After nine days without sugar, obese children saw a drop in insulin levels and an improvement in their cholesterol.

Quitting sugar for just nine days can dramatically improve health, a new study reveals.

The study, published this week in the online journal Obesity, observed 43 obese children over a nine-day period. Researchers replaced sugary foods with starchy processed products, ensuring fat, protein, carbohydrate and calorie levels remained the same as in the kids' previous diets. The were also careful not to let their children's weight fall.

By day nine, researchers observed some "striking" results.

"Everything got better," said study author, Robert Lustig, paediatric endocrinologist at UCSF Benioff Children's Hospital in San Francisco.

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All participants saw a drop in insulin levels and an improvement in their cholesterol, suggesting that sugar is dangerous not because of its calories but because of the strain it places on the body's metabolism.

This study boosted Dr Lustig's previous claims that "sugar calories are the worst, because they turn to fat in the liver, driving insulin resistance and the risk for diabetes, heart and liver disease".

The children, aged between 8 and 18, seemed to be more aware of satisfaction levels, the researchers said, with many expressing it felt as if they'd eaten so much more food over the course of the study.

"[The kids] were consuming the same amount of calories as before, just with significantly less sugar," said Dr Lustig, indicating that not all calories are the same.

Speaking to The Wall Street Journal, Dr Lustig said triglycerides - which can contribute to a hardening of the artery wall and cause acute pancreatitis - showed a "very, very large improvement".

"This ... is the strongest evidence to date that the negative effects of sugar are not because of calories or obesity."

The latest New Zealand Health Survey found 1.2 million Kiwis were obese – that's three in every 10 adults and one in nine children.

Health minister Jonathan Coleman recently stated "action was needed on the way sugar-loaded products were marketed to consumers", and the Government believes that education and "voluntary action by the food industry is the answer".

Senior paper author Jean-Marc Schwarz claimed he had never seen results "as striking or significant".