Taxing unhealthy foods dissuades people from eating junk food, whereas subsides on healthy food end up encouraging people to eat nutritional foods.

According to the Centers for Disease Control and Prevention, a third of US adults and one in five US children are obese.

Researchers at the University of Buffalo in New York conducted a study including psychologist Leonard Epstein. Around 42 mothers have been given more than $US22 to spend at a supermarket in the university. The mothers had the choice of 30 healthy and 30 junk food items, four healthy beverages, juice, skim milk and water and four sugary drinks. All the mothers went for shopping five times with different prices each time.

"It appears that mothers took the money they saved on subsidised fruits and vegetables and treated the family to less healthy alternatives, such as chips and soda pop", added the authors of the study, published this week in Psychological Science.

The study found that taxes on unhealthy foods were more effective in reducing calories purchased over subsides.