Findings from the 2013 Burden of Disease study indicated excess body weight is becoming a bigger health risk than tobacco consumption.
The study used a disability-adjusted life years (DALY) system to measure the degree of health loss.
It measured the gap between the population's current state of health and a population that would be illness and disability-free - so that one DALY represented one year of healthy life lost.
The study looked at diseases, injuries and risk factors between 2006 and 2016 sustained by both genders and all ages and ethnic groups nationwide.
It showed that a combination of high salt intake, high fat intake, low vegetable and fruit intake and excess energy intake accounted for 11.4% of declining health.
Tobacco, alcohol and illicit drugs accounted for 13.7% of DALY.
University of Otago professor of human nutrition and medicine Jim Mann said the findings were unsurprising and obesity was likely to overtake tobacco as one of New Zealand's health-loss leaders.
He said the Government needed to take more action to prevent obesity.
''We have got to treat it as the epidemic that it is and take it as seriously, if not more seriously, than tobacco.''
Prof Mann said steps taken should include greater advertising, more education and at least debating whether a tax could be introduced for unhealthy foods.
He said the Government's half-hearted approach to obesity prevention had not gone far enough.
University of Otago associate professor Nick Wilson, of Wellington, said the study reinforced the country's need to improve its nutrition.
He said options for this were taxing sugar in soft drinks and regulating the maximum salt levels in processed foods.
These ''smart food'' taxes and regulations were increasing in European countries such as France, Finland, Hungary and Denmark.
The overall study showed that life expectancy in New Zealand was increasing. However, the mix of diseases and conditions causing health loss in New Zealand was changing over time.
The survey also showed alcohol-use disorders ranked high for men but not women, and Maori experienced greater health loss than non-Maori at all ages.
Leading health loss causes
• Youth (15-24 years): mental disorders (31%), injury (27%), plus reproductive disorders for women.
• Young adults (25-44 years): mental disorders (25%), injury (15%), plus reproductive disorders for women.
• Middle age (45-64 years): cancers (24%), vascular disorders (16%).
• Older adults (65-74 years): cancers (29%), vascular disorders (24%), musculoskeletal conditions (11%).
• Older adults (75 years and over): vascular disorders (35%), cancer (18%), neurological conditions (10%).
