If you want to lose weight, watch what you drink, not just what you eat. 

That’s because a study suggests that liquid calories, particularly from sugar-sweetened beverages, may have a bigger impact on weight than calories from food.

What’s more, researchers discovered that drinking just one fewer soft drink or sugary beverage a day was associated with just over one pound of weight loss at six months and another 1.4-pound loss at 18 months.

Doctors at the Johns Hopkins Bloomberg School of Public Health in Baltimore, Md., followed the dietary habits of 810 people between the ages of 25 and 79 for 18 months and made unannounced calls to see what they’d eaten over the last 24 hours.

The results, published in the April 1, 2009, issue of the American Journal of Clinical Nutrition, showed that study participants got more than a third of their liquid calories from sweetened drinks like sodas, fruit drinks and fruit punch.

Both liquid and solid calories led to weight change, but only the participants who cut their liquid calories saw significant weight loss after six months.

Liwei Chen, MD, PhD, MHS, was a student at the Bloomberg School when she conducted the study. “We think our data really support that cutting your sugary drinks is a very easy and simple way to help you lose weight or avoid additional weight gain,” she said.

Katherine Zeratsky, a registered dietician with the Mayo Clinic in Rochester, Minn., who was not associated with the study, agrees that the results reinforce the message that small dietary changes can make a big difference. “Making a small change like reducing the amount of empty calories in your diet will result in a change for some people Making that small step can put them on a road to a healthier lifestyle.”

Researchers say greater consumption of liquid calories from beverages has paralleled the obesity epidemic. But they suggest an easy weight loss solution if people trade in their sugar-sweetened beverages for water.

“One big problem for people who try to lose weight is, if they are dieting, after a short time period they feel very hungry and want to eat more,” Dr. Chen said. “But if you cut your calories from beverages you won't feel that much hungrier, so this may mean there's an easier way to cut your calories. “

Previous studies have shown that liquids have very little impact on appetite, making it easy to overindulge.