"I think there are two key messages from this study," said study lead author Jeremy D. Krebs, a senior lecturer with the school of medicine and health sciences at the University of Otago in Wellington, New Zealand. "The first is that no matter what diet we prescribe, people find it extremely difficult to sustain the changes from their habitual diet over a long time. But if they are able to follow either a high-protein diet or a high-carbohydrate diet, they can achieve modest weight loss."
Krebs said this first message conveys flexibility and allows people to choose the approach that best suits them and "even to swap between dietary approaches when they get bored."
The second point "is that for people with diabetes, if they can adhere to either diet and achieve weight loss, then they do get benefits in terms of their diabetes control and cardiovascular risk," he added.
Overweight and diabetic
To compare the potential benefits of two popular dietetic approaches, the authors tracked nearly 300 overweight men and women between the ages of 35 and 75 who were on a new, two-year nutritional programme.
To start, all the participants had a body mass index greater than 27, meaning they were moderately overweight, and all had type 2 diabetes.
The researchers randomly assigned the participants to one of two groups: a low-fat/high-protein group or a low-fat/high-carb group.
For the first half year, all attended twice-weekly group sessions led by a dietitian; for the following six months, sessions took place monthly.
Weight and waist circumference were measured at six months, one year, and two years. Kidney function and lipid (blood fats) profiles were also assessed throughout.
Food diaries indicated that total kilojoule intake went down in both groups. Ultimately, both groups lost a similar amount of weight and reduced their waist size in similar measure, the investigators found. And by the end of the two-year period, both groups had similar blood fat profiles.
Diabetics and cutting kilojoules
Krebs and his colleagues concluded that their "real-world" experiment demonstrated that both approaches afford similar benefits, with the principal driving factor behind sustained weight loss being kilojoule reduction rather than either high-carb or high-protein consumption.
Lona Sandon, a registered dietitian and assistant professor of clinical nutrition at the University of Texas Southwestern Medical Center at Dallas, said the observations were "not at all surprising".
"This is pretty consistent with other research out there that has conducted other long-term comparisons in the general population," she said. "In the first six months you might see a little better benefit from a high-protein approach. But long-term, the initial benefits from a high-protein diet seem to diminish over time, and the two diets end up being essentially equivalent," Sandon explained.
"The bottom-line is that the issue for weight loss is kilojoules," Sandon added. "Not where those kilojoules come from. You need to create an energy deficit to lead to weight loss, and that happens by decreasing those kilojoules. That's just been shown again and again."
Experts note that research presented at medical meetings is considered preliminary because it has not been subjected to the rigorous scrutiny required for publication in a peer-reviewed medical journal.
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