Soaring rates of dementia in Western countries are strongly linked to diet, according to new research. But this need not be the case, says Preston Estep, director of gerontology at Harvard Medical School in the US, who believes diet holds the key to preventing dementia.Central to his theory is cutting down drastically on eating red meat, while not shying away from food made from highly refined white flour.He claims his diet maintains mental faculties well into old age.In The Mindspan Diet, Estep investigates the diets of an elite group of regions of the world where people enjoy both long life and low rates of cognitive decline.Chief among these is Japan, and close behind are the coastal areas of southern Europe, such as Liguria and Sardinia in Italy, and the Provence-Alpes-Côte d'Azur region of France, and areas of north and western Spain.Estep points out that older people in rural parts of these countries, which have not been so exposed to Western influences, seem to remain as healthy as ever.The cuisine of these countries might not seem to have a lot in common, but Estep has identified one vital component - and it's not, as you might expect, olive oil or even oily fish.Instead he believes these populations' low rates of dementia come down to something they don't eat, and that's red meat or, more specifically, iron.Some research suggests that iron reacts with oxygen to cause "rusting" in the body, leading to the deposit of waste products, such as the plaques in cells seen in people with dementia."We always hear about antioxidants whose job is to counter the work of pro-oxidants in the body," says Estep. "Iron is the most abundant and potent pro-oxidant in the body, and the more we have of it in our bodies, the more oxidative stress and damage."Iron, from red meat and iron-enriched grain products, he believes, could be the reason we see high levels of Alzheimer's in countries such as the US and northern Europe.Estep says he is not advocating cutting out meat altogether - iron is an important nutrient, particularly for younger women, many of whom are deficient in the mineral because of menstruation."We should keep it in a range I describe as sufficient but low," he says. "I eat a little bit, but not much."Estep's rules for keeping your brain young:Eat vegetables with every meal, including greens, and herbs and pulses;A small portion of carbohydrates, such as white rice or pasta, or sourdough breads, such as ciabatta;Vinegar and other fermented foods such as pickled vegetables;Drink with meals to inhibit the absorption of iron. Decaffeinated coffee works, as does herbal tea...