New ideas about our diet take time to prove

Press, 10 August 1985, Page 14

New ideas about our diet take time to prove

fPDD ALERT

JANICE BREMER DIETITIAN

Weighing the evidence

Why do people with scientific qualifications tend to dull the glitter of radical ideas that suggest dramatic change of our food styles? They are cautious because they are trained to recognise that what works for one person does not work for all. And besides, even well-accepted scientific opinion is constantly changed by progressive research. Poultry, fish, and eggs, my subjects for this month, are examples of how nutritional concepts change over time. They have each been through their fair share of nutritional controversy. All have had a role in the “antiheart disease” diet. Untested, radical ideas based upon treatments for known illness are often taken to extreme, and promoted as preventing the disease. Such propaganda confounds the average, healthconscious individual because the underlying philosophy has a familiar ring about it. It sounds like something we’ve come across before. When an airline pilot comes to town (and is interviewed and appears in this same newspaper a week ago) expounding the virtues of the “Pritikin diet” — which is a strict version of a therapeutic diet to treat high blood-fat levels and recognised as such — we sit up and listen. But his eating habits are much stricter than even Pritikin. Ross Horne, author of “The Health Revolution,” advocates eating only raw food, mainly as fruit. His diet is not being used to treat anything in a scientific manner. Such diets, and even those such as the strict version of Pritikin, have not stood the test of time to prove they can maintain health over a life-time. The Pritikin is one diet, mass marketed commercially, that has some acceptance by the medical profession. But the strict version allows only one ounce (30 grams) of animal protein each week. This is ridiculously unpalatable amount for even a single serving. Excluding fish and chicken as well as meat is perhaps taking things a little too far, certainly for the young and elderly. White fleshed meats are generally held to be “okay” foods in diets promoted as preventing heart

However, nutritionists now realise that using colour is a simplistic method because chicken meat — if both dark and light meats are eaten — is as high in fat as lean beef, mutton, or pork. It also has two to three times more fat if the skin is left on. The fat of poultry, however, is higher in the polyunsaturated type of fat proportional to the saturated fat, than beef. Chicken meat is equal in cholesterol content with lean meats. The anti-heart disease diet of health authorities now puts the emphasis on a diet low in total fat, and a ratio of 1:1 polyunsaturated fat/saturated fat. Poultry and egg fats have a ratio of about 1:2.5. But oily fish, such as canned salmon, are better with 1:1; and white fish the best with a ratio 1:0.5. Obviously, fish and other high-ratio, polyunsaturated foods, like grains, counterbalance foods higher in saturated fat. So there is no need to eliminate them on those grounds, as long as your choices are lean and low-fat. Therefore, a moderate amount of meat, fish and poultry can be allowed in a diet aimed to delay the onset of heart disease. A diet encompassing levels of intake between Pritikin and our present level is easier to live with, and more likely to safeguard our intake of essential nutrients in the longer term. Fish Emphasis on fish oils has changed over the years. In the early part of this century, cod-liver oil was advocated as a supplement to provide vitamin D for infants. Exposure to sunshine, however, is now known as the preventive measure for rickets, the vitamin D deficiency disease. This is ah example of how extrapolation from one culture to another is not always appropriate. The cod liver oil theory was based on studies of children treated for rickets who lived in poverty and dim, dark houses — circumstances hardly to be found in New Zealand since Victorian times. Fish oils (and fatty fishes) have resurfaced in the nutritional literature in recent years — again to do with heart disease. An increase of fatty fish or cod liver $3

in the diet seems to lower blood cholesterol and reduce thrombosis and artery disease. Being urged to increase fat intake is very confusing. This is especially so, since the original studies derived from observations of the Eskimos, who are probably very different genetically from New Zealanders. There is also concern about increasing the requirement for vitamin E with this dosing. Some people dose with evening primrose oil which contains a similar type of oil. Increasing the fish oil content of our diets as cod liver oil (or eicosapentaenoic acid (the anti-thrombo-sis factor) can only be considered pharmaceutical, not dietary, as it is so concentrated. And we need a good reason to have it as a drug. We need to be aware of the interaction of nutrients, and that preventive nutrition must not be totally • based upon observations of other cultures or primitive tribesmen. Qualifications that provide nutritional credibility are essential for people who take responsibility for others’ lives and health when they define new food styles. We would expect eggs to have suffered most from the promotion of a lowcholesterol diet. They provide about a third of our average daily cholesterol intake. Strict guidelines of the 1970 s frequently recommended limiting total daily dietary cholesterol to the level provided by just one large egg. These guidelines did not take into consideration other foods containing cholesterol. Hence the “putdown” of eggs. Most current guidelines for most people, who do not have high blood fat levels, are not so strict about eggs. They concentrate more on fatty foods. Food alert © Watch out for diets that totally exclude any food group, and if necessary seek professional help to ensure nutritional adequacy. ©Be discerning about popular scientific theory when expounded by unqualified entrepreneurs. @ Keep an open mind about new nutritional trends — they take a long "time to be substantiated.