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# The same banana, two mornings, two very different lines
- URL: https://the-glucose-field-guide.ghost.io/the-same-banana-two-mornings-two-very-different-lines/
- Published: 2026-10-08T12:00:32.000Z
- Updated: 2026-10-08T12:00:34.000Z
- Description: Two tablespoons of peanut butter added 26 percent more carbohydrate to my breakfast. It still raised my blood sugar a third less than the banana on its own.
- Author: The Glucose Field Guide

| My supermarket sells protein water. Not a shake. Water. NIQ, the firm that tracks what people put in their trolleys, counted more than 37,000 products carrying a protein claim on the front of the pack. Around 90 billion dollars a year. A nutrition scientist called Donald Layman has a name for most of it. Fairy dusting. His point is that adding protein to a cookie does not turn it into something other than a cookie. And by the USDA's own analysis, close to nine in ten Americans already get enough protein without trying. Which raises a fair question. If the protein on the box is mostly marketing, does real protein do anything at all? So I went back to yesterday's banana. It raised my blood sugar 52 points, eaten on its own on an empty stomach. This morning I ate the same size banana at the same time, on the same empty stomach. The only change was two tablespoons of peanut butter. No powder. No bar with a number on the wrapper. Just the jar that has been in the cupboard since the kids were small. 🍌 Banana alone +52 27 g carbohydrate 🍌🥜 Plus peanut butter +34 34 g carbohydrate Two tablespoons of peanut butter bring 16 grams of fat and 7 grams of protein. They also bring 7 grams of carbohydrate. Read that last part again. The breakfast with peanut butter carried 26 percent more carbohydrate than the banana on its own. More sugar going in, not less. And it raised my blood sugar a third less… ![Glucose chart of the same banana eaten on two mornings. Eaten alone it raised blood sugar 52 points and peaked at 30 minutes. Eaten with two tablespoons of peanut butter it raised blood sugar 34 points, peaked later and came down more gently.](https://storage.ghost.io/c/cf/1c/cf1c5695-50da-4986-90a3-3727fcbc3f0a/content/images/2026/10/glucose-chart-2026-10-08.png) This is one person's experiment, not medical advice. Everyone's body responds differently. Look at the shape, not only the height. The green line starts later, tops out lower, and comes down gently. The red line goes up fast and then falls off a cliff. That fall is the part you feel. On the banana-alone mornings I was hungry again by ten, and I had put it down to a small breakfast. It was not the size of the breakfast. Why fat and protein do this Food has to leave your stomach before the sugar in it can reach your blood. Fat and protein slow that exit down. The sugar still arrives. It just arrives over a longer stretch of time, so less of it reaches your blood at once. How much does the exit speed matter? A 2021 review in Frontiers in Endocrinology puts it at about a third of the variation in how high blood sugar climbs in the first hour. In other words, a third of the answer is not what you ate. It is how fast it left your stomach. The part I almost left out A randomised trial in the British Journal of Nutrition tested peanut butter properly. Fifteen women, breakfast with and without it, blood drawn all morning. At that breakfast, the peanut butter made no clear difference to their blood sugar. What it changed was lunch. Four hours later, at the next meal, the rise was lower. That result did hold up, and it is the one the researchers could stand behind. Which is a strange and useful idea on its own. What you eat at breakfast can still be working on you at noon, after the breakfast itself is long gone. So a careful trial found something smaller and slower than my monitor did this morning. One person on one day is not evidence, and I am not going to pretend otherwise. The direction I trust. The size I would not bet on. The hack, if you want the bigger version There is one detail in that same 2021 review that might explain the gap. Fat stirred into a meal can float on top of it and slow the stomach less than fat eaten first. Which points at a small change in order… **Eat the peanut butter first.**Take it off the spoon, wait two or three minutes, then eat the banana. The fat and protein get a head start on the stomach instead of riding along with the fruit. **Two tablespoons is plenty.**Four does not slow your stomach twice as much. It mostly adds calories you did not need. **Check the label for sugar.**Plenty of jars list sugar in the first three ingredients. You want one where the list is peanuts, and maybe salt. By the way, about ripeness The University of Sydney runs the database that started glycemic index testing. They put a banana between 47 and 53, which counts as low. Let the same banana go spotty and it climbs to 57. As a banana ripens, some of its starch turns into sugar. The fruit does not get bigger. It gets faster. Which is why the banana you forgot about on Friday is not the same breakfast on Tuesday, even though nothing on the label changed. "More sugar went in. Less of it showed up at once. That is the whole trick." So buy them a little green, and keep the spoon of peanut butter nearby. Tomorrow is Friday. The week's findings in one place, and the first of your questions. — Stay steady |
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