APPENDIX 14
Memorandum by Professor John Blundell
(OB 76)
PERSONAL BACKGROUND
Experience of research on human appetite control
mechanisms for over 20 years; and the impact of physical activity
on appetite control for 10 years. Expertise in fields of behaviour/psychology,
nutrition, physiology and brain systems. Developed and refined
methodology for the study of appetite control in the laboratory
and under natural (free-living) conditions—different procedures
are required for these two environments. Study of appetite control
within a framework of human energy balance; when energy taken
in exceeds energy expended a positive energy balance is created
that leads to weight gain. Energy expenditure is both physiological/metabolic
(resting metabolic rate) and behavioural (movement, exercise,
ophysical activity). However, energy intake is 100% behaviour.
In principle this behaviour is under voluntary conscious control.
In practice the behaviour is heavily constrained by biology and
the environment.
The immediate urgent task is to create a situation
in which there is no positive energy balance; therefore no further
weight gain. At the present time the average body weight and the
number of overweight/obese individuals are both still increasing.
First step is to prevent any further increase. Second step is
to produce a reduction in both of these parameters.
THE HUMAN
APPETITE SYSTEM
. . . is asymmetrical and is characterized by
a strong defence against a negative energy balance (energy deficit
created by dieting or physical activity) and weight loss. There
is a tendency to resist a negative energy balance by compensatory
mechanisms. In contrast, the system does not strongly oppose a
positive energy balance (overconsumption or sedentariness). Therefore
the system (in general) is biased towards overconsumption and
weight gain rather than the opposite. Much eating can be referred
to as "passive overconsumption" because it occurs without
any necessary intention or volition ( most people are not trying
to gain weight). This passive overconsumption is however driven
by the high energy density of foods (particularly high fat) and
their extremely high palatability (tastiness). These food qualities
(high fat/very tasty) are extremely attractive to humans; strong
evidence that they are preferred and sought out. Therefore, there
is a tendency of human system to move towards a positive energy
balance through consumption of highly preferred foods (we can
speak of a disposition or trait). This includes the tendency to
eat opportunistically when food is freely available.
OBESIGENIC ENVIRONEMENT
It is now widely accepted to speak of an "obesigenic"
environment—this means that the environment contains strong
features that simultaneously promote eating and sedentariness
(reduced effort, energy saving strategies, restful leisure activities).
Of concern for appetite control is the food environment that contains
an abundance of food, designed to be highly acceptable to promote
purchase and consumption. The environment is also highly technological—includes
aggressive advertising, seductive packaging, intimate accessibility
and rapid delivery of food. Environment is structured so as to
provide no barriers between the consumer and food consumption;
indeed the environment is designed to facilitate an intimate interaction.
(Examples of this are telephone shopping and delivery, internet
ordering etc—all designed to permit individuals to have
rapid access to foods with a minimum of effort).
Another aspect of the obesigenic environment
is the fast food system providing instant food in almost every
part of the environment. This means there is a multitude of opportunities
to "eat outside of the home" (EOTH). This allows eating
to occur in an unregulated manner (system permits overconsumption).
The environment provides few actual limits to consumption; in
fact the limits have been weakened or eliminated completely. Gaining
weight is associated with the consumption of high fat foods, soft
drinks and eating outside the home.
A further aspect of the obesigenic environment
is the relaxation or weakening of cultural constraint of the pattern
of eating. Indeed there is probably now no culturally specified
pattern of eating in the UK. Families do not eat together; meals
are not organized; children eat alone—often in front of
the TV. Eating therefore becomes an incidental activity disconnected
from hunger—which is the true need (or driver) of eating.
When hunger is no longer the major driver, then pleasure takes
over. Eating can become a source of pleasure (rather than a behaviour
to remove hunger). This is complemented by the extremely high
palatability of foods produced. However, palatability, whilst
powerful as a phenomenon to deliver pleasure, also stimulates
and prolongs hunger therefore leading to extended eating episodes
(meals) The environment therefore triggers frequent eating episodes
of eating ( because of the abundance of foods and their high visibility)
and once eating has started it is prolonged.
FOODS AND
SATIETY
Satiety is the term given to the inhibition
of appetite by the consumption of food; sometimes called post-ingestive
satiety. All foods necessarily induce satiety but some do it strongly
and others more weakly. Foods that are very high in fat and highly
palatable have weak effects on satiety. These foods are highly
preferred and frequently selected. Therefore people prefer and
select foods that have weak action to inhibit their appetite.
Some of the most preferred foods trigger passive overconsumption.
Warning: we are not dealing with a biological
inevitability. Foods do not affect all people in the same way.
There is considerable inter-individual variability (physiological
satiety signals, sensory receptors, stomach capacity, rate of
digestion etc). It is therefore possible to find individuals who
do have a good satiety response to fatty foods—the existence
of such people (and their small number) does not disqualify the
general statement about the effects of such foods). The appetite
control system does not work in exactly the same way in all individuals—therefore
treatment will not be on the basis of a "one size fits all"
model.
ADJUSTING THE
FOOD SUPPLY—WILL
IT HELP?
The reversal of the current ever escalating
epidemic of obesity will require social engineering on a massive
scale. This is not conceivable. First step is to prevent any further
gain in body weight ie to stabilise the situation. Large changes
are needed to prevent further weight gain in populations; small
changes will help some of the people to stabilize their weight.
Increasing consumption of foods known to have
strong effects on satiety will help. Such foods contain certain
proteins, dietary fibre, certain types of fat, complex carbohydrates.
It is possible to design a diet that would exert strong effects
on satiety. The problem is how to change personal eating habits
so as to incorporate a good satiety function. When eating is governed
largely by immediate gratification (ease of access, minimal effort)
and by potent pleasure, then changing such behaviour is very difficult.
It could be claimed that `Eating is the cheapest and most powerful
form of pleasure available to most humans on a daily basis'. One
development worth considering is the development of nutraceutical
foods for satiety; these would be designed to have high satiety
value but would influence only a small portion of the population
(but probably enough of the market to interest food companies).
EFFECT OF
PHYSICAL ACTIVITY
ON APPETITE
Low levels of physical activity have two effects.
First, because of the low level of energy expenditure it will
be easier for individuals to reach a positive energy balance.
Second, a low activity level means that the appetite control system
is made less sensitive. Satiety signals are effectively weakened
and regulation of appetite is weakened; therefore people are more
vulnerable to passive overconsumption. This effect creates a risk
factor equally as important as the low energy expenditure.
INCREASING PHYSICAL
ACTIVITY—WILL
IT HELP?
It is important to recognize the scale of the
adjustments required. Increasing physical activity will help to
prevent weight gain—but large doses are needed; higher than
most people imagine. It has been calculated that, for women who
have lost weight, the equivalent of 80 minutes of walking per
day are required—just to prevent weight regain. This level
of activity amounts to approximately 500 calories ( approximately
4 miles). Even if such individuals are more prone to put on weight
than some others, the scale of the activity needed—just
to prevent any increase in weight—is considerable. To cause
significant prolonged weight loss, large doses of exercise are
needed, on a daily basis, and for ever.
A reasonable expectation of physical activity
is to structure it to prevent weight gain (ie to prevent a positive
energy balance), rather than to try to achieve weight loss. If
the physical activity demand is too high then it will trigger
adaptive compensatory mechanisms. It should be noted that physical
activity has weaker effects in women than in men (for producing
weight loss)—probably because women defend body weight more
strongly than men.
Physical activity habits must be changed on
a permanent basis to be truly effective.
WHAT ARE
THE ACHIEVABLE
GOALS?
Based on my understanding of the control of
human appetite, principles of energy balance, and the impact of
physical activity, my view is that an achievable goal is the prevention
of further weight gain ie—preventing the further spread
of the epidemic. Even this will require strong social engineering
and should be modelled on those individuals who are successful
weight losers (and maintainers). (losing 13kg and keeping it off
for 2 years). Such people display a profile of habits including
regular daily exercise, low fat diet, monitoring of eating and
a disciplined pattern of eating. This means that changing just
a single aspect of behaviour is unlikely to be sufficient to make
much of an impact on the epidemic. The 4 characteristics of successful
weight losers (from the American Weight Loss Registry) could become
the gold standard for "personal change". However, is
this achievable on a mass scale? Is the current climate of personal
choice, freedom for the consumer etc consistent with the type
of discipline (and even self-denial) that will be needed to make
an impact on the obesity epidemic?
WHAT SHOULD
THE GOVERNMENT
DO?
The government must take action. However there
should be a realistic recognition of what is achievable based
on the (1) operation of human appetite control (it is not simply
a question of will power) (2) the nature and forces in the obesigenic
environment, and (3) understanding of physical activity and energy
balance. Only massive interventions can halt the epidemic and
these may be unacceptable politically and economically. Limited
interventions imposed in the areas of (1) supply of foods, (2)
structure of the eating environment, (3) education in health,
(4) organization of programmed physical activity will be able
to produce small effects overall (but large in some individuals).
The first objective (5 year plan) should be to stop the situation
getting any worse. The second objective (20 year plan) should
be to create an environment in which people can tolerate small
negative energy balances so as to begin to lose weight. At the
moment the focus should be on preventing the lean part of the
population (BMI up to 25) from joining the overweight and obese.
A useful strategy would be to target everyone
with a BMI of 25 (top level of normal range) in order to prevent
them from attaining a BMI of 26 (overweight). In other words to
prevent any more peple being recruited to the ranks of the overweight/obese.
WILL PEOPLE
RESPOND? A PERSONAL
VIEW
We live in a morally confusing world with no
clear ethical guidelines, acceptable to all, about what constitutes
a good or bad life (apart from the social rules embedded in law).
In the context of what is evil in this world, how reprehensible
is it to be obese? Is obesity perceived as being an evil condition?
A recent survey has reported that fewer obese people are concerned
about the conritoin than was expected. It is more likely is that
obesity is perceived as being benign; one of life's accidental
happenings (approx 4% of obese people have a genetic mutation
causing the condition). People get great pleasure form eating
(particularly with the range of foods and eating places currently
available) and the environment facilitates and encourages this.
People also get apparent pleasure from relaxing activities which
conserve energy—effort is perceived as painful and unnecessary.
Under these circumstances we can expect people
to behave in apparently irrational (I don't care about losing
weight) and inappropriate (health does not always bring happiness)
ways. There is no guarantee that losing weight (and the effort
that will be required) will bring the happiness, self-esteem and
respect (from others) that may be desired. And, it will require
the denial of activities that deliver significant pleasure into
lives. The epidemic of obesity can only be seriously addressed
when the changes that will prevent weight gain (or better, lead
to weight loss) carry the same degree of pleasure as eating and
relaxing in sedentary activities.
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