Breakfast, Tuesday morning.

I opened the fridge and found two kinds of yogurt sitting side by side.

One was a strawberry fruit-on-the-bottom cup. My kids love those. The other was a big tub of plain Greek yogurt that my wife buys every week.

Both are sold as healthy. Both say yogurt on the front.

So I did what any sensible person with a glucose monitor on his arm would do... I ate the strawberry cup on Tuesday. On Wednesday, at the same time, I ate a bowl of plain Greek yogurt with a handful of berries. Then I watched what each one did to my blood sugar.

My wife watched me eat yogurt while staring at my phone. She didn't ask. She's used to it by now.

In case you're new here, a glucose monitor is a small sensor stuck to the back of my arm. It reads my blood sugar every few minutes, day and night.

And here's why this matters right now.

Yogurt is having a big year. A PwC report this spring found that about one in five US households now includes someone taking a GLP-1 drug like Ozempic or Wegovy. Those shoppers are buying more protein, and Greek yogurt sales rose almost 7%.

But not every cup in that aisle is the same food.

● The Results

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

The strawberry cup raised my blood sugar about 42 points. About two hours later, my blood sugar dipped a little below where it started. I was hungry again by ten o'clock.

The plain Greek yogurt with blueberries and raspberries raised my blood sugar just 14 points. Then it stayed steady. I didn't think about food until lunch.

That's three times less.

● The Science

Here's the thing. This result surprised me a little.

Yogurt is famous for being gentle on blood sugar. The University of Sydney, the lab that invented glycemic index testing, has tested close to 100 yogurts. Nine out of ten scored low.

In other words, even the sweet ones don't act like candy.

So why the gap?

The first reason is sugar. A small fruit-on-the-bottom cup can hold around 20 grams of sugar... that's about five teaspoons. Plain Greek yogurt has around 5 or 6 grams, and all of it comes from the milk.

The second reason is protein. Greek yogurt is strained, so it has about twice the protein of regular yogurt. Protein slows down how fast your stomach empties. That means the sugar in the bowl reaches your blood more slowly.

The Sydney team saw the same pattern across their whole database. Plain yogurts averaged a glycemic index of 27. Sweetened yogurts averaged 41. They said the difference came mostly from how much protein each yogurt had compared to its carbs.

And the berries? Berries bring fiber. The fiber slows down how fast your body absorbs sugar. Berries also taste sweet, which my kids noticed right away.

I don't know if everyone will see a 28-point gap. Some people barely react to flavored yogurt. Others react more than I did. But the reason behind the gap makes sense.

It's revealing.

● The Hack: if you must...

Some mornings the strawberry cup wins. I get it. My youngest will not touch plain yogurt. Here's what helps when you want the flavored kind anyway.

● By the way...

The yogurt aisle has a few other cups that look like health food. Here's how much each one raised my blood sugar.

We don't have to give up yogurt. We just have to check the sugar on the label.

My fridge now has one tub of plain Greek yogurt and a bag of frozen berries. The strawberry cups are still there too. These days they come with a handful of almonds.

Stay steady