Study leader Judy Paisley of Ryerson University in Toronto conducted interviews with 21 people making dietary changes -- most in response to a medical diagnosis -- and with their partners or significant others.

"For most pairs, the significant other's emotional and behavioral responses to the dietary change appeared to reflect the general dynamics of the relationship," Paisley said in a statement.

The study found that a partner's emotional responses varied widely -- from co-operation and encouragement to skepticism and anger.

In most cases, the significant others described themselves as playing a positive, supportive role and some facilitated the change by joining in the new diet, or by changing their shopping or cooking habits.

In other cases, the person trying to make a change felt his or her partner had a negative impact -- for example, by eating "forbidden" foods in front of them.

In only one case did both partners agree that the significant other played a neutral role, Paisley said.

The findings are published in the Journal of Nutrition Education and Behavior.