The primary danger of this deep-vein thrombosis, or DVT, is that the clot, usually in the leg, can dislodge and travel to the lungs, causing a serious blockage known as a pulmonary embolism, or PE.
Slideshow: Best Diet Tips Ever
Less active lifestyle leads to slow-moving blood
Doctors aren’t yet sure exactly why obesity makes you more likely to get blood clots in deep veins. But they know there's a strong link, says Sam Schulman, director of the Clinical Thromboembolism Program at Hamilton Health Sciences, Hamilton General Hospital, Hamilton, Ontario.
People who are obese tend to be less active, and inactivity appears to make clots more likely.
“Immobility and a sedentary lifestyle are clear risk factors for DVT, and we see these in people who are obese,” Schulman says. “Being inactive makes blood flow in the veins sluggish, and this predisposes people to clots.”
Changes in your blood
Also, obesity changes the chemical makeup of blood, making it more likely to clot.
Obesity also leads to inflammation, which makes blood more prone to clotting.
And obesity boosts the risk for diabetes, which is another risk factor for developing a DVT.
Being obese and having a lot of fat around the stomach also stop blood from moving through the deep veins, says Natalie Evans, vascular medicine specialist in the Cleveland Clinic's Miller Family Heart and Vascular Institute.
Get moving and eat fish
The good news: Studies have shown that when obese people lose weight they may reduce their risks by changing some of the chemical makeup of blood that makes blood prone to clot.
Unfortunately, studies haven’t shown that once you have had a DVT you can reduce the risk of a second one in the future by losing weight.
Moderately intense aerobic exercise in overweight and obese adults was shown to improve blood health, even if they didn’t lose weight.
A diet heavy in fish with omega-3 fatty acids may help protect the blood against abnormal clotting. On the other hand, high-carb diets can make the blood more likely to clot.
Ask your doctor to help with weight loss
Going from obese to a healthy weight should be done with your doctor's help, says Marc Passman, MD, director of the vein program at the University of Alabama at Birmingham. “Large weight loss like that should be handled with care under the direction of a medical specialist.”
Obesity is on the rise. At least 700 million adults worldwide -- and 41 percent of Americans -- will be obese by 2015. The number of deep-vein clots is expected to rise right along with that.
In the meantime, research on the connection between the two continues.