05/16/2026
Did you know that blood sugar responses can be different from person to person? They can. In 2015, researchers at the Weizmann Institute studied 800 adults by connecting them to continuous glucose monitors. They then watched what their blood sugar did for a full week after they ate. Each participant ate the same standardized meal four times: 50 grams of carbohydrate from white bread. Identical portion. Identical timing of meals. But, what came back in the form of blood sugar curve data was not identical at all.
People react differently to high carb foods.
The average 2-hour glucose response across the cohort was 44 mg/dL·h. The bottom 10% of responders averaged under 15. The top 10% averaged over 79. Same bread. Same dose. same time of day. But some had more than a fivefold spread in how much their blood glucose rose.
Why?
More important, Zeevi and his colleagues weren't measuring fringe cases. The 800 participants were broadly representative of a Western adult population: 54% were overweight, 22% were obese, 24% with HbA1c in the prediabetic range. None had been diagnosed with type 2 diabetes, but the cohort wasn't strictly "healthy" in any rigorous sense. They were, well, normal.
But the different responses reflect what essentially is going on in the average person. Sure they reflect underlying differences in insulin sensitivity, beta cell function, and metabolic state, that would be expected, especially as the lean mass drops. But, not surprising, people with the higher body fat, higher HbA1c (inflammatory markers), and higher waking glucose tended to spike more.
Again, not surprising, the poorer the physical condition, the worse the response.
What was surprising to the researchers was that the variability extended into the people who had normal blood sugar too. That means that two different adults with the same fasting glucose, the same age, the same body composition can still produce post-bread curves that looked like they belonged to different studies.
Here's the not real surprising part. Most of the residual variation traced to microbiome composition, sleep duration the night before, physical activity around the meal, and what the person had eaten at the previous meal. Each was independently predictive after the standard clinical variables were accounted for.
That means there's a part that doesn't reflect on a nutrition label. The glycemic response of the individual! the index, normally assigned to white bread (around 71 in standard tables), comes from averaging responses across a small group of test subjects, but it's an average and clearly individual responses vary. So, the label tells you about the food, not about your reaction to it. A "high GI" food predicts a high response on average. But, it predicts nothing about your personal response.
A few things to note about this finding. It is not "Glycemic Index useless" it's just an average. For population-level diet research and food-labeling shorthand, it still works as a general guideline. Be assured, it is not telling us that carbohydrate foods and labels are necessarily deceptive. What it does tell still us is that carbohydrates are overall bad for inflammation, and they still remain the single strongest predictor of glucose response, in general. It just doesnt tell us the whole story, your personal response.
It also does not predict anything, other than tell us that the occasional spike in blood sugar is normal, but that repeated spikes still lead to inflammation, insulin resistance, leptin resistance and a higher risk of disease.
But, it does tell us that some foods are more damaging to some people than others. Those people usually have less sleep, lower lean mass, higher body fat and gut dysbiosis (leaky gut). But it still tells us that continuous spikes, day after day and year after year lead to glycation, oxidative damage, mitochondrial dysfunction, accelerated aging and increased risk of disease.
What can we do?
For most people, the most important thing you can do is to get a CGM or continuous glucose monitor. You can now buy a continuous glucose monitor without a prescription. Stelo (Dexcom), Lingo (Abbott), and Libre Rio (Abbott) are all available over the counter, run roughly $50 to $90 per sensor for two weeks of data, and need no clinical justification. Wear one for two to four weeks.
Eat the foods you normally eat. The patterns are usually obvious within a few days. The foods that consistently spike you are not necessarily the foods that spike anyone else, and they are not necessarily the ones with the worst labels. They are just foods you should avoid.
Keep in mind that the same person eating the same food on different days will likely produce somewhat different responses depending on their sleep, prior meal, hormone cycle, activity and athleticism. Within-person variability is very real, and Tom Wolever has argued, fairly, that part of what looks like between-person variability in studies like Zeevi's is actually day-to-day noise. But the fivefold spread Zeevi documented is too large to be explained by noise alone. The signal is real. The eater shapes the response as much as the food does.
The good news is that we finally have tools cheap enough to find out what our own metabolism actually does. We can use them on the foods we eat most often. The ones that show up over and over are the ones worth knowing about and eliminating. But don't just eliminate, fix. Fix your health, fix your resting glucose, fix your gut.
References:
Zeevi et al., Cell, 2015 (PMID 26590418)
Wolever, Eur J Clin Nutr, 2016 See less
