'No Difference Between the Diets' in Reversing Prediabetes

Ian MacDonald, PhD;  Mark Harmel, MPH


October 30, 2019

This transcript has been edited for clarity.

The PREVIEW project is a multinational diabetes prevention project for which I was fortunate to be one of the principal investigators. It is funded by the European Union and includes six European countries plus Australia and New Zealand.

We recruited 2300 people with proven prediabetes. The trial is different from many other diabetes prevention studies in that it had an initial weight-loss period on a low-calorie diet over 8 weeks. Participants had to lose 8% of their body weight in order to qualify for the next phase.

The successful participants, which were the vast majority, were then put into a diet and physical activity program for the next 3 years. The diet alternatives were high protein with a low glycemic index, or moderate protein with a moderate glycemic index. The physical activity interventions had the same total amount of activity but either at higher intensity for a shorter duration or at lower intensity for a longer duration.

Participants were introduced to the diet and activity program by dieticians and exercise therapists who had been trained centrally within the consortium to deliver cognitive-behavioral therapy–based and motivational interviewing–based advice, teaching them about diet, diet composition, and types of physical activity.

Participants had frequent meetings with these specialists to start with, but they became less and less frequent over the 3-year period such that, in the final year, they didn't see them at all. They saw them at 24 months and then at the very end, at 36 months.

Which Diet Was Better?

As you would expect with a program like this, the dropout rate was high. Overall, we had a little over 50% of participants drop out, so we ended up with 950 people at 3 years.

Based upon their initial risk, we had predicted that 21% would develop type 2 diabetes at 3 years. The expectation was that participants on the moderate-protein diet with activity would drop the rate of type 2 diabetes to approximately 15%, and those on the high-protein diet would drop it even further, to about 10%. It was very exciting, then, that only 4% developed type 2 diabetes, but it was disappointing that there was no difference between the diets.

We think that's partly because the initial weight loss was a real determinant of success. Participants maintained at least some of that weight loss over 3 years with good dietary and physical activity advice. It actually didn't matter about the diet composition because both diets were healthy. The diet that was higher in protein and lower in glycemic index was deemed to be healthier, but it wasn't sufficiently better than the moderate-protein diet to make a difference.

The challenge now is what to do going forward. Clearly, 3 years is good, but it's not a lifetime. Somehow, we need to develop systems to help these people manage their problems, keep their weight off, continue to be physically active, and minimize the chance of transitioning from their prediabetic condition to type 2 diabetes.

Interestingly, among the participants who finished, 18% no longer had prediabetes; they had glucose levels in the healthy range. Certainly, they need to maintain that state. The other participants who still have prediabetes need some sort of help in the future to remain in the prediabetic condition or to move toward normal, healthy glucose levels.

Ian MacDonald, PhD, is a professor of metabolic physiology at the University of Nottingham in the United Kingdom. His research is concerned with the functional consequences of metabolic and nutritional disturbances in health and disease, with specific interests in obesity, diabetes, cardiovascular disease, and exercise. He has published over 350 peer-reviewed original research papers, as well as reviews, book chapters, and invited contributions.

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