It’s been one hell of a day. An early morning staff briefing, a meeting about the school trip at break, a constant stream of students to see at lunchtime, topped off by an after-school club. You did manage to grab a sandwich at lunchtime, but it’s 5pm and your energy levels are waning, so you hit the coffee and biscuits. By the time you get home, you’re starving, so you pile your plate high and wash it down with a glass of wine or three.

You go to bed feeling fat and fed up.

Kit Tarry is a newly qualified science teacher from Hampton. Since she started teaching last year, the 45-year-old says she feels constantly tired and sluggish. “When I started teaching, I couldn’t believe how tiring it was,” she says. “I used to have a sedentary, desk-based job, but now I’m on my feet all day and I’m always hungry. I’m constantly craving sweet things, like biscuits, cakes and chocolate. I drink tea to get me through the day - sometimes up to 15 cups.”

She’s also put on more than half a stone and gone up a dress size. “Since I started teaching, I’ve found I need the sugar hit, particularly after a difficult lesson, to get me through the next hour. I’m a single mum in my40s on the graduate training programme, so lack of free time means I have not been to gym since the beginning of term. I know that reaching for the doughnuts or biscuit tin is not the answer, but do it anyway. I’m just too tired to cook in the evening, which means a diet of sandwiches and quick meals. My New Year resolution is to look after the mind and body and find some time for me.”

According to nutritionist Ian Marber, Kit’s experiences are typical. A significant number of his clients are teachers or headteachers who complain of a lack of energy and sugar cravings.

“It’s easy to forget how much physical movement is involved in teaching,” says Marber. “Many teachers are on their feet all day and schools aren’t always the best environments to develop healthy eating habits. And because of the structure of the school day, teachers have to eat when they have a break, instead of responding to hunger.”

Marber says teachers should eat regularly in order to keep blood sugar levels stable and avoid energy slumps. During an energy slump, you may find yourself feeling weak, shaky, moody, nauseous and lethargic. Sugary snacks provide a quick fix, but the rapid rise in blood-sugar level they cause stimulates your body to secrete a large amount of insulin, which then makes sugar levels plummet. Soon, you’re tired and hungry again and may eat more at your next meal.

Marber advises teachers to eat every three or four hours and to aim to include some protein in each meal. An energy-boosting breakfast could be egg on toast or muesli with nuts and seeds. Lunch might be a tuna sandwich on wholemeal bread, followed by an apple and a small handful of brazil or cashew nuts. Dinner could be a portion of lean meat or fish, served with steamed vegetables. Fresh fruit, oatcakes topped with cottage cheese or hummus and crunchy vegetables are all ideal snacks.

A busy working life and high stress levels can also trigger weight loss.

“Since I’ve been teaching, I’ve lost a stone,” says newly qualified primary school teacher, Helen Harris. “I eat on the run and I’m too tired to cook in the evenings.”

A healthy eating plan will help maintain energy levels and ensure you’re getting all the essential nutrients. Fitness, diet and lifestyle expert, Joanna Hall, says teachers should also look at their water intake. Latest figures from the National Diet and Nutrition Survey show that, on average, adults drink in one week the eight glasses of water nutritionists recommend each day.

“Hydration has the greatest impact on energy levels,” Hall says. “This is especially important for teachers, as school buildings are generally not air-conditioned and many have draughty corridors. And because of the way the school day is structured, it can be hard for teachers to find the time to top up their water intake.”

In many staffrooms, coffee is still the preferred refreshment. As caffeine is a stimulant, it can seem like the perfect pick-me-up, but some nutritionists believe that, like sugary foods, caffeine triggers a rise, followed by a sharp fall, in blood sugar levels - which can leave you feeling more lethargic than ever. And research carried out by mineral water company Volvic found that drinking 350mg of caffeine - that’s the equivalent of just three-and-a-half cups - can cause lapses in concentration and increased stress.

But if you enjoy your coffee, Hall believes it’s not necessary to cut it out completely. Instead, drink it strategically; one during morning break and one mid-afternoon should be enough to perk you up. But do keep your consumption below two-to-three cups per day, and match your coffee consumption with water to avoid dehydration.

Remember that if you take milk and sugar, excessive tea and coffee drinking can contribute to weight gain, adding up to 400 calories to your daily intake. Over two weeks you could put on a pound in weight.

Most of us are aware of the benefits of exercise for physical and mental health, but finding the time to exercise regularly can be a challenge. Hall believes that teachers are naturally advantaged as they are constantly moving during the day. Rather than adding to stress levels by trying to squeeze in visits to the gym each week, she suggests you invest in a pedometer and get walking. A pedometer is an inexpensive device that measures the number of steps you take each day. Around the size of a matchbox, it can easily be attached to clothing at the hip. Fitness experts recommend 4,000 steps a day to impact on your health and 10,000 to help with weight management.

Hall suggests an initial daily target of 7,000 steps. “Once you’ve established how many steps you’re taking per day, you can look at small changes in your lifestyle to incorporate walking. That might include a five-minute circuit around the site before you have your lunch, taking a longer route to work or walking instead of driving to the shops. Making small changes to your lifestyle can have a significant impact on your health.”

Joanna Hall’s book, ‘Drop A Size For Life’ (HarperCollins) is out now. Her website is at www.joannahallonline.comIan Marber’s book, ‘The Food Doctor: Healing Foods for Mind and Body’ is published by Collins and Brown. His website is www.thefooddoctor.com

WATCHING THE POUNDS: WEIGHING UP WHAT TEACHERS EAT

Lorna King , history teacher, Sussex. “I’m constantly craving sweet things, like biscuits, cakes and chocolate, and coffee has become like a drug. I was never much of a drinker, but I’ve started having a couple of glasses of wine when I get home, just to relax. I sit down to do some marking and often polish off half a box of chocolates without thinking. I did join a slimming club , but found that recommended amounts of food weren’t enough to keep me going through the school day, so I gave up.”

Helen Forrester science teacher, Catshill middle school, Bromsgrove. “Since I’ve been teaching, I’ve gone down a whole dress size. I only get 35 minutes for lunch, so by the time I’ve supervised detentions or children who have work to finish, I often only have time for an apple or a banana.

In the evenings, I’m often too busy or tired to cook.”

Nicole Ash supply teacher, Manchester. “I followed a weight loss plan while doing my PGCE and found it easy. I had so much to think about, I didn’t snack between meals. I lost two stone in five months. I’d recommend teaching as a weight loss strategy!”