When the food industry or its trade associations are questioned about the global problem of obesity, they tend to draw heavily on the modern rise in the physical inactivity side of the coin rather than the energy intake side. Since they have a significant vested interest in the latter, that is understandable. But it does lay them open to the criticism that they have precious little interest in the caloric intake side of obesity and simply argue that energy imbalance is largely due to the decline in physical activity in the last half century. Much of this criticism comes from those who brand the food industry in the worst possible light right down to the direct comparison with the tobacco industry and scientists who receive money from the food industry in the study of physical activity are drawn into this scenario. I have previously blogged on this issue so I will just highlight here some of the arguments. Those that belittle or reduce the role of physical activity point out that in the last 50 years, there has in fact been a rise in leisure time physical activity. Now this is true for a proportion of the population but it is be no means universally true and endless national reports document the continued domination of a sedentary lifestyle. They are also likely to cite published papers, which argue that the rise in caloric intake exactly parallels the rise in obesity. They are more likely than not to ignore the compelling data that whereas leisure time physical activity has increased, work related physical activity has plummeted. They are also likely to ignore data on daily physical activity among the traditional Amish community who continue to live a life of high work and leisure-related physical activity, a lifestyle now utterly demolished at work due to the advent of multiple labour-saving devices, from automation to the silicon era. They are also likely to downplay the importance of papers that argue that the rise in obesity does not match the rise in caloric intake when correct adjustments are made for rising food wastage. So lets look again at the issue of physical activity in the management of bodyweight.
Question 1: Is physical inactivity really a serious contributor to ill health? The WHO certainly thinks it is. They write thus: “Physical inactivity (lack of physical activity) has been identified as the fourth leading risk factor for global mortality (6% of deaths globally). Moreover, physical inactivity is estimated to be the main cause for approximately 21–25% of breast and colon cancers, 27% of diabetes and approximately 30% of ischaemic heart disease burden.” Rightly they point out the “exercise” is not the same as “physical activity”: The term "physical activity" should not be mistaken with "exercise". They write: “Exercise, is a subcategory of physical activity that is planned, structured, repetitive, and purposeful in the sense that the improvement or maintenance of one or more components of physical fitness is the objective. Physical activity includes exercise as well as other activities which involve bodily movement and are done as part of playing, working, active transportation, house chores and recreational activities”. In short, exercise implies changing into sports gear. Physical activity you can do in your work clothes.
Question 2: Is body weight the correct end point to use when considering physical inactivity and health? Physical inactivity is ranked 4th by the WHO as a major contributor the global burden of disease while obesity is ranked just below that as the 5th biggest cause of global mortality. Two of the major adverse effects of obesity are poor cardio-respiratory function and poor blood glucose control and physical activity can greatly reduce these two adverse effects. So obesity is visible but you can’t eyeball someone to ascertain his or her cardio-respiratory or blood glucose function. Thus, it is far more important to regard the role of physical activity as maintaining optimal heart and blood glucose function than it is to regard enhanced physical activity as a solution to obesity. Nonetheless, the absence of modest levels of physical activity, is, as we will see, a major risk factor for weight gain.
Question3. Is exercise bashing and industry funding really a problem? From time to time, it becomes fashionable to ridicule the role of physical activity. An editorial in the British Journal of Sports Medicine wrote thus: “It is time to wind back the harms caused by the junk food industry’s public relation machinery. Let us bust the myth of physical inactivity and obesity. You cannot outrun a bad a diet”. I Sensationalist rubbish! An important peer-reviewed paper published recently in the leading journal (the American Journal of Clinical Nutrition) that I will now look at, was written by the top US researchers in the field of physical inactivity, health status and obesity. The study was supported by “an unrestricted research grant from the Coca Cola Company” and of course that led to considerable criticism. The fact that it was co-funded by the National Cancer Institute was of course ignored. The University of Colorado Medical School, where one of the leading authors works, recently returned a $1 million Coca Cola grant for physical inactivity research. And of course, the Coke funding was likened to funding of the tobacco industry in the smoking area.
The main feature of the study that these authors published was that it looked at the long-term effects of. The authors go back in time to a very early study of low levels of physical activity in employees in the Ludlow Jute Company in Calcutta. Those with low levels of physical activity included clerks, shopkeepers and supervisors whilst those with high physical activity included blacksmiths, coalmen and bale carriers. The authors of this 60 year old paper introduce their work with the following statement: “It has been stated-or implied-by many workers that the regulation of food intake functions with such flexibility that an increase in energy output due to exercise is automatically followed by an equivalent increase in caloric intake. This view, usually accompanied by a minimization of the energy expenditure due to exercise, has often led to the disparagement of physical activity as a factor in weight control. The fallacies inherent in such an attitude have been discussed.” These authors back in 1956 showed that the following: Body weight was highest among those with the lowest level of physical activity. However, as physical activity increased beyond that point, body weight remained constant. Research techniques have changed dramatically since then and the recent research re-visited this area. 421 subjects were recruited into this 1-year study. Accelerometers were used to repeatedly measure physical activity and subjects were classified into quintiles (fifths) of Moderate to Vigorous Physical Activity (MVPA). Energy intake was assessed by repeated dietary assessment combined with measurements in energy balance. Body fat mass was assessed using sophisticated X-ray technology. The two main findings of the study re-affirm what was shown 60 years ago: (1) above the lowest level of physical activity, there was a positive correlation between rising energy intake and rising physical activity. That was not so at the lowest level of physical activity. (2) The accumulation of fat mass was highest among the least physically active, while across the remaining fifths of physical activity, no changes in fat mass was seen. Both studies point to the dominant role of low levels of physical activity as the problem in body weight regulation. Beyond that lower level of physical activity, additional physical activity had no effect. So sitting as a couch potato has a much more important effect on long-term body weight regulation than pounding the pavement or gym. So what would a couch potato have to do to escape this gloomy fate? The more modern paper can estimate this as steps per day since it measured these. The finding is that just over 7,000 steps per day would get the couch potato out of trouble. That is easily attainable in simple walking programmes of about 30 minutes duration. So to conclude:
- Physical inactivity is a global killer, actually ahead of obesity
- When we come to look at suitable end points of improved physical activity, improved cardio-respiratory fitness and improved management of body weight are best achieved in getting off the couch. Running marathons won’t yield a pro-rata improvement.
- Bashing physical activity and physical activity researchers because of industry funding, is a popular headline grabbing exercise. It particularly helps those who have the view that obesity is caused by large food corporations and who believe that any focus on physical activity detracts from that near criminal activity
 Mayer J et al (1956) Relation between Caloric Intake, Body Weight, and Physical Work: Studies in a West Bengal situation. Am J of Clin Nutr: 12,169-175
 Shook RP et al (2015) Low levels of physical activity are associated with dysregulation of energy intakes and fat mass gain over 1 year. Am J Clin Nutr e-pub ahead of print