A plant-based diet — good for us and for the planet
The current world food system is inequitable and unsustainable, and is creating huge and costly health problems. Of the seven billion people in the world, 1.5 billion are overweight or obese while almost a billion go to bed hungry each night.
Climate change will add pressure to food production, especially if the surging populations in developing countries aspire to a Western-style diet with its high animal content. The modern Western diet also plays a major role in the increasing incidence of non-communicable diseases, which are currently responsible for 63% of deaths throughout the world.
Dietary choices influence not only health, but also greenhouse gas (GHG) emissions, with meals of similar energy content differing in their emissions by a factor of between two and nine. The recommendation to reduce meat consumption in the human diet dovetails with dietary guidelines for increased consumption of vegetables, legumes, fruits, nuts and wholegrain products, and with our knowledge about Mediterranean dietary patterns, whose health benefits are well documented.
The English language has even responded with new terms for those who wish to reduce their meat consumption without going all the way to vegetarianism. These include “flexitarians”, who occasionally add fish or meat to their vegetarian choices, and “vegivores” who describe their meals in terms of the plant foods, adding animal protein almost as a condiment.
Addressing perceptions of likely problems with meat-free diets is particularly useful. Fears that a diet without meat may mean a lack of protein can be put to rest. Concern about adequate intakes of iron and zinc are important, but need to be balanced with the risks of a high meat intake, and specifically with too much haem iron. The World Cancer Research Fund now considers the evidence convincing that a high intake of red meat causes colorectal cancer. One mechanism that has been proposed, and confirmed in ileostomy studies, is that haem iron facilitates the formation of carcinogenic N-nitroso compounds.
The body’s ability to alter its absorption of iron, zinc and other minerals in the context of various diets has not been well addressed in the past. Previous recommendations have also distorted the situation by using absorption studies related only to a single meal.
Valid concerns and solutions are important for vitamin B12 and, possibly, also for long-chain omega-3 fatty acids.
Nutrition is a complex science and much remains to be elucidated. Dietary patterns may be more important than specific foods. The positive aspects of a diet featuring more plant foods may be more important than any adverse effects of meat. It is worth noting, however, that healthy Mediterranean and Asian dietary patterns feature a wide variety of plant foods, and less meat and highly processed foods and drinks than Western diets.
Protein and vegetarian diets:
A vegetarian diet can easily meet human dietary protein requirements as long as energy needs are met and a variety of foods are eaten.
Vegetarians should obtain protein from a variety of plant sources, including legumes, soy products, grains, nuts and seeds.
Eggs and dairy products also provide protein for those following a lacto-ovo-vegetarian diet.
There is no need to consciously combine different plant proteins at each meal as long as a variety of foods are eaten from day to day, because the human body maintains a pool of amino acids which can be used to complement dietary protein.
The consumption of plant proteins rather than animal proteins by vegetarians may contribute to their reduced risk of chronic diseases such as diabetes and heart disease.
It is a common myth among both consumers and health professionals that protein needs are difficult to meet on a vegetarian diet.
Iron and vegetarian diets:
Vegetarians who eat a varied and well balanced diet are not at any greater risk of iron deficiency anaemia than non-vegetarians.
A diet rich in wholegrains, legumes, nuts, seeds, dried fruits, iron-fortified cereals and green leafy vegetables provides an adequate iron intake.
Vitamin C and other organic acids enhance iron absorption, a process that is carefully regulated by the gut.
People with low iron stores or higher physiological need for iron will tend to absorb more iron and excrete less.
Research to date on iron absorption has not been designed to accurately measure absorption rates in typical Western vegetarians with low ferritin levels.
Iron is an essential nutrient for haemoglobin and myoglobin formation and is vital for health and peak performance. Much of our iron requirement is met through recycling of the iron in red blood cells.1 The amount of iron stored is carefully regulated by intestinal absorption, as we have a limited ability to excrete excess iron
Zinc and vegetarian diets:
Well planned vegetarian diets can provide adequate amounts of zinc from plant sources.
Vegetarians appear to adapt to lower zinc intakes by increased absorption and retention of zinc.
Good sources of zinc for vegetarians include whole grains, tofu, legumes, nuts and seeds, fortified breakfast cereals and dairy products.
The inhibitory effects of phytate on absorption of zinc can be minimised by modern food-processing methods such as soaking, heating, sprouting, fermenting and leavening.
Absorption of zinc can be improved by using yeast-based breads and sourdough breads, sprouts, and presoaked legumes.
Studies show vegetarians have similar serum zinc concentrations to, and no greater risk of zinc deficiency than, non-vegetarians (despite differences in zinc intake).
Although vegetarians have an overall lower risk of common chronic diseases than non-vegetarians, there are some nutrients, including zinc, that need special attention in those who follow a vegetarian diet. Since plant sources of zinc contain phytate and other inhibitors of zinc absorption, vegetarians and vegans may potentially be at risk of zinc deficiency.
Omega-3 polyunsaturated fatty acids and vegetarian diets:
While intakes of the omega-3 fatty acid ????-linolenic acid (ALA) are similar in vegetarians and non-vegetarians, intakes of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are low in vegetarians and virtually absent in vegans.
Plasma, blood and tissue levels of EPA and DHA are lower in vegetarians than in non-vegetarians, although the clinical significance of this is unknown. Vegetarians do not exhibit clinical signs of DHA deficiency, but further research is required to ascertain whether levels observed in vegetarians are sufficient to support optimal health.
ALA is converted to EPA and DHA, but the process is slow and inefficient and is affected by genetics, sex, age and dietary composition. Vegetarians can take practical steps to optimise conversion of ALA to EPA and DHA, including reducing intake of linoleic acid.
There are no official separate recommendations for intake of fatty acids by vegetarians. However, we suggest that vegetarians double the current adequate intake of ALA if no direct sources of EPA and DHA are consumed.
Vegetarians with increased needs or reduced conversion ability may receive some advantage from DHA and EPA supplements derived from microalgae. A supplement of 200–300 mg/day of DHA and EPA is suggested for those with increased needs, such as pregnant and lactating women, and those with reduced conversion ability, such as older people or those who have chronic disease (eg, diabetes).
Vegetarians have a lower overall risk of common chronic diseases, possibly due to a lower saturated fat and cholesterol intake than non-vegetarians.1However, vegetarians (and those who eat minimal amounts of oily fish) may be at a disadvantage where intake of essential fatty acids (EFAs) is concerned, and this could potentially counteract some health benefits of the vegetarian diet.
Vitamin B12 and vegetarian diets:
Vitamin B12 is found almost exclusively in animal-based foods and is therefore a nutrient of potential concern for those following a vegetarian or vegan diet. Vegans, and anyone who significantly limits intake of animal-based foods, require vitamin B12-fortified foods or supplements.
Vitamin B12 deficiency has several stages and may be present even if a person does not have anaemia. Anyone following a vegan or vegetarian diet should have their vitamin B12 status regularly assessed to identify a potential problem.
Pregnant and lactating vegan or vegetarian women should ensure an adequate intake of vitamin B12 to provide for their developing baby.
In people who can absorb vitamin B12, small amounts (in line with the recommended dietary intake) and frequent (daily) doses appear to be more effective than infrequent large doses, including intramuscular injections.
Fortification of a wider range of foods products with vitamin B12, particularly foods commonly consumed by vegetarians, is likely to be beneficial, and the feasibility of this should be explored by relevant food authorities.
Vitamin B12 (cobalamin) is an essential vitamin, required for DNA synthesis (and ultimately cell division) and for maintaining nerve myelin integrity.1 It is found almost exclusively in animal-based products including red meats, poultry, seafood, milk, cheese and eggs. As vitamin B12 is produced by bacteria in the large intestines of animals, plant-based foods are generally not a source of vitamin B12. It is therefore a nutrient of concern for vegetarians and particularly for vegans who choose an entirely plant-based diet. A cross-sectional analysis study involving 689 men found that more than half of vegans and 7% of vegetarians were deficient in vitamin B12.
Meeting the nutrient reference values on a vegetarian diet:
Surveys over the past 10 years have shown that Australians are increasingly consuming more plant-based vegetarian meals.
Many studies demonstrate the health benefits of vegetarian diets. As with any type of eating plan, vegetarian diets must be well planned to ensure nutritional needs are being met.
This clinical focus project shows that well planned vegetarian diets can meet almost all the nutritional needs of children and adults of all ages.
Sample single-day lacto-ovo-vegetarian meal plans were developed to comply with the nutrient reference values — including the increased requirements for iron and zinc at 180% and 150%, respectively, for vegetarians — for both sexes and all age groups set by Australia’s National Health and Medical Research Council and the New Zealand Ministry of Health.
With the exception of vitamin D, long-chain omega-3 fatty acids and extended iron requirements in pregnancy for vegetarians, the meal plans meet key requirements with respect to energy; protein; carbohydrate; total fat; saturated, poly- and monounsaturated fats; ?-linolenic acid; fibre; iron; zinc; calcium; folate; and vitamins A, C, E and B12.
Although only 5%–6% of females and 1%–3% of males claim to be vegetarian,1,2 a 2010 Newspoll Survey (commissioned by Sanitarium Health and Wellbeing) found that seven out of 10 Australians are eating more plant-based meals than previously, in the belief that eating less meat and more plant foods improves overall health. As with any dietary practice, vegetarian diets need to be well planned to ensure that meals are healthy, delicious and nutritionally adequate.3
Research has shown that a well planned vegetarian diet can meet nutritional needs for good health and may reduce the risk of cancer, cardiovascular disease, metabolic syndrome, insulin resistance, type 2 diabetes, hypertension and obesity. Choosing plant-based meals is also environmentally beneficial. Vegetarian diets are generally lower in saturated fat and cholesterol and higher in dietary fibre, antioxidants and phytochemicals than non-vegetarian diets. It is likely that the combination of these factors provide vegetarians with a significant health advantage.
Practical tips for preparing healthy and delicious plant-based meals:
It is not only what a diet excludes, but what it includes, that shapes health outcomes. This article is a practical guide for doctors to help them advise patients on nutrient-rich foods, which should form the basis of all types of plant-based diets. Of the recognised types of plant-based diets, the most widely studied is the lacto-ovo-vegetarian diet.
Key points about plant-based diets:
Plant-based diets focus on fruits, vegetables, legumes, nuts, seeds and grains. Some vegetarian diets also include eggs and dairy, and a few traditional (eg, Mediterranean and Asian) plant-based diets include limited amounts of meat and/or seafood.
A varied and balanced plant-based diet can provide all of the nutrients needed for good health.
Plant-based diets may provide health benefits compared with meat-centred diets, including reduced risks of developing chronic diseases such as obesity, heart disease, colorectal cancer and type 2 diabetes.
Plant-based diets more closely match recommended dietary guidelines to eat plenty of fruits, vegetables, legumes and wholegrains, and to limit intakes of saturated fats and sugars.
A 2010 national Newspoll survey of 1200 adults indicated that 70% of Australians consume some plant-based meals in the belief that eating less meat and more plant foods improves overall health (Newspoll Research, Leaders in Nutrition, May 2010, com-missioned by Sanitarium Health and Wellbeing).
A vegetarian diet does not mean just cutting out meat. Careful planning, along with knowledge of practical ideas for using a variety of plant foods, is needed to ensure nutritional requirements are met, particularly for new vegetarians or those with special needs.
Nutrients that may need more attention in a vegetarian diet include iron, zinc, calcium, vitamin B12, vitamin D and omega-3 fats. It may be beneficial to refer people to an Accredited Practicing Dietitian experienced in vegetarian nutrition.
Any dietary change can increase preparation time to begin with, but cooking plant-based meals need not be more time consuming after some training and regular practice.
A minimally processed plant-based diet, with limited (if any) amounts of animal foods derived from animals lower down the food chain, provides environmental advantages over a Western-style meat-rich diet.