The consensus on weight gain is that it is caused by overeating and a lack of physical exercise. However, this is probably not true based on sound observational science in the peer review literature. Weight gain and obesity is highly complex and involves physiological and psychological components. Increasingly obesity is being considered a disease caused by metabolic and psychological abnormalities, and this hypothesis explains the failure of exercise or dieting to cause successful long-term weight loss in obese individuals. The connection between emotional state and eating behaviour has been demonstrated repeatedly in animals and humans. Negative and positive emotions can modify calorie intake and thus the long term emotional state can influence body weight. The concept of food as a drug is not a new concept and it is known that nutrients within food can have drug like effects. For example, opioid-like peptides are formed from the digestion of casein protein (here), suggesting that certain foods may have the potential for addiction.
For example, short term stress that stimulates the release of adrenaline can have a suppressive effect on food intake. In contrast, more prolonged stress that releases cortisol can increase food intake because components within certain foods can act to modify the effects of stress on brain function, and so food becomes an effective coping strategy. Evidence also suggest that the feeding patterns seen in certain eating disorders such as bulimia nervosa, is a conditioned reflex aimed at altering brain chemistry (here). Emotional eating is a term given to those who overeat in response to emotional changes. Such individuals often are able to override the internal satiety signals that prevents overeating, perhaps because the foods they choose are not of high quality, but often processed and sugar-laden foods. Women appear to be particularly at risk of becoming emotional eaters, although the exact reason for this is not clear, but likely relates to differences in sex hormone production and release.
Researchers have investigated the association between emotional eating and body weight in large scale observational studies. For example, in ones such study1, researchers investigated the self reported weights and heights in over 8000 men and over 27,000 women, and then used questionnaires to assess the emotional and dietary status of the subjects. The questionnaire assessed the emotional eating, cognitive restraint and uncontrolled eating of the subjects and attempted to build a picture of whether negative emotions were responsible for alterations in food behaviour. Analysis of the data showed associations between emotional eating and body weight for men and women, and between emotional eating and both dieters and non-dieters. However, the association was strongest for women and those who had never dieted. Therefore these results suggest that emotions can influence feeding behaviour and that this in turn is associated with an increase in body weight, particularly in women.
Studies into emotional erating have reported that the phenomenon has increase significantly in the past two decades. While this may be an artifact reflecting improvements in the detection and understanding of the importance of emotional eating, the increase could be also be real. Mental stress associated with modern living may be a contributory factor in this regard, and while many turn to alcohol and illegal drugs under such circumstances, perhaps the drug of choice for many is food? However, care needs to be taken in addressing the cause and effect of the association, because emotional eating could be a result of overweight status rather than the cause, or the cause and effect may coexist. For example, weight gain might lead to negative emotional feeling that result in a need to overeat various foods, particularly refined carbohydrates. The data in this study showing that non-dieting was associated with high emotional eating responses supports the view that the cause of the relationship may be the weight gain and the response is the emotional eating.
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