Why do some low-carb foods still spike insulin significantly?
The Short Answer
Insulin responds to more than just carbohydrates. Protein also triggers insulin release, and more of it alongside carbohydrate. Dairy products are notable: milk proteins drive insulin, whey above all.[1] Certain artificial sweeteners may trigger insulin responses through taste receptors or gut hormone effects. The glycemic index tells part of the story; the insulin index tells more.
Something to Sit With
If you’ve been focused only on carbs, you’re seeing half the picture. Protein and other factors also affect insulin. This doesn’t mean protein is bad; it means the body’s response to food is more complex than any single number captures.
What matters is the overall pattern, not any one variable.
Learn More
Beyond the glycemic index. The glycemic index measures how much a food raises blood sugar. For decades, this was considered the key metric for understanding metabolic impact. But blood sugar and insulin don’t always move in lockstep.
Researchers at the University of Sydney, led by Susanna Holt, developed the insulin index, measuring insulin response directly rather than inferring it from blood sugar.[2] Protein-rich foods and bakery products drew insulin responses disproportionately higher than their blood-sugar responses.[2]
This matters because insulin regulates fat storage and release. One influential account, the carbohydrate-insulin model, holds that chronically elevated insulin tips that balance toward storage and away from burning. The underlying physiology isn’t disputed; whether it explains weight gain in humans is, and the evidence there is still called inconclusive.[3] Either way, understanding what drives insulin, beyond just carbs, gives a more complete picture.
Protein and insulin. Protein triggers insulin release, sometimes substantially. This seems counterintuitive: why would a macronutrient that doesn’t raise blood sugar require insulin?
The answer involves multiple pathways. Amino acids from protein digestion stimulate insulin secretion directly, independent of glucose. This insulin helps shuttle amino acids into muscle tissue for protein synthesis. Additionally, protein stimulates glucagon, which raises blood sugar slightly, and insulin rises to counteract it.
The insulin response to protein varies by source. Whey protein, in particular, is highly insulinogenic: in one study it brought a 90% higher insulin area than a bread reference despite a 57% lower glucose area.[1]
The dairy paradox. Milk products produce high insulin responses despite their low glycemic index. A study of milk and other food proteins concluded that milk proteins are insulinotropic, the whey fraction most of all.[2]
Several factors are proposed:
Milk proteins. The insulin response tracked early rises in the amino acids leucine, valine, lysine, and isoleucine.[1]
Carbohydrate plus protein. Protein given with glucose drew more insulin than the two apart;[1] that milk’s own sugar, lactose, does the same is an extension, not a finding.
Incretin hormones. Whey’s insulin response came with a 54% rise in GIP, a gut hormone that amplifies insulin secretion.[1]
This doesn’t make dairy universally bad, but it complicates the “low-carb” calculation. A dairy-heavy low-carb diet may still be producing significant insulin.[1]
Artificial sweeteners. Some artificial sweeteners may affect insulin despite having zero calories and no impact on blood sugar. The mechanisms are debated:
Taste receptor activation. Sweet taste receptors exist throughout the digestive system, not just the tongue. Activating them may trigger preparatory metabolic responses, including insulin.
Gut microbiome effects. Certain sweeteners are said to alter gut bacteria in ways that affect glucose metabolism.
Cephalic phase response. The taste of sweetness may trigger insulin release in anticipation of incoming sugar. That this learned response misfires with artificial sweeteners is Swithers’ account, the proposal her review is built to advance rather than an established mechanism.[4]
The evidence is mixed and varies by sweetener. But the assumption that zero-calorie means zero-metabolic-impact may be incomplete.
Practical implications. This doesn’t mean abandoning low-carb approaches or avoiding protein. It means understanding that insulin response is multifactorial:
Consider overall insulin load, not just carbs. Very high protein intake, especially from dairy and whey, contributes to insulin exposure.
Pay attention to food combinations. Protein eaten with carbohydrate drew more insulin than either alone, and that extra insulin blunted the glucose rise.[1]
Don’t overcomplicate. For most people, focusing on whole foods, reducing processed carbohydrates, and eating adequate protein remains sound advice. The insulin index adds nuance, not a complete revision.
Further reading:
- Holt SH, Miller JC & Petocz P, “An insulin index of foods: the insulin demand generated by 1000-kJ portions of common foods”[5] — American Journal of Clinical Nutrition, 1997
- Nilsson M et al., “Glycemia and insulinemia in healthy subjects after lactose-equivalent meals of milk and other food proteins: the role of plasma amino acids and incretins”[6] — American Journal of Clinical Nutrition, 2004
- Pepino MY, “Metabolic effects of non-nutritive sweeteners”[7] — Physiology & Behavior, 2015
- Fung J, The Obesity Code[8] (2016) — Chapters on insulin and weight regulation
Written by AI, directed and approved by me. How this is made →