Table 1 Participant eligibility criteria

Fulfil National Institute for Health and Care Excellence [3] clinical criteria for osteoarthritis:

• Age > 45 years;

• Have activity related joint pain; and

• Have morning stiffness ≤30 min.

Average knee pain severity ≥4 on 11-point numeric rating scale (NRS, where 0 = no pain, 10 = worst pain possible) in the past week

History of knee pain on most days for at least 3 months

Aged < 81 years – due to potential safety reasons and additional co-morbidities

Body mass index (BMI) ≥ 28 kg/m² and < 41 kg/m². The lower BMI limit was chosen according to recommendations [39] that VLCD are effective in supporting weight loss in people with a BMI > 27. The upper limit was chosen as these individuals often require more extensive intervention and for possible safety reasons

Member of Medibank with a level of cover that includes arthroplasty surgery

Able to give informed consent and to participate fully in the interventions and assessment procedures

Willing to follow advice for self-management, participate in exercise/physical activity and/or participate in a weight loss program if part of their treatment program

Have the ability to weigh themselves (e.g. have access to the same set of bathroom scales)

Booked for knee surgery on either knee

Have had all eligible knee joints replaced by arthroplasty

Knee surgery within the past 6 months

Unable to speak or read English

Self-reported diagnosis of rheumatoid arthritis or other inflammatory arthritis

Other medical condition or upcoming medical procedures that in the opinion of the research staff and/or investigators would preclude participation

Private health insurance claims related to cancer treatment or inpatient neurological rehabilitation in the previous 12 months, palliative care, or acquired brain injury

Unable to use/access a telephone and internet

For those identified as at risk from the pre-exercise and falls screening, doctor does not give clearance

Used low-calorie meal replacement products (e.g. Optifast/Optislim) for weight loss in previous 6 months

Currently, or in the past 6 months, undertaking regular strengthening exercises for the knee

Unable to undertake VLCD for medical reasons including:

i. Self-reported diagnosis of Type 1 diabetes

ii. Self-reported Type 2 diabetes requiring insulin or other medication apart from metformin

iii. Self-reported warfarin use

iv. Stroke or cardiac event in previous 6 months

v. Unstable heart condition

vi. Fluid intake restriction