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, particularly in the absence of carbs. Dairy products are notable: despite moderate carbohydrate content, whey and casein proteins are highly insulinogenic.[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 Susanne Holt, developed the insulin index — measuring insulin response directly rather than inferring it from blood sugar.[2] The results were surprising: some foods that barely budge blood sugar still trigger significant insulin release.
This matters because insulin is a key regulator of fat storage and release. Chronically elevated insulin promotes fat storage and prevents fat burning. 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 — it triggers a rapid, significant insulin spike despite minimal blood sugar impact. This is one reason whey protein is popular among bodybuilders: the insulin helps drive amino acids into muscles.
The dairy paradox. Dairy products consistently score higher on the insulin index than their carbohydrate content would predict. Milk, yogurt, and cheese all trigger more insulin than expected.
Several factors contribute:
Whey and casein proteins. Both dairy proteins are insulinogenic, with whey being particularly potent.
Lactose plus protein. The combination of dairy’s sugar (lactose) with its insulinogenic proteins creates a synergistic effect.
Incretin hormones. Dairy appears to stimulate GIP and GLP-1 — gut hormones that amplify insulin secretion.
This doesn’t make dairy universally bad, but it complicates the “low-carb” calculation. A cheese-heavy low-carb diet might be producing more insulin than expected.
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. Some research suggests certain sweeteners 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 — a learned response that misfires with artificial sweeteners.[3]
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. Carbs plus protein plus fat together tend to produce more moderate, sustained responses than any macronutrient in isolation.
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 et al., “An insulin index of foods: the insulin demand generated by 1000-kJ portions of common foods”[4] — 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”[5] — American Journal of Clinical Nutrition, 2004
- Pepino MY, “Metabolic effects of non-nutritive sweeteners”[6] — Physiology & Behavior, 2015
- The Obesity Code by Jason Fung, MD[7] — Chapters on insulin and weight regulation
Written by AI, directed and approved by me. How this is made →