Abstract
This review will focus on changes in attitudes and theories on the role of lipids in the diets of New Zealanders. In the last twenty five years we have seen some changes in the understanding of the role of lipids in health but in general we have not made much progress in actively reducing the mortality due to cardiovascular disease, cancer or diabetes. The death rate due to heart attacks has reduced probably due to a reduction in smoking. A review of the "Lipid Hypothesis" will be given along with a consideration of the role of monounsaturated fats, omega-3 fatty acids, trace metals, sitosterols, antioxidants and the relative new perspective of oxidized lipids and cholesterol in this hypothesis. There have been both positive and negative changes in our lifestyle in the last twenty five years, some of which are beneficial such as the adoption of some principles of the Mediterranean diet and some are negative such as our increase in sedentary activities. There is no panacea for good health but knowledge and sensible practices for all of the NZ population may assist in the battle against these chronic diseases.

Introduction
Over the last twenty five years there has been a concerted effort by Medical Practitioners, Nutritionists and Dieticians to combat the major diseases affecting New Zealanders. These diseases are predominantly cardiovascular disease and cancer. Approaches have been mainly centred on the "lipid hypothesis" whereby cholesterol and saturated fatty acids have been the main targeted villains with polyunsaturated fatty acids seen as the saviour. Although researchers never had any intention of simplifying the diagnosis and the cure, vested interests have ensured that the message remained simple and the nutritional changes required even more simplistic with respect to the role of lipids in the New Zealand diet. These included trans fatty acids, antioxidants, omega-3 fatty acids, dietary fibre, selenium and oxidized fat.

Obesity
The increased incidence of obesity is perhaps the single biggest threat to a major segment of our population. Our increasing sedentary lifestyle and provision of plentiful and cheap fast food has resulted in an alarming statistic showing that over 35% of new Zealanders are overweight and 17% are obese (Ministry of Health, 1999).
To counter this trend in our national diet every research nutrition group in New Zealand has climbed on the low-fat bandwagon with some influential people even suggesting the unworkable "fat-tax". This is not the route to pursue illustrated by the fact that the Americans are increasing in their obesity percentage, despite low fat mania and the fact that Mediterranean populations have average to high intakes fat predominantly of monounsaturated oils. This would suggest that this view is too simplistic an approach.

De Lany et al (2000), suggests that the dietary fatty acids that are more prone to oxidation than to depot storage may be less likely to lead to obesity. This research demonstrated that there was substantial variation in the proportion of the fatty acid which was found to be oxidized; stearate being far more slowly oxidized than linoleate. De lany (et al 2000) concluded that in animal studies the rates of oxidation partially explained the differences in weight gain observed when the animals are fed different types of dietary fat and this mechanism may be a factor in human obesity. The trend toward the consumption of fast foods (predominantly deep-fried) high in energy and saturated fat is a likely link in the obesity epidemic and there are several solutions; one of which is to change the type of fat used to monounsaturated oils from tallow-based and the other is to provide tasty, economical nutritious alternatives to fried food.
The use of polyunsaturated fatty acids in frying is not of great nutritional benefit because of their high susceptibility to oxidation and polymerisation. The early recommendations from nutritionists were that dietary intake, of fats should be reduced so that they contribute 30% of the total daily energy intake, (Coma 1984) however given where our contribution is today we would be more realistic to target reduction down to 33% of total calories so long as our major fatty acid is monounsaturated and not saturated.

Cholesterol
It was the epidemiological studies summarised and reviewed by Keys (1980) that showed that for some populations serum cholesterol levels were correlated with a high incidence of coronary heart disease. It was also later shown that contrary to earlier belief, serum cholesterol is not closely related with dietary cholesterol intake and is primarily related to saturated and trans fatty acid. The whole area is admirably review by Gurr (1999). Predictive equations were drawn up by Hegsted et al (1965) and Keys (1965) that demonstrated the cholesterol lowering effect of polyunsaturated fatty acids.
There does not seem to be any doubt that elevated total serum cholesterol levels are a risk factor for cardiovascular disease and levels above 5.5 mmolL in adult men are seen to indicate a moderate risk. Over the years there has been growing evidence that it is the oxidized low density (LDL) cholesterol lipoprotein that may be responsible for the build up of plaque in arterial walls. Kummerow 2000). Thus further to this the lipoprotein complex ratios (HDL : LDL) are far more important than total serum cholesterol viewed in isolation.
Recent work suggests that for low risk then adult males should have a total serum cholesterol below 4.0 mmol/litre ( 155mg/dL). Furthermore the HDL : LDL ratios should be a key predictor for low risk being approximately 1.5 : 1.0 Kannel et al (1992).

Phytosterols
The plant kingdom, comprising cereal, vegetable seed oils, nuts and fruits contain a number of sterols that differ from cholesterol by having ethyl or methy groups or unsaturation in the side chain. The predominant ones are sitosterol, stigmasterol and campesterol acid are present in diets rich in these food sources and contribute almost equally to cholesterol. The most prominent is beta-sitosterol which differs from cholesterol in that it has an ethyl group at carbon 24 of the side chain. In the early 1950's it was noted that the additon of sitosterol to the diet of cholesterol-fed chickens or rabbits lowered cholesterol levels in both species and inhibited atherogenesis, this was extended to human work by Miettinen (1994). Sitosterols were also studied extensively as cholesterol lowering agents by Lees et al (1997) and no adverse nutritional effects at large dose levels have been observed.
In the past year we have seen the launch of 2 margarines in New Zealand containing hydrogenerated and interesterified beta sitosterol which are reported to lower serum cholesterol by between 10 - 20%. However, these margarines are expensive, and are currently holding less than 0.5% market share. Because of the expense and the reduction in yellow fat consumption it would be advisable to have Phytosterols included in other food products such as dressings and baked goods, despite current ANZFA opposition to such widening of the scope for this effective nutritional change.

Saturated fatty acids
The realisation that it was saturated fatty acids and not dietary cholesterol that raised serum cholesterol, led to the proliferation of polyunsaturated margarines from their launch in 1972 to the present day. In 1972 the only legal yellow spread was butter and in the early years polyunsaturated margarine had only about 10% market share. Compare that to today where the total yellow fat consumption has declined and the butter market share has fallen below margarines to 48% for the first time ever in New Zealand (Anon 2000). This situation was unthinkable 25 years and ago and the repeat of the restrictive margarine act (1908) has further eroded butters market share.
The early polyunsaturated margarines were made to a formula that predominantly blended high linoleic oils such as safflower, sunflower and soybean and were made to achieve a polyunsaturated : saturated fatty acid ratio of 2 : 1 minimum and total saturated acids were at 20% maximum. All saturated fatty acids are not equal in their cholesterol raising activity with myristic seen as having the largest effect followed by palmitic. Stearic acid is currently seen as neutral in its effect. New Zealand is not acting fast enough to reduce the present contribution of saturated fats to the total dietary energy intake. Currently saturated and trans fatty acids make up approximately twenty percent of total energy intake and a desirable target is to get to less than ten percent. The problem is that our current dietary intake favours a high intake of meat and dairy products, fast food (animal fats) snacks and with few New Zealanders eating 5 - 8 servings of fruit, vegetables, and fish twice a week.

Changes in the relative intakes of fatty acids
Having discussed the individual fatty acid intakes it is helpful to assemble all the data and examine a desirable fatty acid intake for the New Zealand diet. This desirable intake was calculated recently for the USA (a) by Simopoulos (1999) and compared with this author's estimate for current New Zealand intake (Eyres 2000). The desirable composition is shown contrasted with an estimate of the New Zealand current intake in Table 1. The arrows in the table indicate the desirable direction of change.

Table 1 Desirable and current fatty acid composition of the New Zealand diet (for a 8400 k joules diet)

	Latest target composition (a)		Estimate current NZ intake (b)
Fatty acid	g/day	% energy	g/day
Saturated F.A.	17.8	< 8	39
Trans	2.0	< 1	6
* Monounsaturated	48	~ 20.0	38.8
Linoleic (w-6)	6.7	3.0	15
Linolenic (w-3)	2.2	1.0	1
E.P.A. + DHA (w-3)	0.7	0.3	0.2
	78g	33	100g

Trans fatty acids
Trans fatty acids occur naturally in the depot fats and milkfat of ruminants. They are also produced during the hydrogenation of liquid unsaturated fish and vegetable oils, which utilises this technique to produce solid and more stable fats for food manufacture. The major controversy over these fatty acids revolved around the discovery that they were even more cholesterol elevating than saturated fatty acids, and also increased LDL levels at the expense of HDL levels Mensink etal (1990).
Levels of trans acids in the US and European diets have been estimated to be between 10 - 20g per day whereas in New Zealand and Australia the intake is approximately 4 - 5g per day (Lake 1995). This has not changed significantly over the last twenty years since our intake of hydrogenerated soy, rape and fish oils is very low in contrast to America and Europe. The trans acids should be counted and added to the saturated fat content of a food. The controversy which surfaces from time to time illustrates that data from one country cannot be extrapolated to another. The British Nutrition Foundation task force concluded that whilst levels around 4 -5g per day posed no significant risk to the consumer, it would be prudent not to allow the average intake of trans fatty acids to rise, by encouraging good food manufacturers to eliminate partially hydrogenated fats from oils and fat products. As shown in the table above they were also recommending that trans fatty acids should not be more than 1 - 2% of energy intake.

Polyunsaturated fatty acids
When the term polyunsaturates was starting to become well known in the early 1970's, most people, technologists and nutritionists equated this with linoleic acid (omega-6) and linolenic acid (W-3) was ignored. The polyunsaturated margarines which emerged onto the market in 1972 following an act of Parliament to legalize them, had linoleic acid levels in excess of 40% and saturated fatty acid levels less than 20% per cent. It is thought that our ancestral diet before the Industrial Revolution had dietary levels of omega-3 and omega-6 in an equal ratio. These essential fatty acids are necessary but current research suggests that we should reduce our intake of linoleic acid to less than 7g per day and increase our linolenic acid (from canola, flaxseed and other sources) to approximately 2g per day ie. A ratio of around 3 - 4 : 1 of linoleic to linolenic is desirable not the current ratio of approximately 15 : 1 (Simopoulos (1999). There are concerns that excessive amounts of linoleic acid may increase the oxidation susceptibility of the atherogenic lipoproteins especially with low antioxidant intakes, Louheranta et al (1996).
The long chain PUFA from fish oils are sadly lacking in the NZ diet and the high price and often unavailability of quality fish is cited as the main reason for this. This is an urban myth and quality fish can be sourced economically and utilized in a variety of "healthy" recipes for most families. Fish and chips, whilst an acceptable meal for most families is nutritionally balanced when it is not overloaded with saturated fat and oxidized cholesterol from heat abused animal fat based frying media. Auckland Health Care have been doing excellent work recently in this vital area.

Monounsaturated fatty acids
The Mediterranean diet has often been cited as the preferred diet and the Lyon Study verified that intervention groups on this type of diet showed a significant reduction in the death rate from CHD with also a reduction in related risk factors such as LDL - cholesterol. (Lorgeril, 1999). Interestingly the total serum cholesterol of the intervention and control groups showed no significant differences. The monounsaturated fatty acids (oleic acid) are the major components in olive oil and avocado oil yet the beneficial influence of these oils may not be solely due their fatty acid composition and may involve the other minor components such as beta sitosterol, tocopherols and other antioxidants.

Conjugated linoleic acid
This unusual cis, trans polyunsaturated fatty acid occurs in dairy products and other animal fats (ruminants) and has been the subject of a review at this conference (McGibbon, 2000). There is an on going research into the beneficial effects of this fatty acid and in fact a major seminar on this emerging nutrient for the 21st century will be held in the UK this year.

Fast food
The last twenty five years has seen a massive change with respect to the role of meals not consumed at home. There has been prolific growth in fast food chains and they have one main item in common, which is their use of tallow based frying fats. These refined and deodorized beef and mutton tallow based fats are stable, economical and are produced by local New Zealand companies to a high quality standard. However, they have several nutritional deficiencies in the light of the developing theory of oxidized lipids and protective antioxidants. These include the fact that they contain a high level of saturated fats (46%), a significant concentration of cholesterol (0.2%), no natural antioxidants such as tocopherols and they generally get used well beyond their oxidative shelf life. Food fried in these fats tend to have a high energy content and be carriers of oxidized lipids which destroy natural antioxidants and leave the consumer saturated. They tend to be marketed towards the younger generation. The current high intake in New Zealand is of major concern to nutritionists.

Frying fats
Frying is a complex process. The reactions taking place are not simple oxidation reactions and their rate of reaction is fast at temperatures between 180 - 190 c. New Zealanders consume large amounts of fried food and sausages, fish, chicken and potatoes are the common ingredients.

Exchange of lipids occurs between the food and the fat. The processors require a stable, cheap and quality frying fat and 90% of the market is tallow based product for this reason. Some manufacturers have turned to canola oil, cottonseed oil, and palm oil but change is slow and none of these products are ideal from a technological point of view. High Oleic sunflowerseed oil, a new vegetable oil is an ideal product for frying. It is high in monounsaturates (80%), contains no cholesterol and contains tocopherols. However it is expensive and this is delaying its successful introduction into the business.

Oxidized lipids
Most nutritionists have been very concerned about the ingestion of oxidized lipids for many years, but this was based on theory and with little scientific evidence that rancid fats or oxidized lipids of any form were directly involved in diseases such as cardiovascular disease or cancer. Despite this, however, there is circumstantial evidence and examination of certain biomarkers suggest that oxidation of all lipids is a logical and plausible source of high risk factors for cardiovascular disease and other inflammatory diseases (Steinberg 1997). There is great interest in this area particularly relating to the molecular mechanisms that lead to atherosclerotic plaque formation and the protective effects of natural antioxidants. The key questions to resolve are (1) whether peroxidized lipoproteins exist in plasma and if they are elevated in subjects at higher risk to cardiovasular disease and (2) what is the source of the peroxides.
Some researchers believe the case is proven and cite experimental evidence from studies of atherosclerosis in the LDL receptors in mice. (Staprans et al 1999). The table below shows some common sources of oxidized lilpids from typical foodstuffs such as imported nuts and imported aged vegetable oils.

Table Source of oxidized lipids in the New Zealand diet.

Common Oil Source	Intermediate Oxygen Species	Likely Products
Imported cheap vegetable oils	Peroxidized linoleic acid	Aldehydes, Hydraperoxide
Rancid imported nuts	Oxidized triglycerides	Polar material
Grilled pizza cheese	Oxidized cholesterol
Fried chicken/sausages/shell fish	Oxidized cholesterol and long chain PUFA	Polar material, dimers, aldehydes, oxidized fatty acids
Barbecued meat	Pyrolysed fatty acids and oxidized cholesterol	Aldehydes, polymers, benzpyrene
Fish Oil supplements	Oxidized PUFA	Aldehydes

Antioxidants
The classical mechanism of lipid oxidation via free radicals has been established for many years. The protection of lipids by hindered phenols such as tocopherols has also been documented, investigated and utilized in food manufacture Reische et al (1997). Again original approaches of supplementing diets with pure derivatives of alpha tocopherol or in some cases beta carotene is not appropriate for human nutrition. Oxidation and antioxidant defense within the body is complex and it appears we mayneed a cocktail of different antioxidants as suggested below in Table 2. (Author's proposal). One of these essential and lements is selenium known to be deficient in the New Zealand diet for over 30 years. Selenium is relatively easily added to the everyday diet and we should possibly emulate the Finnish authorities who decided in 1984 to ensure an average minimum intake of 25 micrograms per day via fertilizers. The whole area of selenium in food is admirably reviewed by Combs (1986).

Table 2 Suggested Antioxidant Cocktail (per day)

The Antioxidant Cocktail
Vitamins A, C, and E together with selenium

• Vitamin E 200-1200 iu/day
• Vitamin C 100-250 mg/day
• Vitamin A 750 µg retinol/day
• Selenium 50-200 µg/day

Conclusions
A significant proportion of the New Zealand population have paid no heed to the nutritional messages of the last twenty five years. The increasingly sedentary population consumes too much energy, too much saturated and trans fat, insufficient monounsaturated and omega-3 polyunsatured fatty acids and has deficiencies in natural antioxidants and their co-activists which include tocopherols (vitamin E) vitamin A, vitamin C, flavanoids and selenium. Most of these imbalances can be traced to current dietary practices with the consumption of fast food, takeaways and high energy snacks dominating the diet with corresponding lack of intake of fruits, vegetables and fish. There are economical ways of improving the day to day diet and more notice should be taken to ensure that the lipids in our diet are free of oxidized species such as the peroxides of polyunsaturated fatty acids and the oxides of cholesterol. Perhaps it is now time to qualify the "no-fat" dogma and to ensure we have a dietary regime comprising the right fatty acids in a pristine state.

Recommendations
The population of New Zealand as a whole needs to focus on the problem of insufficient exercise, obesity, overweight and diabetes. Researchers need to examine new biomarkers as indicators of incorrect nutrition. The role of oxidized lipids and in particularly cholesterol oxides needs to be clarified with respect to their relationship with inflammatory diseases such as heart disease.. This presence of oxygen containing species should be correlated with antioxidant and selenium states particularly in people at risk.
There is a realization that it is not fat which is bad for one but it is excessive amounts of the wrong type of lipids and in the wrong oxidized state that results in the diseases that are prolific in the New Zealand population. If we wish to significantly change the New Zealand diet we must focus on areas of maximum impact such as the nature of frying fats in fast foods, the reduction of oxidized species by better food handling practices, the analysis and identification and incorporation of the necessary antioxidants in our food supply.

Acknowledgements
Professor John Birkbeck was as usual a friend and mentor who helped enormously with ideas for this paper.
Dr Clare Wall was of immense help in commenting on the paper.

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