In some surprising news, lambs are helping researchers understand why babies born to obese mothers are more likely to become fat.
A team from the universities of Wyoming and Texas found a link between maternal and offspring obesity, and is the first to demonstrate that this is the case in mammals which bear 'mature offspring' - as humans do.
"A relationship between maternal obesity and offspring obesity has been clearly identified in rodents but as their young are born immature, it was not clear whether the findings would apply to humans," said lead author Prof Peter Nathanielsz.
For 60 days before conception and throughout their pregnancy, Nathanielsz and his team fed sheep either a normal diet or one that produced obesity, then monitored the appetite and weight gain of their lambs for a further 19 months.
They also monitored the levels of leptin, a hormone regulating appetite.
They found that in lambs born of normal weight mothers, there was a peak in leptin in the sixth to ninth days of life but this peak did not occur in lambs born to obese ewes.
"The neonatal peak in leptin plays a central role in the development of areas of the brain that regulate appetite. We have found that an absence of this peak in lambs born to obese mothers seems to predispose them to increased appetite and obesity in later life," said Nathanielsz.
Blood samples taken from one-day-old lambs also found that cortisol levels were up to 50 percent higher in obese sheep, leading the team to suspect that exposure to higher levels of cortisol in the womb may prevent the normal leptin rise in lambs of obese mothers.
"We propose that cortisol prepares fetal adipose tissue to secrete leptin - and that this process seems to be disrupted in lambs born to obese mothers. The nutrient excess present in the blood of obese mothers throughout gestation seems to inhibit the post-natal leptin peak - which likely has important consequences for the development of the lamb," said Nathanielsz.
"Seeing these hormonal change in lambs, in addition to what we have already found with rodents, is advancing our understanding of what programmes appetite. We are getting closer to understanding what causes obesity in humans," he added.
The findings are published in The Journal of Physiology.