Protein the key to low carb diet success

The secret behind Atkins diet success was protein-induced satiety, according to a recent BBC documentary.

Satiety, a condition that describes the feeling of being full after a meal, is currently at the centre of obesity and weight loss research. The theory is that by controlling appetite with satiety you minimise overall food intake and stick to your diet.

The Horizon documentary, recently aired in Australia on ABC's Catalyst, investigated some of the claims made by Atkins and his proponents about the reasons why the high fat, low carb approach worked.

One of those claims was that the breakdown of fats and proteins burned more calories than the digestion of carbohydrates. Another claim was that all the extra calories consumed from fat were eliminated due to ketosis. Ketosis is a state in which the body relies on fat, not carbohydrates, for energy.

To test these ideas, the report first looked at a Kansas University study.

Twin brothers were put into separate sealed chambers – one on a conventional low fat diet, the other on Atkins. Oxygen input and output was measured to calculate how quickly their bodies were burning fuel. Urine analysis also tested how many calories were lost to ketosis.

After one day, only 22 more calories were lost by the Atkins twin when oxygen was assessed – not significant, according to the study team. After urine analysis, the Atkins twin lost less than half a calorie more than his brother.

So if digestion and ketosis were not getting rid of the extra calories, where were they going?

Focus turned to another study in which four diets – Weight Watchers, SlimFast, Rosemary Conley and Atkins – were tested. Four groups of 60 people each took part, completing diaries along the way. It was found that Atkins, despite its high fat content, was just as successful as the other three diets.

To get to the bottom of where the extra fat calories were going, researchers studied the diaries and found that, although the proportion of fat consumed in the Atkins group was higher, the overall consumption of calories each day was roughly the same as in the other groups. The diet in other words was keeping them full, making them eat less.

Atkins believed cutting carbohydrates helped control appetite. But researchers found another answer.

Arne Astrup, a professor in human nutrition at the University of Copenhagen, invited grocery shoppers to visit his store where one group was allowed to shop for high carbohydrate foods, the other high protein. All were told to eat as much as they wanted until satisfied. It was found after a year that the high protein group was losing 5 or 6 kilos more than the other.

"We could see from the data that the reason why the high protein group had lost more weight was because they had actually consumed fewer calories throughout the study, despite the fact that they had just as the same free access to all the foods they really want to, to eat," Astrup told the reporter.

In another experiment, Cambridge obesity expert Dr Susan Jebb found that people fed spaghetti bolognaise high in fat consumed more calories until satisfied than people eating a low fat version.

"What's absolutely true is that people who consume large amounts of protein seem to feel fuller quicker than people who consume similar amounts of calories as fat," Dr Jebb told the reporter.

Following the broadcast, Jennie Brand–Miller, professor of human nutrition at University of Sydney and expert on the Glycemic Index, said while satiety was a factor, the role of insulin control could not be discounted.

"Atkins (and other high protein diets) are helping people lose weight by reducing insulin levels as well as reducing hunger," Prof Brand-Miller told an ABC online forum.

"When insulin is high, two things happen. You burn more glucose as your fuel source and you inhibit the burning of fat. Our studies suggest that high GI foods gradually increase body fat accumulation, even though the laws of thermodynamics are obeyed."

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