Reasons behind healthy eating may be crucial to women's body weight

Middle-aged women who are self-motivated to eat healthily have a lower body mass index (BMI) than those who do so in order to keep others happy, new University of Otago research suggests.

The Department of Human Nutrition study of 1600 New Zealand women aged between 40 and 50 is the first nationwide research of its kind anywhere. The researchers set out to examine the link between the degree of autonomy and self-determination motivating women’s eating behaviour and their body weight.

The participants were asked to rate the degree to which each different style of motivation for eating healthily applied to them. They were also surveyed on their specific food and eating habits.

Study co-author Dr Caroline Horwath says that more self-determined and autonomous reasons for eating healthily included enjoying creating healthy meals or viewing eating healthily as integral to one’s lifestyle or values. More ‘controlled’ motivation, on the other hand, involved reasons such as being nagged to eat healthily or feeling expected to do so.

Dr Horwath says that after adjusting for other potential explanatory factors, the results clearly showed that the more self-determined or autonomous a woman’s style of motivation for eating healthily, the lower her BMI.

“We found that every 10-unit increase in women’s scores for autonomous motivation to eat healthily was associated with a 1.4kg lower body weight, which was equivalent to a 2% lower BMI in a woman of average BMI in this sample.”

The results suggest that even a modest decrease in controlled motivation could equate to nearly 1kg lower weight, she says.

“As women in this age bracket are known to be at high risk of weight gain, this amount of weight loss could be important in reducing their risk of diabetes and cardiovascular disease,” she says.

While it requires further study to confirm that the type of motivation involved in eating healthily helps determine a person’s weight, the current findings suggest that this is a promising line of research to pursue, she says.

“For example, we found that controlled motivation to eat healthily was closely linked to more frequent binge-eating episodes. So, interventions that improve women’s sense of autonomy could be useful in reducing unhealthy eating behaviours that may potentially lead to weight gain.”

The research appears in the September issue of the Journal of the Academy of Nutrition and Dietetics. The Academy is the United States’ largest organisation of food and nutrition professionals.