For a while, I couldn’t reconcile two things I kept hearing about nutrition.
On one hand, fruits like mangoes, bananas, pineapple, and watermelon were widely considered healthy foods. They contain fiber, vitamins, antioxidants, and are included in many healthy eating patterns.
On the other hand, many of those same foods have surprisingly high glycemic index values.
The more I learned about the glycemic index, the more confused I became.
If a high glycemic index is supposed to be a bad thing, why do so many healthy foods score so highly?
And if these fruits are healthy, why should I care about the glycemic index at all?
I assumed there was something I was missing. Either the glycemic index was being overstated, or the health benefits of these foods were being overstated. The two ideas seemed difficult to reconcile.
What finally shifted my thinking wasn’t a research paper.
It was a comment from one of my nutrition professors.
She mentioned that she rarely uses the glycemic index in practice.
That surprised me.
The glycemic index had been discussed so often in articles, videos, and online discussions that I assumed it must be one of the most important tools in nutrition. If a practicing nutrition professional rarely relied on it, I wanted to understand why.
The answer, as it turns out, wasn’t that the glycemic index was wrong.
It was that I didn’t fully understand what question it was designed to answer.
The glycemic index measures how quickly a carbohydrate-containing food raises blood glucose compared to a reference food under standardized conditions. At the physiological level, the glycemic index is measuring something real. Foods with a higher glycemic index generally produce a faster rise in blood glucose than foods with a lower one.
The problem begins when we start asking the glycemic index questions it was never designed to answer.
Many people encounter a high GI food and immediately conclude that the food itself must be unhealthy. Others see a low GI food and assume it must be a better choice.
But the glycemic index does not measure nutritional quality.
It doesn’t tell us how much fiber a food contains.
It doesn’t tell us whether the food provides vitamins, minerals, or beneficial phytochemicals.
It doesn’t tell us how filling the food is.
And it doesn’t tell us how much of that food people typically eat.
That’s where things start to get interesting.
Watermelon often appears near the top of glycemic index charts, with a GI around 76. Yet a 120-gram portion (roughly three-quarters of a cup, diced) contains only about 6 to 9 grams of carbohydrate, depending on how it is measured.1 Run that through the glycemic load formula (GI multiplied by carbs per serving, divided by 100), and watermelon’s load lands in the single digits, well inside the low range. High GI does not necessarily mean high glycemic load. The chart says watermelon raises blood glucose quickly. The portion you actually eat doesn’t have enough carbohydrate to do so.
This is one reason researchers developed the concept of glycemic load.
Unlike glycemic index, glycemic load takes portion size into account. A food can have a relatively high glycemic index while still producing a modest glycemic load if people don’t consume large amounts of it at one time.
That distinction helped answer part of my original question.
But it still didn’t explain why many practitioners seemed reluctant to place too much emphasis on the glycemic index.
The deeper issue is that people rarely eat carbohydrates by themselves.
The glycemic index is measured under carefully controlled conditions. Real meals are not.
A bowl of rice eaten alone is different from rice eaten alongside dal, vegetables, and yogurt. Protein, fat, and fiber can slow gastric emptying and change the body’s glycemic response. The number on the chart remains the same, but the meal has changed.
That was probably the moment things really started to click for me.
This is also why the glycemic index may be more useful in some situations than others. For someone managing diabetes or trying to better understand their blood glucose response, GI can provide helpful information when used alongside portion size, meal composition, and blood glucose monitoring. For someone simply deciding whether a banana, mango, or bowl of watermelon belongs in an otherwise healthy diet, the answer is usually found in the overall dietary pattern rather than the glycemic index alone.
Then there is the person eating it.
A 2015 study at the Weizmann Institute followed 800 people using continuous glucose monitors and found that responses to identical meals varied dramatically from one person to the next.2 Two people could eat exactly the same food and produce very different glucose curves. In some cases, one person’s blood sugar climbed sharply on a food while another’s barely moved. Insulin sensitivity, sleep, physical activity, medications, and even gut microbiome composition all shaped the result.
The more I learned, the less interested I became in finding the perfect glycemic index score.
The real question wasn’t whether a food had a high GI or a low GI.
The real question was how that food fit into the larger pattern of someone’s diet.
I eventually realized that many of the articles I was reading were not actually disagreeing. They were answering different questions.
One article might ask whether watermelon raises blood glucose. Another might ask whether watermelon is a nutritious food. The first looks at a glucose curve. The second looks at water content, vitamins, lycopene, what the fruit tends to replace on the plate. Both can be right at the same time. Reading them side by side, it’s easy to think they’re arguing when they’re simply standing in different places.
That doesn’t mean the glycemic index is useless.
Far from it.
Large reviews have found that dietary patterns lower in glycemic index and glycemic load are associated with reduced risk of type 2 diabetes and cardiovascular disease.3 The benefit, though, shows up at the level of the overall diet, not in the verdict on any single food. The glycemic index captures something real. It captures one thread of a larger story.
But it is a tool.
Not a verdict.
For a long time, I thought the challenge was deciding whether the glycemic index was right or wrong.
What I eventually realized is that it was never an all-or-nothing question.
The glycemic index was doing exactly what it was designed to do.
The confusion came from expecting it to do more.
That’s a pattern I’ve started noticing in other areas of nutrition as well.
Useful tools often become misleading when they are promoted into complete explanations.
A study becomes a headline.
A metric becomes a philosophy.
A useful idea becomes a rule.
The glycemic index isn’t wrong.
It’s simply answering a narrower question than many of us realize.
And once I understood that, those supposedly contradictory ideas stopped feeling contradictory at all.