Researchers have found that around 35-40 percent of a child's weight is inherited from their parents.
From an analysis of around 100,000 children from six countries - including the United States - researchers found that around 20 percent of a child's body mass index (BMI) is inherited from their mother, while a further 20 percent is inherited from their father.
What is more, the team found that the more overweight parents are, the more overweight their child is likely to be.
Lead study author Prof. Peter Dolton, from the University of Sussex in the United Kingdom, and colleagues recently reported their findings in the journal Economics and Human Biology.
Obesity can have immediate and long-term effects on a child's health, including increased risk of asthma, type 2 diabetes, metabolic syndrome, heart disease, and some forms of cancer. Children who are obese are also more likely to have emotional health problems, such as low self-esteem and depression.
Parental effect on offspring BMI 'more than doubled' for obese children
While a healthful diet and regular physical activity are important in maintaining a child's weight, there are some risk factors for obesity that cannot be controlled, such as genetics. Studies have shown that a child can inherit certain genes from their parents that increase their susceptibility to weight gain.
For the new study, Prof. Dolton and colleagues set out to estimate the "intergenerational transmission" of BMI between parent and child - that is, how much of a child's BMI is attributable to the BMI of their parents.
The researchers came to their estimates by analyzing the weights and heights of around 100,000 children and their parents. Participants spanned six countries, including the U.S., United Kingdom, China, Indonesia, Spain, and Mexico.
The team calculated that the average intergenerational transmission of BMI between a parent and a child is around 0.2. In other words, around 20 percent of a child's BMI is due to the father and 20 percent is due to the mother.
Additionally, the researchers found that intergenerational transmission of BMI is highly dependent on the BMI of offspring. For example, they found that the BMI of children with the lowest weight was 10 percent due to each parent, while the BMI of children with the highest weight was almost 30 percent due to each parent.
Prof. Dalton says this finding shows that children born to obese parents are at greater risk of becoming obese themselves."[...] The parental effect is more than double for the most obese children [than] what it is for the thinnest children," he adds.
Intergenerational transmission consistent across all countries
The researchers say their findings were consistent across participants from six countries, regardless of each country's economy.
"Our evidence comes from trawling data from across the world with very diverse patterns of nutrition and obesity - from one of the most obese populations - USA - to two of the least obese countries in the world - China and Indonesia," Prof. Dalton comments.
"This gives an important and rare insight into how obesity is transmitted across generations in both developed and developing countries," he adds. "We found that the process of intergenerational transmission is the same across all the different countries."
All in all, the researchers believe their findings highlight the importance of genetic factors on the risk of obesity.
"These findings have far-reaching consequences for the health of the world's children. They should make us rethink the extent to which obesity is the result of family factors, and our genetic inheritance, rather than decisions made by us as individuals."
Prof. Peter Dolton