Science@Huddersfield

Steve Bentley: Hi there, welcome to Science at Huddersfield looking at the science behind the headlines. On today's programme I spoke to Dr Clive Hunt. Clive is a nutritionist here at the University of Huddersfield and he told me about the health risks facing people who are significantly underweight. I began by asking Clive how to define underweight and overweight.

Clive Hunt: Well it's officially defined using a measure called Body Mass Index and this is calculated by the weight by the height squared - the weight in kilograms and the height in metres. So using that definition, the World Health Organisation said that the acceptable body weight range, or desirable weight range is between 18.5 and 25 for adults. So over 25 you're starting to get overweight, and under 18.5 you're starting to get underweight.

SB: We hear a lot about people who are overweight or obese, are there a lot of people who are underweight?

CH: There are not as many in our sort of society, but nevertheless for those that are there are some health concerns. Of course at the moment there is a lot of discussion about "size zero models" and so on, and some of those models must be under 18.5 BMI. It has to be realised that there is always variability in biological measures, so you're always going to get people who are naturally thin and naturally not so thin. It's a question of when thin becomes too thin or indeed anorexic, and then there are health risks attached, because for women the normal body fat percentage is between 20 and 25% - this is natural for non-overweight women, and as I say BMI should be between 18.5 and 25. As that percentage goes down below the normal range, one of the things that can happen is that periods can stop, and then the woman in a sense becomes in the same sort of sense as post-memopausal hormonally so oestrogen secretion goes down and this has an effect on the body which affects mineral retention. There is a risk that if somebody remains very thin for too long that their bones could become porous, and if this happens in the late teens, early twenties when the peak bone mass is being formed, this could have serious consequences for the bone mass and possibly even long term consequences.

In addition there is the obvious general health risk of nutrient deficiency, resulting from general lack of food. Because as you take the calories down below a certain level, if you keep on doing this on a regular basis, it becomes more difficult to obtain adequate nutrients in the very small amount of food you're eating. So nutritional deficiencies affecting any nutrients could occur, which is obviously not good for health, because even marginal malnutrition can affect the body's resistance to infections, the immune system and so on. Also there is another effect in woman who become too thin for too long, they become infertile because the normal body fat percentage is needed for the reproductive cycle.

SB: So these size zero models - we should say that size zero is a US term equivalent to a UK size 4 - there have been calls for models to undergo medical checks. Would you support those calls?

CH: I think that women should try and remain more or less in the recommended BMI range. If it starts getting more and more below than then that is a health risk and I don't think it is a good thing to promote that via models as being in some way normal, because it isn't. Where you have someone who is naturally thin and then starves themselves as well, you are getting into a semi-starvation mode and it's not a good image to be portraying in the public domain.

SB: If somebody is in that situation, what would be the safest way of regaining the weight that they need?

CH: Sensible, balanced eating is basically the way to do it. The average woman required 2000 kilocalories a day, and you need a good balance between carbohydrates, fats and proteins. Fats actually have the most calories so obviously if you're trying to put on weight then foods that have a certain amount of fat in them are good. But you want balanced nutrition.

SB: And there are people who can give people advice about their diets?

CH: Yes, here at Huddersfield University we have degrees in nutrition and food science, and our students and other similar people should be able to go out and give expert advice. The Nutrition Society has a register of officially accredited nutritionists so our students and others can apply to be on this. Beyond our particular interests there are other bodies that have good information such as the Food Standards Agency, which has a lot of good scientists employed. This is an arm of the government but it is supposed to be independent scientific advice, and they do a lot of literature which goes out to all sorts of people concerned with food and health education, and they also have a very useful website which gives a lot of information to do with diet, food hygiene and so on.

SB: You talked earlier about this 2000 calories a day, that's the Guideline Daily Amount. We have this situation now where food has two different labelling systems, can you tell us a bit about that?

CH: Yes, I think the present situation is confusing for consumers because of the very fact that we have got two different systems. I actually think that the latest "traffic lights" system which is colour coded, which is being promoted by the Food Standards Agency now, is a good idea because I think it gives people a very quick impresion of whether a food or a portion of food has a lot of fat, or it's medium or it's low fat. The same thing would apply to sugars and salt. Which all of these things we're being advised not to have too much of, but if you don't have a colour coded system and you just have the figures, which is actually the legal requirement, then it's actually quite difficult for people to look at a label and relate that to how much they would eat and then relate that to how much is high, medium or low, or the requirements. You virtually have to be a nutrition expert to do that so just looking at numbers is very difficult to interpret, particularly if people are busy and they haven't got ages to consider the matter. So I think the FSA initiative is good, but the problem at the moment is that they're not insisting that everybody adopts it.

So what we've got is a situation where certain supermarkets are adopting this scheme; other supermarkets have not - or at least not yet - adapted it, maybe they will which would be good, but as yet we don't know. And equally some food manufacturers are adopting this system onto their labels and some are not. Beyond all this, in any case, is the issue that nutritional labelling in the UK and indeed some other European countries is not compulsory on packaged food unless you make a nutritional claim. So it is possible for a manufacturer could have a food that they know is high in fat, sugar or salt but they don't want to advertise it, so they just say nothing and don't put any figures on at all on the label. In the last 10 or 15 years, many maufacturers have voluntarily put nutrition information on labels, and any information is certainly better than none. So I think there are hopeful signs for consumers but at the present time it is quite confusing.

SB: My thanks there to Dr Clive Hunt for joining me on today's Science@Huddersfield. Well that's all for today, if you have any feedback please get in touch with us, it's science@hud.ac.uk. From me Steve Bentley, my guest Dr Clive Hunt and everybody here at the University of Huddersfield, bye for now, we'll talk to you next time.