Once ridiculed, vegetarianism is now being viewed with acclaim by leading nutrition and medical experts from around the world as the proposed benefits of eating more plant foods are being increasingly backed by scientific evidence. Sue Radd reports on the news, views and research trends from the premier scientific meeting on vegetarian nutrition held at Loma Linda University, California, April 2002.
I always get excited about attending the International Congress of Vegetarian Nutrition. Not only is it a time to catch up with colleagues who have a genuine interest in the ins and outs of vegetarian eating - in this case more than 400 of them from over 20 countries - but it is a time for reflection. We ask ourselves the question: What have we learned over the preceding five years since the last congress, and where is more research still needed?
The event fulfilled my expectations. The four-day program was jam packed with the latest findings as well as reviews of previously published research on vegetarian nutrition. Issues covered ranged from chronic diseases, perspectives on different plant foods, ethics, ecology and spirituality. The congress involved around 60 speakers including the "who’s who of the nutrition research world" such as heavyweights from Harvard, Oxford, Cincinnati and Toronto Universities. Australian research was also presented. I was particularly pleased, from a practical perspective, that the morning and afternoon teas constituted ‘real food’. At so many 'nutrition conferences' the food on offer is far from ideal. On this occasion however, you could choose from a selection of nuts, dried and fresh fruits (think berries!) and even herbal teas in place of the typical biscuits, coffee and cake one is usually offered. Even the official banquet dinner was a five star event with a high rating being given by many delegates for flavour and presentation.
I was asked to co-host the evening with a Spanish gastroenterologist as the organisers - the School of Public Health - wanted to create a truly international feel. The choice of venue was significant since much of the early research on large numbers of vegetarians actually began at Loma Linda University in the 1950s. If you ever got bored sitting in the sessions - which was difficult because of the variety of issues covered - or perhaps just needed a stretch, you could wander over to the campus supermarket. This is an event in itself, since the supermarket is entirely vegetarian and stocks a vast range of products. I spent several hours in the evening doing my usual supermarket jaunt and taking many photographs.
A major theme that emerged at the congress was the importance of synergy. What is food synergy? It is the interaction between individual components in food and the overall result that this interaction gives, which is greater than you would expect to see if you added up the effects of the individual components. In other words, just because you think you know what nutrients are in a food and how they might act doesn’t mean that you can exactly predict the overall effect of eating the whole food that contains these nutrients. Phytic acid for example, found in legumes and wholegrains, binds minerals to a certain degree and so was earlier thought to be a negative factor in foods that should be minimised. Some old textbooks still suggest this. Current research shows that in the context of a varied diet, you can still achieve adequate mineral absorption as phytic acid doesn’t bind all the calcium and zinc for example, and actually works to deliver an anti-cancer effect.
Synergy Within Foods
Examples of how we have nearly missed the boat by focussing in the past exclusively on certain nutrients in foods can be found in research conducted on fibre and beta-carotene. Supplementing people’s diets with extracted dietary fibre such as wheat bran has been shown not to have any significant effect on reducing cancer risk, in spite of the early enthusiasm about fibre being the saviour for colo-rectal cancer. Yet habitual wholegrain eaters have up to 50% lower risk of dying from all causes, heart disease, diabetes and cancer compared to those people eating refined grains. Clearly, fibre is important but a study of fibre alone misses other important nutrients or components that live with the fibre. There are interactions going on within wholegrains as these foods contain a lot more than just fibre. They are a rich source of many phytochemicals. With regards to beta-carotene, five randomised cancer prevention trials have now shown that taken as a pill, beta-carotene actually increases cancer risk. Yet eating a diet rich in fruits and vegetables (and therefore beta-carotene) is highly protective against cancer, suggesting that food synergy not only occurs but it is vital for optimal health.
Dr Rui Hai Liu of Cornell University gave a powerful example of synergy within foods. Most people have heard that vitamin C is an important antioxidant. Yet according to his research, the vitamin C content of an apple accounts for less than 1% of the total antioxidant activity of apples. There are thousands of other phytochemicals that work together to provide the full antioxidant potential of an apple - well beyond what would be expected from measuring their individual amounts in the apple. Dr Liu estimated that the total antioxidant activity of 100 grams of apple with skin (about half a large apple) is equivalent to 1500 mg of vitamin C! Yet the vitamin C content of this amount of apple is only 5-7mg. Even factors such as whether you peel the apple can make a remarkable difference. For example, an apple eaten with the skin provides up to twenty times more of the phytochemical called quercetin than a peeled apple. So the skin is an important and integral part of the apple if you want to maximise synergy and health benefits. Tests on growth of cancer cells have shown greater inhibition of liver and colon cancer cells when the skin remains intact than with a peeled apple. The old saying "an apple a day keeps the doctor away" is certainly true. However the public health conclusion at the congress was to eat all the edible parts of plants.
Synergy Between Foods
Dr Liu also spoke about the 'fruit salad effect', meaning the synergy between different foods eaten at the same meal or over the day. He found that different antioxidants from different fruits work together to increase the capacity of each type of fruit to inhibit cancer. In essence, you need a lot more blueberries, grapes, apples and oranges individually to exert the same anticancer effect as you would get if they are eaten together or you include several of these in your daily diet. The combined effect is much greater. Dr Liu recommended eating at least three fruits per day together with a wide range of other antioxidant rich foods.
Vegetarians tend to eat more of these protective plant foods and so can expect better health outcomes. However, it was stressed that taking a pill or supplement of any of these important nutrients will not provide the same effects since no pill contains the full range and level of phytochemicals obtained by eating a variety of plant foods.
Synergy Within the Diet
A study of German women, aged 25 to 65 years, following different diets revealed that the dietary intake of a nutrient doesn’t necessarily correlate with plasma levels of that nutrient. So consuming the highest amount of a particular nutrient doesn’t always translate to having the highest level in the body.
The women were either following a typical Western diet (high consumption of bread, bakery items, meat, dairy, coffee/tea; a 'wholesome' diet (high in fruit and vegetables, low in meat - approximately one serving per week, and some were lacto-ovo vegetarians); or a raw food diet (70-100% of the food was unheated and mainly of plant origin though some animal foods e.g. raw or dried meat/fish were consumed). While the raw food eaters had the highest dietary intakes of beta-carotene for example, it was the women on the 'wholesome' diet that had the highest plasma levels of this nutrient, despite consuming a lower amount of this nutrient. In fact, the probability of reaching protective plasma levels of beta-carotene was five times more likely for the 'wholesome' group than either of the other two groups. This study demonstrates the importance of examining the effect in the body of the complete diet, rather than deducing what this effect might be from the knowledge of the level of nutrients in foods.
It was stressed that a favourable nutrient supply is not guaranteed with the intake of that nutrient or of certain amounts of foods providing that nutrient. Rather, a favourable nutrient supply or optimal levels of preventative factors are attainable with certain dietary patterns where a variety of plant foods is consumed. The importance of favourable dietary patterns such as those observed among Seventh-day Adventists (around half of whom are vegetarians), the Mediterranean diet and the DASH diet (Dietary Approaches to Stop Hypertension) was emphasised for reducing chronic disease risk rather than just promoting single foods. "The whole is more than the sums of its parts".
Synergy - a Lifestyle Effect
Dr Gary Fraser of Loma Linda University presented research on Seventh-day Adventists who are probably the longest-lived population that has been formally described. The National Institutes of Health and various other cancer societies have provided millions of dollars over many decades to research Adventists because of their unique lifestyle and demonstrated health benefits. Overall, Californian Seventh-day Adventist men live 7.3 years longer than the general Californian population and women live 4.4 years longer. However what is intriguing are the findings of the importance of the whole Adventist lifestyle and the synergy this enables. Seventh-day Adventists who are vegetarian, exercise regularly, eat nuts around five times per week, don’t smoke and are not obese have an extra 10 years of life than Adventists not following these health behaviours. So a collection of lifestyle choices is important, not just diet. In fact, when other health behaviours are present, vegetarian Adventists live only one and a half to two years longer than non-vegetarian Adventists. Fifty four % of vegetarian Adventists live to 85 years compared to only 30 % of other Americans.
That synergy exists is obvious, but as we were reminded by Dr David Jacobs from the University of Minnesota who paraphrased Russell Tracey "understanding one leaf in a forest does not necessarily provide insight into the entire forest". We need to further examine the effects of the whole diet and the entire lifestyle. Dr Jacobs urged "many parts are known, let us now grasp for the whole".
Safety of Plant and Animal Foods
The congress included an entire symposium on the safety aspects of food. Dr Clare Trevitt from the MRC Prion Unit, London, gave an overview of the BSE (mad cow disease) situation. The emergence of a variant form of Creutzfeldt-Jakob disease (vCJD) in 1996 has now been both causally and experimentally linked to the BSE epidemic in the UK in the 1980s and early 1990s. While once seemingly a remote possibility, it is now clear that animal diseases are transmissible to humans via inoculation or dietary exposure to altered, disease associated forms of normal prion proteins.
With regards to food poisoning, fresh fruit and vegetables cause significantly less outbreaks of food poisoning compared to meat and seafood according to information presented by Dr Linda Harris from the University of California at Davis. In these cases, the outbreaks are mostly related to cooked and inappropriately handled fruit and vegetables (e.g. canned beans/peas).
Dr David Wallinga, Director, Antibiotic Resistance Project, Institute for Agriculture and Trade Policy in Minneapolis, reviewed antibiotic use in healthy livestock and expressed his concern with the overuse and inappropriate use of antibiotics, which are hastening the development of resistant strains of bacteria in humans. He stated that currently there is no effort to monitor actual antibiotic use in the US. Recent estimates have found that 70% of all antibiotics produced in America each year are given to healthy animals destined for human food. And more than half of these drugs are closely related to antibiotics used in treating human illness. In Australia, some antibiotics are registered for use in cattle, pigs and poultry. The federal government was concerned with the use of antibiotics in animals so they commissioned a technical expert group to review the issue resulting in the publication of the JETACAR report. This report includes 22 recommendations to government on the use of antibiotics.
The Commonwealth government gave an initial response to the JETACAR report and there are progress reports on how the government is responding to these recommendations. One example of the government’s response to the JETACAR report was the withdrawal of avoparcin around two years ago. Avoparcin has been linked with Vancomycin resistance (VRE) in humans.
Antibiotic resistant pathogens can result from the use of antibiotics in food animals, which are transmitted to humans. Typically, transmission occurs through the food supply. However, resistant bacteria can also be transmitted directly through farm contact with animals or their manure, and potentially through contaminated surface water, groundwater, or air surrounding the livestock facility as well. Dr Wallinga commented that emerging evidence for the latter, non-food pathways suggests that antibiotic overuse in agriculture might better be considered an ecological health problem than simply a question of food safety.
Scandinavian countries such as Denmark and Sweden have very strict controls for antibiotic use in humans and animals. In Australia, 'organic' seems to be the only way consumers can tell if a piece of meat or chicken has had antibiotics used in its production.
The concept of what’s good to eat not just for our health but for the health of our planet is taking off. German and Finnish researchers presented new data that clearly showed a plant-based diet or one low in animal products such as meat, to be ecologically superior to a meat-rich diet, commonly consumed in Western societies.
This holistic concept encompasses the complete food system and its effects on health, the environment, society and economy. It looks at food production and harvesting techniques, water usage, processing and packaging, storage, transport and even disposal of waste materials.
Dr Ingrid Hoffmann from the University of Giessen presented a study of German women following three different types of diets:
1. Containing an average proportion of animal foods - note animal food intake is high in Germany
2. A low-meat diet
3. A lacto-ovo vegetarian diet
The researchers found that use of primary energy (required for the production of the foods eaten) was 41% lower in the low meat eaters and 54% lower in the lacto-ovo vegetarians as compared to that required to sustain people on a typical German diet. Also the emissions of gases harmful to our environment were lower as the diets contained more plant foods. Compared to eating the typical German diet:
* Emission of CO2 - equivalents was 37% and 52% lower on the low meat and lacto-ovo vegetarian diet, respectively.
* Emission of SO2 - equivalents was 50% and 60% lower on the low meat and lacto-ovo vegetarian diet, respectively.
Analysis of the environmental impact of individual foods also confirmed that emissions of CO2 and SO2 equivalents are higher for production of foods of animal origin than foods of plant origin. For primary energy use poultry showed the highest use followed by beef. Milk was similar to most plant foods but the emissions were higher than for plant foods. For emissions, beef was the biggest culprit because of the beef specific methane production. Of all the animal foods studied, fresh water fish (not farmed fish) gave the best result for emissions. When it came to plant foods asparagus had the highest environmental impact because of the intense handling and low yields achieved. Lettuce was also high - comparable to eggs, while foods such as potato, carrots, white cabbage, peas and wheat were found to have a much lower environmental impact.
The German researchers concluded that changing from a typical Western diet (German diet) to a low meat diet or a lacto-ovo vegetarian diet reduces ecological impact by one to two thirds, depending on the extent of changes and the indicator studied. A vegan diet was not studied. "Further benefits are possible if we prefer organic, regional, minimally processed and packaged foods" stated Professor Claus Leitzmann.
Finnish scientists set out to estimate how Finns food consumption places stress on the environment and to ascertain what foods would be most recommendable in the Finnish diet from both nutritional and environmental perspectives. They used a myriad of different measures of environmental damage including greenhouse effects, land degradation and ecotoxicity of pesticides and fertilisers.
The foods found to produce the most environmental stress in the Finnish diet were
greenhouse vegetables - since large amounts of energy are used in their production
Exotic fruits - because these are imported into Finland
Meat and meat products
Soft drinks, alcoholic drinks and sweets
The foods the researchers stated should be encouraged from both environmental and nutrition perspectives include:
Domestic vegetables grown in the open air rather than in greenhouses
Domestic apples and berries - rather than imported ones
Fresh water fish - not farmed fish
Evidence is building that there are additional benefits to be gained by eating a plant-based diet beyond just the positive effects on our health. The overall conclusion in the session on nutrition ecology was that the Western way of eating (low plant foods; high animal products) is unsustainable. Nutrition ecology and concern over our environment is likely to become a strong driver towards plant-based diets in the future.
Many health spas provide and promote a vegetarian or vegan diet. When I visited some of these in the US immediately after this congress (a review of these will appear in an upcoming edition of this magazine) I noted that one of the major reasons people booked themselves into health retreats was for help with weight loss. There were many testimonials by people who had lost significant amounts of weight by changing their lifestyle and switching to a plant-based diet.
A study presented at the congress by Dr Amy Lanou compared the effectiveness on weight loss of a low fat vegan diet to that of the typically recommended healthy diet by authorities (containing around 30% fat). Neither of the diets was restricted for total calories but the type of foods the women ate were different. After 14 weeks on the diets - where both groups of postmenopausal overweight women were given food and cooking advice weekly - it was the women on the vegan diet who lost considerably more weight than those following the 30% fat diet. So a diet very high in plant foods seems to be effective for weight loss, despite there being no restriction in calories.
But what about plant foods, which are naturally high in fat you may ask? Studies have shown that rather than making you gain weight, high fat plant foods may actually help you lose weight. Take nuts for example. Dr Joan Sabate from Loma Linda University reviewed the evidence on nut intake and Body Mass Index (BMI) from population-based studies. He showed that despite the high fat content of nuts - nuts are around 70% fat - people who include nuts regularly in their diet have lower Body Mass Indices. In other words, they are thinner than those who avoid nuts. A recent study by US dietitian, Kathy McManus, showed that including nuts in a calorie controlled diet helps promote more sustained weight loss than a diet of the same calories without the nuts and the extra fat they contain. There may be several reasons for this. One possibility, as Dr Sabate pointed out, is that all the fat present in nuts may not be absorbed into the body. This suggestion is based on preliminary data indicating that people who eat more nuts excrete more fat in their stools.
It also doesn’t seem to matter whether you eat the nuts whole or they are ground, according to Dr Gene Spiller, another so called 'nutty professor' renowned for his research in the area of nuts. Including nuts in any diet, particularly one that is restricted in calories, helps to make the diet more palatable so compliance will be better and people are more likely to stick to the diet. Nuts are a regular component of Asian, Mediterranean and vegetarian diets.
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