Why is my blood sugar still high on a low-carb diet?

November 17, 2025 •

4 min read

According to the American Diabetes Association, stress and poor sleep are well-documented factors that can significantly raise blood sugar levels. Many individuals on low-carb or ketogenic diets are surprised and frustrated when their glucose levels remain elevated, defying the expected results. The answer often lies in understanding the body's complex metabolic and hormonal responses beyond just carbohydrate restriction.

Quick Summary

This article explores the less obvious factors contributing to elevated blood sugar levels while on a low-carb diet. It details the impact of stress hormones like cortisol, the physiological phenomenon of 'glucose sparing,' and the presence of hidden carbohydrates. Readers will learn how other elements, such as sleep, protein intake, and specific medications, can influence glycemic control, and how to identify and address these issues effectively.

Key Points

Dawn Phenomenon: Waking up with high blood sugar is often due to natural hormonal shifts (cortisol, adrenaline) that signal the liver to release glucose overnight.
Adaptive Glucose Sparing: Long-term, strict low-carb dieting can lead to 'physiologic insulin resistance,' where muscles preferentially use fat, leaving glucose in the bloodstream.
Stress and Cortisol: Mental and physical stress elevate the hormone cortisol, which prompts the liver to produce glucose, spiking blood sugar even without carb intake.
Hidden Carbohydrates: Processed 'low-carb' products can contain hidden sugars, starches, or sweeteners that cause unexpected glucose spikes.
Protein Overload: Excess protein in a low-carb diet can be converted into glucose by the liver via gluconeogenesis, leading to a delayed rise in blood sugar.
Poor Sleep Quality: Inadequate sleep increases cortisol and worsens insulin sensitivity, directly contributing to higher blood glucose levels.
Medication and Hydration: Certain medications can raise blood sugar, while dehydration increases glucose concentration in the blood, leading to a higher reading.

Unexpected Reasons Your Blood Sugar Won't Go Down

When you commit to a low-carb lifestyle, you expect your blood sugar to stabilize. For many, this is precisely what happens, with glucose levels remaining steady and within a healthy range. However, a significant number of people, even those strictly limiting carbs, experience persistent and frustratingly high blood sugar readings. This counterintuitive outcome can be baffling, but it is often rooted in several key physiological adaptations and lifestyle factors.

The Dawn Phenomenon and Hormonal Shifts

One of the most common culprits for high morning blood sugar is the 'Dawn Phenomenon'. This is a completely natural process in which the body prepares for the day by releasing hormones, including cortisol, adrenaline, and growth hormone, usually between 3 and 8 a.m.. These hormones signal the liver to produce and release more glucose to provide energy for waking up. In people with insulin resistance or diabetes, the body may not produce enough insulin to counteract this hormonal surge, leading to an elevated fasting blood sugar reading.

Physiologic Insulin Resistance

If you adhere to a very strict, long-term low-carb or ketogenic diet, your body becomes highly efficient at burning fat for fuel. This metabolic adaptation, sometimes called 'adaptive glucose sparing' or 'physiologic insulin resistance,' means that your muscles begin to preferentially use fatty acids instead of glucose. While this is a hallmark of fat adaptation, it also means your muscles 'resist' taking up glucose from the bloodstream, causing it to circulate at a slightly higher level than a person with a different metabolic profile.

The Role of Stress, Sleep, and Hidden Carbs

Stress, both physical and emotional, significantly impacts blood sugar levels. High cortisol from stress signals the liver to produce more glucose, causing a spike even with minimal carb intake. Chronic stress exacerbates insulin resistance over time. Similarly, a lack of quality sleep can impair insulin sensitivity, increasing cortisol and blood sugar.

Lists of common culprits:

Hidden Carbohydrates: Many processed foods labeled 'low-carb' or 'sugar-free' contain starches, thickeners, or artificial sweeteners that can cause a glucose response.
Excess Protein: While essential, consuming very large amounts of protein in a low-carb state can lead to elevated glucose through gluconeogenesis, where the liver converts excess protein into sugar.
Certain Medications: Some drugs, such as steroids, decongestants, and certain blood pressure or antipsychotic medications, can raise blood sugar levels by affecting insulin sensitivity or production.
Dehydration: When you are dehydrated, the concentration of glucose in your blood rises, leading to an elevated reading.

Gluconeogenesis and Protein Intake

The body's ability to create its own glucose from non-carbohydrate sources, primarily protein, is known as gluconeogenesis. In a carb-restricted state, this process can increase. If you are eating a lot of protein—especially at one sitting—the liver may convert some of the excess protein into glucose, resulting in a measurable rise in blood sugar. While protein is important for satiety and muscle maintenance, it's a balancing act to find the right amount for your body.

The Importance of Exercise and Nutrient Pairing

Physical activity is a powerful tool for blood sugar management because it helps increase insulin sensitivity. Regular exercise encourages your muscles to use glucose more efficiently for energy. If you are sedentary, this benefit is lost, and your body is less equipped to handle glucose, even if carbs are scarce. Additionally, pairing carbohydrates with fiber, fat, and protein can help moderate blood sugar spikes. Even on a low-carb diet, the specific foods you choose and how you combine them can make a difference.

Low-Carb High Blood Sugar: Addressing the Underlying Causes

To address persistent high blood sugar, it's necessary to look beyond simple carb restriction and identify the specific issue. Using a continuous glucose monitor (CGM) or regular blood sugar testing can help identify patterns related to meals, sleep, or stress. Adjusting your protein intake, focusing on high-fiber vegetables, and incorporating stress-management techniques are also beneficial.


Potential Cause	What to Investigate	Possible Solution	Effect on Blood Sugar
Dawn Phenomenon	Elevated fasting glucose (3-8 a.m.)	Consider avoiding carbs at bedtime; consult doctor on medication or insulin timing.	Highest in the morning, then stabilizes.
Physiologic Adaptation	Consistently strict low-carb/keto for months	Monitor other health markers (HbA1c, fasting insulin); test blood ketones.	Slightly elevated but stable readings.
Hidden Carbs/Sweeteners	Spikes after eating 'keto-friendly' products	Read labels carefully; test glucose after new foods.	Unexpected spikes after specific foods.
Stress/Poor Sleep	High readings during stressful periods or after sleepless nights	Prioritize sleep hygiene; practice mindfulness and relaxation.	Increased variability and higher baseline.
Excess Protein	Rise in glucose a few hours after a large protein meal	Moderate protein portions, especially at one time; balance macros.	Delayed and gradual rise after meals.
Dehydration	Testing after low fluid intake	Increase water consumption throughout the day.	High concentration reading.

Conclusion

Persistent high blood sugar on a low-carb diet can be confusing, but it is not necessarily a sign of failure. The body is a complex system, and factors like physiological adaptation, hormonal fluctuations, stress, sleep, and even hidden ingredients in food can all play a significant role. By understanding these mechanisms—such as the Dawn Phenomenon, adaptive glucose sparing, and the effects of cortisol—you can take a more targeted and holistic approach. Instead of focusing solely on carbs, consider your full lifestyle picture, including sleep, stress management, hydration, and exercise. Always consult with a healthcare provider before making significant changes to your diet or medication regimen, especially if you have diabetes. Addressing these underlying issues will not only help normalize your blood sugar but also contribute to overall better health and well-being. For more information, visit the American Diabetes Association to learn about comprehensive diabetes management.

Frequently Asked Questions

The Dawn Phenomenon is a natural rise in blood sugar that occurs in the early morning hours (3-8 a.m.) due to the release of hormones like cortisol and growth hormone. These hormones trigger the liver to produce glucose to prepare the body for waking, but in individuals with insulin resistance, blood sugar can rise to an elevated level.

Yes, stress can significantly increase your blood sugar. When stressed, your body releases cortisol, a hormone that signals the liver to produce more glucose for a 'fight or flight' response. This can raise blood glucose even when you're not consuming carbohydrates.

On a low-carb diet, your body can convert excess protein into glucose through a process called gluconeogenesis. Consuming very large amounts of protein, particularly in a single meal, can lead to a delayed but significant rise in blood sugar.

Hidden carbs can be found in many processed foods labeled 'keto-friendly' or 'sugar-free,' such as certain sauces, dressings, marinades, and snack bars. Some artificial sweeteners and added fillers can also cause a glucose response.

Poor sleep or sleep deprivation can decrease insulin sensitivity and raise levels of the stress hormone cortisol. Both of these effects make it harder for your body to regulate blood sugar, leading to higher glucose readings.

Physiologic insulin resistance is an adaptation that occurs on very low-carb diets, where muscles become 'fat-adapted' and preferentially use fat for fuel, sparing glucose for the brain and other essential organs. It is distinct from pathological insulin resistance and is not necessarily a bad thing, but it does cause slightly higher fasting glucose readings.

Besides diet, your blood sugar can be affected by factors such as stress, sleep quality, physical activity level, hydration, certain medications (including steroids), and underlying health conditions.