"A brisk 30-minute walk five days a week is more effective than any other form of exercise for keeping weight down," The Times reports. That is the reported conclusion of two researchers who looked at data from the annual English Health Surveys from 1999 to 2012.
As expected, they found people who regularly walk briskly for half an hour five days a week were likely to have a lower body mass index (BMI) than people who are less active.
The study found women and those over the age of 50 were most likely to have a lower weight if they walked regularly. By walking, the researchers mean brisk walking that raises your heart rate and makes you sweat slightly, not a gentle stroll.
Walking was also linked to having a smaller waist size – although, for men, sport and other forms of exercise were more strongly linked to waist size than walking. Sport and exercise were also linked to a lower BMI, although the link was not as strong as it was for walking.
However, this study does not seem to have compared the effects of the two types of activity directly, so we cannot say for sure – as many in the UK media have done – that walking is more effective than other types of exercise.
Walking does have the obvious advantage of being free, as well as being an activity you can easily fit into your day-to-day life. Read more about walking for health and how the 10,000 steps a day challenge can help boost your fitness levels.
The study was carried out by researchers from the London School of Economics and the University of Queensland, and was funded by the Nuffield Trust. It was published in the peer-reviewed journal Risk Analysis.
Many UK media outlets covered the story. Most fell into the trap of assuming walking caused weight loss and, because the link was stronger for walking than for sport or exercise, walking was therefore better for losing weight.
However, the two types of activity were not directly compared, and on some of the analyses in the study, sport and exercise came out better, especially for men.
This data is compiled by the Health and Social Care Information Centre (HSCIC), the same organisation that operates Behind the Headlines and the rest of the NHS Choices website.
Cross-sectional studies can look at the links between factors, but cannot say whether one factor caused another, or vice versa.
Researchers took data from seven separate years of the Health Survey for England to see what people said about how often they took part in specific activities. They compared this with people's recorded BMI and waist circumference. They wanted to find out whether people's weight and waist size could be predicted by how often they did specific types of physical activity.
The study is not clear about how many people were included in the analysis, although the researchers say they had more than 68,000 "observations" about the types of activity people did.
It's possible this means they used data from 68,000 people, although we can't be sure of this. The figures for BMI and waist measurements were based on 26,878 and 38,836 observations respectively.
The researchers put the data through a number of statistical models to work out the relationship between BMI and waist size and any type of physical activity, then looked specifically at brisk walking, heavy manual work, heavy housework, and sport or exercise, including gym workouts, cycling and running.
They adjusted their figures to take account of confounding factors, including people's age, gender, household size, marital status, ethnic background, where they lived, their level of education and employment.
Finally, they calculated the difference in BMI and waist circumference between people who regularly do each activity for more than 30 minutes five days a week (in line with UK government guidelines) and people not getting this kind of exercise.
The first result, not surprisingly, was people who did the most activity, of any type, had the lowest BMIs and the lowest waist measurements. These effects were strongest in women and people over the age of 50.
Brisk walking was linked to the biggest difference in BMI for both men and women. The researchers found men who regularly walked briskly for more than 30 minutes five days a week had a BMI on average one unit less than those who did not, while for women the difference was 1.8 units.
The equivalent amount of sport and exercise was also linked to BMI, but the difference was smaller. Heavy manual work also showed a link, as did heavy housework for women, but not men.
The effect on waist measurement was similar, with one important difference: women who regularly walked briskly had a waist 4.3cm smaller than women who did not. The researchers say this was the biggest difference for any type of activity for women.
However, for men, sport and exercise had a stronger link to waist measurement than walking. Men who regularly took part in sport or exercise had a waist 3.3cm smaller than those who did not.
The researchers said: "The results suggest that those who do five days of any of these physical activities every week for a month could decrease their waist circumference on average by 4.3cm for women and 3.6cm for men."
This is a surprising claim, as the study did not show a change in waist circumference over time, or establish that exercise caused a drop in waist size.
They went on to say: "Overall, we find that brisk walking has the highest association with these measures of weight, with sports/exercise being the runner up in this regard."
They admitted: "We cannot interpret our findings here as causal," but they called for a public health campaign to encourage walking as an "easy policy option" to combat the obesity epidemic.
Walking has long been advocated as a good way to keep fit. It is easy to fit into everyday activities, doesn't need special equipment, and most people can do it.
This study shows people who regularly took brisk walks for at least half an hour five days a week – fast enough to get you out of breath and sweat slightly – were likely to have a lower BMI and smaller waist size than other people.
The results don't mean other types of exercise, such as swimming, cycling, playing sport or going to the gym, are worthless. People who regularly did these activities were also likely to have a lower BMI and waist circumference.
The study does not seem to have directly compared the effect of sport and exercise versus brisk walking. We don't know whether the differences in BMI the researchers found would have stood up as statistically significant in a head to head comparison.
It is interesting that men who did regular sport or exercise had a lower waist measurement than men who walked instead. Waist measurement is important as it shows how much fat you carry around vital organs, which has been linked to heart attacks.
It may be that exercise and sport are less strongly linked to BMI than walking because men who work out gain muscle, which weighs more than fat, so will result in a higher BMI.
The main limitation of the study is it cannot prove people's weight is a result of their activity levels. We know diet is also important in determining weight, as well as other factors such as genetic make-up.
It is possible people are more likely to walk or take part in sport and exercise if they have a lower BMI as slimmer people find physical activity easier and more comfortable. We cannot tell whether the people in this study with a higher BMI would have lost weight by walking or exercising more regularly.
However, this study does add to the evidence that walking is a healthy form of exercise linked to keeping to a healthy weight, especially for women and in later life.