Why is it so easy to gain weight back? (It's not what you think!)

Losing weight is a battle for every pound.

When you've fought hard to burn a little off, the last thing in the world you want is to give any of it back.

Not even an ounce.

Yet as any dieter knows... it happens. It happens so often that most people who lose weight end up gaining much of it back.

Some even end up with more around the middle than ever.

Now, a new study shows why, and it's not just a return of old bad habits.

Your diet success is quietly being undermined by hidden poisons.

They're all around you right now -- possibly in your food and even in the very chair you're sitting in.

They're chemicals called perfluoroalkyl substances, or PFASs, and they're found in furniture... clothing... non-stick pans... and more.

PFASs are even used in fast-food wrappers.

In the new study, researchers tracked more than 621 dieting overweight and obese people to see how they did it. More importantly, they also tracked them afterward to see who gained the weight back, and why.

Overall, the folks with the highest blood levels of the chemicals also had the highest risk of regaining their weight.

And ladies, you're facing the biggest risk here: Women with high levels of PFASs in the blood regained nearly five extra pounds when compared to women with low levels.

Tests also revealed the reason for it, showing how these chemicals can slow your metabolism to a crawl, making it harder to burn off weight and easier to gain it back.

If that's not reason enough to worry about PFASs, they've also been linked to other health risks, including cancer and immune system problems.

You want to avoid them as much as you can.

The real question is: Can you?

Odds are, you can't eliminate them completely, but you can take steps to cut your exposure dramatically.

First, avoid packaged foods -- especially fast foods, as the chemical is often found in the wrappers.

Second, dust often -- and wear a mask when you do -- since the PFASs in your furniture upholstery slowly break down over time and get released into the air, where they join your house dust and can be inhaled.

Consider furniture covers made of natural materials that can help limit the release of the chemicals into the air around your room.

And third, choose products less likely to have PFASs. "Non-stick," "oil-repelling," and "stain-resistant" are all phrases that should trigger warning bells -- whether they're listed on cookware, clothing, or anything else -- as they're almost always a sign of PFASs at work.