Experts have since tried to pinpoint the dangers of crash diets (technically known as "very low calorie" diets).

CNN: How crash diets harm your health

New research shows these diets can help people lose weight faster than traditional low-calorie diets (see article).

ECONOMIST: Convenience food

Experts stress that very-low-calorie diets should only be followed with a doctor's supervision.

CNN: How crash diets harm your health

Unfortunately, agave appears to be an OK short-term, low dose solution that meets the needs of low calorie, low glycemic diets.

FORBES: Is Agave Nectar Healthy For You?

Hernried has lectured on very low-calorie diets for more than a decade and supervises a VLCD program in his California clinic.

CNN: Extreme diets: Life on 800 calories a day

While mice kept on low-calorie diets live longer than their fatter friends, the skinny mice are less fertile and are sometimes sterile.

ECONOMIST: The latest from the wacky world of anti-senescence therapy

But for many, the evidence that low-calorie diets can extend life has remained tantalizing--especially if, as Walford proposed, it was likely to boost the human life span to 120 years or more.

FORBES: Starvation--And Long Life--In A Pill?

He says there is an enormous amount of scientific research that supports low-carb diets - particularly studies which find them superior to low-fat, calorie-restricted diets for weight loss - and the internet shows "first hand accounts from countless individuals who have transformed their health for the better using low-carbohydrate eating".

BBC: Atkins and the never-ending battle over carbs