Fullness feels stronger when IBS meets anorexia nervosa
Marina has had bloating since school, long before her anorexia diagnosis. Her case of anorexia and IBS shows how slower gut movement, stronger fullness and daily food choices can add up, and why her first plan kept energy intake steady.
Marina's casecase study
Marina is 32, and her history links anorexia nervosa and irritable bowel syndrome with bloating, big weight changes and intense fullness after meals. Today she is at the lower end of the healthy weight range. Bloating after eating began in adolescence, long before the anorexia diagnosis, and became more intense while she was taking olanzapine.
This is why we look carefully at gut symptoms in anorexia together with gut sensitivity, the gut-brain axis and gut movement. We also examine the link between low body weight and digestion, the possibility of slower stomach emptying and the possible role of an imbalance in the gut bacteria. The first plan combines testing with practical changes that keep energy intake steady.
Which details in her history shape the picture?
Bloating since secondary school
Marina came to the practice where I work as a scientific collaborator with bloating she remembers from secondary school. The symptom was already there before the anorexia diagnosis. Later, it existed alongside lower food intake and big changes in weight.
A history of big weight changes
During university, her daily routine became irregular and she gradually stopped feeling hunger as she had before, and her weight fell. It rose during treatment with olanzapine and later changed again with nutritional support. Today she is at the lower end of the healthy range. The earlier period of low weight and the changes that followed may still affect hunger, fullness and gut movement.
Olanzapine and more intense bloating
She was diagnosed with anorexia nervosa in 2020 and started olanzapine. Her weight increased during treatment, while the bloating became more intense. This is why we examine whether the medicine may also have affected gut movement.
Grains every day and sweets up to five days a week
Her food diary shows how many days a week she eats each food group. She has grains on 7 days, dairy on 5, sweets on 3 to 5, eggs on 3, fish on 2 and pasta on 1 to 2. She eats poultry on 1 day, while red meat, rice and potatoes appear on 0 to 1 day.
Three glasses of water and no exercise
Her day starts at 06:20 and ends around 23:00. Breakfast often includes bread, honey, cheese, egg or pancakes. Rice cakes or biscuits follow, with a main meal at midday and something sweet in the afternoon. She drinks about three glasses of water a day and does no structured exercise.
Bad breath and episodes of intense appetite
She has also reported bad breath, fibrocystic breast changes and episodes of very intense appetite. Each of these needs its own assessment. Here, we focus on the links between food intake, weight, gut movement and bloating.
How are anorexia nervosa and irritable bowel syndrome linked to bloating?
The bloating was there before the anorexia. Later, reduced hunger, a period of low weight and big weight changes added new factors that can affect gut movement and how strongly she feels fullness. The gut-brain axis is the two-way communication between the digestive system and the brain. Research shows that eating disorders often occur together with IBS and with discomfort after meals.4, 1 The evidence shows that the two conditions travel together, without telling which one influences the other more.4
How common are these digestive disorders?
In a study of women admitted to hospital for an eating disorder, 83% met the criteria for at least one functional gut disorder. Distress after meals affected 45%, and IBS affected 41%.1
Functional gut disorders in people with eating disorders
Wang 2014, Rome III criteria. Heartburn means functional heartburn, and bowel means unspecified bowel disorder.1
How can severe bloating occur after only a small amount of food?
How strongly we feel fullness depends on the size of the meal, how quickly the stomach empties and how the brain reads the stretch. In people with a history of anorexia, more fullness has been measured after the same amount of food. This means that even a moderate meal can cause intense bloating when the stomach empties more slowly and the body senses the stretch more strongly.3
What does low food intake do to gut movement?
When food intake stays low for a long time, the digestive system receives fewer signals to keep moving. In an older study, food took 66.6 hours on average to pass through the whole gut in people with anorexia, compared with 38.0 hours in healthy controls, a statistically significant difference. The time from mouth to the start of the colon did not differ significantly.2 The longer the contents stay in the gut, the more stretching and bloating may increase.
Whole-gut transit time in anorexia nervosa (hours)
Kamal 1991, average time for food to pass through the whole gut.2
Which factors can make bloating more intense?
The amount of food explains only part of the discomfort. For Marina, we look at four factors together: how much she eats and how her weight changes, how quickly her gut moves, how strongly she feels stretch, and which daily foods may increase fermentation. We also include low water intake and lack of movement.
The starting point. Reduced hunger, the period of low weight and big weight changes affect when she feels full and how her gut works.
Long periods of low intake can slow the stomach and the bowel, so contents stay longer and stretch the gut more.2, 3
The brain can read a normal stomach stretch more strongly after anorexia, so the same meal feels bigger.3
Foods that ferment easily, little water and no exercise can add gas and slow the bowel further.
What did the stomach emptying measurements show?
In an MRI study, the stomach emptied more slowly in people with anorexia than in people with a healthy weight or with obesity. Symptoms such as fullness and nausea were also stronger, and with the same amount of food, the anorexia group felt more fullness. After weight restoration, fullness decreased, and stomach emptying tended to improve.3
What role might olanzapine play?
Olanzapine helped Marina gain weight. During the same period, however, the bloating became more intense. In a rat experiment, olanzapine reduced colon contractions as the dose increased, and it also affected two mechanisms involved in gut movement.5 This offers a possible explanation, while in her case it shows a link in time between the medicine and the symptom.
Can olanzapine increase bloating while also helping with weight gain?
Yes, this is possible, because the two effects work in different ways. Olanzapine can increase appetite and support weight gain. At the same time, it may affect serotonin signals and gut contractions, which can change how quickly the bowel moves. Most of the related experimental evidence comes from animals.5 In practice, we look at when the symptoms began, how they changed and what the measurements show.
What does the weekly eating pattern show?
Marina eats grains every day, dairy on five days and sweets on three to five days a week. Her usual foods also include bread, honey, pancakes, biscuits and chocolate spread. Several of these foods contain carbohydrates that ferment in the gut and may increase gas. An imbalance in the gut bacteria remains one possible mechanism. At first, however, we follow the specific foods, the symptoms and the inflammation markers, and we keep energy intake stable, so that tolerance can be tested without further weight loss.
What do we expect the tests to show?
The tests have a clear goal: to see what may be behind the symptoms. Fecal calprotectin, CRP and ESR check for inflammation in the gut or elsewhere in the body. Vitamins and trace elements show whether deficiencies developed during the period of low weight. The remaining tests complete the picture for hormones, metabolism and blood health.
Shows whether there is inflammation in the gut and helps separate a functional problem from an inflammatory one.
Show whether there is wider inflammation in the body and add context to the calprotectin result.
Checks for anemia and gives basic information about red cells, white cells and platelets.
Show whether deficiencies could be affecting blood cell production and homocysteine levels.
May rise when vitamin B12 or folate is too low, so it adds context to those vitamin measurements.
Shows whether vitamin D is at an adequate level, which matters for bones and muscles, especially after low body weight.
Check nutrients needed by the muscles, metabolism and energy production.
Gives extra information about the bones, liver and bile ducts.
A useful hormone measurement for someone who has taken antipsychotic medication.
Check different parts of blood clotting. Their main role is in the overall assessment, with limited direct relevance to bloating.
Adds information about cardiovascular risk and the wider metabolic picture.
Gives basic information about hydration, kidney function and the urinary tract.
How will the results change the next steps?
A raised fecal calprotectin would shift the investigation toward an inflammatory cause. If inflammation markers are normal but bloating continues, we would focus more on gut movement, food fermentation and gut sensitivity. Deficiencies in vitamin D, B12, folate, zinc, magnesium or phosphorus would become clear targets for replacement. At the time of this case, the results were still pending.
Which changes do we recommend first?
How does a short low-FODMAP trial work?
We recommend a trial lasting 4 to 6 weeks and no longer than two months. During this time, we reduce specific foods with carbohydrates that ferment easily in the gut, known as FODMAPs. In Marina's food diary, these include honey, wheat, onion, garlic, legumes, apples, watermelon and some dairy products. Every food that is removed is replaced with an option that gives a similar amount of energy, and we then test one food group at a time. In a four-week trial, more people with IBS had adequate relief of their symptoms on a low-FODMAP diet than on a sham diet.6
Why a steady breakfast with protein and tolerated fiber?
We keep breakfast daily and consistent. A source of protein, such as an egg or a tolerated yogurt, is combined with bread or oats and a gentle source of fiber. We start with a comfortable amount and increase it gradually. This helps gut movement, supports weight and makes it easier to see when fullness appears.
How do we reduce sweets in the afternoon?
Marina eats sweets three to five days a week, often around 19:00. We reduce how often gradually. A biscuit or chocolate spread can be replaced with a snack that combines protein or fat with a carbohydrate she tolerates well. This reduces the amount of sugar in one sitting and makes it easier to see whether the afternoon snack is linked with gas or bloating.
How do we move from three to eight glasses?
The first goal is to raise fluids gradually from about three to eight glasses a day. We spread them from morning to evening, for example one after waking and one between the main meals. The rest are added at times that already fit her routine. More water helps keep stools softer, especially as fiber increases.
Why do we recommend strength training twice a week?
Marina currently has no structured exercise, so she starts with two short strength-training sessions a week. Duration and intensity increase slowly. The goals are to strengthen muscle, add more movement to her day and support bowel function. Food intake is adjusted at the same time, so that weight is kept steady as exercise increases.
Because of her history of anorexia, every step keeps energy intake steady and avoids new long-term restrictions. Every case is different, so Marina's plan describes her care and is not a plan for anyone else. Diet changes after an eating disorder are best made together with the treating team.
How can these changes help?
Each change targets a different part of the problem. The short low-FODMAP trial reduces foods that may create more fermentation and gas. A steady breakfast and enough energy help food intake regain a steady rhythm. Fewer sweets, more water and gentle strength training may reduce the factors that keep bloating going or slow the bowel. In the MRI study, fullness decreased after weight restoration, and stomach emptying tended to improve.3
How will we know whether the changes are helping?
Marina keeps a simple diary: how long bloating lasts after each main meal, how intense the fullness feels, how often bowel movements occur and what they look like, and her hunger before eating. This helps show whether the problem is linked more closely with fermentation, gut movement or the way stomach stretch is felt. The record also helps avoid random food exclusions and leads to clearer decisions with her treating team. The wider causes are covered in abdominal bloating causes.
Frequently asked questions
The two conditions often appear together. The evidence shows an association and leaves open which condition has more influence on the other.4 The link involves gut movement, hunger, fullness, gut sensitivity and psychological factors. To diagnose IBS, doctors look at the type and duration of symptoms together with the appropriate tests.
The gut and the brain need time to adjust to regular meals again, and in one study fullness eased after weight restoration.3 Certain foods, constipation, low water intake and medicines may also keep some of the symptoms going.
Olanzapine affects signals involved in gut movement. In animal experiments, it has reduced contractions of the colon.5 In people, doctors look at when symptoms started, how often bowel movements occur and which other factors may be slowing the bowel. Medicine changes are always made by the prescribing doctor.
It can be used for a short period with enough energy and a structured return of foods, under close follow-up with the treating team. The goal is to find trigger foods while avoiding new long-term restrictions.
References
6 studies
- Wang X, Luscombe GM, Boyd C, et al. Functional gastrointestinal disorders in eating disorder patients: altered distribution and predictors using ROME III compared to ROME II criteria. World J Gastroenterol. 2014.
- Kamal N, Chami T, Andersen A, et al. Delayed gastrointestinal transit times in anorexia nervosa and bulimia nervosa. Gastroenterology. 1991.
- Bluemel S, Menne D, Milos G, et al. Relationship of body weight with gastrointestinal motor and sensory function: studies in anorexia nervosa and obesity. BMC Gastroenterol. 2017.
- Hanel V, Schalla MA, Stengel A. Irritable bowel syndrome and functional dyspepsia in patients with eating disorders: a systematic review. Eur Eat Disord Rev. 2021.
- Zhang J, Qiao Y, Le J, et al. Olanzapine may inhibit colonic motility associated with the 5-HT receptor and myosin light chain kinase. Psychiatry Investig. 2016.
- Staudacher HM, Lomer MCE, Farquharson FM, et al. A diet low in FODMAPs reduces symptoms in patients with irritable bowel syndrome and a probiotic restores Bifidobacterium species: a randomized controlled trial. Gastroenterology. 2017.
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Cite this article
Prevedoros, T. (2026, September 10). Fullness feels stronger when IBS meets anorexia nervosa. Gut Pathways. https://gutpathways.com/case-studies/anorexia-nervosa-irritable-bowel-syndrome/
