Your body depends on carbohydrates for energy (in the form of glucose) — quite simply, you couldn’t survive without them. Still, there are plenty of reasons you might want to limit your carbohydrate intake, such as losing weight or feeling less fatigued after lunch.
However, low-carb diets like the ketogenic diet can temporarily disrupt the body's glucose and insulin response [1].
Carbohydrate intolerance, or a more sensitive response to eating carbs, can occur after following a ketogenic diet as your body becomes more efficient at using fat as a fuel source and less efficient at using carbohydrates. A low-carb diet like keto may cause temporary insulin resistance and carbohydrate sensitivity, but it does not necessarily make it "dangerous" or a reason to avoid it.
Your body on a keto or low-carb diet
The ketogenic diet, commonly known as "keto," is a low-carbohydrate, high-fat diet that switches your body’s main fuel source away from carbohydrates to mainly utilize fat [2].
When carbs are eliminated from the diet, the body enters a metabolic state called ketosis, where it burns stored fat for energy. This can lead to weight loss, improved insulin sensitivity, and other health benefits, but it also has some potential downsides.
Many people who try the ketogenic diet find it works best for their body and lifestyle and will continue the diet permanently. However, others like to switch back from keto once they achieve a specific weight or health goal.
What happens to glucose levels after transitioning out of keto
Those wearing a continuous glucose monitor might notice they’ve become extremely sensitive to carbs and experience a higher-than-normal glucose spike after transitioning back from keto —even if they only eat a small number of carbs. They may also feel very tired or experience digestive issues when they reintroduce the carbs they once enjoyed, and even regain a bit of weight due to higher insulin levels.
This phenomenon (known as carbohydrate intolerance) is a normal response when the body is adapting to these changes in diet. That’s because your metabolism is like a hybrid car that can use both gas and electric power for energy (i.e., fat and carbs). However, unlike hybrid cars, if you’ve been limiting your body to one source of energy (fat), it’ll take some time to gradually become efficient at using the other one (carbs) again.
Carbohydrate sensitivity or intolerance after keto: what it means
Carbohydrate sensitivity or intolerance is a condition where your body has difficulty properly metabolizing carbohydrates —which is also known as temporary insulin resistance.
Your body's cells temporarily become less responsive to the hormone insulin. Insulin regulates blood sugar levels by helping to transport glucose from the bloodstream into the cells, where it can be used as a source of energy [3]. When you have temporary insulin resistance, cells do not respond to insulin as well as they should, leading to elevated blood sugar levels.
Sensitivity to carbs can also result in a variety of symptoms, including abdominal pain, bloating, gas, diarrhea, constipation, and fatigue.
Slowly reintroducing carbs can help the process, starting with foods that have a low glycemic index. Over time, the temporary insulin resistance and carb sensitivity will subside.
If you’ve been on keto for a while (say, one year or longer), you may be wondering how long it will take your body to overcome your carb sensitivity. Right now, there isn't much available literature on long-term keto diets —many studies that follow "long-term keto" participants only last about 6 months.
For most people, however, it can take about 2 weeks to readjust to carbs (though this likely won't be as much of an issue if you've only done keto for a few days).
Key takeaways: how to add carbs back into your diet
When you want to add carbohydrates back into your diet after following keto, it’s important to allow your body to adjust over time. Remember that this is a slow transition (just like starting keto was!), so be patient and keep track of how you feel.
However, since the thing that people tend to miss in a low-carb/keto diet is fiber, you may experience a bit of gastrointestinal discomfort —which is why slowly reintroducing carbs (especially fiber) is key. This is also helpful for maintaining weight loss since fiber intake is associated with more successful weight loss [4].
To start, estimate the number of carbs you are eating in a day on keto and increase that by 25% every week until you hit the number of carbs you’d like to be eating on a regular basis. The key is to work your way up gradually —if you experience constipation, increased appetite (to the point of overeating), energy crashes, or other unusual symptoms, ease up on your carb intake. Mild bloating or fatigue may last a little longer but will dissipate as your body adjusts.
- Some other strategies that may be helpful in preventing spikes in blood sugar include:
Eat fiber (vegetables) and proteins/fats first, and carbs last. (This slows the absorption of glucose into your bloodstream.) - Drink a 10-ounce glass of water with a tablespoon of apple cider vinegar before or during your meal to reduce postprandial glucose spikes.
- Avoid eating carbs later in the evening, when your body is less sensitive to insulin. Incorporating post-meal walks into your daily routine (even just 2-15 minutes)..
- Exercising regularly (preferably both aerobic and resistance training) to improve insulin sensitivity and cardiometabolic health.
- Getting adequate sleep to live in alignment with your body clock. (One night of bad sleep can disrupt your body’s ability to regulate glucose.)
- Use a CGM to track your progress as you reintroduce carbs back into your diet and give you insights into your body’s intolerance to carbs.
