Study finds that only-children are more likely to be overweight or obese

By Sally Robertson, B.Sc.Nov 6 2019

A new study has found that only-children are more likely to be overweight or obese compared with children who have siblings.

Image Credit: Alena Ozerova / Shutterstock.com

The research revealed that families with two or more children tended to have more healthy eating and drinking habits than families with only-children or "singletons," as the researchers called them.

Although the study population was small and the research could not determine cause and effect, the findings do "raise an interesting point that we need to better understand," says Natalie Muth, who chairs the American Academy of Pediatrics Section on Obesity.

Muth, who was not involved in the research, says previous studies have also found that only-children are at a greater risk for overweight and obesity: "Why is that?,” she asks… “While this study doesn't provide the answer to that question, it is helpful in building the body of research that eventually will provide clearer answers.”

Only-children have long fascinated researchers

Researchers have long been intrigued by only-children. Previous studies have focused on the perceived negatives that society holds about singletons such as a tendency for them to be headstrong, competitive, selfish, egocentric, and unlikely to share.

A lot of people assumed only children are defective, and so a lot of research has been done on achievement and personality,"

Psychologist Toni Falbo, University of Texas, Austin

A meta-analysis conducted by Falbo in 1986 showed that only-children excelled in achievement, character, and intelligence, compared with children who had siblings, particularly those with older siblings.

"On average, only children get more education, and they score higher on various achievement tests. On personality achievements, they're doing fine. They have reasonably positive personalities, and they're not prone to mental illness any more so than anyone else," says Falbo.

The only difference the study did identify was that only-children seemed to bond more with their parents than children with brothers and sisters. This finding was later supported by a study in 2018 that looked at 10,000 school children in Germany.

Over recent decades, researchers in Europe and China have also investigated the association between weight and being a singleton. Some studies also investigated the association in the context of birth order.

The single-child policy that had been in place in China between 1980 and 2016 meant that researchers had a plethora of data. One study involving 20,000 only-children in China found that male singletons living in urban areas were 36%  more likely to be overweight and 43% more likely to be obese, compared with male children who had siblings.

The current study found only-children have less healthy eating habits

For the current study, mothers kept daily food logs for three days, and teachers kept logs of any food eaten while children were at school. Mothers also completed a questionnaire called “Family Nutrition and Physical Activity,” which was designed to assess typical family eating habits.

The findings revealed that singletons had less healthy eating and drinking habits than children with siblings. The study also found that mothers of only-children were more likely to be obese themselves.

"We know that obesity is very strongly connected within families, so it is certainly possible that could explain the difference in this study," suggests Muth.

Muth also pointed to several other possibilities., saying that "Perhaps there is more food to go around or only children are less active because they don't have a live-in peer to play with.

“Or maybe there is a biological factor at play. It is hard to say for sure, but this is the question that researchers are trying to figure out," she said.

The planning and organization of meals may be different when mothers have multiple children

Lead author Chelsea Kracht from Louisiana State University's Pennington Biomedical Research Center, thinks the findings could be explained by differences in how mothers plan and organize meals if they have more than one child.  

"With multiple children, you're scheduling a little bit more of your meals. So, we're going to have more at-home meals. We're probably going to have less fast food," she says.

Kracht suggests that nutritionists consider the influence of family and siblings when providing nutrition education for families of young children, to ensure the information is appropriate and tailored: "Efforts to help all children and families establish healthy eating habits and practices must be encouraged.”

Adolescent only-children are not as active as adolescents with siblings

Falbo is currently studying adolescent only-children and has found that they are not as active as children with siblings and tend to spend more time on screens: "They're not bugging their siblings and jumping up and down and doing the kinds of things siblings do.”

Her research has also shown that only children are more likely to east fast food regularly.

Falbo says the positive news is that these behaviors can be changed: "You have to reduce the screen time [and] control the amount of fast food. It's doable.”

Muth agrees, saying that there is a notably increased risk for overweight and obesity among only children and parents who are aware of this increased risk may be able to prevent overweight or obesity in their child by paying extra attention to creating a healthy and active home environment.