Among primates, newborn human infants have the largest brains and also the highest proportion of body fat. However, if the baby does not receive sufficient nutrients via the placenta during pregnancy, a dilemma occurs: should resources be allocated to fat deposition for use as energy after birth or to brain growth?

According to a study published in the journal PLoS ONE, researchers at the University of Southampton have demonstrated that this decision could have an impact on children’s body fatness.

At the Medical Research Council (MRC) Lifecourse Epidemiology Unit at the University, researchers performed ultrasound scans on 381 pregnant women.

The team measured blood flow from the placenta to the unborn baby, and also examined whether this blood was distributed to the baby’s liver or if the blood bypassed the liver in order to supple the brain and heart. These measurements where then compared with the baby’s body fat percentage at birth and again at 4 years old.

The researchers found that children had greater body fatness as an infant and at age 4 if blood flow to the liver was greater in late pregnancy. In addition, when the majority of the blood bypassed the liver and supplied the brain and heart, the team found that the placenta was smaller and provided less essential nutrients to the unborn child.

According to the researchers, these findings are independent of an association between the body fatness of the infant and the body fatness of the mother.

Keith Godfrey, Professor of Epidemiology and Human Development at the University, said: “In our evolutionary past, the demands of a big brain have led the unborn baby to develop blood flow responses which preserve nutrient delivery to the brain when the supply of essential nutrients from the mother cannot meet the baby’s requirements.

However, having a big brain has also led to evolution of a strategy to adjust blood flow through the baby’s liver, which enables the liver to produce more fat – this acts as an energy reserve, protecting brain development during periods of illness or under-nutrition in early infancy. Our data suggests that evolution of this strategy has brought with it a predisposition to obesity and later diabetes in contemporary societies with abundant nutrition in later postnatal life.”

Professors Guttorm Haugen from the University of Oslo and Torvid Kiserud from the University of Bergen, who were part of the study, explained:

“An interpretation of our findings is that there could be programmed effects on the liver that arise from blood flow adaptations in the womb and predispose individuals to gain excess body fat. Although further studies are needed, our findings add weight to current concerns that the current epidemic of childhood obesity and associated disorders may partly have its origins through adaptations made by the developing baby during pregnancy.”

Professor Mark Hanson, Director of the University of Southampton’s Human Development and Health Academic Unit, said: “If the supply of nutrients across the placenta is inadequate or unbalanced, the unborn baby has to decide whether to prioritize fat deposition or spare brain growth – it does this by changing the amount of blood flowing to the liver and brian. A decision to increase blood flow to the liver has lasting implications for the child’s body fatness.

Transfer processes across the placenta for some nutrients such as glucose evolved in environments less affluent than those now prevalent in developed populations, and our findings additionally suggest that in circumstances of maternal obesity and nutrient excess these processes now also lead to excessive fat deposition in the womb.

This strengthens the case for all women of reproductive age having greater access to nutritional, education and lifestyle support to reduce the risk of obesity in their children and improve the health of the next generation.”

Professor Cyrus Cooper, Director of the MRC Lifecourse Epidemiology Unit, explained: “This study is part of a wider body of work by the MRC Lifecourse Epidemiology Unit into how factors during pregnancy might have long-term influence on childhood growth and development. This is a wonderful example of multi-disciplinary research using the unique clinical resource provided by the Southampton Women’s Survey.”

Written by Grace Rattue