From 2006 to 2011, the proportion of Brazilians who were overweight went up from 42.7% to 48.5%.
The health ministry described the trend as "worrying", but said it was not a direct result of rising prosperity.
It highlighted major programmes to promote healthier eating and increased physical exercise, saying now was the time to confront the problem.
The study was based on 54,000 telephone interviews in all the country's state capitals as well as Brasilia.
It found that 52.6% of men and 44.7% of women were overweight.
The proportion of people with obesity increased from 11% in 2006 to 15.8% in 2011.
The health ministry said the consumption of high-fat food was a major cause, particularly among men.
But Health Minister Alexandre Padilha rejected the idea that the increase in the proportion of overweight people was linked to Brazil's rising prosperity.
"Eating habits have not changed much over the last six years, it wasn't in this period that people started consuming full-fat milk and fatty meat," he said.