Dr Toomath wound up the organisation in 2015.
She told the Wanganui Chronicle the government's current approach to obesity is to "tell people to try harder".
"I am totally opposed to personal responsibility being the answer to obesity. People might lose weight for six months, maybe 12 months. But if you look five years out, about 85 percent people are right back where they were and many of them are much fatter.
"About a decade ago, I stopped asking people losing weight. Prescribing weight loss simply doesn't work."
Instead Dr Toomath would like to see the government impose tighter restrictions around food.
"If we really want to deal with obesity need to tackle food in our environment. That means we need to decrease the availability and increase the price of junk food."
She said the public "needs to demand" a healthier environment.
"People have a right to a healthier environment, and they need to demand a response from the government," Dr Toomath said.
In April, her book on the subject was published. It's titled Fat Science: why diet and exercise don't work and what does. It was published by Auckland University Press.
The Porritt Lecture was established by renowned physician Dr Peter Powles, who worked at Whanganui Hospital for most of his career. The lecture was named in honour of Lord Arthur Porritt, a Whanganui-born governor-general and the speaker at the first Porritt lecture more than 50 years ago.