risk factors forcancer, such as oxidising radiation, can operate primarily from childhood or early adult life and antioxidants orother protective constituents of vegetables, including legumes/beans, and fruit may need to be consumedregularly from early life to be effective. 419 Phytochemicals and several vitamins and minerals found in vegetablesand fruit are thought to protect against some cancers by a range of mechanisms. Vegetables in the green leafyand Brassica subgroup are particularly high in folate 9 and inadequate amounts of folate are thought to increasethe risk of cancer by leading to a rise in homocysteine and megaloblastic changes in bone marrow and otherrapidly dividing tissues. 8 Poor folate status is thought to affect the induction of DNA hypomethylation, increasingchromosomal fragility or diminishing DNA repair, as well as increasing secondary choline deficiency, reducing killercell surveillance, and increasing risk of faulty DNA synthesis and metabolism of cancer-causing viruses. 8 Somestudies have suggested that folate, primarily from fruit and vegetables, may be more effective in reducing cancerrisk among those with habitual high alcohol intake. 420,421Several studies have indicated that vitamin C (found in most fruit and vegetables but particularly in citrus fruit,capsicum and tomatoes) is protective against cancer, whereas others have not found convincing evidence ofthis. 8 Lycopenes found in tomatoes are thought to be protective of prostate cancer, particularly when tomatoesare cooked in olive oil. 43 Carotenoids found predominantly in orange, red and yellow fruit and vegetables are alsothought to be associated with maintenance of immune function. 8 Dithiolthiones and isothiocyanates (found inBrassica or cruciferous vegetables) and allyl sulphides (found in Allium vegetables) have been shown to stimulatedetoxification processes. 36 The anti-inflammatory action of other phytochemicals, such as flavonoids, is alsothought to be important in reducing cancer risk. 422 Potatoes are not as rich in phytochemicals as other types ofvegetables, and this may help explain the weaker association with decreased cancer risk and consumption ofstarchy vegetables compared with other vegetables. 43 There is increasing evidence that whole foods are moreeffective in reducing risk of cancer than specific vitamin and mineral supplements, and that some supplementsmay actually increase risk of cancer. 423,424Localised contact with phytochemicals may be an important factor in the aetiology of epithelial cancers of thealimentary system (oral, oesophagus, stomach and bowel). Proposed protective mechanisms include: 8,425• the reduced formation of cancer-promoting substances in the gastrointestinal tract due to antioxidant activity• the part played by phytochemicals and micronutrients in the detoxification of carcinogenic substances• functions relating to the containment and destruction of existing cancer cells by means of a variety ofphysiological processes and improved immunological activity against cancer cells.Enjoy a wide variety of nutritious foodsNational Health and Medical Research Council41