Otago University has found that overweight women lose weight more quickly on the Zone diet than if they follow conventional dietary advice
A study by the university's Edgar National Centre for Diabetes Research found that women also lost weight faster on the controversial Atkins diet, but they started to gain weight again within a year.
The study concludes that the Zone diet, promoted by American doctor Barry Sears, "may be the best overall approach to reducing the risk of cardiovascular disease and Type 2 diabetes".
The lead researcher, Dr Kirsten McAuley, said that although thousands of studies had been made of the Atkins diet, the Otago research was the world's first direct comparison of Atkins, Zone and conventional dietary advice in a test which did not have a high dropout rate.
Eighty-eight per cent of the overweight Dunedin women in the study stuck it out for at least a year, providing data on 96 women with an average age of 45.
All were "insulin-resistant", a pre-diabetic condition where the body's ability to use insulin to absorb sugar is reduced.
In full diabetics, insulin resistance causes a dangerous buildup of blood sugar which the body cannot absorb.
In the pre-diabetic stage, the body copes by producing more insulin.
The women were divided into three groups - one on the Atkins diet, one on the Zone diet and the third being given conventional diet advice.
The Atkins and Zone diets aim to slash intake of carbohydrates, including sugar.
Dr McAuley said the Atkins was more extreme, starting with 20g of carbohydrates a day, equivalent to half a slice of toast or half a banana.
The Zone diet emphasises high protein foods to offset low carbohydrates, advocating a balance of one-third low-fat protein such as meat, eggs and beans, and two-thirds fruit and vegetables.
Conventional dietary advice also emphasises eating plenty of fruit and vegetables, but with less emphasis on meat because of worries about high fat increasing the heart attack risk.
Researcher Kylie Smith told the first conference of the New Zealand branch of the Australasian Society for the Study of Obesity in Auckland yesterday that all the women in the study were seen weekly for four months and then checked again at six months and a year.
After six months the women on the Atkins and Zone diets had lost an average of 8kg. Women following conventional advice lost only 5kg.
After a year, the Atkins dieters were gaining weight again and were 5.4kg below their starting points. The conventional eaters were still 4.5kg lighter, and the Zoners were the winners with average weights 6.5kg below where they started.
Dr McAuley warned that diabetics with signs of kidney disease should avoid the Zone diet.
"There is no one best bet or wonder diet that's going to solve obesity," she said. "We need to consider a variety of options for different people who have different eating habits and preferences."
Surprisingly, the study found that after six months, women on all three diets had about the same amount of "bad" LDL cholesterol, the main warning signal for heart attacks.
"It was expected that LDL would increase under the Atkins diet," Ms Smith said.
Atkins allows people to eat high-fat steaks as long as they have minimal carbohydrates.
After two months, the conventional eaters were getting 49 per cent of their energy calories from carbohydrates, compared with 34 per cent for the Zoners and 11 per cent under the Atkins diet.
But the Atkins dieters paid a painful price - "a significant number" needed to take anti-constipation pills because they missed out on bread and other high-fibre foods.
They ate an average of only 9g a day of dietary fibre, compared with about 20g a day for both the other two groups.
"Those on the Zone diet did seem to enjoy it better," Ms Smith said.
How old and new compare
CONVENTIONAL ADVICE
* Eat plenty of fruit and veges (at least two fruits and three vegetables a day).
* Eat plenty of breads and cereals, preferably wholegrain (six daily slices of bread, half-cups of breakfast cereal or cups of rice or pasta).
* Drink low-fat milk and dairy products (two daily glasses of milk or pottles of yoghurt or four slices of cheese).
* Eat one serving a day of meat, eggs and nuts (two slices of meat, one steak, one chicken leg, one fish fillet, one egg or three-quarters of a cup of beans).
* Aim to get calories from carbohydrates 50-55 per cent, fat 30-33 per cent (including 8-10 per cent saturated fat), protein 11-15 per cent.
* Aim for 30g of fibre a day from vegetables, wholegrains, beans and peas.
ATKINS DIET
* Initial daily limit of 20g of carbohydrate, obtained from unprocessed salads and other non-starchy vegetables. Avoid high-sugar processed foods such as bread, rice, pasta or vegetables grown underground.
* Eat mainly meat, dairy products and salad vegetables to keep you full.
* Gradually increase carbohydrates such as high-fibre veges, fruits, beans, peas and wholegrains to the level that keeps your body at the right weight.
* Take multivitamin pills and an essential oils/fatty acid formula to ensure adequate nutrition.
* No precise aims for calorie intake proportions, but very low carbohydrate means high proteins and fats.
ZONE DIET
* Eat at last three meals and two snacks a day to stay within the "zone" where you are not hungry and have a clear mental focus.
* Divide your plate into three equal sections. One-third should be enough low-fat protein to fit in the palm of your hand, and two-thirds should be fruits and vegetables, with a dash of fat such as olive oil.
* Eat plenty of leafy green vegetables and fruits.
* Eat less pasta, breads, grains and starches.
* Aim to get calories from protein 30 per cent, fat 30 per cent, carbohydrates 40 per cent.
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Related resources:
Australasian Society for the Study of Obesity
