What happens when you cut out all animal-based food products? Or you don't eat anything that's been cooked? They may be good for your waistline, but are extreme diets good for your health? By Katrina Fox

A healthy and balanced diet is the cornerstone of any weight-loss plan - but experts differ in their opinions on exactly what is 'healthy or 'balanced'. Some advocate the exclusion of certain foods, such as meat and dairy, while others believe that severely restricting the number of daily kilojoules is the way to go. But while some extreme regimes promise lasting weight loss, they may also be detrimental to your health.

Vegetarian

What's on the menu? A vegetarian does not eat any animal flesh, including poultry and fish. A lacto-ovo vegetarian does, however, eat dairy and eggs.
Why it's good: Vegetables contain a wide variety of vitamins and minerals. Spinach, for example, is a good source of vitamins A, B2, B6 and E, as well as calcium, iron, folate and selenium. Carrots contain vitamin A (essential for good vision), while asparagus provides folic acid and potassium. Many vegetables (and fruit) contain antioxidant properties that can help to prevent cell damage from free radicals.
Why it's not: There are some concerns about iron and zinc deficiency, says Aloysa Hourigan, senior nutritionist at Nutrition Australia. "You must also be careful to have a balance of proteins." The Physicians Committee for Responsible Medicine (PCRM) in the US says cutting out dairy is sensible because dairy products have been linked to prostate, breast and ovarian cancers, insulin-dependent diabetes and cardiovascular disease. Cutting out dairy won't necessarily lead to a calcium deficiency or osteoporosis, says Dr Neal Barnard, PCRM's president. "You can decrease your risk of osteoporosis by reducing sodium and animal protein intake in the diet, increasing intake of fruits and vegetables, exercising, and ensuring adequate calcium intake from plant foods such as kale, broccoli, and other leafy green vegetables and beans," he says.
Will I lose weight? It depends on the types of food you eat. "One of the things I see with people on vegetarian diets who haven't done their research is they tend to make them really high in fat, so really high in nuts and lots of snack food," says dietitian Trent Watson.

Vegan

What's on the menu? The vegan diet eliminates all animal products, including dairy, eggs and honey. Both Trent and Dr Barnard recommend including a wide range of fruits and vegetables, legumes (beans, lentils), proteins such as tofu and tempeh, and whole grains (breads, cereals, rice, pasta).
Why it's good: "There is little doubt from the medical literature that vegans have less illness if they are eating a balanced diet," says Dr Tracie O'Keefe DCH, a naturopath, nutritionist and clinical hypnotherapist who works with weight control and eating disorders. "They have less cardio-vascular disease including heart problems and stroke and less intestinal problems and cancers." Dr Barnard allays any fears that you won't get enough iron or protein with a vegan diet. He says a person's protein needs are easily met by a eating a combination of nuts, legumes and grains. Iron, meanwhile, is plentiful in green leafy vegetables as well as broccoli, kale, silverbeet, beans, peas, lentils and chickpeas.
Why it's not: It can be hard to get enough vitamin B12, so it's worth a trip to a naturopath or your doctor to check your levels.
Will I lose weight? "Any diet can assist someone to lose weight if it supplies less energy than what they need," asserts Trent. "But it must also be nutritionally adequate and able to be followed continuously."

Raw food

What's on the menu? Although there is a small movement of people who advocate eating only raw meat and unpasteurised milk, the raw food, or 'living' food diet is essentially vegan, except nothing is cooked. Raw foodists believe that the act of heating food over 47C destroys enzymes in food (enzymes assist in the digestion of food). High-quality juicers and dehydraters (an appliance that uses warm air to reduce the water content in food) mean that foods such as raw crackers can be made, plus raw versions of burritos and even raw cakes and desserts.
Why it's good: Raw food proponents cite better overall health, more energy, a stronger immune system and clearer skin.
Why it's not: "The immediate thing that springs to mind is food hygiene and the risk of food poisoning," Trent warns. It's important to wash fruit and vegetables thoroughly and buy organic to avoid contamination with pesticides. Aloysa points out that while you get the maximum amount of vitamins and minerals from most fruit and vegetables in their raw state, others actually increase when the food is cooked. "This is the case with lycopene in red foods such as tomatoes that can help with cancer and heart problems," she says.
Will I lose weight? Probably, but it's important to eat a wide variety of foods, not just a cup of nuts a day. "The art to a raw food diet is to have the time to shop, collect and prepare food, and to study the different meals you can make," Dr O'Keefe says

Very Low KJ

What's on the menu? A very low-kj diet advocates extremely low daily kilojule consumption, usually less than 3,360kj. Some people drink a high-protein, nutrition-rich liquid, as in the CRON-diet (Calorie Restriction with Optimal Nutrition) while others count the kj in their food.
Why it's good: Promoters of these diets suggest they may help you live longer. Aloysa says these diets may be useful if someone is morbidly obese and about to have surgery.
Why it's not: Following this type of diet for a long time can be very dangerous because you are unlikely to be getting the vitamins and minerals you need, Aloysa says. "These diets can be low fibre too and you'd be worried about some muscle breakdown through lack of protein," she warns.
Will I lose weight? Yes, quickly and dramatically, but as soon as you start to eat normally again, you'll put the weight back on just as quickly. "Your metabolism will slow down because it's not being used much, and I'd be really concerned about long-term nutritional health," says Aloysa. And any diet that's akin to virtual starvation will leave you feeling sick and listless, which is neither sustainable or sensible.

The important thing to remember is if you're considering making changes to your diet, do your research and consult a nutritionist or dietitian.

Slimming & Health is a women's magazine in Australia. www.slimmingandhealth.com.au