Advising people that they can lose 15-25 pounds in a year if they "skip one regular soda per day" and drink water or diet pop instead doesn't work. Jacking up the price does:

During a four-week period when the price of a 20-ounce bottle of soda went up by 45 cents—which amounted to a 35% price increase—sales fell by 26%.... Prices for full-calorie soda went back to normal after the test period, but sales ticked back up only slightly. Then researchers posted fliers around the cafeteria that said: "Lose up to 15-25 pounds in one year and decrease your risk of diabetes by 1/2. Just skip one regular soda per day. For zero calories, try diet soda or water."

Those fliers remained up for four weeks, but sales of bottled soda didn’t fall during that period—in fact, they rose slightly. Finally, the researchers reinstated the 45-cent soda tax while keeping the fliers up for another four weeks. That cut into sales of bottled soda, prompting a 36% decline compared with the weeks before the prices first changed.

The researchers concluded that taxes can work—only the price increase had a statistically significant effect on sales of sugared soda.