(CNN)Have you ever wondered why some people seem to stay trim effortlessly, while the majority of Americans struggle with their weight?
Sure, genetics and a healthy lifestyle play a large role, but there are other, more surprising correlations that may be helping them stay slim.
They live near a gym.
A recent study in the journal Lancet Public Health found that people living within a kilometer (a little more than half a mile) of physical activity facilities — including gyms, swimming pools and playing fields — weighed less and had smaller waists than those who didn't. The difference was greater in women and those with higher incomes.
The study was observational, so it does not prove cause and effect, but it does reinforce the impact of the built environment, including city design, on body weight.
Other research has found that more walkable neighborhoods are also associated with lower weight.
The Lancet study also found an effect, albeit weaker, on proximity to fast food restaurants: Study subjects who lived 2 kilometers (1.24 miles) or farther from a fast food outlet versus within half a kilometer (a third of a mile) were slimmer, especially women.
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They fidget a lot.
A review article nearly a decade ago found that people with the highest levels of spontaneous physical activity, including fidgeting, tend to weigh less.
Although fidgeting has a strong genetic and biological component, increasing non-exercise-related physical activity — including walking, standing, cooking and even gardening — can also play a significant role in keeping people trim.
This type of non-exercise activity makes up a significant and modifiable portion of your total daily calorie burning, and it can play an important role in helping you stay lean. It is even more important in our modern environment, filled with labor-saving devices, televisions and technology.
A 2003 study found that the impact of mechanization and labor-saving devices, including dishwashers, washing machines, escalators and cars utilized in driving to work, led to a 111-calorie reduction in daily energy expenditure. Unless this reduction is offset by increased activity, it could lead to significant weight gain over time.
Read about the other surprising factors here: http://edition.cnn.com/