What did you have for lunch today? If, like me, you ate a soggy tuna sandwich at your desk, you’re not alone. According to the British Dietetic Association (BDA), one employee in four eats lunch at his or her desk, a third don’t eat breakfast, and crisps, chocolate, biscuits and cakes are the most frequently eaten snacks at work. And while you can’t move for reams of information about what Turkey Twizzlers are doing to the nation’s children, eating in the workplace hasn’t had the same focus.

The problem is compounded by the poor food served in many staff canteens. Eighty per cent of workplace food is from contract caterers. Cheap ingredients, vats of chips and a salad bar containing wilting iceberg lettuce are still the norm in many places. But things are beginning to change. For example, 3663, a wholesale supplier to caterers, counts 15,000 workplaces as clients. The company runs a healthy eating campaign and gives caterers tips on how to prepare healthy food. A local sourcing scheme has 100 suppliers and 500 products– although when you consider that the firm has approximately 12,000 food and non-food products in its range – it’s a small step.

So if you want to stay awake beyond 3.30pm or ace a meeting, what should you eat?

"There is a magic formula,” says Judy More, a registered dietician at the BDA. “Eat from all four food groups.” This means fruit and vegetables, grains, meat, fish and vegetarian equivalents, such as eggs, and calcium-rich foods such as milk, cheese and yoghurt. But employees are let down, More says, by office vending machines that offer no reasonable healthy snack alternatives. “Crisps are full of fat, chocolate-coated snacks make your blood sugar go up quickly and then fall. It’s best to have some fruit, dried fruit, a small sandwich or crackers with a bit of cheese. Lots of workplaces have cereal and milk - you’d be better off having a bowl of cereal than a bar of chocolate.”

But if you are reaching for the cereal at 4pm instead of 8am, you’re going wrong. Numerous studies have suggested that skipping breakfast reduces performance at work. Bridget Aisbitt, a nutrition scientist at the British Nutrition Foundation, recommends a mixture of protein, such as lean grilled bacon, and carbohydrates, such as wholemeal toast. But something - like a bowl of cereal - is better than nothing.

For lunch you may be tempted to reach for a so-called superfood – blueberries, salmon or spinach perhaps - which you may think will boost your office staying power. Not quite, Aisbitt says. “The concept of superfoods is quite vague. You need a super diet.”

New EU laws back this up – products claiming to be superfoods will now have to provide evidence to back their claims. But that doesn’t mean that you can’t make smart lunch choices. Studies have shown that oily fish, such as tuna and salmon, contain omega-3 fatty acids which help to feed and lubricate the brain. If you don’t eat fish, try something egg-based - an omelette or a Spanish tortilla. Eggs contain choline, which is particularly important in brain function and health, and some studies have suggested that boosting dietary intake could help to slow age-related memory loss.

Patrick Holford, the author of several books on nutrition and a visiting professor at the University of Teesside, says that there is good evidence for some supplements, especially omega-3. “It’s hard to do a randomised mackerel trial,” he points out, but he says that six studies have suggested that omega-3 supplements are effective in reducing depression, details of which can be found on his Food for the Brain website. “There’s an ever-increasing incidence of mental health problems in the workplace,” he says, pointing to stress, anxiety, depression, insomnia and memory decline. “Our world has speeded up immensely with the internet and e-mails, and we have to process much more information, I believe part of the reason for mental health problems is that we need much better nutrition.”

So my tuna sandwich isn’t looking too bad – oily fish, oatmeal bread and cucumber and sweetcorn. But the seventh ingredient listed on the label is Demerara sugar, and other ingredients include saccharine, salt and colourings, including Sunset Yellow FCF, which is under investigation by the Foods Standards Agency and researchers at Southampton University. Beware pre-packaged salads and sandwiches. “It really is important to check the label,” Aisbitt says.

And as for desk-based eating – a universal thumbs down. “Horror,” More says. “The BDA proposes that people enjoy their food and make a bit of a ceremony about it. It’s much better to leave your desk. If you’re sitting at a table with utensils you’re likely to eat something more interesting, and it’s more enjoyable.”

One way of ensuring that you eat healthily at work is to ensure that you are surrounded by healthy foods. Abel & Cole, an organic food delivery service, runs an office fruit delivery scheme called Brain Food. There are two sizes of boxes, and on a typical week contents include apples, nectarines, plums, strawberries, and bananas.

“If you’re pushed for time it’s all too tempting to skip lunch and replace it with chocolate or fizzy pop instead. But this is a really effective way of eating some of your recommended five portions of fruit and vegetables a day at work,” says Ella Heeks, a director at Abel & Cole. The scheme started in November 2006, and more than 120 offices have participated so far.

“I can’t say there is one food that will have any effect on your performance in the afternoon if you eat it at lunch,” Aisbitt says. “But eating properly can certainly stop you reaching for the chocolate and crisps mid-afternoon.”

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