Why Fasting Insulin Beats HbA1c for Early Warning

The ketogenic diet works by lowering insulin levels, but most people only track HbA1c. The problem is HbA1c shows damage that’s already happened. Fasting insulin reveals metabolic dysfunction years earlier – when you can still act.

How Insulin Resistance Develops

Insulin resistance begins when cells stop responding efficiently to insulin’s signal. The pancreas compensates by producing more insulin. This hyperinsulinemia can persist for a decade before blood glucose rises enough to show on an HbA1c test. Studies show fasting insulin predicts metabolic syndrome markers better than HbA1c (Volek et al., 2008).

The HbA1c Blind Spot

HbA1c measures average blood glucose over 2-3 months. It’s excellent for diagnosing diabetes but misses early warning signs. Someone can have normal HbA1c (<5.7%) but dangerously high insulin levels. By the time HbA1c crosses 6.5%, beta cell function may already be compromised.

What This Means in Practice

Private labs like Medichecks offer fasting insulin tests for £29. Tesco sells blood glucose monitors for £9. While NHS guidelines focus on HbA1c, proactive individuals can track both. Seasonal weight gain around Christmas often reveals insulin spikes before January HbA1c tests catch up.

Interpreting Your Numbers

Optimal fasting insulin is under 5 μU/mL. Levels above 10 indicate significant resistance. Each 5 μU/mL increase correlates with higher cardiovascular risk (Kosinski & Jornayvaz, 2017). Pair this with keto electrolyte tracking to address root causes.

Frequently Asked Questions

Can I get a fasting insulin test on the NHS?

The NHS rarely orders fasting insulin tests unless investigating specific conditions like PCOS. Most people pay privately through services like Medichecks or Blue Horizon.

How often should I test fasting insulin?

Every 3-6 months provides useful data. Test more frequently when making dietary changes to monitor response.

Does keto lower insulin levels?

Yes. Carbohydrate restriction reduces insulin demand more effectively than calorie restriction alone (Hyde et al., 2019).

The Bottom Line

Fasting insulin provides a 5-10 year head start on preventing metabolic damage compared to HbA1c. While HbA1c remains important for diabetes diagnosis, insulin levels reveal dysfunction while it’s still reversible. If you’d rather not do the macro maths yourself, the Keto Dieting app does it for you on Google Play and the App Store.

Educational only — not medical advice. This article is for general information. Speak to your GP before changing your diet, especially if you have type 1 or type 2 diabetes, kidney or liver disease, are pregnant or breastfeeding, or take medication for blood pressure, cholesterol, or blood glucose.

References

Volek JS, Phinney SD, Forsythe CE, et al. (2008). Carbohydrate restriction has a more favorable impact on the metabolic syndrome than a low fat diet. Lipids. https://doi.org/10.1007/s11745-008-3274-2
Kosinski C, Jornayvaz FR (2017). Effects of Ketogenic Diets on Cardiovascular Risk Factors: Evidence from Animal and Human Studies. Nutrients. https://doi.org/10.3390/nu9050517
Hyde PN, Sapper TN, Crabtree CD, et al. (2019). Dietary carbohydrate restriction improves metabolic syndrome independent of weight loss. JCI Insight. https://doi.org/10.1172/jci.insight.128308