The Step Diet is based on five principles that Hill and colleagues have determined underlie successful efforts to shed pounds and keep them off:

1. Maintain the proper energy balance.
2. Small changes drive success.
3. Start with physical activity.
4. Anticipate success, but not instantly.
5. The maintenance of weight loss is more important than the speed or amount of weight loss.

“The whole book is based on small, incremental changes,” Hill says. “You can get people to make big changes, but they’re not sustainable.”

The first step is to strap on a pedometer and find out how active you really are: how many daily steps you take on average during a week. The result might be a shock, because it’s easy to confuse being busy with being active. Busy parents, for example, might be exhausted after a day of ferrying kids hither and yon, even though they’ve walked only the 50 steps from the house to the car and back.

During the same week that you’re counting steps, you also need to keep track of what you’re eating and how much you’re eating-that is, portion size.
“We’re not overweight because we’re eating the wrong foods,” Hill says. “We’re overweight because we’re eating too much of everything.”

Once you’ve figured how much you’re walking, add 2,000 daily steps. Although that might sound daunting, it’s only about 15 more minutes of walking. Then set realistic weight-loss goals.
During the 12 weeks of the diet, there are only two requirements: Eat 75 percent of what you normally do, and every week, increase your steps by 500 a day. You can expect a 1-to 2-pound weekly weight loss, and by the end of the three months, you will have added 8,000 daily steps.

Figuring out how many steps you need to lose weight and then maintain the loss is part of the program. The idea that 10,000 steps is ideal came from a Japanese media campaign to promote the use of pedometers. It’s not really equivalent to the surgeon general’s recommendation of 30 minutes of activity most days of the week.
Depending on stride, most people cover a mile in 2,000 to 2,500 steps, so 10,000 steps in 30 minutes would mean covering a mile in less than eight minutes.

Hill’s not a fan of the 10,000-step concept, partly because surveys show the average person walks about half that a day. “If you say the goal is to get to 10,000, you’re asking them to double or triple their level of activity. People get discouraged if you give them that big a goal,” he says. On the other hand, Hill says, 10,000 steps a day might not be enough for some people to lose weight and keep it off.

There’s certainly evidence that 10,000 steps makes a difference. A recent study showed that middle-age women who took at least 10,000 steps a day on average were much more likely to fall into normal ranges for body fat and weight, while those who took fewer than 6,000 a day were more likely to be overweight and carry their weight around their middle-a sign of increased risk for heart disease.

The study of Medicine & Science in Sports & Exercise, the official journal of the American College of Sports Medicine, followed 80 women ages 40 to 66 who wore pedometers to keep track of their daily steps. After one week, researchers put them in three groups: inactive (women who took 6,000 or fewer steps), somewhat active (6,000 to 10,000) and active (10,000-plus). The active women had, on average, 26 percent body fat and fell into recommended ranges for body fat versus lean tissue, while those in the inactive group had a body fat percentage of 44 percent and fell well into the overweight category.

Determining how many steps you need to reach a weight-loss or maintenance goal is a matter of arithmetic, Hill says. The book contains a 13-step formula that could scare anyone without an advanced degree in mathematics, but it’s about to get easier.
The person who’s going to be most successful at the Step Diet is probably someone who has been unsuccessful at maintaining weight loss in the past, Hill says. “Now they’re ready to roll up their sleeves and do what they need to do,” he says.