Carb Tolerance: A Beginner’s Guide

Curious how your body responds to carbohydrates? Then it’s time to understand your individual carb tolerance.

Knowing your carb tolerance helps you make smarter dietary choices. If you know white rice sends your blood sugar to the moon, you can avoid white rice whenever possible. 

But just because you can’t tolerate rice doesn’t mean all carbs are off the table. Different carbs affect different people in different ways. 

In this article, you’ll learn why carb tolerance matters, how to measure it, and how to improve it. Keep reading. 

What is Your Carb Tolerance?

Carb tolerance refers to your unique metabolic and digestive response to dietary carbohydrates. It’s not a medical term, but it’s a valuable concept. 

It’s useful, for starters, because it paints a picture of your metabolic health. For example, if your blood glucose stays above 140 two hours after eating, you’re in a higher risk category for type 2 diabetes.[*]

Carb tolerance is often synonymous with glucose tolerance. Glucose tolerance (which is a medical term) refers to how well your body manages blood sugar (blood glucose) levels.

Glucose tolerance is a crucial metric. Those with impaired glucose tolerance (like those with pre-diabetes and type 2 diabetes) are at higher risk for heart disease, certain cancers, and neurodegenerative diseases.[*][*][*] 

The Keto diet, by the way, is a promising therapy for glucose intolerance. Check out this article for more on that topic. 

But carb tolerance isn’t just about metabolic health. It’s also about digestive health. 

Many people struggle to digest carbs or components of carb-rich foods. These groups include:

• People with celiac disease or gluten sensitivity
• People with IBS
• People with food intolerances or sensitivities

What’s going on here? Those with chronic gut issues often have an overgrowth of unfriendly bacteria, and feeding this overgrowth with carbs (aka, bacteria fuel) can make things worse.

Measuring Your Carb Tolerance

To determine your carb tolerance, you’ll want to do some testing and tinkering. Start here:

OGTT

The OGTT (oral glucose tolerance test) is considered the gold standard for assessing your metabolic response to carbs. To perform the test, you drink a glucose solution and record your blood glucose levels in the hours that follow. 

Clinicians use OGTT results to quantify diabetes risk. Here’s how they stratify risk at 2 hours post-test:[*]

• Normal: under 140 mg/dl
• Prediabetes: between 140 mg/dl and 200 mg/dl
• Diabetes: over 200 mg/dl 

One last note. The WHO recommends consuming at least 150 grams of carbohydrates for three days preceding the OGTT, but some evidence suggests this is unnecessary.[*][*] 

Real-world glucose testing

The OGTT may be useful, but it has limited real-world applicability. Most of us don’t drink pure glucose. 

That’s where real-world testing comes in. To perform your own glucose test:

• Measure your blood sugar before you eat (the Keto-Mojo meter is a good option)
• Consume a carbohydrate-containing food or meal
• Measure your glucose at 1 hour and 2 hours after the meal

You can use the OGTT guidelines above to interpret your results, but keep in mind that optimal levels are likely lower than 140 mg/dl at 2 hours post-meal. After all, whole foods won’t spike your blood sugar like pure glucose will. 

Testing at your doctor’s office

Your primary care physician, endocrinologist, or weight loss doctor may order fasting insulin, fasting glucose, or a Hemoglobin A1c (HbA1c) test to assess your blood sugar during your office visit. These tests can also be quite helpful in determining your carbohydrate tolerance. A HbA1c of 5.7-6.4 indicates pre-diabetes, while an HbA1c of 6.5+ is diagnostic of type 2 diabetes. Elevated fasting insulin or fasting blood sugar levels can also be indicative of your level of carb tolerance.

Digestive tolerance

Your carb tolerance also depends on your ability to digest starch, sugar, and fiber. To decipher your digestive capabilities, some sleuthing may be required.

How do you know if a given food is causing digestive issues? Eliminate the food and see if the symptoms dissipate. Later, reintroduce the food and see if the symptoms return. 

You can eliminate foods individually or accelerate the process with an elimination diet. You might eliminate starch and sugar from your diet for one month, then reintroduce specific foods after the month is up. 

Pro tip: Keep a food journal to track your reactions to different foods. Without it, you may end up reliving your mistakes like Bill Murray in Groundhog Day. 

Other metrics

Beyond digestive symptoms and glucose tolerance, you might also track how carbs in your diet affect your:

• Sleep
• Mood
• Energy levels
• Focus, concentration, and motivation
• Bodyweight regulation
• Exercise performance
• Libido
• Monthly food bill

Remember, your diet influences every aspect of health. Taking this holistic view will serve you well. 

How to Improve Your Carb Tolerance

If your carb tolerance isn’t where you’d like it to be, consider these tips to improve it:

• Exercise. All types of exercise increase the ability of insulin (your blood sugar regulation hormone) to regulate glucose.[*] In other words, physical activity gives you a wider latitude to consume carbs and stay metabolically healthy.
• Sleep well. Getting seven to nine hours of restful sleep per night helps insulin do its job. If you aren’t sleeping well, your glucose regulation will likely suffer.[*] 
• Manage stress. Managing stress isn’t always easy, but it’s crucial for your metabolic health. Why? Because the “stress hormone” cortisol elevates blood sugar and decreases fat burning.[*] Ideas for stress relief include exercise, meditation, yoga, walking, counseling, listening to music, or seeking support from family and friends.
• Eat fiber-rich carbs. Consuming fiber along with starch and sugar blunts the blood sugar response.[*] Fruits and vegetables are your best options here. 
• Try different carbs. Monitor how different carbs—rice, sweet potatoes, apples, etc.—influence your blood sugar, digestion, and energy. You won’t know the results until you run the experiment. 
• Try eliminating carbs. A very low-carb ketogenic diet has been shown to improve glucose regulation in obese and diabetic populations.[*][*] Minimizing carbs may also help with weight loss, gut health, and mental acuity. Try Keto for a month and see how it goes. You can always go back to carbs later. 
• Fast intermittently. Intermittent fasting has similar metabolic effects to the Keto diet: it improves glucose regulation. Fasting also gives your gut time to heal, potentially increasing your tolerance to various foods. 

Knowing Your Carb Tolerance

It’s helpful to know your carb tolerance. It may help you make better dietary choices, improve your metabolic health, and feel better. 

If you know rice skyrockets your blood glucose, you probably won’t eat it. And if bananas make you gassy, why would you subject yourself (and others) to that unnecessary suffering?

This doesn’t mean you can’t improve your carb tolerance. Over time, you can enhance your metabolism and digestion of carb-rich foods. 

Give the above tips a shot and you’ll be in an excellent position to succeed. 

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