Until now, the assumption has been that a slow stroll could provide the same health benefits as a brisk walk, as long as you're willing to expend the same amount of energy. According to Williams' study, however, walking fast is the only way to walk for health. For the research, he pulled results from the National Walkers' Health Study, a database that began documenting the walking habits of middle-aged men and women who walk regularly for exercise in 1998. Williams took 7,375 male and 31,607 female participants, and split them into four categories — numerically equal, but divided by speed. The categories range from the fastest (at less than 13.5 minutes per mile) to the slowest (at 15-16 minutes per mile), representing nearly every speed of walking. Admittedly, the next step of the study got a bit weird.
Williams took his information from the study and cross-referenced it against the National Death Index to see how many of those 39,000 walkers had passed away. He found that nearly 2,000 had died, and many of the deaths were clustered among slow walkers. Those in the slowest category of his study were 18% more likely to die, and were especially vulnerable to heart disease and dementia. Even if these slow walkers expended as much energy per day as someone who walked briskly for 30 minutes, the death rate remained high among them, making them 44% more likely to die than fast walkers. Williams explains that pushing your body to move at a faster pace causes favorable physiological changes that milder exercise simply can't produce, no matter how much time you spend doing it.
Of course, the slower walkers may have had pre-existing conditions that made them walk at a reduced pace and may have contributed to an earlier death. But, Williams claims that notion is just a small detail that doesn't impact the overall truth of his findings. Furthermore, he maintains that measuring your walking speed could serve as a measure of your overall health. This is important to keep in mind when you consider that the walkers who moved just a minute-per-mile faster than the slowest category in the study had a significant reduction in premature death.
So, if you're walking for fun, take your time. But, if you're using walking to meet an exercise requirement, then intensity matters. There remains no study justifying our waiting in lines for cronuts. (The New York Times)