My wife bought granola.

A big bag from the health-food shelf. Oat clusters, honey, dried cranberries. The word "wholesome" was printed twice the size of the ingredients list.

I've had a glucose monitor stuck to my arm for months now. So of course I poured a bowl. With milk, a full cup, the way my kids like it.

Then I waited.

It's revealing.

Forty-five minutes in, my blood sugar had risen 58 points. That's close to what a bowl of frosted cereal does to me. Not what I expected from something sold two aisles from the yogurt and the leafy greens.

Here's why. Store-bought granola bakes rolled oats together with honey or syrup, and that heat partially breaks down the oats' starch. In other words, baking makes the sugar inside the oats easier for your body to grab and use fast. Add dried cranberries and a drizzle of syrup on top, and you've built a bowl that raises blood sugar almost like dessert.

But there's a bigger story here than my one bowl.

This year, the newest Dietary Guidelines for Americans did something they haven't done in 45 years. They named packaged breakfast foods, granola among them, as something to eat less of. Not because oats are the problem. Because of what gets stirred into them on the way to the shelf.

The oats aren't the problem.

So the next morning, I skipped the granola. I grabbed a small handful of almonds, walnuts, and pumpkin seeds instead.

Same glucose monitor. Same empty stomach. Same time of morning.

Barely a blip.

My blood sugar rose just 13 points. And it came back down slowly. No crash, no 10am wall.

Nuts and seeds are almost all fat, protein, and fiber, with very little starch or sugar. In other words, there's barely any sugar in them to raise your blood sugar in the first place. What little sugar does show up gets absorbed slowly, because fat, protein, and fiber all sit in your stomach longer, so nothing rushes into your bloodstream at once.

Researchers at the University of Toronto tested this directly. Adding a small serving of almonds to white bread cut the meal's blood sugar rise by nearly half. A bigger serving cut it further still.

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

I don't know if 13 points would hold for you. Bodies are different, and the research on nuts and glucose is still filling in gaps... but two mornings, two totally different foods from the same "healthy breakfast" aisle, with results this far apart. That's worth knowing before you fill your cart.

● The Hack

We don't have to give up granola entirely. If you're not ready to swap it out, here's how to keep it without the same rise.

● By The Way

Granola isn't the only "healthy" breakfast food hiding a bigger rise than it looks. A few of its aisle-mates, tested the same way.

Stay steady