Motivation and emotion/Book/2016/Negative emotion and unhealthy food

Overview


Obesity in Australia has been described as being in epidemic proportions. According to the Australian Bureau of Statistics (2013), 62.8% of Australians over the age of 18 are overweight or obese. This chapter will explore the relationship between negative emotion and eating unhealthy foods. Several psychological and physiological theories and concepts will be explored with the aim of answering the question: Why do we seek unhealthy foods when experiencing negative emotions?

Definitions


Emotion is defined by Drever (1952, p. 82) as a "complex state of the organism, involving bodily changes of a widespread character - in breathing, pulse, gland secretion, etc. - and, on the mental side, a state of excitement or perturbation, marked by a strong feeling, and usually an impulse towards a definite form of behaviour. If the emotion is intense there is some disturbance of intellectual functions."

Some negative emotions are hate, jealousy, sadness, guilt, anxiety, lazy, boredom, and disgust.

Unhealthy food is defined as "any food that is not regarded as being conducive to maintaining health. Unhealthy foods include fats (especially of animal origin), “fast” foods (which are low in fibre and vitamins), foods high in salt and tropical oils (e.g., fried potato crisps/chips), and cream-based (“white”) sauces (which are high in fat)." (Segen's Medical Dictionary, 2011)

Emotional eating and unhealthy food
Negative emotions have been strongly linked to the consumption of food through the idea of emotional eating. Emotional eating the tendency to overeat in response to negative emotions, such as sadness or anxiety (van Strien et al., 2007). Several theories claim that people over eat when they're emotional in order to temporarily alleviate negative emotions (See: Theories of Negative Emotion and Food Consumption).

Stress and unhealthy food
The consumption of unhealthy foods under stress has been extensively researched. Stress can be psychological or physiological strain and tension, caused by circumstances, events, or experiences that are difficult to experience or endure (Colman, 2015). Several studies have investigated the relationship between stress and food consumption. The range of research on the subject has returned mixed results. Several results from past studies are displayed in Table 1 (Macht, 2008).

The results from past studies show a large degree of variation. This may be a result of varying experimental manipulations or it may be caused by varying responses to the experimental manipulations.

While results from studies testing stress and food intake are mixed, those testing stress and food choice are more clear. An experiment conducted by Zellner et al. (2006) found that when subjects experienced stress, their food choice moved from a healthy food (grapes) to an unhealthy option (M&Ms), while also increasing food intake. Another study found that subjects were more likely to consume sweet energy dense foods when under stressful parameters (Oliver, Wardle, & Gibson, 2000). These studies show people’s tendency to eat unhealthy foods when stressed.

Table 1. Changes of eating in response to emotional stress reported in surveys (references cited by Macht, 2008)



Sadness and unhealthy food
The effect of sadness and depression on food choice and food consumption has been extensively studied. A study conducted by van Strien et al. (2013) linked a sad mood to increased intake of food and sweet foods. Various studies have replicated the results found by van Strien et al., finding that people experiencing sad emotions are likely to overeat and choose unhealthy food over healthy options (Chang, 2013; Liu, 2007). These studies have found the consumption of unhealthy food to commonly follow the experience of sadness. While this has been established, some studies suggest that the consumption of unhealthy foods may incite feelings of sadness, rather than follow them. A study conducted by Macht, Gerer, & Ellgring (2003) tested women’s emotions directly after the consumption of unhealthy and healthy foods. The researchers found that following the consumption of unhealthy foods the subjects reported to feel sad, angry, shameful and tired, while also showing a decrease in happiness. Further highlighting the effect is the relationship between depression and unhealthy food intake. A study conducted by Khosravo et al. (2015) found that people with a healthy diet were significantly less likely to suffer from depression, whereas those with an unhealthy diet were much more likely suffer from depression.

Boredom and unhealthy food
While there is extensive research on the effect of sadness and stress on food intake, there is a lack of research focusing on the effect of boredom. Though there is a limited range of studies exploring the effect of boredom, the available research has yielded significant results. A study conducted by Abramson & Stinson (1977) investigated the effect of boredom on obese and non-obese individuals. Results found that boredom significantly increased food consumption for both obese and non-obese subjects. Another study, conducted by Moynihan et al. (2015) ran three experiments testing the effect of boredom on food consumption and food choice. Researchers noted a spike in calorie, fat, sugar, carbohydrate, and protein consumption in subjects under boredom conditions. Results showed that participants were more likely to eat an unhealthy snack rather than a nutritious meal when under boredom conditions. Moynihan et al. (2015) hypothesize that boredom incites individuals to perceive their lives as lacking meaning and those individuals eat in order to distract themselves from this effect. While this hypothesis is plausible, the effect found may be a result of sadness or depression. These findings highlight the importance of boredom in food consumption although more research is needed to determine how much impact it has on food intake.

Theories of negative emotion and food consumption
Several studies have linked negative emotion and food consumption, the following theories seek to explain the psychology behind our desire to seek unhealthy foods when experiencing negative emotions.

Kaplan & Kaplan's psychosomatic theory of obesity
As first proposed by Kaplan & Kaplan (1957), the psychosomatic theory of obesity stipulates that when obese people are feeling anxious they overeat with the intention of alleviating the anxiety. The researchers offer two hypotheses to explain this phenomenon: there may be a degree of physiological incompatibility to experience intense anxiety while eating, or it may be caused by a by-product of protein and carbohydrate intake, effecting neurotransmitters, particularly serotonin. These processes may create a pattern of behaviour where one is unable to distinguish between hunger and anxiety because they learnt to eat in response to anxiety as well as hunger (Canetti, Bachar, & Berry, 2002).

In more recent years the efficacy of Kaplan & Kaplan’s theory has been extensively challenged. Schachter, Goldman, & Gordon’s (1968) experiment found that obese people ate the same amount of food when they were calm as when they were exposed to a treatment designed to arouse fear and anxiety. Abramson & Wunderlich (1972) replicated these results, finding that there was no significant difference in food consumption in obese people when compared in control and anxiety induced experimental groups.

Schachter's internal/external theory
Like Bruch’s theory, Schachter et al.'s (1968) theory of obesity states that the sensation of hunger and satiation are learnt responses. Where people of normal weight have learnt unconsciously learnt to recognize gastric contractions as physiological cues of hunger, obese people have not. When one experiences stress or anxiety, their stomach decreases contractions with the purpose of reducing hunger. As obese people have not learnt to recognize these contractions, they do not decrease their eating when experiencing a feeling such as stress. As a result of this faulty cognition these people are forced to rely on external cues of hunger such as the sight and smell of food rather than internal cues. While psychodynamic theories hypothesize that people eat in order to reduce anxiety, this theory states that people simply do not reduce their eating when stressed.

Results from Schachter et al.'s (1968) experiment found that exposure to stress reduced hunger in people with normal weight, while overweight people’s hunger levels were not affected by stress. These results supported Schacter’s theory. Results from more recent studies testing the theory have been mixed. Lowe & Fisher’s (1982) study found that obese people’s eating habits was more reactive to emotional cues when compared to those of normal weight. This finding was limited to the consumption of snacks, not meals. Other studies did not support Schachter’s theory (Ruderman, 1983; Pine, 1985; Reznick & Balch, 1977; Keenan, Rogers, Brunstorm, 2016).

Burch's theory
Like Kaplan & Kaplan’s (1957) theory, Bruch’s (1973) psychodynamic theory of obesity hypothesizes that habitual overeating is the result of faulty learning processes. Burch claims that the feeling of hunger is a learnt pattern response, rather than an innate sensation. Incorrect experiences and education in eating habits and hunger sensations in early life can create an improper recognition of hunger. According to this theory, obese people are often inept in differentiating sensations of hunger and satiation from feelings of discomfort (E.g. sadness & anxiety). As a result, they are programmed to eat upon feelings of discomfort, rather than hunger.

The restraint hypothesis
Developed by Herman & Mack (1975), the restraint hypothesis claims that obese people are almost always trying to restrain their food intake. While under this self-restraint, feeling strong emotions such as anxiety or depression, or exposure to alcohol, drugs, or high calorie foods can create a state of disinhibition. During this state of disinhibition, the previously restrained person is hypothesized to overeat (Canetti, Bachar, & Berry, 2002).

The effect of the restraint hypothesis was displayed in a study conducted by Herman, Polivy, & Esses (1987). In their study, researchers found that subjects who were dieting ate less ice-cream than non-dieters. While this is unsurprising, the researchers found that after consuming a milkshake the dieters ate significantly more ice-cream than the non-dieters. Several studies have presented evidence, showing that negative emotions can trigger overeating in restrained subjects (Ruderman, 1985; Schotte, Cools, & McNally, 1990; Baucom & Aiken, 1981).

The five-way model
The five-way model was developed by Macht (2008) in response to the apparent lack of variability in previous theories of eating and emotion. The model was developed in order to take into account emotional characteristics and individual differences. The five-way model was created with the purpose of explaining the interaction between emotions and food intake. Macht (2008) identified five factors to explain the interaction between emotion and eating:
 * 1) Food-induced emotions control food choice - The food induced emotion will lead to sensations of either: avoidance, preference, or craving. Energy-dense foods rich in fat and sugar are likely to induce cravings, while bitter foods are more likely to promote avoidance (Rosenstein & Oster, 1988).
 * 2) Intense emotions suppress food intake - While strong emotions have been found to increase and decrease food consumption, the natural response to intense emotions is to decrease food intake. Stress has been found to both increase and decrease food intake (Schachter, Goldman, & Gordon, 1968; Herman, Polivy, Lank, & Heatherton, 1987). Furthermore, The psychological and physiological mechanisms of intense emotions have been found to interfere with eating (Macht, 2008).
 * 3) Negative and positive emotions impair cognitive eating controls - This factor is consistent with restraint theory (See: Restraint Theory). The theory states that positive and negative emotions disinhibit an individual’s food intake restraints (Herman & Mack, 1975).
 * 4) Negative emotions elicit eating to regulate emotions - This factor is consistent with Kaplan & Kaplan’s (1957) theory of obesity. The theory states that people eat in order to cope with negative emotions (See: Kaplan & Kaplan’s Psychosomatic Theory).
 * 5) Emotions modulate eating in congruence with emotion features - This factor stipulates that positive emotions such as happiness will increase food pleasantness and cravings, while negative emotions will decrease the sensations (Macht, 2008).

Serotonin
Serotonin is a neurotransmitter which researchers regard as being responsible for mood balance, with a key role in mood, aggression, arousal, and the sleep wake cycle (Hine, Martin, 2015). Studies have shown that the consumption of simple carbohydrates can induce a temporary reduction in negative emotions. Researchers hypothesize that the consumption of simple carbohydrates such as brown sugar, maple syrup, and other refined sugars has a direct effect on the release and synthesis of serotonin (Christensen, 1992). Christensen (1992) summarized the findings of Wurtman, Hefti, & Melamed’s (1980) study on the neurobiological effect of simple carbohydrates.



Animal research has demonstrated that consumption of a high-carbohydrate and low-protein meal stimulates the release of insulin from the pancreas. This insulin release in turn has the effect of increasing the uptake of amino acids from plasma but it also causes nonesterified fatty acid molecules to dissociate from albumin and enter adiposites leaving albumin in an unbound state. Tryptophan has an affinity to bind loosely to albumin and when insulin strips the fatty acid molecules from albumin, tryptophan binds to this protein, which spares tryptophan from being taken up by the peripheral cells. This sparing action increases the ratio of plasma tryptophan to the other large neutral amino acids (LNAA), valine, leucine, iosleucine, tyrosine, and phenylalanine, with which tryptophan competes for transport across the blood-brain barrier. An increase in the plasma tryptophan/LNAA ratio facilitates the uptake of tryptophan into the brain, which increases the saturation of tryptophan hydroxylase, the enzyme controlling the synthesis of serotonin, resulting in an increased synthesis of serotonin.

Researchers Wurtman & Wurtman (1995) state that the short term positive effect of simple carbohydrates on serotonin levels and thus emotion may have a negative effect. It is proposed that the effect may cause individuals to overeat in order to make themselves feel better. Wurtman & Wurtman claim this effect causes weight gain. This effect is highlighted in individuals with nicotine withdrawals, Seasonal Affective Disorder, high stress levels, and premenstrual syndrome.

While there is evidence suggesting that simple carbohydrates positively affect emotional states, studies indicate that the effect lasts for a short amount of time. Several studies have shown that a carbohydrate free diet has a positive long term effect on depression and emotion (Christensen & Burrows, 1990).

Dopamine


Dopamine is a neurotransmitter involved in central nervous system functioning, regulating emotional responses, and assisting in controlling the brain's reward and pleasure centers. Dopamine has three main pathways in the brain: midbrain to the basal ganglia, midbrain to the frontal lobes, and midbrain to the limbic system (Colman, 2015). While past research has linked dopamine to drug addiction, recent studies have identified the same reward systems to affect food consumption (Baik, 2013). The consumption of energy-dense, highly palatable, unhealthy foods have been found to enhance dopamine levels (Baik, 2013; Wise, 2006). Researchers hypothesize that the dopamine release caused by consumption of unhealthy foods reinforces one’s propensity to eat such foods, leading to an alleviation of negative emotions (Leigh Gibson, 2006). While research has found a significant link between dopamine release and food consumption, to date, there has not been an experiment conducted which tests this hypothesis as a whole. Research on the subject has been criticized for failing to investigate the underlying mechanisms of the relationship between dopamine reward systems and food consumption (Salamone & Correa, 2013). While there is a lack of research on the link between dopamine, negative emotions and food consumption, research suggests that the three mechanisms may be linked. Further research is needed to explore this relationship.

Conclusion
There is a strong link between negative emotion and the consumption of unhealthy foods. Psychological theories such as Kaplan & Kaplan's Theory, Schacter's Theory, Burch's Theory, the Internal/External Theory, and the Five-Way Model are offered as possible psychological explanations of the underlying drives behind the consumption of unhealthy foods. Physiological mechanisms, serotonin and dopamine were also offered as possible mechanisms facilitating the relationship between food an emotion. While all of these theories and concepts have all been proven to explain why people seek unhealthy foods when experiencing negative emotions, the mechanisms underlying the relationship are still unclear.