The goal of this clinical trial is to understand whether diet can impact mechanisms linked to early-onset colorectal cancer.

The main question it aims to answer is: does a high-fibre modified EatWell diet improve stool, blood, urine, and saliva measures linked to early-onset colorectal cancer, compared to the standard EatWell diet?

Researchers will compare the standard EatWell diet (UK national healthy eating guidance providing 30g/day of dietary fibre) to a modified EatWell diet (UK national healthy eating guidance plus specific thresholds for fibre-rich food groups providing 40g/day of dietary fibre).

Participants will follow the dietary advice for 12 weeks, attend clinic visits at the start and end of the study for stool, blood, urine, and saliva sampling, body composition measures, health checks, and complete health, diet, and lifestyle questionnaires.

BACKGROUND The incidence of early-onset colorectal cancer (EOCRC) is on the rise worldwide. Many EOCRC cases may be preventable through modifiable lifestyle factors, including diet . Colorectal cancer risk reductions have been reported with higher intakes of dietary fibre, and different food sources of fibre may confer varying levels of protection. Dietary recommendations for colorectal cancer prevention advise limiting the intake of red and processed meats and added sugars, while prioritising fibre-rich foods such as fruits, vegetables, and whole grains, aligning with the UK EatWell diet; however, its effects on mechanisms underlying EOCRC remain to be elucidated.

AIM To evaluate whether a modified high-fibre EatWell diet can more effectively modulate metabolomic, microbiome, and inflammatory markers associated with EOCRC compared to the standard EatWell diet.

PARTICIPANTS One hundred adult twin pairs (n=200), volunteers of TwinsUK, will be invited to participate. Interested individuals will complete a screening survey and a food frequency questionnaire to determine eligibility.

METHODS EAT-FIBRE is a single-centre parallel-arm randomised controlled diet intervention trial. Twin pairs will be split-randomised with allocation to either the control arm (standard EatWell diet) or intervention arm (modified EatWell diet) to adhere to for 12 weeks. Participants will attend the clinic for stool, blood, urine, and saliva sampling, body composition measures, health checks, and complete health, diet, and lifestyle questionnaires, and will return at the endpoint for repeat measures. The follow-up will be remote at 12 months, where participants will collect and post stool, blood, urine, and saliva samples, and repeat various questionnaires.

Inclusion

• If female, not pregnant, lactating, or planning a pregnancy within the next 4 months.
• Living in the United Kingdom.

Exclusion

• Dietary fibre intake <16 g/day or >30 g/day.

• Unwilling to comply with the intervention (wholegrains, beans and pulses, and nuts and seeds).

• Are diagnosed with the following food allergies: gluten, peanuts, or nuts.

• Are living or have a past medical history of an eating disorder.

• Alcohol Use Disorders Identification Test - Consumption score > 10 points.

• Have lost significant weight (>10% of original bodyweight) over the past 3 months.

• Use of any of the following drugs within the last month:

  (i) antifungals, antivirals, or antiparasitic medications (ii) methotrexate or immunosuppressive agents.

• Use of systemic antibiotics within the last 3 months.

• Use of commercial probiotics, prebiotics, laxatives, or other gut health supplements within the last month.

• Using Glucagon-Like Peptide-1 Receptor Agonists.

• Acute disease at the time of enrolment. Acute disease is defined as the presence of a moderate or severe illness with or without fever.

• Undergoing dietetic care for chronic conditions.

• History of cancer, except for squamous or basal cell carcinomas of the skin that have been medically managed by local excision.

• Any confirmed or suspected condition/state of immunosuppression or immunodeficiency (primary or acquired), including human immunodeficiency virus infection.

• Major surgery of the GI tract, except for cholecystectomy and appendectomy, in the past five years. Any major bowel resection at any time.

• Any other condition declared by the participant deemed by the medical supervisor to affect the normal conduct of the study and analysis of results.

• History of active, uncontrolled gastrointestinal disorders or diseases, including:

  (i) Coeliac disease (ii) inflammatory bowel disease, including ulcerative colitis, Crohn's disease, or indeterminate colitis (iii) persistent, infectious gastroenteritis, colitis or gastritis (iv) persistent or chronic diarrhoea of unknown aetiology (v) chronic constipation (vi) Irritable Bowel Syndrome (vii) Clostridium difficile infection (recurrent) (viii) Helicobacter pylori infection (untreated).

• Any other condition declared by the participant deemed by the medical supervisor to affect the normal conduct of the study and analysis of results.