However, a more rounded Jackson appeared with Steven Spielberg when promoting their movie The Adventures of Tintin this month.
Jackson's weight gain raised concerns about the effects on his health, said Healthy Food Guide nutritionist Claire Turnbull.
"When people gain weight and end up carrying more body fat than is healthy, it is likely to increase their risk of heart disease, diabetes and other weight-related health issues," she said.
Losing weight and keeping it off was about more than dieting for a restricted time, said Turnbull.
"It's a process of education and integrating it into the way you live," she said.
A busy lifestyle such as Jackson's and any changes in routine could result in those trying to slim down returning to old habits, said Turnbull.
But the biggest effect of regaining weight was a sense of disappointment and failure said Fight the Obesity Epidemic spokeswoman Robyn Too-math.
"Often the most devastating effects are psychological," she said.
Genes caused obesity and people who were prone to it, such as Jackson, should focus on creating a healthier lifestyle rather than losing weight, said Toomath.
Obesity was the biggest global health epidemic and New Zealand was the third fattest nation after the US and Mexico, said Middlemore Hospital weight-loss surgeon Dr Habib Rahman.
One in four Kiwi adults is obese, according to Ministry of Health statistics.
Genetics, but largely lifestyle factors such as food choices and lack of physical activity, contributed to the problem, said Rahman.
"Anyone who is obese needs to realise they need help," he said. Ninety-eight per cent of dieters who lost weight regained it within 10 years, said Rahman.
