Despite previous studies hinting that calcium may help people lose weight, it doesn't seem to help teenagers shed pounds, a new trial suggests.
"The last 10 years of research hinted that calcium would bind to fat and take some of the fat out so you wouldn't absorb it," said co-author Connie Weaver, a nutrition professor at Purdue University. "We showed that didn't happen."
In the study, published in the American Journal of Clinical Nutrition, more than 40 overweight teenagers were split into two groups and then randomly assigned to consume 1,300 or 650 milligrams of calcium a day. It either came from calcium supplements or was hidden in foods like frozen chocolate desserts containing milk proteins, fats and minerals (as opposed to whole milk).
For three weeks, both groups were placed on the same restricted diet of three meals and two snacks a day. Both groups got normal foods with enough protein, carbohydrates, fat and calories to maintain their weight. After a break, the groups resumed the experiment for another three weeks, with teens assigned to a different calcium intake level for the second stage.
In the end, researchers found no differences in body fat and weight between the two groups, suggesting calcium had little to no effect on weight loss among the teens.
They also tested the amount of calcium and fats the teens excreted and found no indication that calcium might help with weight loss by binding to fat in the intestines and preventing it from being absorbed.
The study's small number of participants and short duration are weaknesses, said Michael Zemel, who studies nutrition and obesity at the University of Tennessee.
"There have been recent comprehensive reviews that show calcium has a significant effect on body weight and body fat," said Zemel, who was not involved in the current study. "But those tend to be in adults."
Zemel suggested the findings this time may have been different because teenagers have different dietary needs than adults. "These are growing teenagers so they're using their calcium for growth," he told Reuters Health. "They have different energy needs than adults."
The U.S. Department of Agriculture's Choose MyPlate guidelines recommend three cups of dairy a day for youngsters aged nine to 18. Some of the choices for dairy include a cup of low-fat or fat-free milk or yogurt, 1.5 ounces of hard cheese, two cups of cottage cheese or a cup of frozen yogurt.
A recent Centers for Disease Control and Prevention (CDC) study found nearly 70 percent of children and teens drank milk, but 20 percent weren't drinking low-fat milk.
Though Weaver agreed, "you need your milk or calcium for your bones," she believes that when it comes to weight control, adults and teens alike need to keep an eye on the scale.
"Use your scale to determine if you're eating the right amount calories compared to what you're burning every day," she told Reuters Health.
Zemel also thinks the scale tells the bitter truth. "Either you need to cut calories or increase physical activity if you want to lose weight," he said.