Dozens of diseases can affect the digestive system, ranging from common conditions like acid reflux and irritable bowel syndrome to serious illnesses like inflammatory bowel disease and liver disease. The digestive system includes not just the stomach and intestines but also the liver, pancreas, and gallbladder, and problems can develop at any point along that chain. Here’s a closer look at the most significant categories.
Acid Reflux and GERD
Gastroesophageal reflux disease (GERD) is one of the most widespread digestive conditions. An estimated 25% to 40% of healthy American adults experience heartburn at least once a month, and 7% to 10% deal with it daily. GERD happens when the muscular valve between your esophagus and stomach doesn’t close properly, allowing stomach acid to wash back up into the esophagus. Over time, this repeated exposure can damage the esophageal lining.
Occasional heartburn is normal. GERD becomes a concern when symptoms are frequent, interfere with sleep or eating, or don’t respond to over-the-counter antacids. Left untreated, chronic acid exposure can lead to Barrett’s esophagus, a condition where the cells lining the lower esophagus change in ways that slightly raise the risk of esophageal cancer. Most people manage GERD effectively with dietary changes, weight management, and medication that reduces acid production.
Peptic Ulcers and Gastritis
Peptic ulcers are open sores that develop on the inner lining of the stomach or the upper part of the small intestine. The two leading causes are infection with a specific type of bacteria (H. pylori) and long-term use of anti-inflammatory painkillers like ibuprofen or aspirin. Contrary to an old belief, stress and spicy food don’t cause ulcers, though they can aggravate symptoms.
Gastritis, inflammation of the stomach lining, shares many of the same triggers. It can appear suddenly (acute) or develop gradually over months (chronic). Burning or gnawing pain in the upper abdomen, nausea, and feeling full quickly after eating are hallmark symptoms of both conditions. Treatment typically targets the underlying cause: antibiotics for bacterial infection, or stopping the offending medication when possible.
Inflammatory Bowel Disease
Inflammatory bowel disease (IBD) refers to two chronic conditions: Crohn’s disease and ulcerative colitis. Both involve the immune system attacking the digestive tract, but they differ in important ways.
Ulcerative colitis affects only the large intestine. It starts in the rectum and extends upward in a continuous stretch with no gaps between inflamed areas. The inflammation stays in the innermost lining of the colon. Crohn’s disease can strike anywhere from the mouth to the anus, and it often skips sections, leaving patches of healthy tissue between inflamed spots. Crohn’s inflammation also penetrates deeper into the intestinal wall, which is why it’s more likely to cause complications like fistulas (abnormal tunnels between organs) and strictures (narrowed sections of intestine).
Both conditions cause diarrhea, abdominal pain, fatigue, and unintended weight loss. They tend to follow a relapsing pattern, with flares separated by periods of remission. Treatment focuses on calming the immune response and maintaining remission as long as possible. People with long-standing IBD also face a higher risk of colorectal cancer and need more frequent screening.
Irritable Bowel Syndrome
Irritable bowel syndrome (IBS) is fundamentally different from IBD. It’s classified as a functional disorder, meaning the digestive tract looks structurally normal but doesn’t work the way it should. IBS is diagnosed when recurrent abdominal pain occurs on average at least one day per week for three months, with symptoms that first appeared at least six months before diagnosis. The pain is typically linked to bowel movements and accompanied by changes in stool frequency or consistency.
IBS doesn’t damage the intestines or raise cancer risk, but it can significantly affect quality of life. It’s often categorized by the dominant symptom: constipation-predominant, diarrhea-predominant, or mixed. Triggers vary from person to person but commonly include certain foods, stress, and hormonal changes. Management usually combines dietary adjustments (many people benefit from reducing specific fermentable carbohydrates), stress management, and targeted medications for the most bothersome symptoms.
Celiac Disease
Celiac disease is an autoimmune condition in which eating gluten, a protein found in wheat, barley, and rye, triggers the immune system to attack the lining of the small intestine. Over time, this destroys the tiny finger-like projections (villi) that absorb nutrients, leading to malnutrition even when someone is eating enough food.
Symptoms range widely. Some people experience classic digestive problems like diarrhea, bloating, and weight loss. Others develop anemia, bone loss, skin rashes, or neurological symptoms with little or no gut discomfort, which is part of why celiac disease often goes undiagnosed for years. Diagnosis starts with a blood test looking for specific antibodies that signal an immune reaction to gluten. Genetic testing can rule celiac disease out. Confirmation usually requires an endoscopy with a small tissue sample from the small intestine to check for damage to the villi. The only current treatment is a strict, lifelong gluten-free diet.
Fatty Liver Disease
Metabolic dysfunction-associated steatotic liver disease, previously known as nonalcoholic fatty liver disease, is now the most common chronic liver disease in the world. It affects over 30% of adults globally, and its prevalence has climbed from about 25% in the early 2000s to over 38% in recent years, nearly a 50% increase in three decades. The rise tracks closely with climbing rates of obesity, type 2 diabetes, and metabolic syndrome.
The disease begins with excess fat accumulating in liver cells. Many people have no symptoms at this stage and discover it incidentally through blood work or imaging. In a subset of people, the fat triggers inflammation, which over years can progress to scarring (fibrosis), cirrhosis, and eventually liver failure. There’s no widely approved medication specifically for the condition, so treatment centers on addressing the metabolic drivers: losing weight, controlling blood sugar, exercising regularly, and limiting alcohol.
Gallstones and Pancreatitis
Gallstones are hardened deposits of digestive fluid that form in the gallbladder, a small organ that stores bile. Many people carry gallstones without knowing it. Problems start when a stone blocks the duct that carries bile to the small intestine, causing sudden, intense pain in the upper right abdomen that can last hours. Risk factors include being female, being over 40, carrying excess weight, and losing weight rapidly.
When a gallstone blocks the pancreatic duct, it can trigger acute pancreatitis, a painful inflammation of the pancreas. Heavy alcohol use is the other major cause. Acute pancreatitis is diagnosed when blood levels of a specific digestive enzyme called lipase rise to at least three times the normal upper limit. Most cases resolve within a few days with supportive care, but severe pancreatitis can be life-threatening. Chronic pancreatitis, from repeated bouts of inflammation, can permanently damage the pancreas and impair its ability to produce digestive enzymes and regulate blood sugar.
Diverticular Disease
Diverticulosis refers to small bulging pouches that form in weak spots along the walls of the large intestine, most often in the lower left side. The condition becomes increasingly common with age and is usually harmless. Diverticulitis occurs when one or more of those pouches become inflamed or infected, causing pain (typically in the lower left abdomen), fever, nausea, and changes in bowel habits.
A high-fiber diet is the main strategy for preventing both the formation of new pouches and flare-ups. Fiber softens stool and helps it move through the colon more quickly, which reduces pressure on the intestinal walls. One persistent myth worth addressing: for years, people with diverticular disease were told to avoid nuts, seeds, and popcorn. There’s no evidence these foods cause diverticulitis, and most gastroenterologists no longer recommend avoiding them.
Gastroparesis
Gastroparesis is a motility disorder in which the stomach empties food too slowly, even though there’s no physical blockage. Symptoms include nausea, vomiting (sometimes of food eaten hours earlier), early fullness, bloating, and upper abdominal pain. Diabetes is the most common identifiable cause because high blood sugar can damage the nerve that controls stomach muscle contractions. In many cases, though, no clear cause is found.
The gold-standard diagnostic test measures gastric emptying with a nuclear medicine scan. You eat a small meal containing a harmless radioactive tracer, then images are taken at intervals to track how quickly food leaves the stomach. If more than 60% of the meal remains at two hours, or more than 10% at four hours, the diagnosis is confirmed. Treatment typically involves eating smaller, more frequent meals that are low in fat and fiber (both slow stomach emptying), along with medications that help the stomach contract more effectively.
Colorectal Cancer Screening
Colorectal cancer often starts as small, noncancerous growths called polyps on the inner lining of the colon or rectum. Because polyps can take 10 to 15 years to become cancerous, screening catches them early enough to remove, making this one of the most preventable cancers. The U.S. Preventive Services Task Force recommends that average-risk adults begin screening at age 45 and continue through age 75. Before 2021, the starting age was 50, but rising rates of colorectal cancer in younger adults prompted the change.
Several screening methods are available, from stool-based tests done at home to colonoscopy. The best screening test is the one you actually complete. People with a family history of colorectal cancer, a personal history of inflammatory bowel disease, or known genetic conditions like Lynch syndrome may need to start earlier and screen more frequently.