The PREVIEW study
Your editor attended a seminar held at the Charles Perkins Centre at Sydney University in April, at which several of the international researchers involved in the study presented their findings. A major publication is pending (so we can’t divulge too many specific results) but look out for plenty of publications examining different aspects of this rich data set over the coming years.
PREVIEW stands for PREVention of type 2 diabetes through lifestyle intervention and it’s the largest study of its kind. PREVIEW is a large multi-national, multi-centre randomised clinical trial (RCT) of 2500 overweight or obese pre-diabetic participants studied over three years. A sub-study in children and adolescents was conducted over two years. The study included eight countries, six in Europe plus Australia and New Zealand. The local project collaborators are Professor Jennie Brand-Miller from the University of Sydney’s Charles Perkins Centre and Professor Sally Poppitt from the University of Auckland. Their overall research question was to identify the most efficient way to prevent T2D, and the hypothesis was that a higher protein, low GI diet would be superior.
In addition to the RCT, population studies are also being undertaken including 170,000 individuals.
The RCT consisted of an eight-week weight loss phase using low energy diet (LED) meal replacements (Cambridge Weight Plan products were donated to the study), followed by randomisation into one of two diets, then followed for 34 months:
All groups were counselled using behaviour modification tools, most intensively in the first 12 months (around once per month).
You can read more about the psychological element of the study protocol and the behaviour modification toolbox here.
As expected and hypothesised based on previous studies (eg DiOGenes, which in part inspired PREVIEW), the interventions were highly effective – in all groups- in preventing type 2 diabetes, with a much lower incidence than expected.
Almost four in five completers (those who stayed the course) had a lower weight than they had at baseline, but there were no significant differences between intervention groups. The investigators are yet to determine if there were other differences.
The hypothesis was not confirmed- there was no advantage in the different diets or exercise intensities for lowering risk of type 2 diabetes.
This may be due to the small number of cases of diabetes that eventuated.
The investigators suggest that it was the large initial weight loss (11% of body weight was lost in the first 8 weeks) that was key to diabetes prevention.
Low energy meal replacements are effective for weight loss.
A high protein (energy restricted) diet is effective for body-weight loss and maintenance, and the efficacy is due to the protein, irrespective of carbohydrate content. An amount of >0.8g/kg protein is sufficient for body weight management, but a higher protein diet of 1.2g/kg protein daily is required for preserving fat-free mass.
Diets with moderate or high protein both seem to be effective for weight loss. This is helpful for long term compliance as high protein diets may be more difficult to stick to. There may be metabolic benefits (as well as environmental ones) for combining plant as well as animal protein sources.
Participant compliance with the two diets, although significantly different in protein, drifted over time to moderate amounts. This may suggest that moderate protein intakes, rather than high, are easier to maintain. In general, study participants were reasonably affluent, and they appeared to have a ‘natural’ level of protein intake at around 20% of energy.
There was no benefit in high intensity physical activity, which is reassuring for people who cannot do high intensity or prefer moderate intensity physical activity. This offers clinicians a variety of strategies to use with patients/clients. The most important thing is to increase total physical activity levels and reduce sedentary time.
Behaviour modification approaches are effective in maintaining healthy diet and physical activity, and perhaps more important than dietary composition. It was effective when conducted in a group setting, which has implications for weight management services.
Health professional support is critical to implementing and maintaining positive changes in diet and exercise.
The PREVIEW study presents an opportunity for public health improvement and can provide direction in planning of weight management services.
You can find out more about PREVIEW including the many publications at preview.ning.com
Interview with Dietitian Ros Muirhead
Ros Muirhead is Clinical Trial Coordinator for the PREVIEW study at the University of Sydney. We asked her some questions about her experience.
What do you think PREVIEW teaches Dietitians?
We need to be able to offer a choice in the way we provide dietary help, and we need to develop behaviour change skills. We need to think creatively, to provide support and encouragement and don't be afraid to try a new approach, such as total diet replacement or group sessions. Research shows dietitians can be hesitant to use low energy meal replacements.
We have to breakdown some of the preconceptions people have about dietitians and what we provide. When prompted, patients often know what they need to change and more importantly what they are willing to change - they need support to do this. They need information and they need to be reminded that they will lapse and relapse, but this is a cue to review their goals which may be unrealistic. Some people need more help than can be provided by a dietitian, such as psychological help/support.
Which results delighted you?
Small changes that become habits can make a big impact on health outcomes such as being able to stop taking blood pressure medication and achieving normal blood glucose levels. Success opens patients up to the possibility of making more changes and improves their self-efficacy.
It was delightful to see how life-changing the study has been for quite a few of our participants. No longer needing blood pressure medication, sleeping well (no sleep-apnoea), going skiing with the grandchildren, re-discovering the joy of dance, travelling (long walking tours overseas), living and enjoying their lives when they really thought they would never be able to experience life in this way.
Did any of the results surprise you?
The success of total meal replacements for weight-loss. Weight loss with the Total Meal Replacement was very effective both for, losing weight in a population that had struggled to lose weight, and it was very motivating for the participants. As participants lost weight, they were more open to making changes to their dietary and exercise habits. It often revealed some of their unhealthy habits/relationships with food and provided a starting point for discussion and examples of how behaviour could be changed.
At the beginning of the study I was a bit uneasy about having group sessions as dietitians often work one-on-one. It was a good format to promote support from the other members of the group who had had similar experiences. Some people are quite lonely, and it is refreshing for them to be with people who are faced with similar challenges.