Slow movement of patients guts is referred to as intestinal dysmotility, and is increasingly recognised as a debilitating manifestation of mitochondrial disease both in adults and children.

To date, symptoms of slow gut movements have been managed with laxatives and drugs that increase movement of the guts with variable results. A low residue diet is a form of low fibre diet (<10g fibre per day) that is used to minimise symptoms of poor movement of the guts. This reduces fecal volume and bulk, and hence gut workload, ensuring limited bowel activity and colonic rest. It has been shown to be well accepted in other conditions associated with slow gut movements. However, its role in patients with mitochondrial disease is unknown. The investigators are particularly interested in:

• Does a low residue diet (low fibre) cause a change in the number of stools per week and stool consistency?
• Is a low residue diet tolerated well and easy to comply with?
• Does a low residue diet reduce gut symptoms of abdominal pain, bloating, and constipation?
• Does a low residue diet improve quality of life and disease burden?
• Does a low residue diet affect the bacteria in the gut?
• Can we prove by X-ray that movement of food through the gut is slowed in patients with mitochondrial disease, and whether a low residue diet alters the speed of movement of food through the gut?
• Can a low residue diet change patients physical activity levels?
• Does a low reside diet change dietary patterns and food intake?
• Does a low residue diet alter anthropometrics, such as weight, body mass index and waist to hit ratio?
• Can a low residue diet improve kidney and liver function and lipid profile in blood samples?

The investigators hope that by looking at these areas that a low residue diet may be able to improve patients slow gut movements, health, quality of life and disease burden.

Intestinal dysmotility is increasingly recognised as a debilitating manifestation of mitochondrial disease both in adults and children (1). It is a frequent symptom of other neurological conditions including Cerebral Palsy, Multiple Sclerosis and Parkinson's Disease. Symptoms of intestinal dysmotility are often overlooked and frequently under-diagnosed in its early stages.

Indeed, in its most severe form, intestinal dysmotility may manifest as intestinal pseudo obstruction (IPO), characterised by a clinical picture suggestive of mechanical obstruction, exemplifying the need for early detection and management. To date, symptoms of intestinal dysmotility in slow transit time constipation, limited fluid and calorie intake, weight loss, and small intestinal bacterial overgrowth and in severe cases intestinal pseudo obstruction (2, 3). Moreover, the bacteria that reside within the gastrointestinal (GI) tract compete for nutrients, contributing to weight loss due to malabsorption of fat (4), protein and carbohydrates (5, 6), vitamin (7-11) and iron deficiency (12) are often evident. Further problems include poor digestion and absorption food, an impaired immune system, and an impaired drug absorption ability, all of which influence patient health, quality of life and increases National Health Service (NHS) costs.

A low residue diet is a form of low fibre diet (<10g fibre per day) that is used to minimise symptoms of intestinal dysmotility by reducing faecal volume and bulk and hence bowel workload, ensuring limited bowel activity and colonic rest. It has been shown to be both tolerable and efficacious in other conditions associated with intestinal dysmotility; however, its role in patients with mitochondrial disease and intestinal dysmotility, is unknown.

This feasibility study proposes to systematically gather data on whether a low residue diet is tolerable and has an effect on intestinal dysmotility and health-related quality of life in in patients with mitochondrial disease.

Inclusion Criteria:

• Male or female, aged 18 and over.
• Genetic or biochemical confirmation of mitochondrial disease.
• ROME III criteria of constipation (Appendix 2).
• Stable gastrointestinal drug regimen prior to commencement of study, at least 3 months prior study inclusion.
• No known hypersensitivities to any of the ingredients in the preparations.
• Not already implementing a low residue diet.
• Competent to make such decisions in the opinion of the investigator.
• Females of child bearing age require a negative pregnancy test.

Exclusion Criteria:

• Patients with known allergies to any adjuncts in the dietary preparation
• Patients with bowel obstruction
• Females who are pregnant, lactating or planning a pregnancy.
• Planned surgery during the course of the trial.
• Participation in another drug trial concurrently or in the preceding 12 weeks.
• Any condition which would put the participant at risk if they were to take part in the trial.

Patients will be anonymised, and only raw outcome data will be shared in conjunction with collaborators of the Wellcome Centre for Mitochondrial Research .