Why do different people have different insulin responses to the same food?
The Short Answer
Genetics, metabolic health, body composition, gut microbiome, and lifestyle factors all affect how blood sugar responds to food. One person’s glucose might rise modestly after bread while another’s rises sharply. The authors of one study suggest this is why universal dietary advice may have limited use. Your individual biology determines how foods affect you. The only way to know your response is to observe it, ideally through continuous glucose monitoring or structured self-experimentation.
Something to Sit With
Your body is not the same as anyone else’s. The diet that works for your friend might not work for you, not because you’re doing it wrong, but because you’re different people.
Knowing your own response is more valuable than following general rules.
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The spectrum of insulin response. When two people eat the same meal, their glucose responses can differ widely. Studies using continuous glucose monitors (which measure glucose, not insulin) have shown that:
- The same food can spike blood glucose (and, generally, the insulin that follows it) significantly in one person while barely affecting another
- Individual responses are consistent: if you spike from bread today, you’ll likely spike from bread tomorrow
- Responses to the same meal vary widely between people, the paper’s “high interpersonal variability”[1]
This means that glycemic index tables and general dietary advice are averages, useful starting points but not necessarily accurate for you.
Factors that influence response. Several variables affect how your body handles a given food:
Genetic variation: less of it than you would think. Genes influence insulin production, insulin sensitivity, glucose transporters, and enzyme activity. But identical twins show substantially different responses to the same meal, and while heritability estimates run near 30%, the share traceable to known genetic variants is closer to 9%. Most of what separates two people’s responses is modifiable.[1]
Insulin resistance. If you’ve developed insulin resistance (often alongside excess weight or a sedentary lifestyle; that long high-carbohydrate eating causes it is the carbohydrate-insulin model’s claim, which remains debated), your cells don’t respond well to insulin. The pancreas compensates by producing more, creating larger spikes.
Body composition. Muscle mass acts as a glucose sink. More muscle means more places for glucose to go, reducing the insulin needed to clear it.
Gut microbiome. The bacteria in your gut affect how food is digested and absorbed. Microbiome features help predict glycemic response, though in the larger of two such studies meal macronutrients explained more of the variance than the microbiome did: 15.4% against 6.0%.[1]
Sleep and stress. Poor sleep and high cortisol can reduce insulin sensitivity acutely. The same meal after a bad night’s sleep may spike you more than usual.
Meal timing and order. Eating fiber before carbohydrates, or protein and fat with carbohydrates, can blunt the glucose and insulin response.
Physical activity. Exercise depletes glycogen and increases insulin sensitivity. A meal after a workout often produces a smaller spike than the same meal eaten sedentary.
The research. A landmark 2015 study from the Weizmann Institute of Science measured glucose responses across 46,898 meals in 800 people.[1] The paper’s own phrase for what it found is high interpersonal variability, and responses were highly reproducible within each person (R = 0.71 to 0.77 across repeated standardized meals).
The researchers were able to build personalized prediction models based on individual factors. Their reading is that universal dietary recommendations “may have limited utility.”[1]
Practical implications. This doesn’t mean general guidelines are useless. Reducing processed carbohydrates and sugar helps many people. But it means:
Self-observation matters. Pay attention to how you feel after eating certain foods. Energy crashes, mental fog, and rapid return of hunger may suggest your body didn’t handle that food well.
Experiment systematically. If you want to know your specific responses, try a continuous glucose monitor for a few weeks. It can quickly show how your glucose responds to particular foods.
Personalize your approach. What works for someone else may not work for you, and vice versa. Trust your data over general advice.
Further reading:
- Zeevi D et al., “Personalized nutrition by prediction of glycemic responses”[2] — Cell, 2015
- Berry SE et al., “Human postprandial responses to food and potential for precision nutrition”[3] — Nature Medicine, 2020
- Segal E, Elinav E & Adamson E, The Personalized Diet[4] (2017) — Book based on the Weizmann research
- Ludwig DS, “The glycemic index: physiological mechanisms relating to obesity, diabetes, and cardiovascular disease”[5] — JAMA, 2002
Written by AI, directed and approved by me. How this is made →