When New York City public schools made the switch from whole milk to skim or low-fat milk, students cut their annual fat and calorie consumption, department researchers found.
Milk-drinking students consumed 5,960 fewer calories and 619 fewer grams of fat per year after they made the switch, Philip Alberti and colleagues reported in the Jan. 29 issue of the CDC's Morbidity & Mortality Weekly Report.
At 3,500 calories per pound, the reduction would be the equivalent of 1.7 pounds of body weight over the course of a year.
"The switch to lower-fat milk likely has improved the overall nutritional environment of New York City public schoolchildren," Alberti and colleagues wrote.
On the other hand, most of the low-fat milk consumed was chocolate milk, which has a substantially higher sugar content than unflavored milk, the researchers found.
In 2005, the New York City Department of Education began reviewing its food policies and determined that replacing whole milk with fat-free or low-fat milk could decrease students' fat and calorie intake.
At subsequent board meetings, milk industry advocates suggested that without whole milk or chocolate- or strawberry-flavored milk, student milk consumption would decline, thus decreasing calcium and vitamin intake.
Nonetheless, the Department of Education began phasing out whole milk in 2005, and limited flavored milk to fat-free chocolate milk.
The researchers didn't have data on student consumption of milk, so they analyzed system-wide school milk purchases.
They found that per-student school milk purchases dropped 8 percent between 2004 and 2006, but then gradually began to increase. By 2009, purchases had risen 1.3 percent from five years prior: from 112 per student in 2004 to 114 in 2009.
Fat-free milk accounted for 42 percent of all purchases in 2009, compared with less than 7 percent in 2004.
In 2004, students purchased more than 18 billion calories and 520 million grams of fat in the form of milk. That fell to less than 14 billion calories and 98 million grams of fat in 2009, representing a 25 percent and 81 percent decrease, respectively.
Over that five-year time period, the researchers calculated that if calorie and fat savings were distributed among all students -- including those who don't drink milk -- they would consume 3,484 fewer calories and 382 fewer grams of fat were each year.
If the data were limited to students who do drink milk during the school day -- 62 percent of students in 2004 and 63 percent in 2009 -- the savings increased to 5,960 calories and 619 fat grams per year.
Alberti and colleagues wrote that the data show the milk policy change reduced fat and calorie intake while still providing protein, calcium, and vitamins A and D.
"Other school systems can use these results to guide changes to their own school food policies," they said.
They noted, however, that the majority of low-fat milk consumed -- 60 percent of all milk purchases -- was chocolate milk, a concern because sweetened milk has more calories than reduced-fat white milk and contains twice as much sugar.
But limiting its availability would "further reduce milk consumption," they wrote.