FOOD FELONY #4
BOILING VEG

You may think five-a-day guarantees your vit-hit, but prepare with care. "If vitamins were on the beach, C would be getting sand kicked in its face," says nutritionist Carina Norris. "It's destroyed by air, light, heat above 70°C and is water-soluble, so leaks out when you boil or defrost veg." Studies by Warwick University in the UK found boiling broccoli for just 10 minutes reduced its immune-boosting, cancer-fighting glucosinolates by 80 per cent.

Get out of jail "Boiling is for potatoes only," says Norris. "Ideally steam your other veg, ensuring the water's piping hot to minimise cooking time." The Warwick study found reducing broccoli cooking time to just five minutes meant only a 10 per cent loss of glucosinolates. Whatever your method, remember crunchy veg is nutrient-dense. And don't slice too much before cooking as outer skins harbour vitamins. "Stir-frying locks nutrients in as it uses more intense heat for less time," says Norris.

FOOD FELONY #5
SOARING TEMPERATURES

If you can't resist turning up the heat, stay out of the kitchen. Studies in The American Journal of Clinical Nutrition found cooking animal products such as meat and cheese on high heat ups the amount of advanced glycation endproducts (AGEs) in your meal. This is worse news than forgetting the tomato sauce as AGEs have been linked to diabetes, Alzheimer's, arthritis and heart disease. "It's time we paid attention to these toxins," says Dr Helen Vlassara, of the Mount Sinai School of Medicine in New York. "They accumulate in the body, leading to inflammation which, over time, causes organ damage and disease."

Get out of jail "AGEs occur when sugar, protein and fat are exposed to high heat without water," says Norris. "Limit them by cooking at lower temperatures, and stew or poach rather than dry-fry. A steamed meal has one fifth the AGEs of a fried one. Marinating meat in acidic liquids such as vinegar, lemon juice or tomato sauces also cuts AGEs." Sadly, adding a large portion of chips does not.

FOOD CRIME #6
PLAYING WITH PLASTIC

Storing fatty foods like meat, dairy or last night's korma in plastic containers means dodgy chemicals can leak into your lunch. "It's a myth that plastics don't break down," says Frederick vom Saal, professor of biology at the University of Missouri. "Chemicals can get into food from plastic whether it's heated or not."

Re-heating that korma in the plastic container is a double offence. "Microwave heating means more chemicals escape," says Dr Rolf Halden, of the John Hopkins Bloomberg School of Public Health in the US. "The fattier the food, the more it will absorb."

Get out of jail "Only use plastic items for their intended purpose," says Halden. "Use heat-resistant glass, ceramics and steel whenever possible for cooking and storage." Vom Saal agrees: "Never use plastic dishware in the microwave or place hot food in it. Non-polycarbonate plastics like polypropylene and polyethylene are good to freeze food, but then heat it in glass containers."

And what of the ever-handy cling wrap? "In the microwave, reduce contamination risk by ensuring it doesn't touch the food," says the US Food Standards Agency's Grace Money.

FOOD FELONY #7
BEING HEAVY WITH METAL

Baking, or just wrapping acidic food in foil can leave more than just a bad taste in your mouth. The metal can leach into food whether you're cooking it or not, but heating certainly speeds the process. Scientists from Ondokuz Mayis University in Turkey found that baking meat in foil increases its aluminium content by up to 378 per cent. And the more acidic the food, the more it corrodes aluminium.

"Tomatoes are particularly prone to dissolving aluminium," says Richard Barrans Jr, a chemist at Argonne National Laboratory in Chicago. "And although it's not as poisonous as metals like arsenic, lead or copper, there's evidence linking it to Alzheimer's."

As for that half can of beans in the fridge: "Once a can is opened, it starts to corrode," says Money. "And though no long-term health problems have been linked with consuming tin, it can cause nausea, vomiting, diarrhoea, wind, abdominal cramps and bloating." And you thought that was just the beans.

Get out of jail "Don't cook soft fruit, tomatoes, rhubarb or cabbage in aluminium pans," warns Money. Don't bake your meat in foil and the US Food Standards Agency advises transferring leftover canned food into a glass bowl.