SAN FRANCISCO – And to the surprise of researchers, the results were the same regardless of dietary and exercise interventions more than 3 years after the initial weight loss.
Dr. Ian MacDonald
There’s a big limitation, though: About half of the participants who initially lost weight dropped out during the 3-year study, and data about them are not yet available. Still, only 4% of those who completed the study converted to diabetes, compared with expected rates of as much as 16%.
This is a “fantastic success,” co-lead investigator and physiologist, Ian Macdonald, PhD, of the University of Nottingham (England), said in a presentation of the PREVIEW study at the annual scientific sessions of the American Diabetes Association.
The randomized, controlled, multicenter trial recruited 2,223 participants with prediabetes in several European countries and Australia and New Zealand. The participants, of whom about two-thirds were women, were aged 25-70 years (average, 52 years) and had an average body mass index of 35 kg/m2.
They were assigned to a 2-month, rapid weight-loss program in which they were limited to no more than 800 calories per day. “The participants were fully briefed on the risks to health associated with prediabetes and on the problems of diabetes itself, and they were highly motivated to take part in the study,” Dr. Macdonald said in an interview after the presentation.
A total of 1,857 participants achieved the required weight loss of at least 8% and were then assigned to one of four interventions: a high-protein, low-glycemic diet (either with moderate- or high-intensity physical activity) or a moderate-protein, moderate-glycemic diet (either with moderate- or high-intensity physical activity).
A total of 962 participants remained in the study for another 34 months until completion, with roughly the same number (235-244) in each of the four intervention groups.
The researchers expected that 16% of those in the moderate-diet group would convert to type 2 diabetes, as would 11% of those in the high-protein, low-glycemic group, Dr. Macdonald said in the presentation.
The researchers, who offered limited statistical detail about the study, did not disclose how many participants in each group actually developed diabetes by 36 months (January 2019). Dr. Macdonald said in the interview that those numbers would not be available until the study has been accepted for publication. He noted, however, that the numbers in the two groups were nearly identical, and the researchers disclosed that the overall number was just 4% (n = 62).
That number is “substantially less than would be predicted,” Dr. Macdonald noted in the presentation, adding that “there is no difference” between the interventions.
He said protein consumption in the high-protein diet was not sustained, probably because of lack of adherence. In contrast, the physical activity in the groups increased significantly at the beginning of the study, he said, and “it did not fall off too badly.”
According to Dr. Macdonald, the prevention of progression to diabetes “was almost certainly because of this large, initial weight loss, which was at least partially and impressively sustained. A high-protein, low-glycemic diet was not superior to a moderate-protein, moderate-glycemic diet in relation to prevention of type 2 diabetes.”
The study was funded by the European Union and various other sources, including national funds, in the participating countries. Dr. Macdonald reported advisory board service with Nestlé Research, European Juice Manufacturers, and Mars.