A 15-minute walk to a light-rail station might not seem like much of a workout. But such walks, twice every workday, could help millions of people meet exercise guidelines and get fitter without setting foot in a gym, researchers say.

Commuters who switched from driving to walking, cycling or public transit lost more than 2 pounds in two years on average, according to a recent study of 4,000 adults in the U.K. The longer the commute, the greater the weight loss: People with one-way active commutes longer than 30 minutes lost more than 15 pounds on average over two years.

Another study of 12,000 people in U.S. metro areas published in July in the online journal PLOS One found a robust association between biking or walking to work and lower body-mass index. Researchers say active commuting holds promise to help people keep weight off once they lose it, which is particularly striking as most people who diet eventually regain the pounds.

The results seem so convincing and yet commuting is a highly difficult habit to change. Every minute counts to people rushing to get a family out of the house in the morning or scrambling to get dinner on the table in the evening. Workers in metro areas spent 47.8 minutes commuting via public transportation, versus 24.2 minutes for those who drove alone, according to a 2009 analysis of U.S. Census data.

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