Heavier men have been found to earn more, while heavier women earn less than their trimmer counterparts.
The University of Otago's Christchurch Health and Development study discovered obese men with a body mass index (BMI) of more than 30 earn on average $140 a week more than men with a normal BMI.
Obese women earn on average $60 less than women with normal BMI ratings.
The study set out to find links between a person's size, measured by the BMI index, and their net weekly income, depression and life satisfaction, but found only women suffered from poorer outcomes due to being overweight or obese.
Associate Prof John Horwood, of Christchurch, said the results were surprising.
''There was a small but pervasive relationship between growing body size in women and lower income, depression, low self-esteem and dissatisfaction with life,'' he said.
For men, a larger circumference did not negatively impact their mental health or self-esteem.
Prof Horwood said the study was not set up to answer why such relationships existed and he could only offer conjectures.
He said one reason why obese women earned less and had poorer mental health could be society's general view that obesity in women was unattractive and undesirable.
''Not only is there more stigma attached to weight and body composition for women but they may also be more likely to perceive being overweight or obese as a source of stress or adversity.''
He said larger men earning more could be because of the link between stature and body size, or busy schedules leading to poor eating habits. Obesity was commonly unrelated to mental issues and life satisfaction in New Zealand, Prof Horwood said.
''The findings are an important starting point to fully understand the growing obesity problem.
''These sorts of things will impact [on] treatment programmes.''
More than 1000 participants aged 30-35 were studied and Prof Horwood hoped to revisit the study when the participants were older.
The study used the BMI index, a generally accepted indicator of excess body weight, as set out by the Ministry of Health, and acknowledged the limitations of using BMI as a measure, as it does not distinguish between the weight of muscle and fat and what proportion of them each person has.
• Allison Hess
BMI classifications
Underweight: Less than 18.5
Healthy: 18.5-24.99
Overweight: 25-29.99
Obese: Over 30
(To calculate BMI divide weight in kilograms by height in metres squared)
Source: Ministry of Health
