Calcium mechanism for weight loss gets clinical support
and increasing its excretion from the body, say Danish researchers,
who have provided the first clinical evidence to support a
mechanism for the weight loss effect of dairy produce.
Several epidemiological studies in recent years have showed an inverse relationship between calcium intake and body weight. In 2002, a US team reported that a high calcium diet resulted in greater weight and fat loss in obese adults on a low-calorie diet than in those on a low calcium diet.
Researchers have suggested some possible mechanisms for this effect but there has been little evidence so far to support the observational findings.
The new study, published in the March issue of the International Journal of Obesity (vol 29, no 3, pp 292-301), shows that fat excreted in the faeces increased 2.5-fold in people on a high calcium diet compared with when they lowered their calcium intake.
Lead author Professor Arne Astrup at the Royal Veterinary and Agricultural University in Denmark says that this mechanism could be enough to explain a 4kg drop in weight over a year.
"I had this hypothesis that calcium could bind fat in the GI tract and had to find out if it could affect weight through faecal fat excretion. But it surprised us that it was so much," he told NutraIngredients.com.
A short-term boost in dietary calcium increased faecal fat and energy excretion by around 350 kJ per day.
"This is a very solid finding and seen across all of the subjects," added Professor Astrup.
The researchers set up a trial that tightly controlled the diets and energy expenditure of 10 healthy, moderately overweight volunteers. The randomized crossover study tested three diets with different calcium and protein levels, mainly from low-fat dairy products.
These were low calcium (500mg) and normal protein (making up 15 per cent of energy), high calcium (1800mg) and normal protein and high calcium and high protein (23 per cent of energy).
Calcium intake had no effect on 24-hour energy excretion or fat oxidation, ruling out one previously suggested mechanism that the mineral could affect the mineral's role in fat metabolism by influencing fat's oxidation.
However faecal fat excretion came to 14.2g per day for the high calcium, normal protein diet, compared to 6g for the low calcium diet and 5.9g for the low calcium, high protein diet.
The high calcium diet also increased faecal energy excretion as compared with the other diets.
There were no effects on blood cholesterol, free fatty acids, triacylglycerol, insulin, leptin, or thyroid hormones.
The findings are important because this is the first human intervention study to support calcium's fat-binding mechanism through consumption of dairy products.
"The mechanism by which calcium increases fat excretion is probably an interaction between calcium and fatty acids, resulting in the formation of insoluble calcium fatty acid soaps and hence in reduced fat absorption," write the authors.
Professor Astrup noted: "We now have a very good explanation for this effect on weight but there may be others. There could be an effect of calcium on appetite but we wouldn't have seen it as we controlled energy intake among the subjects."
Astrup's team has begun working on further human trials to test the mechanisms of calcium on weight.
The study does not explain the differences seen previously between dairy products and a lower effect from supplements.
