Examination of Witnesses (Questions 280-299)
17 JULY 2003
Q280 Dr Naysmith: What sort of things
are you talking about when you say that the evidence is not there,
it is not good, but the answers are blindingly obvious?
Professor Prentice: Let me give
you an example. In relation to our BMJ 1995 paper Gluttony
or Sloth, the evidence as to whether or not we in this country
are actually consuming any more calories per capita of the population
is actually pretty small and contentious. In that paper we presented
evidence from a variety of different sources which showed that
there was little evidence we were eating any more, hence this
paradox: How are we becoming fatter when we are consuming no more
or perhaps even less than we were before? The resolution of that
paradox, of course, is that our levels of physical activity have
dropped even faster than our levels of energy intake. I hope we
will get the chance to explore that paradox a bit more because
I think that is incredibly important to finding solutions.
Q281 Dr Naysmith: When you say the
evidence is not very good, you are talking about measurements
Professor Prentice: Measurements.
The national global food supply figures. If you look at food surveys
with individuals, within populations, that evidence is not very
strongand again that has allowed people to misuse it to
their own endsbut, having said that, I do no think we really
need that evidence. We know that we are gaining calories, or gaining
fat gram by gram day by day and clearly there is an imbalance
in that. We know alsoand we can argue this point in more
detail if you wish, but I think it has already been pretty well
covered by previous evidencethat both sides of that energy
balance equation are critical.
Q282 Mr Burstow: You mentioned rogue
elements in the food industry. I wonder if you might be able to
give us some of the characteristics of such rogue elements in
order that we can better identify them at a later stage.
Professor Prentice: In my background
evidence I made it pretty clear that we have been less than pleased
at the way that paper has been wilfully misused by certain parts
of the food industry, saying, "It is nothing to do with our
products, it is nothing to do with food; it is all down to physical
Q283 Chairman: Can you be specific?
It would be helpful if you were to name names, so that we would
know who you are talking about. You have been extremely polite.
In this Place we are often not politeand sometimes to good
Professor Prentice: Correct. I
think the fact that I am being so polite and so cautious actually
has a message in itself, because a lot of the food industry is
intimidating people and scientists such as myself. Let me give
you an example. If you go into "pubmed"this is
the way we search for publications about scienceand you
put in the words "obesity" and "fast foods"
you get 11 papers out; if you put in "obesity" and anything
else you generally get something like 45,000 papers out, which
you spend the next 10 months trying to sort out. Somehow there
has been very little research on obesity and fast foods. Why is
that? I do not know but I think we scientists are actually to
blame: even if not in an explicit way, we have subconsciously
been intimidated from looking at the problem. I think it is no
secret that the food industry are in disarray at the moment. A
large proportion of them would like to do something. They are
very conscious of the problems and would love to do something.
Within organisations such as the Food and Drink Federation I think
there are some elementsand I will point a finger at the
sugar industrythat are holding things back.
Q284 Chairman: Could I take it back
to the evidence issue. One of the things that has struck me, as
one of those who go back to being at school in the fifties and
sixties, is that certainly my recollection is that health was
more thoroughly measured in respect of children at that stage.
What are your views on the role of the school health service,
the role of the wider NHS in respect of monitoring the changes
taking place in children's health, particularly in respect of
obesity? It was raised with me recently by a head teacher in his
fifties that he personally is fitter than many of his children,
and that worries him, but we have no apparent mechanisms for noting
over various decades these changes. Is that an issue that you
have worked at in the work that you have done?
Professor Prentice: Yes, it is.
It is again an issue that I feel strongly about. I think we have
lost the plot a bit here. I think we should be looking at it more.
Q285 Chairman: Why have we lost the
Professor Prentice: I think we
have partly lost the plot because in past decades there has been
so much of an improvement in health. You have to understand that
initially all that monitoring of height and growth was to look
at growth failure, to look at the flip side of it, and then we
were all growing so well, or by and large we were all growing
so well, that the usefulness of those measure dropped out of sight,
and it has taken a lag time for us to realise that actually we
need to be starting to do this again, to look at the other side
of the equation. I am working this very week in fact to try to
get some standards on body fat in children developed. We are trying
to go into schools with what are called bio-impedance monitors,
to measure body fat and to develop up a national standard of fatyou
can pop children on these monitors very easily, they just stand
on them and you measure the body fatand reference that
to a 50th centile, a normal growth within children. I think we
need to go further than height and weight, and measure body fat,
and we can do it perfectly easily.
Q286 Chairman: We may come back to
that point later on. Professor Hardman, may I welcome you to the
Committee. We appreciate that you and several other witnesses
have had difficulties getting here this morning and we are grateful
for your participation. Would you like briefly to introduce yourself
to the Committee.
Professor Hardman: I am an exercise
physiologist and my title is Emeritus Professor of Human Exercise
Metabolism at Loughborough University. I am essentially a laboratory
scientist but I do have, I suppose, these days, 30 years of experience
in teaching and research concerned with energy expenditure in
exercise. I do not have first-hand professional experience with
working with obese people but I have a good feel for the energy
demands and the metabolic demands of ordinary exercise in ordinary
Chairman: We are grateful for your help
in this inquiry.
Q287 Dr Taylor: Could I ask Professor
Prentice to expand on his and Professor Blundell's comments on
appetite control. I have been retired a few years now but it is
all complete news to me. Professor Blundell: "Foods that
are very high in fat and highly palatable have weak effects on
appetite control." You yourself: "Appetite control is
readily undermined by very energy dense foods." Could you
expand on that and explain it to us because I am sure it is news
to most of us.
Professor Prentice: We have triedand
I have given some very brief summaries of this in the background
documentationto examine how different foods affect the
regulation of human body weight, which is largely through appetite.
Our energy expenditure, our basal metabolic rate with normal processes,
changes very littlea little bit but very littlein
response to different diets, so we have to be looking at the food
intake side. What emerges is that we have what we call an asymmetry
of appetite control: we are very good at recognising hungerit
is an evolutionary obligatory fact that we should respond to hunger
very wellwe are very bad at recognising satiety. Indeed,
if you think it through, we are almost predesigned to lay down
fat, and this is the thrifty geno-type sort of story with which
I am sure you are familiar. This asymmetry is important because
it means that people who are very physically active generally
have an energy need that is below the sort of societal norm that
tends to throw food at them. Therefore, they are generally hungry
and they are controlling their body weight on their hunger drive
which is very efficient and well designed. The reverse is true,
though, if you are very physically inactive. The environment is
pressing on you much more food than you need and your body, physiology,
is just not designed to stop it; in fact it is designed to say,
"Thank you very much, I will lay that down as fat."
It is this asymmetry which is very important and that is one of
the reasons why ranking up the physical activity side of the equation
is so important because it will help the body's normal body weight
regulation systems to come back into how they were designed to
Q288 Dr Taylor: Could you explain
why fat is so conducive to weight gain and why it has no effect
on inhibiting appetite?
Professor Prentice: Yes, indeed.
We can look at it in several ways. First of all, if you do experiments
with covert manipulationso you have experimental volunteers
who you ask to eat normally but you secretly change the content
of their foodsthen, as soon as you add fat in and increase
the energy density they overeat. It is extremely easy to replicate
under any experiment: they automatically overeat. The reason they
do this is they continue to eat the same bulk of food, the same
amount of food, without recognisingtheir bodies simply
do not recognisethat it has more calories, more energy
in it. Under those experiments, fat is not actually the issue,
because if you very cleverly manipulate the foods so that the
energy density is constant across different fats, then you find
that on a high fat diet they do not overeat as long as the energy
density is held down. This is a key point: the energy density
of diets is really the driver of this effect at the physiological
end. However, on top of that you have another levelwhich
is the level that some of you may have seen on the BBC Big
Mac Attack programme which I did not see but which I think
was on Tuesday eveningwhich is the thesis that fat may
have specific addictive properties. If Professor Blundell were
here, he would be the man to talk to about that. I will not say
any more about that, I think maybe you should address questions
in writing to him. Of course fat is very palatable: we all love
Q289 Dr Taylor: That is why the double
bacon-cheeseburgers by Burger King that are about that tall do
not fill you up at all and yet taste extraordinarily good.
Professor Prentice: Correct. They
have very high energy densities. Again in the background documents
you will see one graph which shows the energy density of all the
products from fast-food outlets compared to our normal diet and
compared to traditional diets, and they are simply off the scale.
Q290 Dr Taylor: Would you say a word
about soft drinks and appetite control.
Professor Prentice: Yes. Soft
drinks also are very important. You have to consider the energy
density of soft drinks rather differently from solid foods because
they have different physiological actions. Again, parts of the
food industry have been trying to say, "Our soft drinks have
a low energy density because they contain a lot of water."
But that is not the issue. They have a high energy density compared
to other drinks. The consumption of soft drinksand, again,
this is an area where the experimental proof, the evidence, has
only emerged even in the last 12 months actuallyadds on
to normal caloric intake. When we drink soft drinks, we do not
recognise that we have taken in that extra energy and take that
energy out of the rest of our diet; we simply add it on. There
is very good evidence in support of that.
Q291 Mr Burstow: Companies like,
for example, Kraft who are now saying they are taking certain
fats out of their foods are not really going to be addressing
the issue that you are talking about because they are not necessarily
addressing the density levels of energy within the foodstuffs.
Professor Prentice: Correct. I
think we as scientists have to hold up our hands with a mea
culpa here, because 20 years ago we told the food industry
to get fat out of all their products. They have, by and large,
been doing that relatively successfully, though perhaps not as
fast as we would like, but they have substituted that fat very
often with other highly energy-dense foods, which are generally
your refined carbohydrates and sugars, in order to keep selling
the products to all of us who like energy-dense foods. We have
partly given them faulty guidance, and that is why I do think
it is important that we get this issue of energy density on the
table pretty clearly, and in terms of labellingwhich I
hope we will come back toso that we avoid that trap into
which we have fallen.
Q292 Dr Taylor: May I go on to variability
between individuals. Many people who are overweight claim absolutely
that they are eating very little and that it is a difference in
their makeup. Professor Blundell does say that there is some individual
variability in physiological satiety signals, for instance. Could
you expand on that a little bit?
Professor Prentice: There is no
doubt that there is individual variability but not at the sort
of extreme end of: "Doctor, it is my metabolism." Again,
very careful physiological studies, not only ours but around the
world, have shown that with the greatest of clarity. Twenty years
ago I think the world probably spent $200 million or $300 million
trying to look at subtle changes in energy expenditure, in diet-induced
thermogenesis that may explain obesity, and we have all come to
the conclusion that that is not the major part of the explanation
of the obesity epidemic and genetics are also very, very important.
There is variability. Some of us are fortunate enough to have
a lean physique and find it easy to stay there; others are very
prone to weight gain. But that is actually a side issue compared
to the epidemic. The epidemic puts all of us more vulnerable,
so those at the vulnerable end are even more vulnerable. In terms
of research now, one of the directions we are taking is to ask
the question: What keeps lean people lean? rather than: What makes
fat people fat? In a way we have come to such a situation, that
that is now a more interesting research question than: What makes
fat people fat? because what makes fat people fat is clearly obvious.
Q293 Dr Taylor: So the fat lazy mice
are no longer of any interest.
Professor Prentice: It is not
that they are of no interest, but where they are particularly
of interest is in the development of pharmacological treatments
of obesity. I would not want to inhibit those at all but would
again make the point that they have their own special nicheand
you will be dealing with this, you will be taking evidence on
thisand they are not a major part of the solution we need
for the epidemic.
Q294 Dr Taylor: Thank you. If I could
go to Tim: Why has the obesity epidemic accelerated recently?
Dr Lobstein: We have talked through
the physiology, we have the energy in and the energy out. Are
we expending less energy? Are we eating more energy? The figures
I have looked at for adults reporting how much they consume are,
in my view, extremely unreliable. If you look at, for example,
the confectionary which adults admit to eatingwhich they
are usually rather reluctant to dothe latest national diet
survey says they are eating 82 grams of confectionary each week,
self-reported. If you look at industry sales figures, those are
250 grams per week being sold to somebody. Clearly there is a
huge gap between what industry is selling and what people are
reporting they are eating. That is a very significant number,
particularly for soft drinks, confectionary and snack foods, which
are, as Andrew has just been saying, those products which are
the most likely to encourage obesity because they are snack foods
that you do not compensate for in your meals. That said, I also
recognise the obesogenic environment; that is to say, the unsafe
streets for kids so they stay in doors, the loss of school playing
fields so these are not perhaps as many hours of games at school
as they might have been in the past, and so on. It is a combination
of the two factors, in my view, of increased energy consumption
and decreased expenditure. When I say that, I know Andrew says
it is quizzical, but certainly if you look at food moving into
our food supply, the FAO figures, the agriculture figures, have
shown since the 1970s a 250 calorie per day rise. Now, 250 calories
does not sound like too muchwe are supposed to eat 2,500but
250 eaten in excess every day for week after week after month
after month would very quickly turn an average person into an
overweight person. If that is genuinely going into our bodies
as opposed to just into our food supply and wasted, that is a
very significant increase over the last 30 years.
Q295 John Austin: Whether the figures
of average energy intake are right or not, it has been suggested
that it is this imbalance in the equation, with a lessening of
activity, which has been the cause. Yet if you look at some of
the figures, if you are saying that physical activity is the answer,
some of the evidence we have been given would suggest that if
a cheese sandwich has 500 calories then it takes a five mile run
to burn that off. The question really is: Is activity sufficient
to redress the equation?
Dr Lobstein: I would agree with
you. Yes, it is very hard. It is much easier to eat a Mars bar
than to burn it off. I work as a journalist sometimes and you
are sitting there snacking while you are working. The effort I
would have to undergo to undo that damage would be enormous. I
would agree particularly for snack foods, which, as we have just
heard, do not tend to get counted into your daily intake.
Q296 John Austin: I wonder if Professor
Hardman could say how much activity is needed to avoid weight
gain in both children and adults.
Professor Hardman: There are two
very obvious ways to look at the role of physical activity. Tim
has illustrated one of them nicely. If you take a confectionary
bar which has about 300 or 400 Calories,
then if you say, "I'm going to go out immediately to exercise
and dissipate that energy," it is going to take you five
miles or so of walking or running. But I think we should turn
the coin over and look the other way at this. Just as I pointed
out in some of our written evidence, if one takes the net energy
expenditure of walking a mile, it is about 60 Calories per mile
for your average man and a little less for a woman. If you do
an extra one mile of walking every day for a year, you are going
to expend a considerable amount of energy. I think we need to
think about the long term and the short term. Population issues
to me are much more concerned with long-term weight change and
improving long-term weight regulation. Certainly people who are
more physically active are less likely, much less likely, to gain
clinically important amounts of fat or body weight over long periods.
Physical activity or exercise is very important in the long term.
It is not a very good way to expend a lot of energy in the short
term but it is in the long term.
Dr Lobstein: There is also a psychological
factor: you feel good after you have done the extra mileand
you reward yourself with half a pint of beer and there go the
Professor Hardman: I think it
is true that energy intake, whether of alcohol calories or others,
tends to increase spontaneously after exercise, but the good studies
that I have seen show that that increase is not sufficient to
offset the deficit which is created by the additional exercise,
so it turns somebody into a slightly higher-energy-turnover person,
expending more and taking in a little more.
Professor Prentice: If I may add
a slight point here, I think it is very dangerous to go down this
line of trying to do the sum of the 500 in and how long . . .
I would urge you not to do that, because the sums come out very
badly and we do not want to get that message out there. I think
you need to think of it as a cumulative change. What has happened
in our environment in terms of the history of human evolution
is remarkable in the last two generations. We have never seen
anything like this, where we have the coming together of the technological,
electronic, television revolution and the highly available, high
energy-dense and very cheap foods. We have to address all those
aspectsand you are well aware of that already. Where physical
activity comes in, is that you rapidly get into a vicious cycle
of inactivity, sloth and weight gain: as soon as you start to
gain a load of weight, it is all the more difficult to go up those
stairs; as soon as you start to become a little less fit, you
resist doing those things which in the first place will help you
not to become overweight, and so it rapidly becomes a vicious
cycle. I think that is a very important element.
Q297 John Austin: Has this lessening
of activity been quantified in any way? We all know it is taking
place. Whether it is television, computers or whatever, we know
activity has reduced, but do we know how much physical activity
has reduced and do we know how much physical activity we need
to reinvent and replaceparticularly for children?
Professor Hardman: I think there
are some gross estimates available, certainly as far as adults
are concerned, and we can show that more people are sedentary
than were before. For instance, even in the early nineties, we
were talking about maybe 30% of men and 35% of women reporting
less than one occasion of physical activity lasting 30 minutes
in a week and by 1998 or so those had gone up by 5% or so. So
we do have evidence for increased prevalence of sedentariness,
sedentary living. As far as estimates of how much the inactivity
has increased, it is obviously very difficult to quantify but
estimates I have seen suggest that since the end of the Second
World War, say, there might be an average decrease in activity
which is as much as 800 Calories per day. That would be of the
order of 20% and equivalent, say, to walking 10 miles or so. So
it is not trivial, it is a big decrease in the physical activity
in which we all engage daily.
Q298 John Austin: Do you know whether
we compare favourably or unfavourably with other European countries?
Professor Hardman: I could not
say that without going to the literature and looking. I suspect
that it is of the same sort of order.
Q299 Chairman: Dr Jebb, we are very
pleased to see you. We know you have had difficulties in getting
Dr Jebb: Yes, and Dr Wareham is
shortly behind me, I think.
4 Note by witness: Calorie is a recognised abbreviation
for the correct unit of energy, ie Kilocallloric. Back