Author: Verónica Rodríguez Herrero (Master´s student of Biotechnology and Bioengineering 2015-2016)
Obesity is considered to be one of the most important pandemics of modern society. The decision to eat and what to eat vary among people and situations.
The individual differences in tastes and desire for food develop throughout life, due to the different experiences and attitudes. New-borns are capable of recognizing and responding preferentially to the smells and tastes just a few hours after birth. However, with time the responses change due to their experience (for example, the acceptance of the taste for black coffee or alcoholic beverages). In this manner, the socio-economic and cultural environment of an individual largely determines the opportunities and context for certain sensorial experiences. In order to integrate the specific tastes for each individual, it is necessary to understand what foods were taken during a part of their life cycle, as well as the frequence and conditions of the experience with that food.
In this context, the efforts to prevent or treat obesity/weight gain generally requires a certain level of control in food choice, as well as the decisions of when and how much food to eat. To this end, it is important to recognize that taste is not related to “want” or “desire.” The difference between the desire to eat and the pleasure that is derived from eating can be observed by studying the individual´s behaviour and using neurophysiological tools. For an individual in a certain situation, the desire or motivation to eat a food (incentive motivation) can be distinguished from its hedonic value (taste). The desire and expected taste can be strongly influenced by the perceived benefit, in other words, if a food correlates with a determined situation or context. The coincidence of foods and context can be determined by the social and individual convictions, englobing a unified signalling system: eat specific foods under specific circumstances. Therefore, besides taste and desire, the immediate psychophysiological state can give rise to a consumption of specific foods. Therefore, the consumption of certain foods can alter a state of necessity, and this can also enforce the development of certain tastes.
A large part of the literature concerning food choice is focused on the organo-sensorial responses, apparently assuming a certain chain of events: the taste preference, likings, purchase and consumption of food. Based on this, many studies have examined if a predisposition to excess eating could be related to hedonic responses to specific qualities of the foods, or to the fact that it consumption is performed in specific circumstances. Therefore, a key question is to know if obesity is associated with a higher pleasure for foods in general or for certain foods. In one study, Saelens and Epstein compared the value of food as a method of reinforcement in obese and non-obese women. Although both groups gave similar results, the reward of food was more reinforcing for obese women. This can be observed experimentally measuring neuronal processes related with the response to food. In a similar fashion, Karhunen et al indicated a significant increase of blood flow in the temporal and right parietal cortex in response to exposure to food in obese compared to non-obese women. However, despite the majority of the literature assuming a positive correlation between reward and food, a recent study seems to differ. In this fashion, Wang et al described a low affinity of D2 dopamine receptors (implicated in rewards) in association with high BMI valued in individuals with extreme obesity. Therefore, this research area requires more work to solve these questions.
The desire for certain foods and their consumption are the result of interactions between external and internal signals and specific physiological and psychological characteristics of each individual. The theory of externality of obesity proposed by Schachter and Rodin postulate that, compared to their normal-weight homologues, obese individuals are more reactive to external stimuli (time, presence and quality of foods, situational effects, etc) and less sensitive to hunger and internal satiety signals. Overweight and obese individuals tend to choose tastier and energy-rich foods, which contribute to the development and maintenance of these pathological conditions. However, although taste is an important part of food choice, it could only contribute partially to the development of food behaviour. In fact, the difficulties in weight control could reflect signalling problems and food motivations, instead of the pleasure derived from eating. Interestingly, the individuals highly preoccupied with food intake and weight control can be especially susceptible to thoughts, emotions and signals that may incite to excess eating and hamper their consumption restriction.
In summary, the sensorial information and food intake is related to obesity risk, with a taste pattern for food, being more prone the choice of energy-rich foods. However, food choice is not only by taste preferences. There is clear evidence that weight control problems reflect specific attitudes towards certain external stimuli. Therefore, it is important to distinguish between desire and motivation to eat certain foods and the real pleasure from eating them.