The thing is, grandparents are more likely to let the kids indulge in sugary foods as a "treat", but by doing this they are teaching the children to use food as an emotional tool. Some try to justify it because "there are two sets of grandparents - and you don't want to be the one that isn't giving them the nice piece of cake," but it still has the same result. Teaching a child to eat emotionally will stick with them for their whole lives and can cause weight gain in the future.
The study showed that despite the potential damage, "children benefit enormously from having close relationships with their grandparents right through childhood into adolescence."
What they hope, is that by revealing how much of an impact they have, that grandparents will put a greater emphasis on teaching kids the proper life skill. "If healthy habits begin early in life, it's much easier to continue them as an adult."
They hope that by emphasizing healthy choices, grandparents will be able to encourage their grandchildren to make better choices and be healthy later in life.