The raw-food diet, a subset of the vegan/vegetarian diet, advocates that at least 75 per cent of the food we eat should be uncooked plant foods, such as fresh fruit and vegetables, sprouts, dried fruit and seaweed.
Its proponents argue that the health-giving enzymes in food are destroyed when heated to above 116o F (47o C). The raw-food diet, they say, results in increased energy, better skin, better digestion, weight loss and a lower risk of heart disease.
In fact, there's plenty of evidence to support these claims. It can help people who have gastrointestinal problems, as researchers discovered when they gave raw vegetable salads to 93 patients who suffered from various chronic diseases of the alimentary tract, including duodenal ulcers (Vopr Pitan, 1984; 6: 22-6).
Among patients who ate 200 g of raw carrot every day with breakfast for three weeks, cholesterol levels fell by 11 per cent, and it improved their gut flora and metabolism. What's more, these benefits continued for three weeks after stopping the diet (Am J Clin Nutr, 1979; 32: 1889-92).
A raw-food diet also reduces hypertension and encourages weight loss. In 32 hypertensive patients-28 of whom were also overweight-having raw foods comprise 62 per cent of their total dietary intake helped them to achieve a mean weight loss of 3.8 kg, and reduced their diastolic blood pressure by 17.8 mmHg, after six months. As an added bonus, 80 per cent of those who smoked or drank alcohol spon-taneously abstained while on the diet (South Med J, 1985; 78: 841-4).
Significant weight loss was also seen in a study of 216 men and 297 women who ate a primarily raw-food diet for more than three years. The men achieved an average weight loss of 9.9 kg, and the women, 12 kg. However, around a third of the women developed partial or complete amenorrhoea (loss of menstruation), usually because they were too underweight (Ann Nutr Metab, 1999; 43: 69-79).
The diet can also reduce LDL, or 'bad', cholesterol levels. In a studyof 201 patients who had either high LDL or low HDL cholesterol levels, a diet comprising 1500-1800 g of raw food helped to reduce total cholesterol levels. However, it also reduced HDL levels, and increased total homocysteine levels among the 38 per cent of study participants who became deficient in vitamin B12 (J Nutr, 2005; 10: 2372-8).
Raw food and cancer
The raw-food diet also has positive effects beyond those suggested by its advocates. Several studies have found that it can protect against cancer, and reduce the risk among those who may be especially susceptible.
According to a study of 8861 women, a diet of salad vegetables can protect against HER-2 breast cancer, one of the most virulent forms of the disease. In this case, the raw-vegetable diet was tested against three other diets that involved cooked foods, and was found to have a far greater protective effect (Int J Cancer, 2007; 121: 911-4).
In another, separate study, a diet that included 85 g of raw watercress every day for eight weeks reduced the risk of cancer among people with DNA damage, and the positive effect was even more marked among smokers (Am J Clin Nutr, 2007; 85: 504-10).
Raw vegetables, and cabbage in particular, appear to be protective against stomach cancer. This was the conclusion on comparing the profiles of 379 newly diagnosed cases against 1137 healthy controls who consumed a diet of raw cabbage, carrot, garlic and broccoli (Medicina, 2005; 41: 733-40).
Despite these health-giving benefits, the diet can nevertheless cause a few health problems. People who ate a raw-food diet for up to 10 years had a low bone mass compared with those who ate a standard diet. But despite this, they were not at any greater risk of osteoporosis because their lower body weight put less stress on their bones. They also had higher levels of vitamin D, which was sur-prising as the vitamin is usually only available from foods such as dairy and oily fish, which were excluded from the diet. It may be that these participants were compensated by a greater exposure to the sun, another source of vitamin D (Arch Intern Med, 2005; 165: 684-9).
The diet can also lead to a deficiency in vitamin B12, and loss of periods in women, especially after a year or more (see the studies above). The diet may also cause deficiencies in calcium, iron, protein and calories.
Not for everyone
The raw-food diet is not for everyone and is certainly not for all the time. Children, pregnant/nursing women, people with anaemia and those who are at risk of osteoporosis are advised to avoid the diet.
Exponents of Ayurveda, the classical Indian form of medicine, traditional Chinese medicine and the macrobiotic diet all warn that a raw-only diet may not suit people living in colder climates. Even the UK's Vegetarian Society cautions against a diet that is exclusively of raw foods. Instead, it advocates a balanced healthy diet that also includes high-protein foods, carbohydrates and dairy products.
The greatest benefits of the diet can be seen in a relatively short time-a few months at the most-and there is evidently little merit in maintaining it exclusively for much beyond that time.