Memorandum by Professor Andrew Prentice
(OB 74)
HEALTH COMMITTE INQUIRY INTO OBESITY
BACKGROUND
MRC scientist with 20 years experience researching
the physiological and environmental factors causing changes in
body weight and obesity.
BREADTH OF
EVIDENCE SUBMITTED
My evidence will only address bullet point 3
of the Committee's terms of reference:
What are the causes of the rise in obesity in
recent decades?
What has been the role of changes in diet? To
what extent have changes in lifestyle, particularly moves to a
more sedentary lifestyle, been influential? How much is a lack
of physical activity contributing to the problem?
1. Causes of obesity
Obesity is a perfectly predictable biological
response to the massive change in the external environment caused
by the technological/electronic and agricultural revolutions of
the late 20th century. Both sides of the energy balance equation
have been affected and causality can be attributed with roughly
equal measures to sedentariness and the super-abundance of cheap,
highly-refined energy-dense foods.
A corollary of the fact that obesity results
from normal physiology doing what nature intended it to do (ie
lay down fat in times of plenty) is that we should be very concerned
about the widespread use of drugs or surgery to fix the
problem. Genetic explanations (eg the "thrifty gene"
theory) are interesting, but largely irrelevant to finding a global
solution to the epidemic.
2. The role of inactivity
In 1995 Prentice & Jebb published a much-cited
paper in the BMJ entitled "Obesity in Britain: Gluttony or
Sloth?" (see Annex 1). This gathered evidence from a number
of epidemiological studies and government statistical sources
to examine the relative role of diet and physical inacitvity in
the causation of nationwide obesity. The evidence suggested that
physical inactivity was a major driver of the change. However,
we were very careful in the wording of our conclusions and stated
that "Evidence suggests that modern inactive lifestyles are
at least as important as diet in the aetiology of obesity and
possibly represent the dominant factor". We and others
have written extensively about the nature and extent of changes
in energy expenditure in recent decades, so this does not need
to be rehearsed here. Suffice it to say that inactivity is incontrovertibly
a major predisposing factor enocuraging weight gain.
Our BMJ paper was important in being the first
to really draw attention to the "sloth" side of the
argument. Unfortunately it has since been wilfully misused by
some arms of the food manufacturing and retail industries to assert
that physical inactivity is the only cause of the problem, and
hence to deflect blame from themselves. The edvidence does not
support this, we never stated it, and we welcome the public opportunity
to refute the contention.
3. The role of diet
Clearly the nation is consuming considerably
more energy that it requires. This does not necessarily equate
to an absolute increase in energy intake, rather to an
increase relative to our new lower energy needs caused
by sedentary lifestyles (see Annex 2).
A considerable amount of research by our group
and others has demonstrated that the energy density of
foods (kcal or kJ per unit weight) is a key determinant of overall
energy intake, and that human appetite control is readily undermined
by very energy-dense foods (see Annexes 2 and 3). We believe that
a focus on reducing the energy density of modern diets will be
helpful in combating obesity trends. An advantage of concentrating
on energy density is that it side-steps the currently polarised
views about the relative impact of carbohydrates and fats. It
should be noted that energy density needs to be viewed differently
for liquid and solid foods due to the lower satiating value of
liquids. Sugars contribute greatly to the energy-density of soft
drinks, whilst both fat and refined sugars contribute to the energy
density of solid foods.
Certain food outlets, notably "fast food"
restaurants, have menus which are almost universally composed
of very energy-dense foods (see Annex 3). We believe that these
put regular consumers at particular risk. The risk is exacerbated
by marketing techniques designed to encourage the consumption
of larger portion sizes.
In general, the recent changes in the British
diet (ie larger portions of energy-dense foods consumed with greater
frequency) are diametrically opposed to what would constitute
the logical response to the reduction in our energy needs caused
by technolgoical change. Manufacturers and retailers need to be
made more aware of this paradox, and brought on board to assist
with engineeering a more rational dietary environment.
Like the tobacco industry, companies with products
now deemed to be causing a health hazard (eg soft drink manufacturers,
fast food outlets) did not set out to create unhealthy products.
However, now that the consequences of high levels of consumption
are clear, it is reasonable to hold them morally responsible for
amending their products and marketing practices. In the absence
of firm government action vested interests in the food industry
will demand absolute proof about the involvement of their particular
products in causing obesity before agreeing to change. We will
face a re-run of the tobacco denial story. In my (rather limited)
experience of discussions with some of the key players in the
field, most companies would be likely to comply with voluntary
agreements or legislation so long as they have a level playing
field on which to compete (see Recommendations 4, 5).
Recommendation 1
The debate about whether diet or activity is
primarily responsible for the obesity epidemic is unhelpful. Both
are critical, and both should be the subject of government-led
multi-sector initiatives. Propagation of the debate allows certain
sectors of the food industry to exploit the perceived controversy
as a diversionary tactic. The Health Committee should accept and
promote the fact that both sides of the energy balance equation
are critical—probably in about equal measure.
Recommendation 2
Encourage any and all possible means to increase
public awareness about the damaging health consequences of inactivity.
We need people to appreciate that inactivity is a major risk factor
for ill health. The CMO's forthcoming report will be an important
step in this direction and should be translated into simple media
messages for widespread propagation.
Focus interventions towards increasing children's
and young people's enjoyment of active pastimes and sports. Policies
aimed at young adults are also important, since this is when many
people abandon sports and activities. Consider the advantages
of extending the school day by staggering the employment hours
of academic and physical education staff so that time can be created
for sports and active leisure training within the formal curriculum.
I strongly endorse the many suggestions made
by others concerning changes to the urban and architectural environment,
and to transport policy, which will foster more active lifestyles.
Since these have been dealt with in detail by others I will not
expand on them here.
Recommendation 3
Educate the public about the importance of energy
density in regulating an approriate energy balance. Note that
existing (and the proposed stronger) food labelling laws already
list energy per 100g and per portion.
An advantage of this approach is that it will
inhibit manufacturers from replacing fat by other energy-dense
ingredients (usually highly-refined carbohydrates and sugar).
It also gets around the fat versus carbohydates controversy).
Recommendation 4
Legislate to enforce labelling with fat, added
sugar, energy and salt content of foods and meals. Meals should
be listed per serving. In fast food outlets the listing should
be prominently displayed and printed on the meal packaging.
Consider adopting a similar labelling system
to the US where recommended "Daily Amounts" for men
and women are listed on the labelling panel in order to give the
consumer a point of reference. Fats, energy, salt and sugar might
profitably be listed as a percentage of the DA.
Recommendation 5
Seek voluntary agreements from industry (or
legislate if necessary) to outlaw marketing practices based on
"supersizing".
In this respect, outlaw the pricing of products
such that larger sizes are relatively cheaper. This could be applied
only to certain foods categories such as soft drinks, confection
and fast foods.
Recommendation 6
Urgently consider measures to control the advertising
of "unhealthy" drinks, snacks and foods to children.
July 2003
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