It has been shown that babies with low birth weight suffer more health problems in adulthood. For example they are more susceptible to obesity and Type 2 diabetes in adulthood. The idea is that if the mother is pregnant during a famine then the child will compensate by eating more than normal whenever food is available. However, trying to fatten up a low birth weight baby immediately after they are born may actually be detrimental. A group in Cambridge (Ozanne and Hales, Nature 427 , 411-412 (2004)) showed that mice that were born to underfed mothers experienced a fast catch up in weight if they were nursed by normally fed mice. However, their lifespans were significantly shortened. On the otherhand, if a normal birth weight baby was nursed by an underfed mother, their lifespan was actually lengthened. This experiment can never be repeated in humans so we'll never know if carries over. However, it appears that to maximize the health of a baby, all mothers should make sure they eat enough when pregnant and maybe eat a little less when they are nursing.