Years of strict dieting slowed the bowel
Kate's case is one of constipation from dieting. Her long diet history, bowel pattern and pain after certain foods point to the link between gut hormones and gut movement, and to a plan that rebuilds a steady daily rhythm.
Kate's casecase study
Extreme dieting can cause lasting shifts in the hormone and nerve signals of the gut, which may lead to a wide range of IBS-type symptoms. Kate had constipation and left-sided abdominal pain after eating vegetables and legumes. Her case shows how weight cycling can reshape appetite, bowel rhythm and food tolerance.
At 53, she has a normal BMI, two decades of constipation, bowel movements that depend on coffee and cigarettes, and left-sided pain after vegetables and legumes. Her pattern links weight cycling, meal timing, the gut microbiome and appetite hormones.
What did years of extreme dieting change?
Repeated restriction and regain can train eating around urgency, while constipation continues in the background. Kate came to the practice where I work as a scientific collaborator after large weight changes from extreme diets, a 20-year history of constipation and a bowel movement that usually arrives only after coffee and smoking. Meanwhile, eating in front of screens, occasional night eating and high anxiety leave her digestive system without a settled rhythm between meals and the bowel.
Weight cycling beside a normal BMI
Years of strict diets and large weight changes sit beside Kate's current BMI of 24, so the assessment of her digestion draws on her whole diet and symptom history.
A morning routine built around outside cues
Coffee and cigarettes have become the cue for daily stool passage, while constipation, changing stool form and abdominal discomfort continue through the rest of the week.
Vegetables and legumes keep coming before the pain
Left-sided abdominal discomfort after fiber-rich foods puts transit, fermentation, gut bacteria and gut sensitivity together in the assessment.
Kate's gut function has three layers that interact
The foundation. Restriction, eating in front of screens and late meals set the daily conditions for digestion.
Appetite hormones and nerve signals prepare the gut for a meal and move the bowel. Years of restriction can change them.
Gut bacteria, transit time and gut sensitivity decide how fiber and fermentable foods feel in the colon.
Restriction changes the signals that prepare a meal and move the bowel
Ghrelin receptors in the gut's own nerves and in the vagus nerve link the stomach's energy signal with gut movement and appetite. In a 12-week trial, weight loss through energy restriction changed ghrelin, GLP-1 and CCK, hormones that are central to hunger, fullness and the coordination of digestion.1 As a result, Kate's long diet history adds important context to her current weight and bowel pattern.
Restriction also lowers leptin, a hormone that signals energy stores. In a meta-analysis of 12 trials with 495 people, energy-restricted diets lowered blood leptin, and the drop was larger when intake was at or below half of daily needs.2
Leptin falls more with severe energy restriction (ng/mL)
Varkaneh Kord 2021, meta-analysis of 12 trials with 495 people, average change in blood leptin.2
I have spent years moving between strict diets and weight regain, and now I often need coffee or a cigarette before my bowels move. Could the dieting have changed how my gut works?
It could. Energy restriction changes the appetite hormones that coordinate hunger, fullness and gut movement: a 12-week trial found changes in ghrelin, GLP-1 and CCK after weight loss. Ghrelin receptors sit in the gut's nerves and in the vagus nerve, linking the stomach's energy signal with gut movement. Coffee and nicotine can then become strong morning triggers for the bowel, so a daily bowel movement can sit inside a wider pattern of constipation, defined by effort, stool form, slow transit and abdominal discomfort.
Why did vegetables and legumes trigger left-sided pain?
Vegetables and legumes bring fermentable carbohydrates and fiber into a colon whose transit already feels slow. When that material reaches a sensitive left colon, gas, stretch and retained stool can make abdominal pain and bloating stronger. Kate noticed the pattern especially after legumes and vegetables, while an artichoke extract coincided with more formed stools and less pain.
The food pattern is a useful clinical signal. A structured food and symptom record can separate portion, preparation, meal timing and stool pattern, while the articles on bloating and gas after eating and abdominal bloating causes give the pattern practical context.
How dietary restriction can reshape the colon
Restriction changes the colon environment in more than one direction. In a review of human studies, low-carbohydrate diets (below 30% of energy) tended to reduce Bifidobacterium and short-chain fatty acids in stool.3 On the other hand, in a meta-analysis of 47 weight-loss trials, weight loss was linked with higher gut bacterial diversity and lower intestinal permeability.4 The way a diet restricts food seems to shape the gut as much as the weight lost.
A morning trigger routine can hide slow transit
Coffee and nicotine both give a repeatable morning stimulus, so daily passage can coexist with constipation between those cues. Kate's assessment therefore records the full stool story, including form, effort, pain and timing, next to the daily count.
I am trying to eat more vegetables and legumes for my gut health, but they give me left-sided pain and bloating. Why do foods that are meant to help digestion make me feel worse?
Vegetables and legumes carry fiber and fermentable carbohydrates into the colon, where gut bacteria turn part of that material into gases and short-chain fatty acids. Slow transit keeps that material in the colon for longer, which increases stretch in the bowel wall and makes left-sided pain more noticeable when the gut is sensitive. Research on restrictive diets also shows that low-carbohydrate diets can reduce Bifidobacterium and short-chain fatty acids, so food tolerance depends on the wider gut microbiome and transit.
Infographic
Appetite signals change
In a 12-week trial, weight loss through energy restriction changed ghrelin, GLP-1 and CCK, hormones tied to hunger and fullness.
The colon environment shifts
In a review of human studies, low-carbohydrate diets tended to reduce Bifidobacterium and short-chain fatty acids in stool.
A morning trigger
Coffee and nicotine give a repeatable morning stimulus, so daily passage can coexist with constipation between those cues.
Fiber meets slow transit
Vegetables and legumes bring fermentable carbohydrates into a colon whose transit already feels slow, which can strengthen pain.
Sources: Coutinho et al. 2018, Schoonakker et al. 2025.
gutpathways.com
Save this infographicImage 4:5, with sources, from gutpathways.comWhat should we test before changing the plan?
The assessment looks for nutritional limits, signs of inflammation and the microbial context that can shape chronic constipation. The selected blood, urine and molecular stool tests give Kate's broad history a focused clinical structure.
Blood count, iron, ferritin, folate, zinc, magnesium, calcium, vitamin D3, albumin, kidney markers, lipids, CRP, ESR, PT-INR and urinalysis. It maps nutrient status, inflammation and metabolic context after years of restrictive eating.
Homocysteine, iodine, Lp(a), D-dimer, alkaline phosphatase, bilirubin and uric acid. They add detail where the history, family diabetes risk and food pattern point to it.
The make-up and functional pattern of the gut microbiome. It connects stool pattern, fiber tolerance and digestive symptoms with a measurable colon environment.
Restriction can also echo into the following days. In a study of 18 lean adults, one day at 25% of energy needs increased food intake on the next day by about 7%, compared with a day at full energy needs.5 At the time of this case, the test results were still pending.
One severe restriction day can echo into the next (%)
Clayton 2016, 18 lean adults received 25% or 100% of their estimated energy needs for one day.5
Which changes support digestion and bowel rhythm?
Chew each meal thoroughly
Thorough chewing switches on the cephalic phase of digestion, increases contact between food and saliva, and gives the stomach and nervous system an early signal that food is arriving. A slower pace lets fullness signals develop before the meal ends and supports a steadier digestive response.
Keep a clear fluid boundary around meals
Keeping drinks outside the meal, and waiting 60 minutes after eating, gives each meal a clear start and end. This boundary reduces constant grazing and supports regular meal times. A defined eating sequence also helps the digestive system coordinate stomach filling, stomach emptying and the bowel response that follows food.
Move dinner into an earlier, predictable window
Dinner at 18:00 to 19:00 gives the stomach and small intestine more time to process the meal before sleep. A steady evening meal and a stable overnight gap strengthen the daily rhythm that coordinates appetite hormones, gut movement and bowel activity. This timing also separates physical hunger from late eating in front of screens.
Take magnesium before sleep
A magnesium supplement is taken 30 minutes before sleep. Magnesium takes part in normal nerve and muscle function, including the smooth-muscle activity involved in gut movement. Taking it at the same time each evening links it with a stable bedtime routine and supports a steadier bowel rhythm.
Simplify the solanine-rich foods for a while
Potatoes, tomatoes, eggplants, peppers, goji berries and cinnamon are removed for a while. Reducing these foods simplifies the diet during the first phase and limits the number of overlapping food triggers. The aim is to reduce digestive irritation while her response to vegetables, legumes and other fiber-rich foods becomes clearer.
Reduce alcohol and add diaphragmatic breathing
Alcohol is limited to three occasions a week for three months, each followed by two glasses of water. Alcohol can affect gut permeability, the gut microbiome, sleep quality and gut movement, so less of it lowers a recurring strain on digestion. Five minutes of diaphragmatic breathing during the day supports the calming branch of the nervous system and the gut-brain connection.
A short probiotic course and a steadier breakfast
A probiotic is used for 20 days, and eggs are chosen more often at breakfast. The short probiotic course supports the gut microbiome during the first diet changes, while a breakfast with protein gives a steady morning signal. Protein also stimulates fullness hormones such as GLP-1, PYY and CCK, linking breakfast with appetite and the pace of digestion.
Every case is different, so Kate's plan describes her care and is not a plan for anyone else. Supplements and diet changes are best agreed with the treating doctor.
How will we know that the gut is responding?
Progress shows first as a more predictable bowel rhythm, less left-sided pain and a wider range of vegetables and legumes that she tolerates. Kate can record meal times, screen use, the timing of coffee and nicotine, stool form, where the pain sits and night waking, and then read those notes next to the lab and microbiome results.
The goal is a routine that no longer depends on dramatic restriction or a morning trigger. In addition, an earlier dinner and a steadier breakfast make it easier to see whether the bowel is finding its own rhythm.
Timing, effort and stool form show whether bowel movements follow a more predictable rhythm.
Portion, preparation and meal context reveal a clearer pattern of fiber tolerance.
Where the pain sits, how strong it is and night waking show how digestion is responding.
Frequently asked questions
Yes. A current BMI is one measurement within a longer history of repeated restriction, weight changes, constipation and pain after certain foods.
They can become the daily cue for passing stool, so timing and effort add important detail to the bowel pattern.
Fiber and fermentable carbohydrates meet the transit, microbiome and sensitivity already present in the colon, so gas and stretch of the bowel wall can become painful.
The first assessment combines a broad nutritional and inflammation panel, targeted markers and a molecular stool microbiome test.
References
5 studies
- Coutinho SR, Halset EH, Gåsbakk S, et al. Compensatory mechanisms activated with intermittent energy restriction: a randomized control trial. Clin Nutr. 2018.
- Varkaneh Kord H, Tinsley GM, Santos HO, et al. The influence of fasting and energy-restricted diets on leptin and adiponectin levels in humans: a systematic review and meta-analysis. Clin Nutr. 2021.
- Schoonakker MP, van Peet PG, van den Burg EL, et al. Impact of dietary carbohydrate, fat or protein restriction on the human gut microbiome: a systematic review. Nutr Res Rev. 2025.
- Koutoukidis DA, Jebb SA, Zimmerman M, et al. The association of weight loss with changes in the gut microbiota diversity, composition, and intestinal permeability: a systematic review and meta-analysis. Gut Microbes. 2022.
- Clayton DJ, Burrell K, Mynott G, et al. Effect of 24-h severe energy restriction on appetite regulation and ad libitum energy intake in lean men and women. Am J Clin Nutr. 2016.
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Cite this article
Prevedoros, T. (2026, September 19). Years of strict dieting slowed the bowel. Gut Pathways. https://gutpathways.com/case-studies/extreme-dieting-constipation-left-sided-abdominal-pain/
