ECO: High Calcium Levels Fail to Improve Success of High Protein Diets in Weight Loss
By Mark Pownall
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HELSINKI, FINLAND -- June 3, 2003 -- Weight loss is no greater if overweight and obese patients are on a restricted calorie high protein diet that is either high or low in calcium.
A researcher who presented new findings here May 31st at the 12th European Congress on Obesity said weight loss is greater when the diet includes appropriate energy expenditure and increased feelings of satiety.
Dr. Peter Clifton from the University of Adelaide, in Australia, said his study showed that a diet high in dairy protein -- and therefore high in calcium -- had the same effect in achieving weight loss as a high protein diet containing mixed protein -- and therefore a much lower intake of calcium.
His dietary comparison in 50 patients was prompted by research from Michael Zemel (Lipids 2003 Feb;38(2):139-46), which suggested that a high calcium diet could play an important role in weight loss.
Dr. Clifton's comparison involved two diets, each providing 5500 kj/day (about 1400 kcal/day), which is moderate restriction on energy intake. Both diets were similarly high in protein, providing 35% of the diets' energy from protein. Energy provided by fat in both diets was 24%.
The key difference was in the source of the protein and therefore on calcium intake. Subjects on the dairy diet were taking a daily 2400 mg dose of calcium compared to those on the mixed high protein diet, who took in 460 mg a day of calcium.
Results did not support Dr. Zemel's hypothesis. There was no difference between the two high-protein diets, not only in terms of weight loss, but also in body fat, abdominal fat and glucose tolerance.
There were, Dr. Clifton said, some "subtle differences" initially in the glycaemic response to a meal and to glucose challenge between the two diets, but the differences disappeared by the time the patients had lost weight.
Overall, patients on the high protein diets lost about 10% of their own body weight, similar to results recorded in previous high protein diet trials.
"These results do not support the hypothesis that high dietary calcium leads to additional weight loss," Dr. Clifton said. "Dr. Zemel was wrong, and the primary determinant of weight loss remains energy constraint."
Dr. Clifton noted several differences between the two studies. The Zemel study had a longer period of energy restriction, a lower level of calcium in the high-calcium group and a smaller sample size. These differences did not help explain the contrary outcomes of the two studies, Dr. Clifford said.
The high-protein high-calcium diet included skimmed milk powder, low-fat cottage cheese and low-fat yoghurt, while the mixed-protein diet included meat, poultry and fish.
Dr. Clifton said, "High protein diets have been shown to be effective in weight loss, at least over 6 weeks. But it does not seem to matter what level of calcium they contain, at least in our population."
Dr. Clifford said that previous observational studies suggested a role for calcium because there was five times more obesity among individuals with the lowest intakes of calcium compared to those with the highest calcium intakes (J Nutr 2003 Jan;133(1):268S-270S. J Am Coll Nutr 2002 Apr;21(2):152S-155S).