The Corrections Department has been urged to give prisoners healthier food and more servings because it would help them behave better and do more physical activity.

But the departments heads say they have no plan to improve the prison menu or cut off inmates' access to junkfood.

In a select committee this morning, Green Party corrections spokesman David Clendon asked officials whether the budget for feeding prisoners would be raised.

At present, the department spent $5.30 per prisoner each day, which covered three meals.

The last review of prison food was in 2009. It found that rations were adequate, but would need to increase if Corrections wanted prisoners to do more physical activity.

Mr Clendon said servings should increase now that all prisons were being converted into working prisons.

Corrections Minister Sam Lotu-Iiga said the department was always looking at ways to improve the prison system, but changing prison menus was not a priority.

In a nationwide tour of prisons, he had found the meals and variety to be "fulsome".

Corrections chief executive Ray Smith said the department had received no complaints about food, and it had already made some arrangements to provide more meals to inmates who were working.

He added: "I think some people need more exercise than they're getting, quite frankly, not more food."

Prisoners could also spend up to $70 a week on other food items from prison stores, but Mr Clendon said the range was limited and of low nutritional value.

The Green MP cited British research which showed that prisoners who ate more nutritious meals were better-behaved.

"There's a correlation between the adequacy of diet and inmate behaviour," he said.

Mr Smith was reluctant to regulate the sort of items that were sold in prison stores.

"When you take away people's liberty for long periods … and they've got to entertain themselves then I think we've got to give them some freedom of choice about the right to choose."

A Corrections spokesman said prison menus were developed with help from the Ministry of Health and the Heart Foundation.

Sample menu for male prisoner

Breakfast - two Weetbix with milk, three slices of toast with spread and a cup of tea.

Lunch - three sandwiches, a piece of fruit and tea.

Dinner - sausages with gravy, potatoes and two seasonal vegetables, a piece of fruit and tea.