Why Is My A1C Still High on Keto? Uncovering the Complex Truth Behind Glycemic Control
Hidden dietary, hormonal, and metabolic factors can undermine strict low-carb efforts.
Many people adopt the ketogenic diet with the goal of improving blood sugar management, especially in the context of type 1 or type 2 diabetes. While scientific reviews highlight that keto diets often reduce HbA1c (a marker of average blood glucose over 2–3 months) for many individuals, some still struggle with elevated A1C despite rigorous adherence. This article explores the reasons behind this phenomenon, delves into practical solutions, and provides a comprehensive view based on the latest research.
Table of Contents
- Understanding A1C: What Does It Measure?
- How Does the Keto Diet Affect Blood Sugar and A1C?
- Why Might Your A1C Stay High on Keto?
- How to Troubleshoot and Lower A1C on Keto
- Common Misconceptions and Pitfalls
- When to Seek Professional Help
- Frequently Asked Questions (FAQs)
Understanding A1C: What Does It Measure?
Hemoglobin A1C (HbA1c) is a laboratory measure that reflects average blood glucose levels over the past two to three months. An elevated A1C (>6.5%) typically indicates chronically high blood sugar and an increased risk of diabetes-related complications. Lowering A1C is associated with reduced risk of cardiac and microvascular complications.
- A1C is an average—not a real-time snapshot. Frequent spikes, even if rare, can keep your average high.
- Factors like red blood cell lifespan and certain medical conditions may impact the accuracy of A1C readings.
How Does the Keto Diet Affect Blood Sugar and A1C?
The primary mechanism of the ketogenic diet (high fat, moderate protein, very low carbohydrate) is to limit the amount of carbohydrate available for blood sugar spikes. In clinical studies, many people observe reductions in fasting glucose and A1C on keto. For instance, one meta-analysis reported average HbA1c reductions of 0.6% to 3.3% in people with diabetes on keto diets.
- Keto often improves glycemic control and reduces insulin needs, especially in type 2 diabetes.
- For type 1 diabetes, evidence is less robust; risk of hypoglycemia and diabetic ketoacidosis (DKA) requires close monitoring.
- Some report dramatic HbA1c improvements, while others see minimal change or persistent elevation.
Case Example
A patient with type 1 diabetes tried keto, closely monitored with a continuous glucose monitor (CGM), and achieved a sustained HbA1c in the normal range (5.5%), with drastically reduced insulin requirements. However, lipid issues arose due to diet composition.
Why Might Your A1C Stay High on Keto?
Despite documented A1C improvement for many, some individuals experience stubbornly high A1C on ketogenic diets. Below are common reasons, ranging from physiological to dietary and behavioral factors:
Poor Basal Insulin or Medication Adjustment (Type 1 and 2 Diabetes)
- Keto often prompts changes in how insulin or medications need to be administered. Inadequate adjustment can lead to hyperglycemia, especially if basal needs are underestimated.
- Self-directed weaning or reduction of medications without medical supervision can cause chronically high blood sugar.
Hidden Carbohydrates and Underreported Intake
- Even on keto, label inaccuracies, hidden sugars (in condiments, processed low-carb foods), and portion miscalculations can result in higher-than-expected carb intake, leading to persistent high blood glucose.
- Alcohol, sugar alcohols, and “net carbs” marketing can all contribute to actual carbohydrate intake being higher than assumed.
Gluconeogenesis from Excess Protein
- Consuming large amounts of protein—common in some keto plans—can increase gluconeogenesis, the process by which the liver converts protein to glucose. This might raise blood sugar and A1C for some people, despite low carb intake.
Physiological Insulin Resistance (Adaptive Response)
- Some individuals on long-term keto develop “physiological insulin resistance”—the body becomes less responsive to insulin in peripheral tissues to prioritize glucose delivery to the brain. This can cause mildly elevated fasting glucose and A1C, though overall insulin demand is reduced.
- Though traditionally considered benign in non-diabetics, in someone with diabetes, this can contribute to problematic glycemic patterns.
Stress, Illness, or Poor Sleep
- Stress hormones (cortisol, adrenaline), infections, and chronic sleep issues all increase blood glucose regardless of diet. Chronic inflammation and illness further blunt the effect of diet alone.
Medication Interactions or Incompatibility
- Certain diabetes medications, such as sodium-glucose cotransporter 2 (SGLT2) inhibitors, are not recommended on keto due to increased DKA risk. Medication mismatches or abrupt discontinuation can destabilize blood glucose.
Underlying Hormonal Disorders and Comorbidities
- Conditions such as thyroid dysfunction, Cushing’s syndrome, or polycystic ovarian syndrome (PCOS) can cause high A1C regardless of dietary carbohydrate intake.
Irregular Monitoring and Inadequate Data
- Without frequent blood glucose checks or CGM data, short-term spikes (post-meal or overnight) may go unnoticed but still elevate A1C.
Red Blood Cell Turnover and Laboratory Factors
- Certain conditions (anemia, hemoglobinopathies) and supplements affecting red cell lifespan alter A1C results regardless of glucose control.
How to Troubleshoot and Lower A1C on Keto
If you’re diligent with keto but your A1C remains above goals, consider the following systematic approach:
- Review carbohydrate intake—scrutinize food labels, weigh and measure portions, and consider keeping a detailed food log for several weeks.
- Check protein intake—aim for moderate, not excessive protein. Protein goals should be based on ideal body weight, activity, and medical needs.
- Test blood sugar more frequently—use a continuous glucose monitor (CGM) or perform structured testing, especially post-meal and overnight.
- Consult your healthcare provider on optimal insulin or oral medication adjustments. Never stop prescribed medication abruptly in hopes of further improving A1C.
- Evaluate stress, sleep, and non-diet factors—address sleep hygiene, stress management, and treat any underlying illnesses that may affect glucose control.
- Consider additional lab work for thyroid, adrenal, or other hormonal issues if progress stalls despite perfect effort.
- If using high saturated fat intake, consider shifting to more unsaturated fats to benefit both glycemia and lipid profiles.
Sample Troubleshooting Table
| Possible Cause | How to Identify | Action Steps |
|---|---|---|
| Hidden carbs in diet | Compare food log with actual measured portions, check ingredients | Read labels, use apps & scale, verify “net carbs” claims |
| Excessive protein | Track daily protein intake | Adjust to moderate levels (about 0.8-1.2g/kg ideal body weight) |
| Medication not optimized | Frequent highs despite good diet | Medical review for appropriate adjustments |
| Stress/Illness | Poor sleep, ongoing health issues | Address root causes with provider; improve sleep & stress management |
| Physiological insulin resistance | Elevated fasting sugars, but healthy overall | Monitor trends; sometimes no action is required |
Common Misconceptions and Pitfalls
- Keto is not always low calorie. Some may actually gain weight or plateau if energy intake remains high, reducing insulin sensitivity.
- Weight loss is not guaranteed. Especially if consuming excess fat and calories, weight loss—closely linked to improved A1C—may be blunted.
- Not all keto foods are equal. Processed “keto-friendly” snacks can still spike blood glucose due to hidden carbs and poor ingredient quality.
- Not everyone responds the same way. Genetics, hormonal health, existing insulin resistance, and other factors can make keto more or less effective for glycemic control across individuals.
When to Seek Professional Help
If repeated troubleshooting fails to yield A1C improvements despite good effort and monitoring, or if you experience symptoms of high blood sugar (thirst, frequent urination, fatigue) or hypoglycemia, it’s time to:
- Consult an endocrinologist or diabetes specialist knowledgeable about low-carb diets.
- Consider a referral to a registered dietitian specializing in diabetes/keto nutrition.
- Request advanced testing for secondary causes of dysglycemia or comorbid conditions.
Frequently Asked Questions (FAQs)
Q: Can my A1C go up even if my daily blood sugars look fine on keto?
A: Yes. Occasional high spikes (post-meal surges, overnight highs, or after missed medication) may not be reflected in point-in-time measurements but contribute disproportionately to A1C.
Q: Does being in ketosis guarantee better A1C results?
A: Not always. While ketosis signals low carbohydrate intake, excess protein, unrecognized stress or illness, and improper medication adjustment can all keep A1C high despite ketosis.
Q: How quickly should I expect A1C changes after starting keto?
A: A1C reflects the last 8–12 weeks of blood glucose, so significant changes may become apparent after 2–3 months of consistent diet and medication adherence.
Q: Is keto safe for all types of diabetes?
A: Greater caution is advised for those with type 1 diabetes due to risk of hypoglycemia and ketoacidosis if insulin therapy is not properly managed. Medical supervision is essential.
Q: Could a plant-based or Mediterranean diet work better for A1C control than strict keto?
A: Some studies suggest that for certain individuals, whole food plant-based or Mediterranean diets can provide similar or even better reductions in A1C by promoting weight loss and reducing inflammation, though both approaches can be effective.
Key Takeaways
- Stubbornly high A1C on keto is not uncommon and often reflects issues beyond carbohydrate intake alone.
- Systematic troubleshooting—diet analysis, medication review, glucose monitoring, and addressing lifestyle and medical issues—is essential for meaningful improvement.
- Success requires partnership with a knowledgeable healthcare team and a willingness to individualize approaches.
References
- https://www.ccjm.org/content/88/10/547
- https://pmc.ncbi.nlm.nih.gov/articles/PMC10786817/
- https://www.nature.com/articles/s41387-020-00142-z
- https://health.ucdavis.edu/nursing/news/Events/PDF/Other_presentations/A1c%20Levels%20A%20Comparison%20of%20Plant-Based%20vs.%20Ketogenic%20Diets%20in%20Type%202%20Diabetes.pdf
- https://med.stanford.edu/news/all-news/2022/070/keto-mediterranean-diet-diabetes.html
- https://pmc.ncbi.nlm.nih.gov/articles/PMC2690585/
- https://www.heart.org/en/news/2022/11/17/some-reduced-carb-diets-may-decrease-diabetes-risk-but-others-may-raise-it
- https://jamanetwork.com/journals/jamanetworkopen/fullarticle/2797714
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