You are what you eat. Diet affects well-being in all sorts of ways, from protecting you against cancer to influencing your moods. So it’s pretty depressing if lunch is a choice between a cheaply produced, highly processed school dinner (which is what they have nearly all become since nutritional standards were scrapped in 1980) and a quick trip to the nearest sandwich bar or chippie.

You get full points if you are one of the minority who brings in a packed lunch full of freshly chopped vegetables and wholemeal bread every day. But what about the rest? Teaching is a strenuous activity, requiring physical stamina and mental alertness. Given the demands on your time, how can you avoid resorting to crisps, chocolate bars and a cup of tea to provide your body with the fuel it needs?

According to Mary Whiting, a former teacher turned food writer and nutritionist, the best single thing you can do to improve your diet is to have a good breakfast. Many dietitians regard breakfast as the most important meal of the day. It fires up the metabolism and rovides a reservoir of energy that lasts through into the afternoon. But to do that, it needs to be substantial and contain protein. Eggs are ideal, or a bacon sandwich, or even - in the tradition of proper continental breakfasts - cold meats with bread and yoghurt. If you usually have toast, make it wholemeal and have a chunk of cheese with it, and some milky tea or coffee.

A bowl of sugar-coated wheaty-what-evers will not provide the protein and energy you need. Skipping breakfast altogether is the worst option - your energy levels will flag all day, increasing your cravings for a sugary snack mid-afternoon (followed by an energy crash an hour or so later).

After a hearty breakfast, a skimpy lunch won’t do so much harm. Other tips are to stop working and sit down while you eat - a habit which is as important for stress-busting as it is for digestion. Substitute one of your daily cups of tea or coffee for unsweetened fruit juice. As the weather gets warmer and classrooms heat up, also try taking a bottle of refrigerated water into class with you in the morning and drinking it throughout the day.