The other day I walked into a small-town cafe and ordered a wrap and a banana.

"Anything else?" the cashier asked.

"No thanks," I said.

"Since you ordered a meal you can add a cookie for 50 cents," she said, pointing to a tray of chocolate chip cookies.

The cookies were easily five inches in diameter and oozing with melted chocolate. They looked fresh and moist and... and gee, 50 cents seemed like a great deal.

"Why not?" I thought.

Then I read an article on the FitnessGenes blog about the impact of upselling on weight gain and obesity. (A previous article I wrote about FitnessGenes and genetic testing was read by a couple hundred thousand people. Clearly I'm not the only fan of DNA testing, since it provides data that lets you tailor your diet and fitness training based not on hunches or feel, but on what is truly best for you.)

Upselling is a sales strategy designed to persuade a customer to buy something extra or more expensive than what they otherwise would have purchased. My cookie is a great example. So is an extended warranty. So is being offered the "opportunity" to super-size a fast food combo.

Of course upselling involves an implied benefit to the customer. My cookie cost less than if purchased it separately. Typically it's a better value for the money to buy a bigger portion or receive a "discounted" extra side; the best upselling appeals make you believe your decision is based on logic.

As the FitnessGenes folks write, paying 17% more money to get 55% more food is a good deal, since you get more for your money.

But so does your waistline.

According to the same research, up 78% of us experience upselling at least once a week. All else being equal, that means the average person consumes over 17,000 extra calories per year, which adds up to a weight gain of about 5 pounds.

People between the ages of 18 and 24 are the most likely to experience upselling, consuming an extra 750 calories per week. That adds up to about 11 extra pounds a year. (Not a "freshman 15," but close.)

Being offered a 50 percent discount on a $2,000 sofa isn't a deal unless you need a new sofa. If you don't need it, you aren't saving $1,000 -- you're spending $1,000 you didn't need to spend.

The same is true for being upsold in restaurants and coffee shops and fast food chains. I didn't walk in the cafe intending to buy a cookie. Worse, I didn't walk in needing a cookie; the wrap and banana were enough to fill me up. (I usually don't even finish all of the flatbread.)

50 cents was certainly a good deal, but still: I spent 50 cents for something I not only didn't need, I spent 50 cents on something that wasn't good for me -- or my waistline.

More food for relatively less money may seem like a great deal... but like most things that are too good to be true, we pay for it later.

A few more of my health and fitness articles: