Tooth fairies have gone high-tech this week – innocently abandoned molars left under pillows can now be laser ablated and mass spec’d to reveal a youngster’s very early dietary habits.

With their collection of youngsters’ teeth – not garnered from local pillows, presumably – scientists from the Natural History Museum and University College London found they could distinguish between breastfed and formula-fed babies by analysing the ratio of strontium to calcium in tooth enamel. (L T Humphrey et al, Proc. Natl. Acad. Sci, 2008, DOI: 10.1073/pnas.0711513105). This is the first day-by-day analysis of a baby’s early diet.

Strontium and calcium are both taken up in the diet, and incorporated into tooth enamel. The higher up in the food chain an animal is, the higher the ratio of calcium to strontium. Lead author Louise Humphrey from the Natural History Museum explains that each digestive system the elements pass through acts as a kind of strontium filter – the more digestive systems the strontium and calcium pass through, the more strontium is filtered out in favour of calcium. This means that babies fed on breastmilk – which is the milk of an omnivore – have less strontium in their teeth than those fed on cows’ milk – the milk of herbivores.

Tooth enamel is laid down in a clear pattern on a daily basis. There is even a line visible in the tooth that indicates day 0 – or birth. You can see this ‘neonatal line’ in the researchers’ micrographs.