A new study casts doubt on earlier, highly publicized findings suggesting that dairy foods burn off body fat.
Only last April, a University of Tennessee study found that people on high-dairy, low-calorie diets lost a lot more weight than those on low-dairy, low-calorie diets.
The National Dairy Council funded that study. Another dairy industry-supported study was expected to confirm these findings. But that didn't happen, says study leader Jean Ruth Harvey-Berino, PhD, professor and chairwoman of the department of nutrition and food science at the University of Vermont.
"When we got our results, it was quite disappointing that there were no differences between the high- and low-dairy groups in our study," Harvey-Berino tells WebMD. "It may be that a low-calorie, high-dairy diet may offer just two pounds more weight loss than a low-calorie, low-dairy diet. But it is not going to be a magic bullet."
Harvey-Berino presented the findings at this week's Las Vegas meeting of the North American Association for the Study of Obesity.
Calories Trump High-Dairy/Low-Dairy Difference
Harvey-Berino and colleagues studied 54 borderline-obese people with an average age of 45. All got a low-calorie diet and a behavior-modification plan that included plenty of exercise. Half the subjects were restricted to only one serving of dairy food each day. The other half got three or four servings of dairy food daily.
After six months, everybody lost weight — 22 pounds in the high-dairy group and 20.5 pounds in the low-dairy group. The difference is not statistically significant; that is, the difference is so small it could be due to chance.
That's a far cry from findings reported last April by Michael Zemel, PhD, director of the University of Tennessee Nutrition Institute. Zemel's high-dairy group lost about the same amount of weight: about 24 pounds. But his low-dairy group lost a lot less: only 15 pounds if they didn't get calcium supplements and only 19 pounds if they did get calcium pills.
What's going on? Zemel says the weight of evidence in multiple studies since 1999 shows that dairy foods help the body burn fat. He suggests that people in the Harvey-Berino's low-dairy group may have eaten so few calories that they didn't get any additional benefit from dairy foods.
"You can only metabolize so much body fat," Zemel tells WebMD. "If you are on a diet with modest calorie restriction, you can improve that effect with dairy foods. However, if you are already restricting calories a lot, you may be at your body's maximum effect and may not see any extra effect of dairy foods."
That opinion gets the endorsement of Selena Ball, RD, a dietitian at the National Dairy Council.
"What Zemel's research has found, and what we see in other studies, is that dairy does enhance weight loss," Ball tells WebMD. "You can restrict calories by a smaller amount and still get a weight loss benefit if you take in plenty of dairy food — three to four servings a day."
But Harvey-Berino says it's too soon to jump to this conclusion.
"In the clinical trials so far, the dairy industry has pulled the strings," she says. "This is a very selected group of individuals who participate in these trials. You are cherry-picking people and cherry-picking their diets. So when you compare people getting lots of dairy foods to people not eating enough dairy food for bone health, you see a difference in weight loss."
All Agree: Dairy Foods Essential
Whether dairy foods can really make a person burn body fat may be controversial. But everybody agrees that dairy foods are essential for good health.
The good news, Harvey-Berino says, is that people trying to lose weight can still eat all the dairy foods they need.
"Women on diets tend to cut out dairy, and that is not good," she warns. "You can eat high levels of dairy foods and still do very well with your weight loss."
That gets a hearty endorsement from both Zemel and Ball.
"People often lose bone when they diet," Zemel says. "So having a dairy-rich diet is the best protection against that bone loss — and it [blunts] the bone effects of calorie restriction."
SOURCES: North American Association for the Study of Obesity 2004 Annual Meeting, Las Vegas, Nov. 14-18, 2004. Jean Ruth Harvey-Berino, PhD, professor and chairwoman, department of nutrition and food science, University of Vermont, Burlington. Michael Zemel, PhD, professor of nutrition and medicine and director, University of Tennessee Nutrition Institute, Knoxville. Serena Ball, RD, registered dietitian, National Dairy Council.