Why Is My Body Not Digesting Carbs? Understanding Intolerances and Malabsorption

According to NIH data, lactose malabsorption, a common type of carbohydrate intolerance, affects a significant portion of the worldwide population. If you find yourself asking, 'Why is my body not digesting carbs?', you may be experiencing symptoms of an undiagnosed intolerance or another digestive issue.

Quick Summary

Carbohydrate malabsorption can stem from enzyme deficiencies, intestinal damage, or FODMAP sensitivities, leading to uncomfortable digestive symptoms like bloating, gas, and diarrhea.

Key Points

• Enzyme Deficiencies: Lack of key digestive enzymes like lactase or sucrase is a primary reason for carbohydrate malabsorption, leading to symptoms like bloating and diarrhea.

• FODMAPs: High intake of Fermentable Oligosaccharides, Disaccharides, Monosaccharides, and Polyols (FODMAPs) can cause issues if not well absorbed, contributing to gas and abdominal discomfort.

• Underlying Conditions: Inflammatory bowel diseases (like Crohn's) and Small Intestinal Bacterial Overgrowth (SIBO) can damage the small intestine, impairing its ability to absorb carbohydrates.

• Diagnosis is Key: Using methods like hydrogen breath tests or an elimination diet is crucial for identifying the specific carbohydrates causing your symptoms.

• Dietary Management: Adjusting your diet to limit or avoid problematic carbohydrates is the main treatment for intolerance, sometimes supplemented with enzyme replacements.

• Symptom Recognition: Unabsorbed carbs in the colon ferment and produce gas, resulting in bloating, gas, abdominal pain, and often watery diarrhea.

The Journey of Carbohydrate Digestion

To understand why your body might not be digesting carbohydrates, it's essential to first know how proper digestion works. Digestion of carbohydrates begins in the mouth, where salivary amylase starts breaking down starches. The food then travels to the stomach, where this enzyme is inactivated by stomach acid. Most carbohydrate digestion occurs in the small intestine. Here, the pancreas releases pancreatic amylase to continue breaking down starches. Enzymes in the brush border of the small intestine, such as lactase, sucrase, and maltase, then split disaccharides (complex sugars) into monosaccharides (simple sugars). These simple sugars—glucose, fructose, and galactose—are absorbed into the bloodstream. Any undigested carbs, like fiber, pass into the large intestine, where gut bacteria ferment them.

Common Causes of Carbohydrate Malabsorption

Several factors can disrupt this process, causing carbohydrates to be incompletely digested or absorbed. This leads to common and uncomfortable symptoms as the undigested sugars travel to the large intestine and are fermented by gut bacteria.

Enzyme Deficiencies

• Lactase Deficiency (Lactose Intolerance): This is the most common form of carbohydrate malabsorption, resulting from a reduction or absence of the lactase enzyme that digests lactose, the sugar found in milk. Symptoms appear after consuming dairy products and can range from mild to severe, depending on the individual's lactase activity.
• Congenital Sucrase-Isomaltase Deficiency (CSID): A rarer genetic disorder where there is a lack of sucrase-isomaltase, the enzyme needed to digest sucrose and starch. Symptoms, including chronic diarrhea and poor weight gain, typically start in infancy when an infant is weaned and introduced to starchy foods.

Intestinal Damage and Other Conditions

• Small Intestinal Bacterial Overgrowth (SIBO): This condition occurs when there is an abnormal increase in the bacterial population of the small intestine. These bacteria ferment carbohydrates too early, causing excess gas production, bloating, and diarrhea. SIBO can be a secondary result of other conditions, such as irritable bowel syndrome (IBS) or intestinal surgery.
• Intestinal Diseases: Conditions that cause inflammation or damage to the small intestinal lining can impair its ability to absorb nutrients, including carbohydrates. Examples include:
  • Celiac disease: An autoimmune disorder where gluten ingestion damages the small intestine.
  • Crohn's disease: An inflammatory bowel disease that can affect any part of the digestive tract.
• Fructose Malabsorption: This condition arises when the intestinal lining has a limited capacity to absorb fructose, a sugar found in fruits, vegetables, and many sweetened products. When the intake exceeds the absorption capacity, symptoms like bloating, gas, and diarrhea can occur.

Symptoms of Poor Carb Digestion

When carbohydrates are not properly digested, they move to the large intestine where they are fermented by bacteria, causing a range of gastrointestinal symptoms.

• Bloating and Abdominal Distention: A feeling of fullness and visible swelling of the abdomen due to gas buildup from bacterial fermentation.
• Gas and Flatulence: The fermentation process produces gases like hydrogen and methane, leading to excessive flatulence.
• Diarrhea: Unabsorbed sugars create an osmotic load in the intestines, drawing in water and resulting in watery stool.
• Abdominal Pain and Cramping: The stretching of the intestines from gas and the increased movement caused by diarrhea can lead to pain.
• Fatigue and Brain Fog: Can occur due to poor nutrient absorption and the general distress on the body.
• Weight Loss or Malnutrition: In more severe, chronic cases, the inability to properly absorb nutrients can lead to malnutrition and weight loss.

How Is Carb Intolerance Diagnosed?

A medical professional can use several methods to diagnose carbohydrate malabsorption. The first step typically involves a detailed medical history and dietary assessment.

1. Elimination Diet: A patient may be asked to remove the suspected carbohydrate from their diet for a period and then reintroduce it to see if symptoms return. This can help pinpoint the specific trigger.
2. Hydrogen Breath Test: This non-invasive test is commonly used to detect specific sugar intolerances, like lactose or fructose malabsorption. The patient drinks a solution containing the specific carbohydrate, and the hydrogen content of their breath is measured over several hours. An increase in breath hydrogen indicates bacterial fermentation of the unabsorbed sugar.
3. Endoscopic Biopsy with Enzyme Measurement: Considered the gold standard for diagnosing primary disaccharidase deficiencies like CSID, but it is invasive and less common.

Managing Carb Intolerance Through Diet

Managing carbohydrate malabsorption primarily involves dietary adjustments. While a doctor's guidance is crucial, especially for persistent issues, here are some general strategies.

Comparison of Carb Intolerance Management

Condition	Cause	Dietary Strategy	Other Management	Potential Complications
Lactose Intolerance	Reduced lactase enzyme	Avoid or limit milk, yogurt, and soft cheeses; choose lactose-free products or hard cheeses	Use lactase enzyme supplements (e.g., Lactaid) with meals	Calcium and Vitamin D deficiency if dairy is completely removed
Fructose Malabsorption	Limited fructose absorption capacity	Reduce intake of high-fructose foods; be mindful of high-fructose corn syrup	Balance fructose intake with equal or greater amounts of glucose; avoid sorbitol	Can be worsened by sorbitol, another carbohydrate
SIBO	Bacterial overgrowth in small intestine	Low-FODMAP diet to reduce fermentable carbs; may require long-term dietary control	Targeted antibiotics to reduce bacterial load; probiotics may help rebalance gut flora	Recurrence of symptoms is common if underlying cause isn't addressed

Other Strategies to Aid Digestion

• Increase Fiber Intake (Mindfully): While undigested fiber contributes to gas, soluble fiber helps regulate digestion and feeds beneficial gut bacteria. A diet high in fruits and vegetables, which also contain fiber, is recommended to support a healthy gut microbiome. However, individuals with severe intolerance may need to get fiber from lower FODMAP sources initially.
• Embrace Mindful Eating: Eating slowly and chewing food thoroughly breaks down carbohydrates mechanically, reducing the load on your digestive enzymes.
• Combine Macronutrients: Pairing carbohydrates with protein and healthy fats can slow down the overall digestion process, preventing rapid blood sugar spikes and easing digestive symptoms. For example, pairing fruit with nuts or yogurt.

Conclusion

Understanding why your body is not digesting carbs? is the first step toward finding relief from uncomfortable digestive symptoms. Common causes range from specific enzyme deficiencies like lactose intolerance to broader issues like intestinal damage or bacterial overgrowth. Identifying the root cause through medical diagnosis, often involving a breath test or elimination diet, allows for targeted dietary changes. While some individuals can manage their symptoms by reducing intake of specific sugars or fermentable carbohydrates (FODMAPs), others may require enzyme supplements or treatment for an underlying condition. For comprehensive nutritional guidance, consulting a Registered Dietitian is highly recommended.

Sources

• Diagnosing and Treating Intolerance to Carbohydrates in Children, National Institutes of Health (NIH), https://pmc.ncbi.nlm.nih.gov/articles/PMC4808885/
• What is Carbohydrate Malabsorption?, Nicklaus Children's Hospital, https://www.nicklauschildrens.org/conditions/carbohydrate-malabsorption
• Malabsorption Syndrome: Causes, Symptoms, and Risk Factors, Healthline, https://www.healthline.com/health/malabsorption
• Carbohydrate Intolerance, MSD Manuals, https://www.msdmanuals.com/professional/gastrointestinal-disorders/malabsorption-syndromes/carbohydrate-intolerance
• Digestion and Absorption of Carbohydrates, Pressbooks.pub, https://openoregon.pressbooks.pub/nutritionscience/chapter/4c-digestion-absorption-carbohydrates/
• Carbohydrate Intolerance and Disaccharidase Measurement, National Institutes of Health (NIH), https://pmc.ncbi.nlm.nih.gov/articles/PMC6892707/
• Carbohydrate Intolerance: Symptoms to Look for and Ways to Combat, F45training.kr, https://f45training.kr/article/carbohydrate-intolerance-symptoms-to-look-for-and-ways-to-combat/
• Carbohydrate malabsorption in patients with non-specific abdominal complaints, National Institutes of Health (NIH), https://pmc.ncbi.nlm.nih.gov/articles/PMC4171253/
• Malabsorption Syndrome: Causes, Symptoms, Diagnosis, Treatment, WebMD, https://www.webmd.com/digestive-disorders/malabsorption-syndrome
• What is Carbohydrate Intolerance?, Gutivate, https://gutivate.com/blog/what-is-carbohydrate-intolerance

Frequently Asked Questions

What is the most common cause of poor carbohydrate digestion?

The most common cause is lactase deficiency, or lactose intolerance, which is the body's reduced ability to digest lactose, the sugar found in milk and dairy products.

Can intestinal diseases cause carb digestion problems?

Yes, conditions that damage the intestinal lining, such as celiac disease and Crohn's disease, can significantly impair the small intestine's ability to properly absorb carbohydrates.

What are FODMAPs and how are they related to carb digestion?

FODMAPs are types of short-chain carbohydrates that can be poorly absorbed in the small intestine. When they reach the large intestine, they are fermented by bacteria, causing gas, bloating, and other digestive issues.

How is lactose intolerance diagnosed?

Lactose intolerance can be diagnosed with a clinical history, a trial of a lactose-free diet, and often confirmed with a non-invasive hydrogen breath test after consuming a lactose solution.

What can I do to improve my carb digestion?

Management strategies include keeping a food diary to identify trigger foods, reducing intake of processed sugars, eating more fiber, and pairing carbs with protein and fat to slow digestion. A registered dietitian can provide a personalized plan.

Can I use enzyme supplements to help with carb digestion?

Yes, for specific intolerances like lactose, over-the-counter lactase enzyme supplements can help the body digest the sugar. For rare deficiencies, prescription enzyme replacement may be needed.

Is it normal to have some gas from carbs?

Yes, some gas production is a normal part of digestion, as bacteria in the large intestine ferment indigestible carbohydrates like fiber. However, excessive gas, bloating, and pain are indicators of malabsorption.