Diet or drugs, the weighty dilemma

Our weekly science feature turns this week to dieting, with the help of Dr Clive Hunt, senior lecturer in nutrition at Oldham’s degree partner the University of Huddersfield

Many adults have a constant battle to control their weight. In fact, nearly one quarter of British adults are obese (body mass index of 30 or above) and a further 30 per cent more mildly overweight (BMI 25-30).

But is this due to simple gluttony? In some cases, no doubt it is, but in most cases it is probably due to only a slight imbalance between calories eaten and expended over a period of time.

For example, theoretically, only an extra 50 calories eaten over requirement every day for a year would result in a 3kg (about 61/2 lbs) gain in body fat (given that 1kg of body fat is equivalent to about 7,000 calories). If continued for 10 years, this would be 30 kg weight gain which would make the person grossly obese — and 50 calories is equivalent to only half a slice of dry bread!

So, it is hardly surprising that many people despair of dieting and wonder if drugs are the answer.

Many types of drug have been tried over the years. The main category includes various forms of appetite suppressants. These are intended to reduce the strength of hunger pangs and have been prescribed to many people, particularly the very obese.

Unfortunately, they have various side-effects and, in any case, tend to get less effective over time. The latest drug in the news with fat-busting claims is Orlistat.

This has been available, on prescription, for some time but recently has been granted licence to be sold over-the-counter in the UK.

However, the pharmacist will still ask questions of the individual before selling, as it is contra-indicated if certain other drugs are being taken, and if particular medical conditions are present. Also, it is not suitable during pregnancy or lactation.

But, assuming someone can take it, how does it work? Basically, by inhibiting fat-digesting enzymes in the small intestine, such that a proportion of dietary fat is not absorbed and passed out in the stools. This therefore diverts some of the food calories away from metabolism and can result in weight loss, particularly if combined with lowering fat in the diet anyway, and with exercise.

However, (surprise, surprise) this drug can also have side-effects including loose-bowels. Also it can reduce absorption of the fat-soluble vitamins (A, D, E and K), although it is recommended to take a multi-vitamin with it to offset this.

But overall, evidence suggests that rapid weight loss, whether via drugs or crash-diets is rarely maintained in the long term unless lifestyle is changed.

So what principles should we bear in mind in relation to long-term diet? Most people are familiar with the basic principles of healthy eating but, regarding weight-control, it is worth emphasising what a key role fat plays.

Firstly, fat, whatever the type, is the most concentrated source of energy in the diet, having nine calories per gram compared with alcohol at seven, and protein and carbohydrate at four. Water, of course, has no calories and therefore the energy content of any food is largely dependent on the fat and water content so that a high fat, low water food has to be high calorie and a low fat, high water food will be low calorie.

Obviously how many calories we get from a food will depend on both its calorie density (calories per 100g) and the weight of food eaten, but there may be more subtle factors at play as well.

Many people eat a relatively high fat diet with approximately 40 per cent of calories from fat, but we are recommended to reduce to about 30 per cent.

Generally, the satiety centre (in the hypothalamus of the brain) does a good job in regulating our energy balance (calorie intake versus calorie expenditure) but, critically, what recent research has shown is that the centre is much more likely to make small but significant positive errors on a high fat diet than a lower fat diet.

This is probably because we evolved on a relatively low fat diet and have not yet adapted to high fat. Anyway, over time this can lead to substantial weight gain and even obesity, particularly if combined with a sedentary lifestyle.

So what’s the answer? Well, evidence is increasingly showing that lowering the calorie density of the diet can help a great deal.

This effectively means avoiding too much fatty food (and alcohol) and “diluting” calorie density with low fat, higher water, foods such as fruit and vegetables and also cereal (bread, pasta, rice, etc.) and potato products that have not had a lot of fat added. But does this work in practice?

Various studies, including a recent one of obese women in America, suggest that it does. They were advised to eat ad lib but to cut down on fatty foods. This led to substantial and sustained weight loss, even more so when they were also advised to increase fruit and vegetable consumption.

We need some fat from our food, but avoiding too much appears to be critical to weight control.