Why You’re Experiencing Carbohydrate Intolerance After Keto
Written by: Sarah Jayawardene, MS
Reviewed by: Emily J., MSc RD
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When carbohydrates are reintroduced after following a ketogenic (or any low-carb) diet, your body may struggle to process them properly. Understanding the physiological mechanisms behind these effects can help manage symptoms and make informed decisions about your diet.
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 .
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.
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 . 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 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. 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 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 . 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.
The good news is it won’t last forever. There is nothing inherently wrong with carbohydrate intolerance after following a keto diet—this is just your body’s transition period, as it adjusts to using carbs as the main fuel source again. 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).
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.
To reverse carbohydrate intolerance, it's important to add carbs back in slowly, starting with small servings and low-GI foods like fruits, vegetables, and whole grains. These foods have “good carbs,” which are higher in fiber, which can help prevent large blood sugar spikes.
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 .
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.
Sarah Jayawardene is a nutrition and health writer who focuses on metabolism and metabolic diseases. She has obtained a Bachelor’s degree in Biochemistry from Loyola Marymount University and a Master’s degree in Biochemical and Molecular Nutrition from Tufts University. Sarah is an avid baker, fiction reader, and dog mom.