When Morgan Spurlock went on a fast-food binge for his documentary "Super Size Me," he not only packed on pounds, he felt increasingly awful.

And it wasn't just because of all that bad food in his gut. It turns out that eating a high saturated fat diet actually alters the genes that control your muscle metabolism.

Researchers from the department of Human Nutrition, Food, and Exercise at Virginia Tech put 12 healthy, college-age guys on a diet for five days with 55 percent of their calories coming from fat and 18 percent from saturated fat.

That is all it took to alter the genes that influence metabolism, making their muscles unable to efficiently burn the fuel food provides.

Those once calorie-burning sinews turned into calorie-hugging, weight-adding machines.

So what does this mean?

You can actually make it harder to avoid weight gain and stay healthy — even if you're eating healthy a lot of the time — if you indulge in French fries, three-cheese pasta dishes, or a super-size deli sandwiches.

If you need special tasty treats, try 100 percent whole-wheat pasta with broiled salmon in a fresh tomato basil sauce; or oven-roast some sweet potatoes along with root veggies; or whip up a fruit smoothie with nonfat Greek yogurt.

As a rule, stick with 100 percent whole grains, lean proteins, and plenty of veggies and fruit.

Treating yourself well will leave a great taste in your mouth!