The Oxford Science Lecture Series

JANET THORN

Senior Lecturer in Nutrition, Oxford Brookes University

"Cafe Science (or you are what you eat)"

Martin Wood Lecture Theatre, Oxford, 26th June 2003

On 26th June 2003, Janet Thorn, a nutritionist at Oxford Brookes University, gave a thought-provoking talk on the food we eat and the effects it can have on us.

She first explained that the science of nutrition seeks to explain why we choose the foods we do, investigates the composition of our food and also looks at the health effects of food. Given that the average adult eats 10 times their body weight of food a year (about 60,000 kg of food in a 70-year lifespan!), the study of food and nutrition is obviously a very important one.

One of Janet's main themes was that of obesity. This is on the increase in the UK, where 21% of women and 17% of men are obese. Obesity can take 9 years off the average lifespan and causes 6% of all deaths in the UK. Obesity is now defined by waist measurement (over 80cm in women, 94cm in men) as the really important criterion is your amount of abdominal fat rather than the overall amount of fat in your body. This is the area of fat deposit that seems to lead to the main health risks of being obese.

Humans are programmed to eat fatty and sugary foods - being fat was an advantage to our hunter-gatherer ancestors in times of famine. Unfortunately our lifestyles are now very different but we still prefer to eat these kinds of food, a habit encouraged by many food manufacturers in an effort to get us to consume more of their products. This is particularly worrying in children. Anecdotally, children starting at school have been reported as not knowing how to use cutlery since all their food consumption to the age of 5 has been of finger food.

So what can we do about obesity? The main thing is to eat the right amount of energy for our lifestyles. This varies widely, but on average is 2000 kcal/day for women and 2500 kcal/day for men. Losing a relatively small amount of weight eg 10kg, can make a significant difference to our health and of course regular exercise is important.

A second theme of Janet's talk was health and food hygiene. The main threats to our health caused by food are food-poisoning, cancer, heart disease and obesity. Food-poisoning in particular is becoming increasingly common although it could be prevented in many cases by simple food hygiene. The average J-cloth in a kitchen has about 100 million organisms growing on it after a week, and 80% of us change J-cloths less than monthly! Many of us don't wash our hands before cooking and use the same chopping boards for raw and cooked foods. There are some less obvious risks too that not all are aware of such as the danger of food poisoning from cooked rice that has not been refrigerated quickly enough, and the organisms present in soil on vegetables which can be easily spread around the kitchen. On the other hand, some of the practices of food hygiene which are very prevalent actually have very little effect, eg bleaching the floor. If food falls on the floor it should be thrown away - it is the work surfaces which must be kept clean (and not with old J-cloths!). Similarly, soaking cloths in bleach is not good practice - it may lead to the evolution of bleach-resistant bacteria rather than keeping the cloths clean.

After this rather frightening peak at the nation's kitchens, Janet finished by giving us some advice on what we should be eating to improve our diets. Certainly we should aim to eat less fat, and low fat dairy products such as skimmed milk and half-fat cheddar are good for this. The slogan of '5 portions a day' for fruit and vegetables is becoming increasingly well known, though is not always helpful if you don't know what a portion is. As a guide, it can be taken to mean 500g of fruit or vegetables (not including potatoes) a day. We should eat more fish, particularly fatty fish, and lower salt - there should be no need to add salt at the table. Finally, high fibre is good for us and we should aim for 18g per day.

A lively session of questions followed the talk, with questions on such diverse aspects of nutrition as detox diets (not a good idea) and food cravings (not shown to be related to actual body requirements). Overall the talk was a useful insight into a topic which is so vital to our lives.

Catherine Hobbs