The purpose of this study is to evaluate the impact of replacing usual snacks with alternative snack foods on gut health in a population of habitual snackers with low fibre intake.

Diet is a crucial target for the improvement of human health. In the modern world, diets are diverse and diet related diseases are becoming more and more common. In particular, it is becoming increasingly apparent that the bacteria that live in the gut are strongly linked to both diet and health. Bacteria in the gut can be beneficial or harmful, and the health of the gut relies on the beneficial bacteria outnumbering the harmful ones. Diet has a great impact on the bacterial composition of the gut. In turn, the gut bacteria play diverse roles in human health, influencing not only the gut but also the health of the immune system, heart and brain. Therefore, optimising the composition of the gut bacterial is vital to human health and wellbeing.

It has been shown that snacks between meals contributes 420 - 480 calories per day, almost a quarter of the recommended intake. Therefore, snack choices are an area of diet and lifestyle that have the potential to influence diet and in turn the health of our gut and gut bacteria. We would like to assess the effect of replacing usual snacks with alternative snack foods that we believe have benefits for gut health.

The primary aim of the study is to investigate whether the replacement of usual snacks has an effect on gut bacterial composition, specifically the abundance of Bifidobacteria. Secondary aims include the effect of the intervention snacks on additional measures of gut health such as gut transit time, the frequency and consistency of bowel movements and gut symptoms e.g. heartburn, nausea, belching etc. The effect of snack foods on metabolites in the blood (e.g. glucose, insulin, lipids) will also be determined. Finally the impact of snack replacement on mood and quality of life will be assessed.

Inclusion Criteria:

• Male or female
• Aged between 18-45 years
• Body mass index (BMI) of 18.5 - 29.9 kg/m2
• Regular consumption of snacks (≥2 per day, excluding fruit and nut snacks)
• Low fibre intake (<22 g/d)
• Willing to follow the protocol and provide consent

Exclusion Criteria:

• Allergy or intolerance to snack ingredients (assessed at screening)
• Dislike of study snacks
• Regular consumption of intervention foods as snacks (twice a day in last month)
• Diabetes
• Major active psychiatric conditions (e.g. schizophrenia) or current eating disorder
• Active treatment for cancer in the last year
• Severe renal, cardiac or pulmonary disease or any other chronic medical condition
• Severe oesophagitis, gastritis or duodenitis
• Active diverticulitis or intestinal/colonic strictures
• Crohns disease or Ulcerative colitis
• Abdominal surgery (except appendicectomy or cholecystectomy)
• Irritable bowel syndrome
• Functional constipation
• Functional diarrhoea
• Antibiotics (past 4 weeks)
• Ongoing therapy with drugs affecting gastrointestinal motility
• Use of medical devices (Pacemakers, infusion pumps, insulin pumps)
• Women who are pregnant/lactating/planning pregnancy
• Recent/ongoing consumption of probiotics/prebiotics (past 4 weeks)
• Ongoing abuse of alcohol/drugs/other medication
• Very high physical activity levels
• Unexplained/unintentional weight loss in the past 6 months