Four Reasons You Can't Lose Belly Fat

Your friends, your cold, your spending habits--science can blame just about everything for filling our jeans to overflowing. But how much extra poundage are these surprising factors really responsible for? We dug through the research to find out what's stalling womens weight loss.

The risk: Your Flabby Friends - 2 lbs

Palling around with a tubby crowd could be worse than having Rosie O'Donnell as your diet coach. A study in the New England Journal of Medicine looked at the social networks of 12,067 people over 32 years and found that for every 10 pounds a person gained, close friends of the same height gained an average of one to two pounds.

Improve your odds Instead of making plans to go out for drinks and dinner, catch up with your buds as you sweat on side-by-side elliptical machines, play racquetball, or cruise town on your bikes. Don't take no for an answer!

The risk: Credit Cards - 5 lbs

Your plastic may be affecting more than just your credit score. Visa conducted a study of 100,000 fast-food restaurant transactions and found that people who pay for their food with a credit card spend 30 percent more than those who pay with cash. Opt to swipe and you could end up with a double quarter-pounder with cheese and a large Coke instead of a quarter-pounder with cheese and medium drink. For the average woman, who visits a fast-food restaurant once a week, that adds an extra 17,160 calories, or 4.9 pounds, per year.

Improve your odds If you must hit the drive-thru, pay cash. You're likely to spend less. Better yet: Go home and make a sandwich. It'll be better for your body and your wallet.

The risk: The Sniffles - 40 lbs

Forget feeding a cold--a 2007 review in Advances in Food and Nutrition Research found that in animal studies, critters infected with adenovirus-36--one of about 50 human viruses that cause upper-­respiratory infections--gained up to four times as much weight as those without it. Scientists speculate that the bug increases the number of fat cells in the body and that it could leave humans lugging around an extra 40 pounds.

Improve your odds Believe it or not, a vaccine to fight the fat culprit is in the works. And adenovirus-36 has already been deactivated in lab studies (there are no human tests yet). Until then, wash your hands often, as adenoviruses typically are transmitted through direct contact.

The risk: Your Meds - 45 lbs

Popping pills for allergies, birth control, depression, or diabetes could be an Rx for a wider rear. According to a report in Pharmacist's Letter, side effects of drugs such as the antidepressant Nardil and the allergy medication Zyrtec can stimulate appetite; that can leave you eating more and gaining up to 45 pounds.

Improve your odds If you suspect a scrip is to blame for your suddenly bloated belly, talk to your M.D. about alternative options for the drug you're prescribed. Just make sure you don't stop your current meds without your doctor's say-so.

A 2004 study in General Hospital Psychiatry revealed that 5 percent of patients surveyed would never take meds that caused weight gain--even if they had a life-threatening condition.