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Having obese brothers and sisters is more revealing indicator of child obesity than having obese parents, according to a new study. 

Investigators surveyed adults in 10,244 American households and found that the likelihood of childhood obesity varies with the number of children in a household, as well as their gender. In a single child household, a child is 2.2 times more likely to be obese if a parent is also obese, the study found. 

In families with two children, the study noted a stronger relationship with sibling obesity than with parental obesity. 

"For youngest boys in two-child families, obesity is 11.4 times more likely with a male older sibling," authors wrote in the study. "If that younger boy's elder sibling is a girl, the boy is 6.6 times more likely to be obese. In two-child families, youngest-girl obesity is 8.6 times more likely with a female older sibling and is not significantly more likely if the older sibling is male. Thus, for younger children, there is a discernible gender correlation in sibling obesity status: having an obese elder same-gender sibling is associated with an increased likelihood of the younger child being obese."

The study also highlighted the fact that exercise and food consumption play important roles. 

"Younger siblings with more vigorous physical activity are significantly less likely to be obese, though having an elder sibling who is extremely active is associated with a higher risk of younger-sibling obesity," lead investigator Mark C. Pachucki, PhD, Mongan Institute for Health Policy, Massachusetts General Hospital, Boston, MA, said in a press release.

"In seeking to reduce the prevalence of childhood obesity, it may be productive to consider prevention and treatment models that meaningfully recognize siblings as interconnected."

The study has been published in the American Journal of Preventive Medicine.