Here's the full text original British Medical Journal article: http://www.bmj.com/content/342/bmj.c5955.full
From just a quick perusal, I think the media reports are badly skewed. The media is taking an "OMG, exclusive breastfeeding might be harmful!" angle because that makes for a controversial, eye-grabbing headline. Whereas it seems to me that the paper is making the case that earlier introduction of solids may be beneficial.
This is from the discussion: "At one extreme, it has been suggested32 that there is insufficient scientific evidence for any lower age for weaning and that “infants should be weaned on demand, which is what most infants and their parents actually do in practice.” It can be argued that, from a biological perspective, the point when breast milk ceases to be an adequate sole source of nutrition would not be expected to be fixed, but to vary according to the infant’s size, activity, growth rate, and sex, and the quality and volume of the breast milk supply. Signalling of hunger by the infant is probably an evolved mechanism that individualises timing of weaning for a mother-infant pair.19 However, others would adopt a more cautious approach, based on data suggesting that the introduction of solid foods before 3 to 4 months may be associated with increased fatness and wheeze later in childhood,33 with an increased risk of allergy, and with higher rates of coeliac disease and type 1 diabetes in infants at risk.26 27 Recently, after a detailed review commissioned by the European Commission, the European Food Safety Authority’s panel on dietetic products, nutrition, and allergies concluded that for infants across the EU, complementary foods may be introduced safely between four to six months, and six months of exclusive breast feeding may not always provide sufficient nutrition for optimal growth and development.5"