Can drinking water before main meals help with weight loss?

Dr Helen Parretti made ripples with international press and social media earlier this year when her research on using water to support weight loss was published1. Helen kindly let CIRC’s Translational Research team interview her to find out how her insights can support GPs in their day to day work with patients.

What is your advice for GPs and practices to support patients with weight loss?

The research evidence does not yet support GP-led in house weight management services. However, we do have a role in raising the topic of weight and signposting to appropriate services; given that obesity affects so many health problems there are ample opportunities to discuss weight with patients. These are a few suggestions for those consultations:

  1. Weigh patients opportunistically and ask them to weigh themselves at home regularly 
  2. Raising the topic – phrases such as “How do you feel about your weight?” or “Is it OK if we talk about your weight?” can work well
  3. Help the patient to understand the link between weight, activity and health, in particular for those with co-morbidities
  4. Ask about their weight trajectory – have they lost weight in the past, are they currently losing weight, is their weight stable or increasing?
  5. Signpost to appropriate support – be aware of local services available, NICE and local referral criteria
  6. Discuss that the aim is to improve health and well-being, not just to get to a lower number on the scales
  7. Encourage regular physical activity, walking is free
  8. Offer a follow up appointment after their weight loss programme.  Weight maintenance is problematic for the majority of patients and regular self-monitoring or monitoring at the surgery may help

Your research has received international recognition, as a GP what do you feel is most useful about your research and the implementation of research into practice?

Obesity is a significant problem in the UK with more than a quarter of the population classified as obese and impacts on many areas of patient care and co-morbidities frequently seen during GP consultations. As a GP, I am well aware of the pressures on consultation times and in studies this is frequently cited as a reason why GPs don’t discuss weight management with patients. Therefore, we wanted to investigate the effectiveness of a simple weight loss intervention that could easily and quickly be delivered in a GP consultation. Drinking water before main meals is a very simple message that can easily be given to patients with obesity when discussing weight loss. This type of intervention, although it may result in only modest weight reduction, has the potential to help reach the many people needing to lose weight, and even small reductions across the whole population can have important public health benefits.

We found that there were some initial small laboratory studies that suggested that drinking water before main meals might help with weight loss, but we didn’t know whether it would work in an everyday setting over a sustained period of time. So we recruited 84 people into a randomised controlled trial. The intervention group were asked to drink 500ml (or a pint) of water 30 minutes before each main meal (“preloading water”) while the comparator group was asked to imagine their stomachs were full 30 minutes before each meal as an attention control. We found that the people in the preloading water group lost, on average, 1.3kg (2.87lb) more than those in the comparator group over 12 weeks. Those who reported preloading before all three main meals in the day reported a loss of 4.3kg (9.48lbs) over the 12 weeks, whereas those who only preloaded once, or not at all, only lost an average of 0.8kg (1.76lbs).

The article and the messages from your research have gone viral. Do you have any reflections on this?

We have been very pleased by the interest in our research. I think the fact that it is such a simple intervention that is easily implemented has made it very accessible to members of the public. It is something that you can easily imagine yourself doing and can fit into a busy life. I hope that it will also help GPs when consulting with patients who want to lose weight as an additional piece of advice that they can give.

Are there other issues you would like to study relating to the topic?

We would like to carry out a larger trial with 12 month follow up to allow us to gain more definitive evidence that water preloading is effective and also to investigate the potential mechanisms of action more fully.  We are now looking to gain funding to carry out this trial. Our focus is very much on investigating potential simple, pragmatic interventions that are feasible to deliver in a busy GP surgery.

What is the impact of the SFB research funding?

My experience has been that SFB funding provides an excellent opportunity for early career academic GPs such as myself to carry out research projects. The experience I have gained by carrying out this study has helped to develop my research skills and my aim now is that my SFB funded project will form the basis of an application for a larger trial. Therefore the SFB funding has had a positive impact on my career progression.

Is there any advice you can give for GPs who are wanting to test an idea or considering carrying out research?

I would very much encourage GPs to get involved in research whether it is becoming a research ready practice or carrying out your own research. A research project doesn’t necessarily need to be a large trial to be interesting and have potentially significant results. From a personal point of view I find being involved in research intellectually rewarding (and challenging!) It has also given me the opportunity to meet colleagues who are established experts in their fields and provided me with access to additional educational opportunities.  I feel that being an academic GP overall has a very positive impact on my own patient care and I am also able to disseminate my learning to my practice colleagues. One good starting point for GPs thinking about carrying out their own research would be to attend the RCGP conference.  At the conference there are plenty of opportunities to meet with people who have carried out primary care research as well as getting a feel for the different types of research being carried out.  Another possible route would be to contact your local primary care research department.  Academics are usually very happy to hear from clinicians interested in research and about new good research ideas!

Click here to read the research paper. 

Helen’s research was supported by a grant from the RCGP Scientific Foundation Board (grant number SFB 2013-28) and a European Hydration Institute (EHI) Student Research Grant. For more information about research activities and opportunities from the RCGP click here.


1. Parretti, H. M., Aveyard, P., Blannin, A., Clifford, S. J., Coleman, S. J., Roalfe, A. and Daley, A. J. Efficacy of water preloading before main meals as a strategy for weight loss in primary care patients with obesity: RCT. Obesity, 2015  23: 1785–1791. doi: 10.1002/oby.21167.


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