In this large multi-centre epidemiological study including 11 Latin American countries, we found that the overall prevalence of allergic symptoms in children aged 6–7 years fluctuated between 9.9% (current eczema) and 12.5% (current wheeze). We found a consistent trend across countries of a statistically significantly negative association between fruit, and vegetable, and allergic symptoms in the younger children. Such associations were attenuated in older children. We also found that frequent intake of fast foods or burgers was positively associated with a greater prevalence of allergic symptoms in adolescents and with wheeze in the younger children.
The meta-analyses on fruit intake and wheeze, eczema, and rhino-conjunctivitis showed very small heterogeneity in the group of 6- to 7-year-old children. The large sample size of the study, and the use of a standardised protocol to ascertain the prevalence of allergic symptoms and of frequency of food intake, might have contributed to the small heterogeneity. The fact that the effect sizes were fairly consistent across countries suggests that these associations might be biologically plausible. The heterogeneity and effect sizes were less consistent in the meta-analyses that examined dietary intake of vegetable and fastfood in adolescents, which might partly be explained by the increasing differentiation in the diet of older children.
Our findings also showed that three quarters of all the children studied had a sedentary lifestyle, reflected in the low frequency of physical exercise practised per week. Similarly, despite the strong public health promotion of daily intake of fruits and vegetables in children, we found that only 60% of the children eat these foods at least three times per week.
Diet is one of the key factors that can influence the susceptibility to allergic diseases  and can explain, at least in part, the current rates of asthma prevalence in Latin American countries. Latin America groups the Spanish and Portuguese-speaking countries south of the United States. In addition to the language, the population in this region has several common characteristics. The Latin American nations are largely composed of ‘Mestizos’ (those having Indigenous and Spanish/other European/African ascent) and indigenous people. The staple diet in most of these countries includes fresh cereals and vegetables (potatoes, maize, rice), although as with most growing economies, the effects of ‘Westernisation’ are increasingly departing the traditional diets towards consumption of fast food and other energy-dense and low-cost foods.
The ISAAC study provided for the first time standardised estimates of childhood asthma prevalence worldwide. ISAAC Phase Three produced internationally comparable estimates of direction and magnitude of change in symptoms of asthma, rhino-conjunctivitis, and atopic eczema . The study also showed that in developing countries asthma and allergic disease were increasing.
We found that 75% of children had a fruit and vegetable intake below the five portions a day recommended by the WHO . Worldwide variations in frequency of consumption of fruits and vegetables were reported for the first time in 2009 for adults from 52 countries, showing that lower income countries also have difficulties adhering to these recommendations . The study showed figures for four countries from Latin America (Brazil, Ecuador, Paraguay, and Uruguay), all of which reported having at least 50% of adults eating less than 5 portions of fruits or vegetables per day. Our study is the first to demonstrate that the vast majority of Latin American children are not meeting these recommendations.
Despite the fact that asthma is an important public health burden in countries from this region , there have been few studies investigating the role that diet and other lifestyle-related risk factors might play in the risk of allergic diseases in Latin America. A negative association between fruit intake and childhood asthma has been suggested in low- and high-affluent countries . A recent overview of high-quality systematic reviews on diet and asthma concluded that there is evidence to suggest that children who have a higher intake of fruits, or have diets which are rich in these foods, are less likely to suffer from asthma or allergic symptoms .
There is biological plausibility for the possible effect of fruits and vegetables on allergic symptoms. Oxidative stress plays a role in the inflammatory process that leads to the clinical expression of asthma and other allergic conditions such as eczema and rhino-conjunctivitis. Fruits and vegetables are rich in a number of antioxidant vitamins and minerals, as well as flavonoids whose antioxidant and anti-inflammatory properties have been suggested to reduce and modulate airway and allergic diseases. Experimental studies have demonstrated that flavonoids can inhibit the release of histamine and of several inflammatory cytokines including IL-4 and IL-13 , which are closely involved in the chain of events leading to the clinical manifestation of symptoms. Several well-designed randomised controlled trials (RCTs) have been carried out to test the demonstrability of such effects, but have so far shown little or no effect of the use of nutritional supplements on allergic outcomes .
A new concept of ‘indigenous microbiota’ which suggests that food consumed directly from the soil where it is harvested (rather than industrially produced) might also protect against the risk of asthma and allergies. It is known that fruits and vegetables are densely covered with microbiota (ectophytes), but the idea that these fresh products harbour a microbial world within (endophytes) has been only recently shown . A low gut microbiota might be linked to poorer respiratory  and allergic  outcomes in children, and a rich microbiota is facilitated by freshly produced plant-based foods. Developed countries in Europe are now often able to market fruits and vegetables regardless of their seasonality, due to the high processing and artificial maturation these foods undergo. In Latin America, food markets are still common and widely accessed by the general population, often preferred to supermarkets (grocery shops) for their lower cost. Our findings could lend support to educational and intervention strategies to make fruits and vegetables more accessible to the population, like those investigated in other populations .
The introduction of a more ‘Westernised’ lifestyle has been increasingly suggested to play a role in the current burden of asthma in countries that are shifting towards a higher consumption of more energy-dense diet, which are characterised for their lower cost and high content of saturated fats. Our findings show that fast food intake in Latin America is very common in children, particularly in adolescents, of whom nearly a 20% reported eating these foods three or more times per week. The risk of current wheeze was positively associated with intake of fastfood in younger and older children, but this risk was higher in the adolescents. As consequence of the Westernisation of diet and of lifestyle in Latin America, the rates of cardio-metabolic diseases is increasing and the rates of obesity are a major public health challenge in the region . The low cost of these foods and the high calorie content make fast food an appealing option for many families, in particular to those in a more vulnerable socio-economic position. The easy access that children have to processed and sugary food is also a major issue in many primary schools across the continent.
A major challenge to improve childhood global health in Latin America is to provide evidence from studies that can translate in public health interventions and in affordable and sustainable health care to the population . Latin America is a region with large economic and social variations, and where public health resources are usually limited. Our results suggest that dietary intake of fruits might reduce the risk of allergic diseases in children, and that Westernisation of diet might contribute to the increase in the prevalence of allergic symptoms as children grow older. Timing appears to be an important factor, as the protective effect observed from higher intake of fruits and vegetables in younger children attenuates or disappears in older children. These results provide a foundation to inform public health policy.