Bloating
Also called: abdominal bloating, bloated stomach, distension
Bloating is the sensation of pressure or fullness in the abdomen, usually with a visible increase in belly size by the end of the day. It is mostly caused by gas from gut bacteria fermenting food, plus slow gut transit and fluid shifts. It is very common, reported by roughly 1 in 6 people in any given week, and most cases are functional rather than disease-driven.
What is actually happening
Bloating is the combined effect of three things. First, gas produced when bacteria ferment carbohydrates that did not get absorbed earlier in the gut. Second, water held in tissue around the gut and elsewhere. Third, the speed at which the gut moves food along, which decides how long fermentation has to build up.
All three change through the day, with the menstrual cycle, with stress, and with what you ate the night before. That is why most bloating feels worse by evening.
The three patterns most people sit in
- Gas bloating: distension that gets visibly bigger after meals, often with wind. Usually fermentable carbohydrates (FODMAPs) or large meals.
- Water bloating: puffy, ring-tight, no real wind. Usually high salt intake the day before, the second half of the menstrual cycle, or poor sleep.
- Slow-transit bloating: feels heavy and stuck, often with infrequent or hard stools. Usually low fibre, low movement, or dehydration.
What usually moves the dial
- Stop eating 3 hours before bed. The single biggest fix for morning and next-day bloat.
- Walk for 10 to 15 minutes after meals. A randomised trial found this reduces post-meal bloating, belching and flatulence.
- Drink water with meals, not after. Helps moisten fibre and reduces hard stools later.
- Check sodium the night before any morning that matters. Restaurant food and takeaways are repeat offenders.
- Track your cycle. In the luteal phase (the second half of the cycle), hormonal changes including progesterone can slow gut transit and fluid shifts, so bloating in that window is often hormonally driven rather than triggered by food.
When bloating needs more than this
Bloating that is daily, painful, comes with weight loss, blood in stool, or that wakes you at night deserves a GP visit. Coeliac disease, SIBO, ovarian conditions, and inflammatory bowel disease can all present as bloating in the early stages, and a simple set of blood tests rules most of them out quickly.
Common questions
- Why am I bloated even when I eat healthily?
- Healthy food is often the culprit. High-fibre foods like beans, broccoli, onions, garlic, apples, and oats are rich in fermentable carbohydrates that gut bacteria turn into gas. The fix is rarely less fibre, it is more variety and slightly smaller portions until your bacteria adjust.
- Why is my stomach flat in the morning and bloated by night?
- That is the normal pattern. Overnight, the gut clears and water shifts. Through the day, food, water and gas accumulate. By evening the belly is measurably bigger than at waking. It is not weight gain, it is normal fill.
- Can stress make me bloated?
- Yes, reliably. Stress alters gut motility and increases visceral sensitivity, which means the same volume of gas feels more uncomfortable. This is one reason bloating tends to spike during exam weeks, hard work cycles, and periods of bad sleep.
- Is bloating the same as gas?
- Related but not identical. Gas is the volume produced. Bloating is what you feel and see. People with sensitive guts can feel bloated with normal amounts of gas. People with low sensitivity can have lots of gas and not feel bloated at all.
Sources
- Bloating and abdominal distension (overview, causes, when to see a GP) (NHS)
- Management of Chronic Abdominal Distension and Bloating, Lacy, Cangemi, Vazquez-Roque 2021 (Clinical Gastroenterology and Hepatology (PMID 32246999))
- AGA Clinical Practice Update on Evaluation and Management of Belching, Abdominal Bloating, and Distention, Moshiree, Drossman, Shaukat 2023 (Gastroenterology (PMID 37452811))
- Prevalence and Associated Factors of Bloating: Rome Foundation Global Epidemiology Study, Ballou et al 2023 (Gastroenterology (PMID 37315866))
- About FODMAPs and IBS (fermentation, gas, high-FODMAP foods, low FODMAP diet) (Monash University)
- European Consensus on Functional Bloating and Abdominal Distension (ESNM/UEG), Melchior et al 2025 (United European Gastroenterology Journal (ESNM/UEG))
- The effect of short-term physical activity after meals on GI symptoms in functional abdominal bloating: a randomized clinical trial, Hosseini-Asl et al 2021 (Gastroenterology and Hepatology From Bed to Bench)
- Ambulatory abdominal inductance plethysmography: diurnal variation of abdominal girth, Lewis et al 2001 (Gut (PMID 11156643))
- Microbiota-neuroimmune cross talk in stress-induced visceral hypersensitivity of the bowel, Van Thiel et al 2020 (Am J Physiol Gastrointest Liver Physiol)
- Symptomatology of irritable bowel syndrome and inflammatory bowel disease during the menstrual cycle, Bharadwaj et al 2015 (Gastroenterology Report (Oxford))