The potato lied to me.

I baked a plain Russet for dinner last week, clipped on my glucose monitor, and waited.

No butter. No sour cream. Just a potato, split open, with a little salt.

My wife raised an eyebrow. "That's supposed to be the healthy option," she said.

Forty-five minutes later, my glucose monitor told a different story.

This is one person's experiment, not medical advice. Everyone's body responds differently.

A plain baked potato raised my blood sugar about 85 points. That's a bigger jump than a bowl of white rice gave me a few weeks back.

Here's why. A potato is almost pure starch.

Once it hits your stomach, your body breaks that starch into glucose fast, almost as fast as a spoonful of sugar.

In other words, a potato and a slice of white bread aren't as different as people think.

The University of Sydney has been testing potatoes for years in its glycemic index database. Depending on the variety and how it's cooked, a potato can score anywhere from the 50s to over 100 on that scale, where pure glucose sits at 100.

A baked Russet, the kind sitting in front of me that night, tests near the top of that range.

A potato this size also carries a heavy glycemic load, not just a high glycemic index. That's the number that accounts for how much carbohydrate is actually on your plate. It's why the size of the potato matters as much as the type.

A potato does have real nutrients. Potassium. Fiber. Vitamin C. But none of that slows down how fast the starch turns into sugar.

This isn't just happening in my kitchen. Right now, nutrition researchers at Harvard are debating whether the potato should even count as a vegetable, or get moved closer to a grain, because of exactly this: how fast it raises blood sugar.

That debate isn't settled. But it's revealing that scientists are even having it.

● Meanwhile... The Hack

So does that mean no more potatoes? I don't think so.

A few nights later, I made the same potato. Boiled it, then put it in the fridge overnight. Ate it cold, the way you'd eat potato salad.

This time... it only raised my blood sugar about 42 points.

Here's what's going on. When you cook a potato, then let it cool, some of the starch changes shape.

It turns into something researchers call resistant starch, because your body can't fully break it down.

In other words, a chilled potato has less digestible starch than a hot one, even though it's the exact same potato.

A study on cold-stored potatoes found that chilling alone cut the insulin response by close to 30 percent. Adding a splash of vinegar pushed the reduction even further.