A lack of protein in the modern diet is a cause of overeating and is a big factor in causing obesity, an Australian university study has found.

Research from the University of Sydney's Charles Perkins Centre found the instinctive appetite for protein in humans is so powerful people continue to eat until their bodies get the right amount of protein.

It said the overriding drive for dietary protein was a core factor in the global obesity epidemic, especially as diets shifted towards an increased proportion of foods higher in carbohydrates and fats and with protein reduced.

"We found that regardless of your age or body mass index, your appetite for protein is so strong that you will keep eating until you get enough protein, which could mean eating much more than you should," said lead author Dr Alison Gosby.


The research collated the results of 38 published experimental trials measuring the unrestricted energy intake of people on different diets, and is published online in Obesity Reviews.

It found, for the first time, that reducing the percentage of dietary protein will result in total energy intake increasing as the percentage of protein in diets decreases.

"When you consume things like soft drinks, which are fairly low in proportion of protein but high in calories, your energy intake will increase because you'll need to keep eating to get the protein you need," Dr Gosby said.

Most people ate the right amount of protein but ate too much to get it.

More than a million adult Kiwis, or 28 per cent of people aged 15 and over, are obese, says this year's Ministry of Health annual report.

But AUT Professor of Public Health Grant Schofield did not think lack of protein was the cause of Kiwi obesity.

"I think the major problem in New Zealand is over-supply and eating of processed dietary carbs."

He said processed carbohydrates upset the hormonal and neural mechanisms in the body, which controlled eating and hunger.


Student Mosab Askar, 28, from Saudi Arabia, says he finds himself eating more in New Zealand.

"We eat out often here and most of the food we get are not really balanced meals."