The following correction was printed in the Guardian's Corrections and Clarifications column, Monday June 14 2004

In the article below we describe the subject as a vegetarian, having made it clear that she eats fish. Fish-eaters fall outside definitions of vegetarianism. The Vegetarian Society is unequivocal: vegsoc.org/fish

Nicola Schierz, 34, in the early stages of pregnancy with her first baby. She works as a PA at the Automobile Association, doesn't eat meat but does eat fish and doesn't smoke, drink alcohol, tea or coffee.

Sunday

10am Bowl Rice Krispies, full-fat milk, 2 dessert spoons of sugar, glass of white grape juice

2pm White plain bagel, light cheese spread (lots), Marmite, can of diet fizzy orange

4pm Approx 100g dairy milk chocolate

6pm Mashed potato, full-fat cheddar, pint of water

9.30pm Pint of Diet Coke, packet of Quavers; pregnancy supplement with folic acid

Monday

8am Whole grapefruit, 2tsp caster sugar

10am Packet crisps, can diet fizzy orange

12.30pm 2 slices granary bread, tuna mayo, cucumber, apple, pint of water,

6pm 100g dairy milk chocolate, glass of grape juice

9pm 3 cod fishfingers, mashed potato, full-fat cheddar, pint of water, 250g tinned sliced peaches in juice; folic acid tablet

Tuesday

8am grapefruit, 1tsp sugar

10am Packet crisps. One can of diet fizzy orange

12.30pm 3 slices white bread, light cheese spread Marmite, pint of water

3.30pm Apple. 75g chocolate buttons

9pm 10 potato skins, cheese, strawberry milkshake, pint Diet Coke, few spoons of ice cream

12 midnight Glass of water; pregnancy supplement with folic acid

The verdict

Many of us believe we can eat for two when pregnant but this is a misconception: "Your metabolism changes during pregnancy," explains nutritionist Dr Toni Steer of MRC HNR in Cambridge. "You become less active and your body is better able to absorb energy and some nutrients from your food." What matters more than quantity, says Steer, is "the nutritional quality of your diet - making sure you include foods packed with nutrients such as fruits and vegetables, lean meat and fish, low-fat dairy products and unrefined carbohydrates".

Nicola has cut out the so-called "danger" foods - such as mould-ripened or unpasteurised cheeses (eg stilton, brie) and raw, or partially cooked meats, patés or seafood. But as a vegetarian, she also needs to pay special attention to what she includes. Most of Nicola's protein comes from cheese, which, while a good source of calcium, is also high in fat. She could substitute some of her cheese for pulses, tofu or more fish. And she could switch to lower-fat dairy products: "The calcium content of semi-skimmed dairy products is actually very similar to full fat ones," says Steer.

Nicola's diet lacks fruit and vegetables: essential sources of vitamins and minerals and, for vegetarians - especially during pregnancy - an important source of iron. Your body is actually more efficient at absorbing iron during pregnancy, so simply eating green leafy vegetables can really help (red meat, for non-vegetarians, is the best source of iron). If your iron levels are low, though, you may need supplements (this is not ideal as they can cause tummy upsets and constipation). Nicola's daily folic acid supplement is excellent: "Ideally, you should take 400 micrograms (mcg) of folic acid for 12 weeks before you get pregnant, and in the first 12 weeks of pregnancy as this can reduce the risk of neural tube defects in your baby," says Steer.

Nicola's regular high-fat, high-sugar snacks like chocolate and crisps are not a great idea. She should try snacking on foods that give her more sustained energy instead (see tips). These kinds of foods will also help to top up her rather low fibre intake which, combined with her habit of going for fairly long periods without fluids, might increase the risk of constipation.

Pregnancy eating tips

· Make sure your diet contains adequate iron. If you are vegetarian, get this from green leafy vegetables and pulses

· Keep constipation at bay with plenty of fluids and high-fibre foods (fruit, vegetables and wholegrain foods)

· Eat snacks for sustained energy: a banana, a wholemeal hot-crossed bun, wholemeal toast topped with Marmite, tinned sardines or cottage cheese, unrefined breakfast cereals.