Lunchbox

Stuart Batlock, 30, works in advertising. He ate two rounds of mackerel sandwiches and a packet of crisps, and drank a cup of tea with semi-skimmed milk.

"I get really hungry because I cycle to and from work each day," says Stuart, "a distance of about 30 miles. I also play basketball once a week and go to the gym three times a week. Because I do so much exercise, I tend to eat constantly throughout the day, but never put any weight on. Today's lunch is quite typical for me - I bought my sandwiches and crisps in from home. But as well as eating these, I had a doughnut in the middle of the morning and will probably have a bar of chocolate this afternoon."

The fact that Stuart eats such a lot of calorie-packed foods during the day and yet still remains slim just goes to show how regular physical activity can help to control body weight. To keep fit and healthy, most of us should aim to exercise at least five times a week and preferably every day. Walking is one of the cheapest and best forms of exercise you can do, so if you're not used to taking much exercise it's a good idea to get in the habit of walking more frequently.

It's also important to balance an active lifestyle with a healthy diet. Almost half the 795 calories in Stuart's lunch came from fat - higher than the recommended proportion of one third. Surprisingly, it was the canned mackerel in tomato sauce which contributed most of it, rather than the crisps, or the low-fat spread in the sandwiches. However, this isn't too much of a problem because one of the fats in oily fish helps to keep the heart healthy, and may stop blood clots from forming. For this reason, healthy eating guidelines recommend one portion of oily fish each week, such as mackerel, sardines, salmon or pilchards.

However, it's likely that Stuart's overall fat intake will often be very high if he fills up between meals with doughnuts and chocolate. Because he does so much exercise he needs plenty of calories. But he'd be better off choosing sandwiches filled with lean meat, chicken, egg, banana or peanut butter; wholemeal scones or muffins; whole-grain cereal and semi- skimmed milk; or soup and a wholemeal roll.

The fibre content of his lunch is good because the sandwiches were made with wholemeal bread. Intakes of most vitamins and minerals were also reasonable, especially the B vitamins and vitamins A and D - in fact, oily fish is one of the few good sources of these latter two vitamins. However, his lunch didn't contain any fruit or vegetables, so it might be hard for Stuart to reach the recommended five daily servings. Adding a tomato or salad to the sandwich and having a piece of fruit with this lunch would be a good idea.