Select Committee on Health Minutes of Evidence

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 of—

  Professor Prentice: Measurements. The national global food supply figures. If you look at food surveys with individuals, within populations, that evidence is not very strong—and again that has allowed people to misuse it to their own ends—but, 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 also—and we can argue this point in more detail if you wish, but I think it has already been pretty well covered by previous evidence—that 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 inactivity."

  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 polite—and sometimes to good effect.

  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 science—and 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 elements—and I will point a finger at the sugar industry—that 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 plot?

  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 fat—you can pop children on these monitors very easily, they just stand on them and you measure the body fat—and 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 healthy people.

  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 tried—and I have given some very brief summaries of this in the background documentation—to 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 little—a little bit but very little—in 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 hunger—it is an evolutionary obligatory fact that we should respond to hunger very well—we 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 operate.

  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 manipulation—so you have experimental volunteers who you ask to eat normally but you secretly change the content of their foods—then, 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 recognising—their bodies simply do not recognise—that 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 level—which 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 evening—which 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 it.

  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 drinks—and, again, this is an area where the experimental proof, the evidence, has only emerged even in the last 12 months actually—adds 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 labelling—which I hope we will come back to—so 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 niche—and you will be dealing with this, you will be taking evidence on this—and 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 eating—which they are usually rather reluctant to do—the 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 much—we are supposed to eat 2,500—but 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,[4] 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 mile—and you reward yourself with half a pint of beer and there go the calories again!

  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 aspects—and 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 replace—particularly 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 here.

  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

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