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[1].
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[2].
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 [3]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
[2]
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
[3]
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
