Healthy choices on raw vegan diets
A raw food vegan diet may be defined in various ways, but usually entails at least 80% by weight being raw plants. Many people report feeling healthier and more energetic on adopting such diets, but there are too few long-term raw food vegans for direct evaluation of the success of raw vegan diets versus other diets. We can, however, evaluate such diets against known human nutritional requirements to gain a better understanding of the ways in which appropriate raw vegan diets could benefit health.Raw vegan diets comprise three key food groups: sweet fruit, high-fat plants and green leafy vegetables. Raw food authorities differ in the proportions recommended, some suggesting that 2% of calories from green leafy vegetables (about 300 g of lettuce per day) is sufficient while others recommend that about 30% of calories should come from green vegetables. Similarly, recommendations on high fat foods such as avocados, olives, nuts, seeds and cold-pressed oils range from a few percent to about 40% of calories. The Hallelujah diet founded by George Malkmus puts particular emphasis on carrot juice and barley grass, which contribute about 15% of calories.
Getting 30% of calories from green vegetables is probably unrealistic for most people, even with the use of blended salads and juices. For instance, 900 g of lettuce plus 450 g of kale provides just 300 kcal or about 15% of calories. Fortunately, however, such high intakes are unnecessary for nutritional adequacy. Green leafy vegetables and broccoli contain higher levels of zinc, calcium and protein than fruit and are therefore an important part of raw diets, but about 500 g per day of green vegetables, including a mixture of lettuces, broccoli and darker leaves such as kale and spinach, is sufficient to bring mineral and protein intakes into line with general recommendations. Such vegetables also provide vitamin K, which promotes healthy bones. Other raw vegetables can be useful: for instance, carrots are a good source of calcium and peas a good source of zinc and protein.
The best balance between sweet fruit and fatty foods is probably a matter of individual constitution. Some people experience dental problems with a very high fruit intake. This can be a particular problem for young children. Many people will struggle to maintain weight if they do not include significant amounts of high fat foods. More than 10% of calories as polyunsaturated fat is not recommended. Olives, avocados, almonds, hazelnuts and macadamias are all dominated by monounsaturated fats, which are the safest fats to consume in large quantities. Obtaining up to 40% of calories from these foods according to individual energy needs should be perfectly healthful. It is also important to include a good source of omega-3 fats such as crushed flax seed or its oil. Selenium can be low if the food is grown in selenium deficient soil, so a Brazil nut a day provides a useful insurance policy.
In selecting fruits, there is no need to rely on unusual or exotic items. Bananas are a good energy food, being relatively low in fibre and high in potassium. Oranges are rich in calcium, folate, potassium and vitamin C. The high potassium and low sodium content of raw vegan diets reduces the need for calcium by reducing calcium losses and can be expected to reduce blood pressure and risk of stroke.
The various raw vegan dietary schools differ in their approach to B12. Some recommend that B12 supplements should not be taken unless clear deficiency symptoms occur. David Wolfe (Nature's First Law) recommends seven different potential B12 sources, including unwashed or wild plants, nori, spirulina, fermented foods or a probiotic, with a B12 supplement as an alternative if these are not available. George Malkmus has recommended regular use of a B12 supplement since a study of Hallelujah dieters showed signs of inadequate B12 in most of them and showed that a B12 supplement or fortified nutritional yeast corrected this reliably while probiotics did not.
The confusion in this area arises from a conceptual error. Many raw food or natural hygiene advocates believe that our evolutionary diet and that of our great ape relatives did not include an external source of B12 and then conclude that humans shouldn't need such a source. In fact, all the other great apes - even the gorillas - consume insects incidentally along with their normal diet of fruits, shoots, leaves and nuts. Chimpanzees show particular enthusiasm for collecting and eating termites, which have high measured levels of B12. After capture, the blood B12 levels of most primates drops rapidly when they are fed on a hygienically grown and prepared plant-based diet. It is therefore not surprising that humans also need an external source of B12.
Many of David Wolfe's proposed B12 sources have been directly tested and shown to be inadequate. Nori and spirulina failed to correct deficiency in macrobiotic children and did not maintain adequate blood B12 levels in a Finnish raw food community. Probiotics did not consistently correct low B12 availability in Hallelujah dieters. A UK raw food vegan went B12 deficient while growing his own food and eating it unwashed: based on measured B12 levels in soil this is unsurprising. Other proposed sources have not been tested so directly, but the only two published studies of B12 levels in raw food vegans both showed inadequate B12 levels. Low B12 levels give rise to elevated homocysteine levels with an associated increased risk of many illnesses, including stroke and heart disease, without any classical B12 deficiency symptoms. In children the onset of full-blown deficiency can be very rapid with much greater risk of long-term damage or even death. At least 3 micrograms per day of B12 from fortified foods or supplements is needed to minimise homocysteine levels in adults. Breast milk is an adequate source for infants only if the mother's intake is adequate.
The main argument for the desirability of high raw diets derives from comparison with our evolutionary diet and the diets of our great ape relatives. All the great apes eat diets centred on raw fruit (chimps, bonobos, orangutans, lowland gorillas) or raw leaves (highland gorillas) and including a mixture of fruit (including large amounts of seeds), leaves, shoots, insects and often nuts. Use of cooked foods and large amounts of grains is unique to humans. It is further suggested that a return to a diet more like that of our ape relatives would bring great benefits to health as it is the diet to which we are evolutionarily adapted. This is a plausible argument and the nutrient content of such a diet matches modern nutritional knowledge in many ways: e.g. high folate, vitamin C, vitamin K, potassium and magnesium intakes along with low saturated fat and cholesterol. However, there are important limitations to using the plant content of great ape diets as a model for ideal human diets.
Firstly, insects cannot be part of a vegan diet and are probably the key source of B12 in most primate diets. As all B12 comes from bacteria, the absence of insects is readily compensated for by using B12 produced by bacteria in commercial fermenters and used in fortified foods and supplements.
Secondly, human exposure to sunlight at high latitudes and when spending most of the day indoors is greatly reduced compared with our evolutionary exposure. During the UK winter, vitamin D from foods fortified with the vegan form (ergocalciferol, D2) can help to compensate for limited light exposure. A trip to sunnier climes during the winter allows the vitamin D to be topped up more naturally. Infants are particularly vulnerable to vitamin D deficiency due to read more
