Tuesday, 3 p.m.

I was at my desk, hungry, with a protein bar in my bag. The wrapper said "low sugar" in big letters. It promised 20 grams of protein and only 2 grams of sugar.

It felt like the responsible choice. I even felt a little smug about it.

So I ate it. And my glucose monitor, the small sensor on the back of my arm that tracks my blood sugar all day, showed something I didn't expect.

That protein bar raised my blood sugar about 42 points in 40 minutes.

The next afternoon, I tried a small handful of almonds and cashews instead.

The nuts raised my blood sugar 8 points.

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

That gap is revealing.

Why test protein bars this week? Because the companies that make them are rebuilding them for a new kind of customer.

On Tuesday, the dairy ingredient maker Lactalis Ingredients held a webinar on high-protein bars. Ahead of it, one of its product managers told the trade site Nutrition Insight that GLP-1 drugs like Ozempic are changing what goes into a bar. People on these drugs eat less, so they want more protein, more fiber, and less sugar in every bite.

So the protein bar aisle is about to get a lot more crowded.

That sounds great. But "low sugar" on the front of a wrapper doesn't tell you how much a bar will raise your blood sugar.

● The Science

Here's the thing. Sugar isn't the only ingredient in a bar that turns into sugar in your blood.

Flip a typical "low sugar" bar over and read the ingredient list. You'll often find rice crisps, tapioca starch, or something called maltitol.

Rice crisps and tapioca are starches. Your body breaks starch down into glucose, and it does it fast. In other words, those ingredients act a lot like sugar once you eat them, even though the label doesn't count them as sugar.

Maltitol is a sugar alcohol. Companies use it to make the bar taste sweet. Its glycemic index is about 35, which is roughly half of table sugar's score of about 65. So maltitol raises blood sugar more slowly than sugar does... but it still raises it. Eaten in large amounts, maltitol also upsets some people's stomachs.

And the label math makes this easy to miss. Many brands print "net carbs," a number that subtracts fiber and sugar alcohols from the total carbs. That number can look tiny while the bar still raises your blood sugar. I trusted that number for years.

Nuts work differently.

A handful of almonds is mostly fat, protein, and fiber. There's very little starch or sugar in there for your body to turn into glucose.

Researchers in Toronto tested this. They gave people mixed nuts, sometimes alone and sometimes with white bread. The nuts on their own had little effect on blood sugar after eating. And when people ate nuts with the bread, the more nuts they ate, the less their blood sugar rose.

The studies were small, with about a dozen people in each group. But they point the same way my glucose monitor did.

Could a swap this simple make that much difference? For me, on those two afternoons, it did. Your numbers might look different, and I don't know yet if it holds for everyone.

So is the protein bar the bad guy? I don't think so. Some bars are built with real food and little starch. And on a busy day, a bar in your bag beats skipping lunch.

● The Hack: If You Must...

My wife keeps a box of protein bars in the car for the kids' soccer weekends. We're not giving them up. We're just choosing them better and eating them in a smarter way.

● By the way...

Protein bars aren't the only snack with a healthy reputation that raised my blood sugar more than I expected. Here are three more from my glucose monitor.

What do rice cakes, dried mango, and veggie straws have in common? Each one is mostly fast starch or concentrated fruit sugar, with very little protein or fat to slow it down.

Rice cakes get their own trial later this fall. I have a feeling they won't do well...

Anyway, the next time you're hungry at 3 p.m., try the handful of nuts. If you wear a glucose monitor, I'd love to hear what the nuts did to your blood sugar.

Stay steady