 Asthma is the most common chronic disease in children, and the prevalence is increasing around the world. Despite this, most research dollars are spent on adult chronic diseases. One might ask whether this is because our politicians and senior administrators feel themselves to be more likely to suffer from the latter and ignore allergic diseases because they have their major impact on children and young adults who don't vote. Imagine how much more effort would be put into elucidating causes of a disorder that increased at the same accelerated rate in the Middle Ages and elderly. Well, finally, an international study of asthma and allergies in childhood studying more than a million children in nearly 100 countries, making it the most comprehensive survey of these diseases ever undertaken. What did they find? They found a wide variability in the prevalence and severity of asthma, allergies, and eczema. We're talking 20-fold, 60-fold difference in prevalence of symptoms of asthma, allergic runny nose, and atopic eczema around the world, striking worldwide variations in the prevalence of allergic symptoms. What does it all mean? Well, the large variability suggests a crucial role of some kind of local characteristics, determining the differences in prevalence between one place and another. What kind of environmental factors? Like, why does the prevalence of itchy eyes and runny nose range anywhere from 1% in India, for example, up to 45% of kids elsewhere? There are some associations with regional air pollution and smoking rates, but the most significant associations were with diet. Adolescents showed a consistent pattern of decreases in symptoms of wheeze, current and severe allergic rhino-conjunctivitis, and atopic eczema associated with increased consumption of plants. The more their calories and protein came from plant sources, the less allergies they seemed to have. In general, there seems to be an association between increased in asthma prevalence and decreased consumption of fresh fruits, green vegetables, and other dietary sources of antioxidants, helping to explain why the prevalence of asthma and respiratory symptoms is lower in populations with high intake of foods of plant origin. These types of high-fat and sodium and low-fiber and carbohydrates are linked with asthma, while traditional vegetarian diets are associated with lower rates. For example, if you look closer within India in a study of more than 100,000 people, those who consume meat, for example, daily or even occasionally, were more likely to report asthma than those who are strictly vegetarian, which meant also avoiding eggs. Eggs have been associated, along with soda, with an increased risk of respiratory symptoms, and asthma in schoolchildren, whereas consumption of soy foods and fruits were associated with reduced risk of respiratory symptoms. In fact, removing eggs from the diet, along with dairy, may improve lung function in asthmatic children in as little as eight weeks. So maybe it's a combination of eating less animal foods and more plants. High vegetable intake, for example, has been found protective in children, cutting the odds of allergic asthma in half. And fruit showed a consistent protective association for current and severe wheeze and runny nose and adolescence, and for current and severe asthma allergies and eczema for children. But why? I've talked about the endocrine-destructing industrial pollutants building up in the meat supply that may increase the risk of allergic diseases, but the increase in asthma may be a combination of both a more toxic environment and a more susceptible population. The dietary changes, which have occurred over recent years, may have led to reduction in these natural antioxidant defenses, resulting in a shift to the antioxidant status of the whole population and leading to increased susceptibility to oxidant attack and airway inflammation in adults, for example. The risk of airway hyperreactivity may increase sevenfold among those with the lowest intake of vitamin C from plant foods, while the lowest intake of saturated fats gave a tenfold protection, and presumably, saturated fats have a role in triggering inflammation. The protective effect of plant food may also be mediated through effects on intestinal microflora. It turns out that differences in the indigenous intestinal flora might affect the development and priming of the immune system in early childhood. Kids with allergies, for example, tend to be less likely to harbor lactobacillus, the good bacteria that's found in fermented foods, and also just naturally on fruits and vegetables. And lactobacillus probiotics may actually help with childhood asthma, which may help explain why children raised on largely organic vegetarian diets may have lower prevalence of allergic reactions. Infants raised in this way tend to have more good lactobacilli in their guts compared to controls, though they were also more likely to have been born naturally, breastfed longer and not given as many antibiotics. So you really can't tell whether it's the diet until you put it to the test, which we'll explore next.