Nutritional science for mind health products
DSM Nutritional Products
However, as milk and other dairy products consistently delivered better results than calcium supplements alone, other bioactive components in dairy such as the branched chain amino acid leucine also appear to be playing a role, said Dr Michael Zemel, professor of nutrition and medicine at the University of Tennessee in Knoxville.
Zemel, who was speaking at Weight Management 2011, a virtual conference organized by NutraIngredients-USA and FoodNavigator-USA last week, said the “bulk of the evidence – and there are contrary studies - does show that increased calcium slows weight and fat gain and accelerates fat and weight loss, and preserves lean mass”.
However, data on children and adolescents was less conclusive, he acknowledged.
Notably, a three-week study on 42 adolescents from Purdue University recently published in the American Journal of Clinical Nutrition showed no effects from dairy or calcium on fat loss, he said. “This study strongly argues against an effect in adolescents.”
Meanwhile, the evidence for calcium as an appetite suppressant was also “quite spotty” in humans, he added.
A serendipitous discovery
As for fat loss, the mechanism of action in adults appeared to be a combination of reduced fat synthesis, increased fat breakdown and increased fat excretion (where unabsorbed calcium binds to fat, reducing its absorption), said Zemel, who started thinking about the role of calcium in weight management in the late 1980s.
“We were feeding hypertensive obese African American men high calcium diets and high dairy diets where their baseline calcium intake was quite low – less than 400 milligrams per day. We gave them an additional 600mg of calcium a day in the form of yogurt.”
While reductions in blood pressure and other cardiovascular risk factors were predicted, said Zemel, he was also “shocked to see nearly a 5kg decrease in body fat. We really didn’t have a good explanation for it.”
He then went on to conduct a series of clinical studies to try to determine if this was a fluke.
And repeated trials on subjects fed a calorie-restricted diet showed that they lost more weight, more body fat and more trunk fat in particular when fed 1,300-1,400mg of calcium compared with those on a lower calcium diet (400mg), he said.
The calcium paradox?
So what was going on? “When we have sub optimal intakes of calcium we get elevations in intracellular calcium via calcitriol [1,25-dihydroxyvitamin D], and that results in a suppression of lipolysis [fat breakdown] and a concomitant increase in the activity of lipogenic enzymes,” he said.
“The combination of the two is an expansion of fat storage.”
He added: “Calcitriol also acts on the traditional or classical nuclear vitamin D receptor to increase the expression of lipogenic genes and to suppress the expression of the fat cell uncoupling protein UCP2. Suppressing that results in an increase in metabolic efficiency.
“All of these things conspire to increase fat storage in the fat cell under low calcium conditions. But if you increase or normalize dietary calcium intakes, you suppress calcitriol and so all of this is switched in the other direction.”
Trunk fat loss
But why the loss of trunk fat in particular for dieters fed high calcium diets?
A “plausible mechanism” was that “calcitriol, acting on the nuclear vitamin D receptor, stimulates 11β-HSD, which results in an increase in cortisol production, especially in visceral adipose tissue, and it is this increase in cortisol on a low calcium diet, that exaggerates the addition of central fat”, said Zemel.
“It is the corresponding suppression of calcitriol and suppression of local cortisol production that we believe to be responsible for the disproportionate reduction in trunk fat.”
The Weight Management 2011 virtual conference and Expo featured speakers covering a wide range of topics from the merits of hoodia as an appetite-suppressant to the role of dairy in weight control. If you missed the conference, you can view the webinars on demand for the next three months.
Click here to find out more.