Some fat activists are rejecting those who try to lose weight, says a New York academic.

In a keynote presentation at a Massey University conference, Katie LeBesco said the edict against weight loss was a fascinating contrast with the attitudes toward bodily modifications in the trans community.

LeBesco said as she studied the fat acceptance movement's shift towards the mainstream she noticed a tension around weight loss.

Warwick Smith/ Fairfax NZ Katie LeBesco was a keynote speaker at a fat studies conference in Palmerston North.

"It tends to be a difficult conversation for fat activists. Many of them get out and walk out of the room if intentional weight loss comes up."

That tension only increased as more body-positive images, such as Dove's Real Women have Curves ad campaign, appeared in the media.

She said she'd hoped to examine what was behind that tension by comparing the two groups' approaches.

Whereas some fat activists believed people needed to be satisfied with their body the way it was, trans people often required a physical change to fit their identity.

Her presentation at the Fat Studies: Reflective Intersections conference at Massey University on Wednesday focused on her work with people at the crossroads between the two groups.

LeBesco had conducted a series of in-depth interviews with fat activists who were also trans, gender-queer or fluid.

There were many similarities between the movements; both fight to change the assumptions people make based on appearance, both have to deal with doctors and "medicalisation", and both are looking to reclaim control over how they express their identities.

The two movements could learn a lot from each other, LeBesco said.

"Autumn", one of the interviewees in LeBesco's research, said the disdain often directed at dieters showed the fat activist community was still struggling with what it meant to let people have control of their bodies.

The trans community tended to be more accepting of other people choosing to express their gender, LeBesco said.

"There needs to be a fundamental shift in the way we all see weight and bodily transformation," LeBesco said.

"People deserve dignity whether they've chosen to become how they are, or whether they were born that way.

"I don't think the only way your identity gets de-stigmatised should be that you don't have control over it."