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Shane Bilsborough explains the fact and fiction of four popularised diets.
On the popular reality show The Biggest Loser it's not uncommon for people to shed 10 kg in a week, making a 1 kg weight loss to the "average Joe" seem like hard yakka. Open up a glossy magazine and it's littered with inspirational feats of mammoth weight loss. Search for how it's done and the answers include cutting out carbohydrates, cutting out fats, not eating carbs after 6 pm, a low glycaemic index diet, a low glycaemic load diet, the South Beach diet... the list goes on. Do popular fad diets work?
Low Carbohydrate Diets
Made popular by the now-deceased Dr Robert Atkins, the popularity of eliminating carbohydrates from the diet truly was a revolution and the testimonials numbered thousands. Atkins' science was based on the hormone insulin, and it is worth mentioning that almost every diet since has ridden on the back of insulin's coat-tails. Atkins told the world that when we eat carbohydrates, such as bread, rice, cereal, pasta and even fruit, these foods are converted into glucose and travel around the bloodstream. This part is true. Glucose from carbohydrates then stimulates the release of insulin, a powerful anabolic hormone produced by the pancreas. Atkins said that insulin converts this glucose or sugar into fat, and hence his diet is constructed around what he believed reduces the production of insulin: a carbohydrate-free diet. As we will see later, the action of hormones is much more complicated than this incorrect oversimplification of insulin.
Basic science, however, shows that pasta, rice, fruit or vegetables eaten on their own do not get converted to fat. They are converted to glycogen and stored in muscle and liver cells, which can store about 400 g and 70 g, respectively. Even in large carbohydrate feeding studies such as those by Kevin Acheson (American Journal of Physiology, 1984 and Metabolism, 1982) where people are fed over 500 g of carbohydrate (the same as eating 1.3 kg of cooked pasta), the conversion of carbohydrate to fat is roughly 10 g, with large amounts stored as glycogen and large amounts used as part of the day-to-day metabolism. This is certainly not advocating eating so much food; however, the...