Why do some people tolerate carbohydrates better than others?
The Short Answer
Carbohydrate tolerance varies based on genetics, metabolic health, muscle mass, physical activity, gut microbiome, and insulin sensitivity. Some people process carbohydrates efficiently with minimal blood sugar and insulin spikes. Others spike dramatically from the same foods. The authors of one study suggest this variation is why universal diet advice may have limited use: your personal carbohydrate tolerance shapes how a given food affects you.
Something to Sit With
The person who eats bread without gaining weight isn’t more virtuous than you. They may simply process carbohydrates differently.
Your tolerance level is yours to discover, not to compare.
Learn More
The variation is real. Research using continuous glucose monitors has confirmed what many people intuit: the same carbohydrate-containing food produces very different responses in different people.
In the Weizmann Institute work, responses to identical meals showed high interpersonal variability, the paper’s own phrase, while staying highly reproducible within each person (R = 0.71 to 0.77 across repeated standardized meals).[1]
This isn’t about willpower or adherence.
Factors that affect tolerance. Several variables determine how well you handle carbohydrates:
Genetics: a smaller share than it feels like. Genes influence insulin production, insulin receptor sensitivity, glucose transporter activity, and metabolic enzyme function. But identical twins respond substantially differently to the same meal, and the share of variation traceable to known genetic variants is around 9%.[1] Which is why the section below is not wishful thinking.
Insulin sensitivity. How well your cells respond to insulin determines how much insulin is needed to clear glucose. Highly sensitive people need less insulin and process carbohydrates smoothly. Insulin-resistant people need more insulin and struggle more.
Muscle mass. Muscle tissue is a major sink for glucose. More muscle means more capacity to absorb blood sugar without elevated insulin. Athletic, muscular people often tolerate carbohydrates better.
Physical activity level. Exercise depletes glycogen stores and increases insulin sensitivity. An active person who just exercised handles carbohydrates very differently than a sedentary person.
Gut microbiome. The bacteria in your gut affect carbohydrate digestion and absorption. Microbiome features help predict glycemic response, though meal macronutrients explained more of the variance than the microbiome did: 15.4% against 6.0%.[1]
Current metabolic health. If you’ve accumulated visceral fat, your tolerance is likely lower. That months of low-carb eating restores it is the carbohydrate-insulin model’s claim rather than a measured result.
Age. Insulin sensitivity typically decreases with age, reducing carbohydrate tolerance.
Can tolerance change? Yes, significantly:
Improving tolerance:
- Losing visceral fat improves insulin sensitivity
- Building muscle increases glucose disposal capacity
- Regular exercise enhances carbohydrate handling
- Periods of low-carbohydrate eating are proposed to restore insulin sensitivity (the carbohydrate-insulin model’s claim)
- Fasting appears to improve metabolic flexibility
Worsening tolerance:
- On the carbohydrate-insulin model, chronic high-carbohydrate intake can lead to insulin resistance
- Weight gain, especially visceral fat, decreases sensitivity
- Sedentary lifestyle reduces metabolic flexibility
- Aging gradually decreases tolerance
Practical implications. Knowing that tolerance varies should inform your approach:
Don’t compare to others. What works for your friend may not work for you.
Experiment personally. Pay attention to how you feel after carbohydrate-heavy meals. Monitor blood sugar if possible.
Consider context. Your tolerance is said to vary: higher after exercise, lower when sedentary; higher when lean, lower when carrying excess fat.
Adjust over time. As your health improves, you may be able to reintroduce carbohydrates that once caused problems. Or you may discover that your baseline tolerance is simply lower than average.
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) — Individualized carbohydrate tolerance
- Reaven GM, “The insulin resistance syndrome: definition and dietary approaches to treatment”[5] — Annual Review of Nutrition, 2005
Written by AI, directed and approved by me. How this is made →