Birth Order May Determine Obesity Risk

Firstborn sons are more likely to become obese, according to a new study.

Researchers compared middle-aged men in New Zealand to their younger brothers and found that older brothers weighed more and were less sensitive to insulin.

Researchers said the study involved 26 firstborns and 24 second children who were between the ages of 35 and 55.

The findings revealed that while men in both groups were about the same height, there were significant differences in weight. Researchers found that the average weight for firstborns was just over 200 pounds, while the younger brothers averaged 185 pounds.

Researchers noted that the both groups had similar amounts of body fat, with the older brothers averaging 32.2 percent body fat compared to the younger brothers who had 29.9 percent body fat.

The findings also revealed a significant difference in insulin sensitivity. Researchers found that insulin sensitivity was 33 percent lower in firstborn men than their younger brothers. Researchers said these findings held true even after they accounted for the amount of exercise the men got, their fat mass and other factors.

Researchers explain that the differences could be caused by placental blood flow. Researchers explain that a first pregnancy causes changes in certain arteries in the uterus that are sometimes permanent. Researchers explain that these changes mean that second children, and not firstborns, get the benefits of these changes from the moment of conception.

The findings are published in the journal Scientific Reports.