Diets: Win some, lose some

Rena Mendelson, a professor of nutrition at Ryerson University School of Nutrition in Toronto, rates four of today's most popular diets: Atkins, Glycemic Index (GI), South Beach and Weight Watchers.

Dr. Atkins' New Diet Revolution
CLAIMS: A low-carb, high-protein diet (all the protein and fat that you want) paves the road to weight loss and good health. One study that followed low-carb and low-fat dieters for one year found that both groups lost about the same amount of weight (5.1 to 8.7 kilograms and 3.1 to 8.4 kilograms, respectively), but the low-carb group had a better lipid (triglyceride and "good" HDL cholesterol) profile.

WHAT'S ON THE MENU: The first phase may be from two weeks to many months and stipulates no carbohydrates (no fruit, bread or pasta) but unlimited proteins and fat (seafood, poultry, meat, eggs, cheese, oils and butter) along with a few leafy green vegetables. Followup phases add some carbohydrates (limited nuts; fruits, such as berries, pears, apples, grapefruit and oranges; wine; beans; and veggies) up to a maximum of 40 to 120 grams of carbohydrates per day.
THE SCIENCE: A high-protein diet helps curb appetite and reduce water retention.
PLUS: Causes quick and significant weight loss, largely due to loss of water (fewer carbs results in fewer spikes in blood-sugar levels and less output of insulin, the hormone that makes the body retain sodium and therefore water).
PLUS: Insufficient carbohydrates for the brain. New guidelines indicate that 100 to 130 grams are required each day for optimal brain and nervous-system function and for energy. Lack of fibre increases risk of constipation.
CAVEAT: Many people cannot tolerate this diet because they have strong cravings for carbohydrates and they feel weak.

CLAIMS: Low-glycemic-index foods keep you feeling satisfied longer and help you burn more body fat and less muscle. The glycemic index (GI) measures how quickly the food you eat is converted into sugar (glucose) for the blood. High-GI foods rapidly convert into glucose, while low-GI foods take longer, which leads to a more sustained level of glucose and energy. The GI value of a food may change depending on how and for how long it's cooked and with which foods it's combined.

WHAT'S ON THE MENU: Low-GI foods, many of which are also high-fibre foods, such as beans, pasta, most fruits and veggies as well as low-fat dairy, poultry, lean meat and seafood. On the no list: high-GI foods (potatoes, white bread, full-fat dairy and watermelon) and fatty meats.
THE SCIENCE: The theory is that these foods will help you sustain a sense of satiety: when you feel full longer, you don't eat as much – and lose weight.
PLUS: Puts emphasis on healthier foods and lower fat intake, which helps protect against heart disease and is useful for people who have diabetes.
PLUS: Diet guidelines may be challenging. Since GI values may change according to cooking method and food combinations, it may be difficult to follow.
CAVEAT: None.