What to eat at work without paying for it later.

Half past twelve. Twenty minutes between meetings, and the shop downstairs does a meal deal: pre-packed sandwiches, sausage rolls, tubs of pasta salad. You grab whatever's quickest and eat it over your emails. By two, your head is full of cotton wool.

Work usually gets the blame. I look at the plate first. No weighing out rice, no lunchboxes in your bag. You're at work all day, so you eat out.

Your afternoon is decided at lunch

When lunch is almost all bread, pasta or rice, your blood sugar shoots up and comes down just as fast. You know the way down: heavy eyelids, then hunger, mostly for something sweet.

The same bowl of pasta, in a balanced meal, behaves differently. Protein, vegetables and good fats slow the sugar down, so the rise is gentler and you stay full longer. You can keep the pasta.

Where you eat, what you choose

• At the sandwich shop. A sandwich or wrap with real protein in it: egg, chicken, turkey or tuna, plus salad. A sausage roll or a sandwich with a scrape of filling is mostly bread and pastry. Have two and you're hungry again by mid-afternoon.
• In the canteen. Pick your protein and vegetables first, then decide whether you need the pasta, rice or potatoes too. If you do, skip the bread roll.
• At a business lunch. The bread basket arrives first, when your stomach is empty. Leave it alone until your food arrives. Order fish or meat with vegetables. Nobody at the table notices, and you stay sharp right through to coffee.
• At your desk. If you know there won't be time, order mid-morning, before you're hungry. A big salad with chicken, eggs or pulses, or a rice or grain bowl with protein and vegetables.

And pudding? If you fancy it, have it at the end of the meal. After vegetables and protein, it raises your blood sugar less than the same slice of cake on its own at 4pm.

In busy spells, pick two lunches that work in your usual places and order those every time. One less decision, on a day like yours, is welcome.

The 4pm hunger

Mid-afternoon is when the vending machine calls. Crackers, cereal bars and biscuits feel light, but they send your blood sugar up and down. About two hours later you're left with a hunger that isn't yours. The snack switched it on.

After a balanced lunch, you often won't need a snack. When you do, pick one that fills you up: a handful of nuts, plain yoghurt, a piece of fruit with a few almonds. Fruit on its own hits faster; the almonds slow it down.

Coffee straight after lunch is fine. It's also your last of the day.

Two things beyond the plate

Water. Lose about one per cent of your body's water without topping up during the day, and mind and body both start to underperform. Keep a bottle on your desk. And check the colour of your urine: pale is fine, dark means drink more.

Ten minutes on foot. Your muscles are the first place the sugar from lunch goes. Get them moving and they soak it up straight away. Take the long way back to the office, or make your first call on the move.

One caveat. If you eat like this and still feel very sleepy after lunch, every day, talk to your doctor. It's a sign worth getting checked.

Otherwise, you just need to know what to choose when time is short and you didn't choose the menu. Start with tomorrow's lunch, and see how you feel at three.