There is evidence to show that daily probiotic Lactobacillus casei Shirota (LcS) in the form of Yakult fermented milk supports a healthy balanced population of "friendly" gut bacteria. This, coupled with evidence from four European trials showing probiotic benefit for recurrent diverticulitis and an understanding of how the disease develops, indicates that LcS may also be beneficial. The investigators plan to undertake a pilot study investigating whether consumption of once daily probiotic LcS as Yakult fermented milk would help either prevent attacks of diverticulitis completely or significantly reduce frequency of attacks. Subjects will be recruited from Surrey primary care units and will be closely monitored for 12 months whilst being supplied with a daily dose of for the full 12 months to see if this improves gut health.

Because dietary fibre, obesity and diabetes are all confounding factors that influence the frequency and severity of attacks of diverticulitis, the research project will take account of this by:

1. Monitoring dietary fibre using a diet diary
2. Measurement of height and weight to determine BMI
3. Screening for undiagnosed diabetes and pre-diabetes

As well as keeping a diet diary, subjects will be asked to keep a general health diary, and to complete gut health questionnaires at start, 6 months and 12 months.

Inclusion Criteria:

1. A history of two episodes of UAD treated with antibiotics in the last five years.
2. Diverticulosis confirmed by colonoscopy, barium enema, USS, CT or MRI imaging or at surgery.
3. Agreement to consume one bottle of Yakult daily for 12 months
4. Availability of space in the domestic refrigerator for storage of Yakult units
5. Able to access depot (local primary care premises or chemist) to collect regular supplies of Yakult
6. Able to cope with keeping a diary etc.
7. Willing to take Yakult supplies and a cold bag on holiday to ensure as near as possible continuous daily doses (certainly never more than one week break as Lactobacilli casei will persist in the human gut for at least one week
8. Capable of giving informed consent
9. Aged ≥ 50 and ≤ 75 years at commencement of trial.

Exclusion Criteria:

1. Recent history of peptic ulcer
2. Chronic renal insufficiency
3. Ongoing or past major diverticulitis complications
4. Any serious debilitating illness (cancers, cardiovascular disease etc. but not DM)
5. Dementias or memory problems
6. Regular probiotic consumption over the past year.
7. Undergoing immunosuppressive therapy or treatment
8. Lactose intolerance or intolerance to dairy products
9. Immunosuppressed patients