The boffins reckon that sweet drinks give individuals a 'sugar rush', which helps supply the brain with the fuel needed to suppress outspoken opinions.
To reach the conclusion, the researchers gave a group of students lemonade, some with sugar, and some with an artificial sweetener.
They were then shown a picture of Sammy, a young man said to be gay, and asked to write for five minutes about his typical day.
Using a list of 58 stereotypes associated with gay men, the researchers then counted the number of times they were written.
Those who had drunk the sugary drink used far fewer stereotypes in their essays than those who had the artificial sweetener, leading to a theory that people can use restraint to keep objectionable thoughts to themselves when they have higher amounts of glucose in their body.
"The findings suggest a link between glucose levels and the expression of prejudice and the use of stereotypes," the Telegraph quoted the report, as saying.
"People with lower glucose levels are more likely to use stereotypes when describing others and, if they are high in prejudice, are more likely to make derogatory statements," the report stated.
The researchers added: "When people engage in the act of trying to control public expressions of prejudice or the use of stereotypes, they consume the energy required for self-regulation.
"However, once the energy source is restored to normal levels, people regain the ability to control conscious responses towards others.
"Because self-control depends on processes that consume glucose as an energy source, people who have lower levels of blood glucose may be more likely to express prejudice."
The study has been published in the Journal of Experimental Social Psychology.