Remember the old song about the old lady who swallowed the fly? By the end of the song, she'd swallowed a cow to catch the goat to catch the dog to catch the cat to catch the bird to catch the spider (it wiggled and jiggled and tickled inside her) to catch the fly.

But, it concludes, "I don't know why she swallowed the fly ..."

Well, if you're swallowing foods marketed as "low-fat," "low-sugar," or "low-sodium" to help improve your nutrition or lose weight, you might just be swallowing a spider to catch a fly.

And you should ask yourself, "Why am I eating that?"

A new study looked at more than 80 million foods and beverages purchased among 40,000 U.S. households over five years, and found that "in many cases, foods containing low-sugar, low-fat, or low-salt claims had a worse nutritional profile than those without claims."

For example, low-fat chocolate milk has more sugar than plain milk, and more fat and sugar than many other beverages.

Even more confusing, a brownie can be labeled "low-fat" if it has 3 grams of fat per 40-gram serving, but low-fat cheesecake has 3 grams of fat per 125-gram serving.

The brownie has a relatively higher fat content.

The lesson here: You have to read the nutrition labels, not just packaging claims.

Remember, if a company has to make a low-content version in the first place, chances are the original wasn't healthy and the new one isn't much better.