The lure of “thinner thighs” has been used to market countless books, DVDs, and diets over the years. If new research published today is confirmed by other studies, though, perhaps there should be an addendum: but not too thin. The researchers who followed 2,800-plus people for longer than a decade reported that—believe it or not—a smaller thigh circumference is associated with a bigger risk of heart disease and premature death. This effect was independent of body fat percentage and BMI.

First, it’s not the case that the bigger the thighs, the lower the risk, no matter what. People with thighs measuring less than 60 centimeters (a little more than 23 ½ inches) around were at higher risk of heart problems and early death than those with larger thighs, but no extra benefit accrued to either men or women whose thighs were more than 60 centimeters around. (And that’s not that big—go measure yourself, just below the point where your seat meets your legs.)

Even if your thighs are smaller than the cutoff, you do not have permission to eat until they reach that milestone. This study—as well as similar research that found an association between wider hips and a lower rate of heart disease and early death—doesn’t pinpoint the mechanism that might be behind the link.

But another hypothesis is that larger muscles—in the thighs and in the rear end, in the case of hip circumference—are the protective element. Other research shows that low amounts of muscle mass in the lower body may mean the body is less able to use insulin to help process glucose, possibly leading to type 2 diabetes and perhaps, eventually, heart disease.

- By Jimmy Saroch