(Disponível em Português)
Many experts think that obesity is essentially the result of being hooked on food. But a new study reveals a much more complex reality.
In collaboration with other Portuguese centers, scientists at the Champalimaud Centre for the Unknown (CCU), in Lisbon, have quantified the link between hedonic motivation for eating and body weight. They conclude that the pleasure people get from food only explains a small fraction of the weight differences between obese and non obese persons. That is, “hedonic hunger” – the crave to eat for pleasure and not for gaining energy – is not, by far, the only risk factor for obesity. Their results were published this week in the Nature group journal Scientific Reports.
“The issue in question has become part of folklore psychology: we often hear that obesity ‘is like an addiction’”, says Albino Oliveira-Maia, the psychiatrist and neuroscientist from CCU who led the study. “But the truth is that concrete data in favor of this idea is weak. There is no clear evidence that hedonic hunger is associated with weight.”
“The pleasure of ingesting food is a natural and healthy behavior which becomes extreme in obesity”, adds the study’s first author Gabriela Ribeiro, a clinical nutritionist who is doing her PhD in neuroscience in Oliveira-Maia’s lab. “Obviously, to become obese, you have to ingest food in excess – and not just enough to fill your energy needs. And naturally, the pleasure you get from eating contributes to this excess. But what we showed in our study [also co-authored by psychologist Marta Camacho] is that this behavior does not account for the majority of obesity cases.”
The data the scientists used to clarify the correlation between obesity and hedonic hunger came from three adult populations: 123 clinically obese patients – that is, with a Body Mass Index, or BMI, greater than 30 –; 278 college students; and finally, to confirm their conclusions on a larger group, 865 people, globally representative of the Portuguese population, who had replied to a survey from Deco Proteste (the major consumer association in Portugal).
To evaluate the participants’ hedonic hunger, the team used a scale known as the “Power of Food Scale” (PFS), in use around the world and which, based on a questionnaire, attributes a score to hedonic hunger from 1 (minimum) to 5 (maximum).
They then performed a statistical analysis of the collected data to examine the relationship between body weight and hedonic hunger. The result, as expected, was that in the group of people with PFS scores of 1 or 2, only 10% were obese, whereas among those whose score was 4 or 5, the percentage grew to 40%. This is clear evidence that hedonic hunger is related to obesity. The analysis also showed that, for each additional score point, the probability of being obese almost duplicated.
Seen this way, it may seem that hedonic hunger is highly predictive of obesity. However, the scientists also showed that the list of risk factors for obesity does not end there: in fact, hedonic hunger explains less than 10% of BMI variability. “Food reward is not the main reason for obesity”, Oliveira-Maia points out. “Therefore, food addiction is not the whole story.”
Still, factors such as age, education and gender together only predict 6% of weight variability, the authors explain. This means that the 10% that are attributable to hedonic hunger are relatively important. “But we still have to find the remaining 84%”, says Oliveira-Maia.
Excessive high-energy food consumption and physical inactivity are the main determinants of obesity, he explains. These behaviors are in turn influenced by a wide set of biological, genetic and psychological factors, as well as environmental, social and cultural ones. And the very structure of urban environments, which favors sedentarity, as well as modern lifestyles, which induce stress, and educational and socioeconomic levels, also contribute to the overall positive balance that characterizes obesity. The new study thus suggests that BMI variability can only be explained in terms of multiple factors, many of which are not yet clear.
Why are the new results important? “Because we need to base our decisions for people’s health on real results rather than opinions”, replies Oliveira-Maia. “As far as we know, this is the first study to characterize and quantify the associations between PFS and BMI”, the authors write in their paper.
In particular, notes Oliveira-Maia, this study could “inform public health interventions designed to control the food environment” to which people are exposed. “We need to better understand what determines the presence of obesity and what determines feeding behaviors. Only then will we be able to develop better interventions in health education and have a stronger mandate to sustain policy options that might restrict food choices.”
Ana Gerschenfeld works as a Science Writer at the Science Communication Office at the Champalimaud Neuroscience Programme
Edited by: Catarina Ramos(Science Communication office). Photo credit: Dean Hochman
(Creative Commons CC BY 2.0)