Grandparents can be a bad influence on kids' weight, researchers say.

That's the upshot of an analysis of 23 studies conducted in the United States and eight other countries by a team from the Brown School at Washington University in St. Louis.

The study found that kids who were cared for by grandparents had nearly 30% higher odds for being overweight or obese.

While Grandma and Grandpa may mean well, they can affect their grandchildren's weight in various ways, including eating habits, physical activity and perceptions of what represents a healthy lifestyle, according to the researchers.

"Through offering wisdom, teaching traditions, providing guidance and making memories, grandparents are often able to leave behind a legacy that their grandchildren will cherish and benefit lifelong," said lead author Ruopeng An, an assistant professor.

"However, some negative influences from grandparental care may also be present and cannot be overlooked," he added in a university news release.

One of those negative influences affects a child's diet and exercise habits.

"The notion of 'the bigger the healthier' is still relevant," An said.

Some grandparents may urge their grandkids to eat bigger and more frequent meals, and will offer sweets and fried foods as a way to show love, he pointed out.

"In fact, in some cultures, grandparents may also be more likely to excuse children from doing household chores, a key form of physical activity," An added.

He said he was surprised that the studies — from the United States, the United Kingdom, China, Japan and five other nations — showed similar trends across cultures.

"Affluence and being well fed is valued and desirable to many grandparents as they had experienced hunger and poverty in their youth, which they may pass on to their grandchildren, who, to the opposite, are fighting against a world of food swamps and ever-expanding portion sizes," An said.

The findings were recently published online in the journal Childhood Obesity.