Why does eating trigger pain in the lower intestine?

Why Eating Triggers Pain in the Lower Intestine

Eating can trigger pain in the lower intestine primarily due to exaggerated gastrointestinal responses to food, including heightened visceral sensitivity, altered motility patterns, and peripheral/central sensitization mechanisms.

Physiological Mechanisms Behind Food-Related Pain

• The most consistent motor abnormality recorded in the colon of patients with irritable bowel syndrome (IBS) is an exaggerated motility response to meal ingestion 1
• Approximately two-thirds of patients with IBS show enhanced pain sensitivity to experimental gut stimulation, a phenomenon known as visceral hypersensitivity 1
• When symptoms were systematically investigated using detailed diaries, pain was aggravated within 90 minutes of eating in 50% of occasions, whereas pain was relieved by defecation in only 10% of occasions 1

Types of Sensitization Contributing to Pain

Peripheral Sensitization

• During tissue injury and inflammation, peripheral nociceptor terminals are exposed to inflammatory mediators (prostaglandins, leukotrienes, serotonin, histamine, cytokines) that upregulate sensitivity and excitability 1
• This peripheral sensitization causes pain hypersensitivity at the site of inflammation, known as primary hyperalgesia 1
• Peripheral sensitization is likely a factor in post-infectious IBS, where increased mucosal T lymphocytes have been reported 1

Central Sensitization

• A secondary consequence of peripheral sensitization is the development of hypersensitivity in surrounding uninjured tissue (secondary hyperalgesia) 1
• This occurs because of increased excitability and expanded receptive fields of spinal neurons, resulting in amplification of both non-nociceptive and nociceptive inputs 1
• Evidence for central sensitization includes greater radiation of pain to somatic structures in response to colonic stimulation and hypersensitivity of proximal regions of the gut 1

Specific Food-Related Triggers

• Over 80% of individuals with IBS report food-related symptoms, especially to fermentable carbohydrates and fats 1
• Chemical sensitivity to both exogenous and endogenous acid can worsen dyspeptic symptoms, particularly nausea, and is associated with decreased duodenal motility 2
• Low-grade mucosal inflammation, especially in the duodenum, has been observed in patients with functional dyspepsia and may contribute to symptom generation when exposed to irritants like coffee 2

Relationship Between Eating and Intestinal Motility

• Small bowel disturbances, such as discrete cluster contractions, are associated with pain 1
• Higher rates of duodenal retrograde contractions during phase II of the migrating motor complex directly correlate with worsening gastrointestinal symptoms in IBS patients with diarrhea 1
• Over 90% of high-amplitude propagating contractions (HAPCs) coincide with abdominal pain or cramps, while 40% of postprandial HAPCs occurred immediately before defecation in IBS patients with diarrhea 1

Common Food Triggers and Management

• The types of foods and beverages that commonly induce IBS symptoms include milk products, caffeine, alcohol, fruits, fruit juices, spices, diet products, fast foods, fried foods, fatty foods, multigrain breads, and high-fiber foods 3
• Better tolerated foods typically include water, rice, plain pasta, baked potatoes, white breads, plain meats, eggs, and certain fruits like applesauce, cantaloupe, and watermelon 3
• A low FODMAP diet can be considered as second-line dietary therapy for global symptoms and abdominal pain, but implementation should be supervised by a trained dietitian 4

Practical Management Approaches

• First-line dietary advice should focus on regular meals and adequate fluid intake 4
• Antispasmodics are effective for abdominal pain, particularly when symptoms are exacerbated by meals 4
• Soluble fiber (such as ispaghula/psyllium) should be started at a low dose (3-4 g/day) and gradually increased to avoid bloating 4
• Insoluble fiber (e.g., wheat bran) should be avoided as it may exacerbate symptoms 4

Important Caveats

• Food intolerance in gastrointestinal disorders covers a wide range of products and may be nonspecific rather than of pathogenetic importance 5
• Eating disorders can masquerade as IBS and may need specialist treatment 6
• Complete symptom resolution is often not achievable; managing patient expectations is important 4
• Excluding organic disorders that can mimic IBS symptoms, such as celiac disease, is essential before initiating treatment 4