Key Points:

An American woman who tipped the scales at 135kg has been refused residency in New Zealand because of her weight and health.

The 41-year-old, who had a body mass index (BMI) of 50 when she applied in January last year, suffers from morbid obesity and type 2 diabetes.

At her heaviest, she was said to weigh 148kg. A "normal" BMI ranges from 18.5 to 25.

Though she had taken steps to lose weight since making her application with her 31-year-old husband and two-year-old son, she still had a BMI of 47.

Immigration New Zealand (INZ) turned down their application for residence on account of the woman's unacceptable standard of health.

Now the Residence Review Board has thrown out their appeal.

"It is difficult to see how the INZ officer could have come to a different conclusion on the (medical) advice and information placed before her," the board said.

While the unnamed couple did not have job offers and indeed had no connection with the country, they scored well on other aspects of their application.

The husband was a butcher with an Arts degree and culinary qualification, and the wife who had business qualifications also had 17 year's experience in design.

INZ concluded that although the couple "had the potential to have a relatively significant contribution to New Zealand through their skills and experience, it was not compelling enough to outweigh the potential cost (the wife) was likely to impose on the NZ health service", the board said.

As a result, the INZ refused to grant a waiver to the couple.

A medical assessor said there was a relatively high probability that the wife would cost the health service more than the threshold $25,000 over the next four years.

He noted that the guidelines said that people with BMI over more than 35 should not be considered.

The assessor also said that the woman was at high risk of developing other diseases including heart disease, arthritis, cancer, gout and increased blood pressure.

Since starting the weight-loss programme, the woman said she had lost 24.5kg.

She said her diabetes was manageable and said that the amount spent controlling the disease was only $1090 a year, so it would take 23 years to hit the $25,000 cut-off point.

Her contribution to New Zealand would far outweigh the medical costs, she said.

However, the board said that while medical costs had so far been low, the medical assessment was that diabetes was a chronic condition with significant complications and costs over the lifetime of the condition.

The board said that the substance of the plea for special consideration was that the woman had been following a weight loss regime, which the couple believed would succeed.

"The appellant submits that his application should be considered as an exception to policy in preference to waiting for her to achieve this reduction.

"In effect, the appellant seeks to anticipate the success of his wife's weight reduction programme."