Oddly, french fries figure as major plot points in movies:

• The scene in 1986's "Cobra" when Stallone tells a ketchup-crazed girl her fries are drowning

• A french fries food fight in a moving car in "The Getaway" (1994)

• The scene about freeway french fry agony and ecstasy in "Freaky Friday" (2003) when a nutrition-conscious mom in the body of her teenage daughter gets to enjoy a fry for the first time in eight years

Americans' favorite side dish may seem lighthearted on the silver screen, but they're definitely heavy-hearted when they show up on your plate.

One eight-year study even found that people who ate fried potatoes two or more times a week doubled their risk of early death.

But that's not all the harm that french fries, as well as hash browns and home fries, can do.

According to a new study in the journal Cell Metabolism, combining french fries and other processed carbs with a low-calorie beverage that contains the equivalent of two packages of Splenda creates a chemical mix that ends up reducing your body's ability to metabolize sugar and alters your brain's response to sugar.

That, suggest researchers from Yale's Modern Diet and Physiology Research Center, can lead to weight gain, glucose intolerance, and diabetes.

The bottom line: An occasional diet drink doesn't mess up your metabolism of sugar or trigger weight gain (and may help you reduce calorie intake), so long as you never drink it along with fries or other carbohydrates.