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How To Use Continuous Glucose Monitoring to Improve Your Keto Performance


Many people get into ketosis with a very high-fat, low-carb diet. And by and large, this approach works. By keeping your carb intake to ~5-10%, you can be pretty sure that you’re minimizing excess glucose, keeping insulin low, and tapping into fat burning, ketone-generating pathways for energy.

But what if this “one-size-fits-all” low-carb dietary approach isn’t necessarily the best way to achieve a ketogenic state? What if you can actually eat more carbs, keep glucose low, and still get your ketone pathways churning?

This is where continuous glucose monitoring (CGM) may be poised to usher in the era of Keto 2.0. By tracking your glucose patterns 24-hours a day with a tiny wearable sensor, you can develop finely-tuned, data-driven, personalized diet plans, instead of taking a one-size-fits-all approach. In this article, written by the team over at Levels, you’ll learn about the world of continuous glucose monitoring and why you might want to consider it.

Continuous Glucose Monitoring For Keto

Recent research suggests that two different people eating the exact same amount and type of carbohydrates, can see drastically different glucose responses. In fact, carbohydrate content of a meal is only a modest predictor of post-meal glucose elevations.

That’s because the way that a carbohydrate in the gut translates into glucose in the blood is incredibly complex and highly person-specific.

It depends on many different factors including microbiome composition, genetics, recent physical activity and sleep quality, meal composition, and baseline metabolic health[*][*][*]. When you factor these in, the prediction of a glucose response to a meal can be much more accurate.

It’s not carbs, per se, that directly block the production of ketones. Rather, it is elevations in blood glucose and the resulting hormonal response (primarily involving insulin) that impairs the burning of fat required to produce ketones[*]. Considering this, simply limiting carbohydrates seems like an imprecise and unpersonalized approach, and one that may needlessly limit our food options while working towards ketosis.

It’s possible that if we rethink the idea of a “low-carb” diet and focus instead on a diet that “limits glucose elevations,” we’d see an evolution in the mindset for achieving and sustaining ketogenesis. What’s more, the diet that “limits glucose elevations” is going to look drastically different for each person.

Armed with this insight, you may be able to utilize CGM to push the envelope on what you include in your personal keto diet. Over time, consistent feedback from CGMs may let you refine your daily choices until you can maintain the low glucose levels that lend themselves to successful ketosis.

Avoiding Keto Setbacks: CGM Helps with the Guesswork

CGM works by measuring glucose in the interstitial fluids (fluid around cells) of the body. Instead of a finger stick to draw blood, CGM uses a small, disposable, painless sensor worn for 10-14 days, which transmits glucose information to a smartphone for real-time observation.

Your glucose level is the read-out of a complex set of inputs and variables including sleep, exercise, meals, stress levels, baseline metabolic health, and microbiome diversity.

With this complexity of factors, it can be hard to know exactly what’s driving your glucose levels. This is where advanced data analytics can be helpful. Levels has developed software that creates actionable insights from the noise.

How could this help us avoid dietary setbacks that could kick us out of ketosis? Some hypotheticals:

  • You may not have noticed that including tomatoes in your stir fry raises your glucose an extra 10 mg/dL compared to when you don’t.
  • Maybe you’ve missed that apples always seem to spike your glucose to above 100 mg/dL unless you pair them with a hefty serving of almond butter.
  • Perhaps it hasn’t been obvious that every time you get less than 6 hours of sleep, your fasting glucose is around 8 mg/dL higher than your average.

CGM gives you laser-focused visibility into a multitude of factors that may be involved in maintaining a ketogenic state. Combining a wearable sensor, real-time biofeedback, and software-driven insights can reveal how your daily choices affect your glucose levels.

Hypothetically, this could mean less guesswork, increased clarity, and more rapid progress in optimizing ketogenesis.

A few ways CGM can offer insight

  • CGM can show that certain foods—whether they’re officially keto-friendly or not— may not raise your blood sugar. Because these foods aren’t making glucose available, your body may be more likely to stay in ketosis. These realizations can potentially broaden the possibilities of what you can eat while still achieving ketogenesis.
  • CGM can help you avoid foods that raise your glucose levels. Some keto-friendly foods may not be friendly for you, and foods that are labeled “low sugar” or “low glycemic” can potentially send glucose through the roof.
  • With heightened interest in the keto diet, manufacturers are offering products that make big promises. Unfortunately, no matter how they’re labeled, these foods may spike blood sugar and impair ketosis. CGM can reveal these hidden “glucose bombs.”

Image: A Think! high protein bar, advertised as “low GI” and “0g sugar” sends one individual’s glucose through the roof (increase of +50 mg/dL in glucose in the 2 hrs after eating). 

Real world example of personalizing a keto diet

Levels co-founder, Casey Means, MD, follows a largely whole-foods plant-based diet and is a bean and legume fanatic: not your typical keto profile. Or is it?

By using CGM coupled with Levels insights for 6 months, she was able to identify what food combinations, exercise regimen, and sleep habits keep glucose low and flat, and support consistent mild nutritional ketosis.


Image: Casey Means, MD using Levels app to track real-time glucose response to meal. 

While a standard keto diet recommends avoiding beans and legumes, and allows some “low glycemic” fruits like strawberries or blueberries, these recommendations didn’t hold true for her. In fact, they were the opposite!

For Casey, strawberries could send her glucose well above 100 mg/dL, while a meal with a cup of kidney beans barely raised her glucose, and kept her ketone level at 1.0 mmol/L.

For her, daily beans and legumes are perfectly compatible with keto, something she learned from consistent CGM use supported by the Levels program. When personalized diet insights are presented on a silver-platter like this, life becomes a bit easier: all of a sudden, the struggle of having to make guesses on dietary and lifestyle choices disappears.


Image: Bean-rich dinner causing minimal glucose response (glucose response +7 mg/dL, to a peak of 81 mg/dL). 

Research has shown a variety of factors that can alter the extent of glucose fluctuations after a meal. An overview:

  • It’s well established that adding fat and protein to meals can blunt post-meal glucose elevations[*].
  • Drinking lots of water along with a meal can actually raise post-meal glucose elevations[*].
  • Vinegar and cinnamon added to meals can reduce post-meal glucose levels[*][*].
  • Meditation, quality sleep, many forms of exercise, meal timing, and various fasting regimens have all been associated with reduced post-meal glucose elevations and improved glycemic control[*][*][*][*][*].

The question becomes, what will keep glucose low for you? If the goal is to keep glucose and insulin levels low, how are you to make sense of all these variables? CGM allows for this self-experimentation and rapid prototyping of diet and lifestyle, and uses advanced data analytics to understand what’s driving your glucose levels.

No more one-size-fits-all keto?

In short, CGM coupled with powerful data analytics can help you create a diet that works with your keto lifestyle, without just relying on the methods that are tried and true but that can also be restrictive and polarizing.

Knowing that the connection between carbohydrate content and post-meal glucose levels isn’t always strong, and that there are plenty of other factors involved in our glycemic response to foods, it seems like the right time to utilize the new tools at our disposal to optimize our progress. CGM is one of these tools.

As we enter an exciting era of personalized nutrition, wearable devices enabling continuous dietary and lifestyle biofeedback, and increased access to digital health tools, CGM is poised to offer an upgrade to how we shape our daily choices and optimize our health.


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