"Fat hatred" should be banned like racism or sexism, says a pro-fat scholar who argues that obesity isn't a health problem.

Massey University lecturer Cat Pause says "the war against fat" and "fat phobia" were much more damaging than carrying a few extra kilos or, in her case, a lot.

"Obesity is not a big health problem. If you really look at the science, that is what comes through."

MAARTEN HOLL/Fairfax NZ BIG AND BOLD: Janeen Nowicki created Big, Bold and Beautiful aerobics to cater for clients who are larger than life.

Her claims fly in the face of an obesity epidemic taking hold of the Western World. Governments are fighting health budget blowouts, hospitals are buying bigger beds and equipment, and airlines are charging travellers for their overflowing flab.

In New Zealand – the world's third-fattest nation – more than a quarter of the population are classed as obese.

But Dr Pause, who has a PhD in human development, says it is "fattism" that should be feared, not expanding waistlines.

She called on New Zealand to be the first country to outlaw discrimination against fat people, which has been described as the "last socially acceptable form of prejudice".

Fat people were having to live in a culture that openly hated them, she said.

"We always hear about the war on obesity, and any time a politician or someone studying public health policy talks about solving the obesity epidemic ... they're talking about a programme of social eugenics to get rid of me."

The relationship between weight and health was much more complicated than people thought, and none of the "obesity myths" were backed by science, Dr Pause said.

"If what we want is a healthier, happier country, then I think one of the ways we get there is by changing the way we talk about fatness, because ... it's not just about all these fat people that have to live in a culture that openly hates them ... it's also about what that fat hatred does for non-fat people as well.

"So whether it's young girls who are going on diets by 5 because they're terrified of being fat, or middle-aged women who would rather lose years off their life than gain five kilos, fat hatred is bad for people of all sizes, not just for fat people."

Obesity expert and Otago University Associate Professor Rachael Taylor said people could be fat and fit, but overweight people were still at a higher risk of obesity-related illness, such as high cholesterol and diabetes.

There was "no doubt" genetics played a role in obesity, but what people did obviously had an important and increasing role to play, she said.

New Zealand's first fat studies conference – entitled New Zealand Fat Studies: Reflective Intersection – begins in Wellington tomorrow.

It is organised by Dr Pause, and topics include fat pride and teaching children about fitness and fatness.

Dr Pause, a 32-year-old American, doesn't use scales and is proud of her size, though her body mass index – which exceeded 30 – nearly stopped her from being allowed into New Zealand four years ago because of immigration rules.

"I'm usually the fattest person in the room. There was a time in my life when that horrified me and I've gone to war on my body so many different times."

She has done Weight Watchers "a bazzilion times", and every celebrity fad fast. All worked in the short term, but then the kilos came back. The last time she weighed herself she tipped 135 kilograms.

ATTITUDES HAVE CHANGED

When Janeen Nowicki started as a fitness instructor 25 years ago, fat people had a rough time.

After being turned away from gyms because she was overweight, Ms Nowicki created Big, Bold and Beautiful aerobics to cater for clients who are larger than life.

At 118kg, Ms Nowicki admits she is overweight but has no doubt she leads a healthy lifestyle. On top of running fitness classes, she walks every day. "There's fat and fit and there's fat and unfit, that's my view. I get my cholesterol and blood pressure checked all the time because I'm a big girl so if it's gone up ... I'll make sure I take care of it."

Ms Nowicki says society is now more understanding. "Compared to when I started 25 years ago society has changed. When I started my class no gym would hire me because I was 95kg. How I would love to be back to that!"

Many gyms have now embraced classes for overweight clients, and instructors who push the scales beyond those of leaner colleagues are not uncommon.

Despite believing the situation is better for overweight people, Ms Nowicki supported this week's fat conference if it pushed a positive message.

WHAT IS FAT?

The body mass index (BMI) is commonly used to classify weight categories in adults.

It is calculated by dividing your weight in kilograms by your height in metres squared, but is only a rough guide. A person with a BMI greater than or equal to 25 is overweight and BMI greater than or equal to 30 is obese.

Common health risks for overweight and obese people include heart disease and stroke, diabetes, osteoarthritis - a highly disabling degenerative disease of the joints - and some cancers.

The basic cause of obesity is an imbalance between calories consumed and calories used. Source: World Health Organisation