Here is the design of a clinical trial:

Official Title: The POWER Study: Effects of a Physiotherapist-delivered Dietary Weight Loss Program in Addition to Exercise in People with Knee Osteoarthritis Who Have Overweight or Obesity - a Randomised Controlled Trial

Included conditions:
- Knee Osteoarthritis
- Overweight and Obesity

Study Armgroups:
- {'label': 'Diet plus exercise', 'type': 'EXPERIMENTAL', 'description': 'The initial physiotherapy consultation for participants in this group will last 75 minutes, with 30 minutes for the exercise component and 45 minutes for the diet component. Thereafter, consultations will last 50 minutes, with 20 minutes for the exercise component and 30 minutes for the diet component. The exercise component will be the same as that described for the exercise alone group.', 'interventionNames': ['Other: Diet plus exercise', 'Other: Exercise']}
- {'label': 'Exercise', 'type': 'ACTIVE_COMPARATOR', 'description': 'Physiotherapy consultations for participants in this group will last 30 minutes initially and then 20 minutes thereafter, consistent with clinical practice. Physiotherapists will prescribe 5-6 strengthening exercises from a pre-determined list to be performed at home three times/week, including two quadriceps exercises, one each for hip abductors, hamstrings and calf, and any other as appropriate and a personalised physical activity plan.', 'interventionNames': ['Other: Exercise']}

Interventions:
- {'type': 'OTHER', 'name': 'Diet plus exercise', 'description': 'The diet program has two phases: 1) intensive weight loss through a ketogenic very low calorie diet VLCD, and 2) transition from ketogenic VLCD onto a healthy eating plan for weight maintenance. Meal replacements will be provided to participants free of charge from the start of the trial to a maximum of 14 weeks (12 weeks for the ketogenic diet and 2 weeks for transition). If a participant does not wish to transition off the ketogenic diet after 14 weeks but wants to continue or if they wish to recommence the ketogenic diet any time after week 14 they will need to purchase meal replacements themselves at their own cost.\n\nParticipants will be encouraged to aim to lose at least 10% body weight.', 'armGroupLabels': ['Diet plus exercise']}
- {'type': 'OTHER', 'name': 'Exercise', 'description': 'The trial coordinator will have provided participants with educational material about OA, handouts of home exercises including photographs and descriptions, a logbook for recording home program completion and resistance exercise bands ahead of their first appointment. Physiotherapists will prescribe 5-6 strengthening exercises from a pre-determined list to be performed at home three times/week, including two quadriceps exercises, one each for hip abductors, hamstrings and calf, and any other as appropriate. Review and modification will occur at each consultation to maintain moderate intensity (effort of ≥5 out of 10 (hard) on a modified Borg Rating of Perceived Exertion scale). The physiotherapist will also prescribe a personalised physical activity plan in collaboration with the participant that is supported and progressed over time.', 'armGroupLabels': ['Diet plus exercise', 'Exercise']}

Primary Outcomes:
- {'measure': 'Body weight', 'description': 'Measured using calibrated digital laboratory platform scales (TCS-2 series) to 2 decimal places, the percentage of body weight change (baseline-follow up/baseline x100%) will be calculated as the primary outcome', 'timeFrame': 'Change between baseline and 6 months post randomization'}

Please estimate the sample size based on the assumption: 
A power of 0.8 and a two-tailed significance level of 0.05 are assumed. A 15% loss to follow-up is also considered. The sample size calculation does not adjust for clustering by physiotherapist and is conservative due to unknown correlations between percentage weight loss and baseline weight.
Trial sample size
        Clinical practice guidelines for knee OA recommend patients who have overweight or obesity should lose at least 5â7.5% of body weight [62]. We therefore powered the trial to detect a conservative between-group difference in weight loss of 5% of body weight assuming no change in weight in the exercise group based on previous research [13, 63]. While the between-participant standard deviation of percentage change in body weight was 5% in another study [63], we were more conservative and assumed a larger standard deviation of 7.5% given that our program has substantially less therapist contact (6 in ours compared with up to 12 individual sessions and 42 group sessions in the previous study [63]), which could result in more variation in response. For a power of 0.8 and a two-tailed significance level of 0.05, we required 37 participants per group. We increased this to 44 participants per group (88 in total) to allow for a 15% loss to follow up [34]. Since physiotherapists treat participants in both arms of the trial, we have not adjusted the sample size calculation for clustering by physiotherapist. Due to unknown correlations between percentage weight loss and baseline weight in this population, sample size calculations are conservative and do not account for the adjustment of baseline weight which will further increase the statistical power.