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Intuitive eating is a nutrition philosophy proposing the negation of externally imposed dietary regimens in favor of following the guidance of the body’s internal cues. The term was coined by Evelyn Tribole and Elyse Resch. It is comprised of ten principles outlined in Tribole’s and Resch’s Intuitive Eating (2012) book:
 * 1) Reject the Diet Mentality
 * 2) Honor Your Hunger'''
 * 3) Make Peace with Food
 * 4) Challenge the Food Police
 * 5) Feel Your Fullness
 * 6) Discover the Satisfaction Factor
 * 7) Cope with Your Emotions without Using Food
 * 8) Respect Your Body
 * 9) Exercise – Feel the Difference
 * 10) Honor Your Health with Gentle Nutrition

The authors suggest intuitive eating is preferable to dietary restriction because it allows for a “healthy relationship with food, mind, and body.”

Tribole’s and Resch’s (1995) original framework has spurred a substantial and growing body of research in the fields of psychology and clinical nutrition regarding the measurement, practices, correlates, and outcomes of intuitive eating.

History
Exactly when the intuitive eating movement began is uncertain, but among the early pioneers was Susie Orbach, whose book Fat is a Feminist Issue was first published in 1978. Also, in the early 1970s, Carol Munter and Jane Hirschmann began Overcoming Overeating workshops in New York City and eventually published a book by that name. Susie Orbach was a participant in Munter & Hirschmann's workshops. Geneen Roth's first book on emotional eating, Feeding the Hungry Heart, was published in 1982. All recommended intuitive eating (also called "attuned eating" or "the non-diet approach") instead of conventional weight loss diets,  making their works precursors of Tribole and Resch's (1995) Intuitive Eating.

Theory
Objectification theory suggests that women whose bodies are objectified, or assigned value according to their physical appearance or utility, devote greater energy to “monitoring” their appearance. They also experience greater shame, anxiety, and distraction as they perceive that their bodies do not align with the “cultural standard” for females. Ultimately, this may increase their risk of mental health disturbances, including eating disorders. In other words, feelings of inadequacy relative to the “thin ideal” seem related to eating pathology, though not directly. Following this logic, Avalos and Tylka (2006) postulated that body acceptance from others and from themselves as opposed to scrutiny would encourage intuitive eating, a style of “adaptive eating," in female populations.

They explained their body acceptance model using the following constructs and research: (see Figure 1 for description of model)



General Unconditional Acceptance
Drawing from Carl Rogers' (1964)  humanistic theory, the authors state that feeling fully accepted by others encourages people to embrace the  “real self” rather than strive for the  “ideal self.” They reasoned that this  unconditional acceptance from someone significant in a woman’s life allows her to prioritize her “body function” rather than others’ evaluations of her physical self. They also explained that women who feel unconditionally accepted will likely believe others accept their bodies. “Perceived unconditional acceptance from the most influential other” was measured using a condensed version of the Barret-Leonard Relationship Inventory (BLRI).

Body Acceptance by Others
Research shows that others’ imposition of dietary restriction may compromise a female child’s attention to her hunger and fullness. Thus, the researchers reasoned that others’ acceptance rather than regulation may enhance the individual’s focus on body function. Additionally, Avalos and Tylka (2006) speculated that since women’s negative appraisals of their own bodies often stem from their perceived shortcoming relative to the cultural standard, those who feel accepted by others would not be similarly disturbed, thereby allowing for greater body appreciation. Body acceptance by others was measured using the Body Acceptance by Others (BAOS) scale, which was derived from the Perceived Sociocultural Pressures Scale (PSPS).

Body Function
In their construction of the Body Appreciation Scale (BAS), Avalos, Tylka, and Wood-Barcalow (2005) found a negative correlation between females’ “body surveillance,” or evaluation and management of physical appearance, and body appreciation among female undergraduates. Tylka (2006) speculated that valuing inner experience over physical attributes fosters greater body appreciation by encouraging attendance to one’s needs, allowing for optimal body function. Accordingly, Avalos and Tylka (2006) viewed the emphasis on body function as predictive of body appreciation and intuitive eating. They measured body function using the Objectified Body Consciousness Scale.

Body Appreciation
Numerous studies have suggested a link between women’s negative appraisals of their bodies and disordered eating behaviors. Conversely, Avalos and Tylka (2006) theorized a positive relationship between body appreciation and intuitive eating. They measured body appreciation using the Body Appreciation Scale (BAS).

Avalos and Tylka’s (2006) own studies suggested the viability of their model in multiple samples of undergraduate females. Details regarding the strengths of relationship pathways can be found in their Figure 2. They go on to note, in particular, the implications of this model in the counseling setting. According to their theory and research, those who encourage the practice of intuitive eating can do so via attention to the mediators outlined in the body image acceptance model.

For Adolescents
Researchers Andrew, Tiggeman and Clark (2015) sought to evaluate the body image acceptance model of intuitive eating among adolescents. They noted the research showing adolescents, particularly girls, are especially susceptible to body dissatisfaction and may engage in unhealthy weight loss activities. Furthermore, problematic eating behaviors during adolescence have been shown to predict later eating pathology as well as other negative psychological outcomes such as depressive affect.



In their investigation of this younger population, the researchers predicted that Avalos and Tylka’s (2006) model of intuitive eating would generalize to adolescent girls. However, they theorized an additional mediator of the relationship between body acceptance and intuitive eating:  social comparison. A robust body of research suggests the relationship between social comparison and body dissatisfaction, and there is evidence of this relationship specifically within the teenage population. Andrew and colleagues (2015) hypothesized the intermediary link of social comparison between body acceptance by others and body appreciation. They hypothesized that those granted body acceptance by others would engage in social comparison less and appreciate their bodies more.

They tested the model using a sample of 400 adolescent girls ranging between ages 12 and 16. Besides the Intuitive Eating Scale for Adolescents, they used the same measures as those employed to evaluate the original body image acceptance model of intuitive eating. Andrew and colleagues (2015) also measured social comparison using the Physical Appearance Comparison Scale (PACS). As shown by the significant relationships displayed in their Figure 2, their data supported the modified body image acceptance model among adolescent girls.

For Early and Middle Adults
Augustus-Horvath and Tylka (2011) tested whether the body image acceptance model of intuitive eating applied to older women, given the potential eating and body image changes that come with aging. They proposed a few notable changes to the original model and its measurement, which are displayed in their Figure 1.

The researchers added body mass index (BMI) to the model. They hypothesized that the increase in BMI that tends to occur with age could undermine women’s body appreciation, citing Lewis and Cachelin’s (2001) research showing normal, overweight, and obese women exhibit greater “drive for thinness” and body dissatisfaction as measured by the Eating Disorder Inventory (EDI). Additionally, they modified the “General Unconditional Acceptance” construct in the theory to instead encompass “Perceived Social Support,” taking into account Avalos and Tylka’s (2006) argument that assessing the acceptance from the most influential person in someone’s life does not allow for evaluation of the acceptance garnered from the community at large. They measured this construct using the Social Provisions Scale (SPS). Though they continued to employ the Body Surveillance subscale of the Body Consciousness Scale, they renamed the “Body Function” construct “Resistance to adopt an observer’s perspective.”

Augustus-Horvath and Tylka (2011) hypothesized that the body image acceptance model of intuitive eating would hold for emerging, early, and middle adult females. Furthermore, they hypothesized that body acceptance by others would operate as a mediator between perceived social support and body appreciation. Additionally, they predicted that “resistance to adopt an observer’s perspective” and body appreciation would serve as separate mediators between body acceptance by others and intuitive eating.

They found that the body image acceptance model held among emerging, early, and middle adult females. Women who felt more social support also felt their bodies were more accepted by others. Those who felt more accepted by others were more resistant to adopting an observer’s perspective and more appreciative of their bodies. BMI was inversely related to acceptance by others, with the strongest negative relationship demonstrated among early and middle adult women. Because acceptance by others mediated the relationship between BMI and body appreciation, Augustus-Horvath and Tylka (2011) suggested body acceptance as a target for intervention in order to encourage women to appreciate their bodies.

Expanded Model
Tylka and Homan (2015) focused on differentiating “appearance exercise motives” versus “functional exercise motives.” Though appearance-related motives are associated with a host of poor psychological outcomes such as body image disturbances and disordered eating, among others,     the researchers sought to investigate how functional exercise motives or lack thereof relate to body image. They noted Tylka and Wood-Barcalow’s (2015) work highlighting the role of “positive embodiment,” including body appreciation and body functionality, in positive body image. Since the body image acceptance model of intuitive eating encompasses these facets of positive body image, Tylka and Homan (2015) added functional and appearance exercise motives to the model to gain insight into their interplay with the other constructs. Unlike previous studies, they hypothesized that it would apply to both men and women. However, they speculated the relationships will be weaker among men than among women, for whom the body image acceptance model was originally constructed. A theoretical diagram can be found in their Figure 1. Additionally, the researchers postulated that women would have higher average scores for appearance motives and lower scores on all other measures because of sociocultural factors.

Using the Function of Exercise Scale (FES) to measure exercise motives in addition to measures employed by Avalos and Tylka (2006) to test their original model, the researchers concluded the viability of the expanded model within a sample of 258 females and 148 males. Details regarding the strength of relationships can be found in their Figure 2.

As predicted, body acceptance by others positively related to functional motives for exercise, and internal body orientation mediated the negative relationship between body acceptance by others and appearance motives for exercise. Functional exercise motives appeared associated with intuitive eating in both men and women (via body appreciation as a mediator in women). Accordingly, Tylka and Homan (2015) propose the potential worth of interventions aimed at encouraging functional motives for exercise in order to foster body appreciation in both men and women. In contrast, appearance motives for exercise demonstrated a negative relationship with intuitive eating, with and without body appreciation as a mediator. Lastly, though the model generally fit the males’ data, correlations were weaker, and the relationship between body appreciation and intuitive eating was not significant.

Measurement
Originally, intuitive eating was defined and measured by a lack of disordered eating behaviors. However, Tylka (2006) sought to construct a measure that could indicate positive eating behaviors rather than only the absence of disorder. Drawing heavily from Tribole and Resch’s (1995) original Intuitive Eating, she defined intuitive eating more concisely with three overarching principles, derived from prior research and theory:

“Unconditional permission to eat”
Tylka (2006) explained that chronic dieters tend to eat beyond their physiological needs when in distress due to a myriad of emotional reasons. Similarly, those who purposely limit their food intake tend to overeat after initial violation of their diets. Additionally, children whose parents limit their dietary consumption eat more and weigh more than those who do not.

“Eating for physical rather than emotional reasons”
The researcher refers to Herman and Polivy’s (1983) “boundary model for the regulation of eating,” which explains that organisms are biologically driven to eat within the “boundaries” of hunger and satiety. However, dieting tends to distort these boundaries, making those individuals susceptible to over- or under-consumption.

“Reliance on hunger and fullness cues”
Tylka (2006) cited research showing that children who are allowed to eat according to their own appetites at each meal naturally regulate their caloric consumption from day to day. However, regulating girls’ eating may encourage a lack of internal regulation as well as a greater degree of eating for reasons other than hunger.

IES-1
Tylka (2006) conducted four studies to construct and improve the IES-1. Internal consistency scores were as follows: .85 to .89 for the measure in total, .87 to .89 for the Unconditional Permission to Eat subscale, .85 to .86 for the Eating for Physical Reasons subscale, and .85 for the Reliance on the Hunger and Fullness Cues subscale. Test-retest reliability scores were as follows: .90 for the total IES-1, .88 for Unconditional Permission to Eat subscale, .88 for the Eating for Physical Rather Than Emotional Reasons subscale, and .74 for the Reliance on the Hunger and Fullness Cues subscale. Tylka (2006) inferred the measure’s validity by noting its negative relationship with BMI and symptoms, behaviors, and disturbances associated with eating disorders as well as its positive correlation with numerous beneficial psychological outcomes, such as “satisfaction with life.”

IES-2
Upon completion of these studies, Tylka and Kroon Van Diest (2013) published a subsequent scale, which they believed would improve upon the original. Influenced by Tribole and Resch’s (2003) addition of “gentle nutrition” to their Intuitive Eating framework, the Intuitive Eating Scale-2 (IES-2) includes an additional factor entitled “Body-Food Choice Congruence” (B-FCC). Scores on this factor indicate the degree to which participants eat to maximize their physical capabilities. Additionally, the IES-2 was designed to assess, to a greater extent, intuitive eating behaviors in the affirmative rather than concluding adaptive eating practices from a lack of disordered behaviors. The authors also hoped to improve upon the internal consistency of the IES-1.

Tylka and Kroon Van Diest (2013) conducted three studies to evaluate the psychometric properties of the IES-2. They found the following:

Convergent validity
Convergent validity reflects the degree to which scores on a measure relate to similar constructs. It was measured using Pearson r correlations between IES-1 and IES-2 scores, which were as follows for women and men, respectively: .87 and .91 for the total scale, .95 and .94 for Eating for Physical Rather Than Emotional Reasons (EPR) subscale, .90 for the Unconditional Permission to Eat (UPE) subscale, and .86 and .90 for the Reliance on Hunger and Satiety Cues (RHSC) subscale.

Scores on the IES-2 in total were negatively related to poor interoceptive awareness, defined as attunement to emotions and bodily cues, internalization of media appearance ideals, and body mass index (BMI). Scores on the IES-2 were positively correlated with self esteem, positive affect, and life satisfaction.

Scores on the Eating for Physical Rather than Emotional Reasons (EPR) subscale demonstrated a negative relationship with poor interoceptive awareness, internalization of media appearance ideals, negative affect, and BMI. They were positively related to self esteem, positive affect, and life satisfaction.

The Unconditional Permission to Eat (UPE) measure exhibited an inverse relationship with eating disorder symptomology, internalization of media appearance ideals, poor interoceptive awareness, and BMI. However, scores were inversely correlated with negative affect and directly correlated with self-esteem only for females. Few to no relationships with life satisfaction and positive affect were detected in women, nor were any significant relationships between UPE and life satisfaction, positive or negative affect, and self-esteem found within the male sample.

Scores on the Reliance on Hunger and Satiety Cues (RHSC) subscale were negatively related to eating disorder symptomology, negative affect, internalization of media appearance ideals, poor interoceptive awareness, and BMI. These scores were positively related to self esteem, positive affect, and life satisfaction.

Lastly, scores on the Body-Food Choice Congruence subscale were negatively correlated with negative affect in both men and women, BMI in men only, and poor interoceptive awareness, and internalization of media appearance ideals in women only. B-FCC scores were positively correlated with self esteem and life satisfaction. However, these scores exhibited no significant relationship with eating disorder symptomology in men or women; interoceptive awareness and internalization of media appearance ideals in men; and BMI in women.

Construct validity
Construct validity reflects the degree to which a construct is empirically related to those to which it should be theoretically related as outlined in a nomological network. To assess the construct validity of the IES-2 and its subscales, Tylka and Kroon Van Diest (2013) examined the relationship between scores on their measure with those measuring theoretically related constructs as traced in the body acceptance model of intuitive eating: unconditional acceptance, body acceptance by others, body function, and body appreciation.

The total scale’s validity was supported by its negative correlations with body shame and body surveillance, two indicators of a lack of focus on body function, in men and women, as well as its positive relationship with body appreciation.

Similarly, scores on the Eating for Physical Rather than Emotional Reasons (EPR), Reliance on Hunger and Satiety Cues (RHSC), and Unconditional Permission to Eat (UPE) subscales demonstrated negative relationships with body shame and body surveillance and positive relationships with body appreciation among both males and females.

Scores on the Body-Food Choice Congruence subscale were negatively correlated with body surveillance in women only. Scores were positively correlated with body appreciation. However, these scores exhibited no significant relationship with body shame in men or women or body surveillance in men.

Incremental validity
Incremental validity is demonstrated when a measure predicts variation in outcomes of interest that an already existing measure does not predict. The researchers’ regressions indicate that scores on the EPR, RHSC, and B-FCC subscales predict levels of self-esteem, positive and negative affect, and life satisfaction apart from participants’ scores indicating eating disorder symptomatology. However, participants’ scores on the UPE subscale predict variation on these constructs similar to that predicted by scores of eating disorder symptomatology.

Discriminant validity
A measure’s discriminant validity reflects the degree to which scores on a measure are predicted independently of scores on other measurements of discrete constructs. Tylka and Kroon Van Diest (2013) found little to no indication that men and women were responding according to social desirability when measuring their practice of intuitive eating.

Internal consistency
Internal consistency is the extent to which items on a measure are related to one another. Internal consistency scores indicated by Cronbach’s alpha were as follows for women and men, respectively: .87 and .89 for the total IES-2, .93 and .92 for EPR, .81 and .82 for UPE, .88 and .89 for RHSC, and .87 and .85 for B-FCC. Internal consistency scores at or above .80 are considered indications of “good” reliability.

Test-retest reliability
Test-retest reliability is indicated by the consistency of scores on repeated trials of a measure. To evaluate test-retest reliability, 219 participants completed the IES-2 initially and repeated the assessment three weeks later. Intraclass correlation coefficients were as follows for women and men, respectively: .88 and .92 for the total scale, .81 and .94 for EPR, .86 and .89 for UPE, .80 and .90 for RHSC, and .77 and .75 for B-FCC.

Correlates
In a growing body of cross-sectional research, scientists have identified numerous psychological and social correlates of intuitive eating. Several of these are outlined in Bruce & Ricciardelli’s (2016) literature review. Furthermore, numerous physical health indicators, many of which are featured in Van Dyke and Drinkwalter’s (2014) review, have been linked to intuitive eating.

Interventions
Studies examining the outcomes of intuitive eating interventions have tended to incorporate approaches in line with the principles of Tribole and Resch (2012) rather than employing intuitive eating principally as a validated psychological construct. The observed efficacy of multiple intuitive eating interventions or treatments including intuitive eating in a broader framework are highlighted in Van Dyke and Drinkwalter’s (2013) review of the literature. Among the most cited of these interventions is that of Bacon, Stern, Van Loan, and Keim (2015) summarized below.

Obesity
In 2005, Bacon, Stern, Van Loan, and Keim sought to address the problem of obesity through a “health at every size” paradigm characterized by the following:


 * Accepting and respecting the diversity of body shapes and sizes.
 * Recognizing that health and well-being are multidimensional and that they include physical, social, spiritual, occupational, emotional, and intellectual aspects.
 * Promoting eating in a manner which balances individual nutritional needs, hunger, satiety, appetite, and pleasure.
 * Promoting individually appropriate, enjoyable, life-enhancing physical activity, rather than exercise that is focused on a goal of weight loss.
 * Promoting all aspects of health and well-being for people of all sizes.

As they note, awareness and responsiveness to the body’s internal cues posited in the above figure is characteristic of intuitive eating. The researchers investigated whether implementation of these ideals would promote positive health outcomes – both mental and physiological – among 78 women, ages 30 to 45, characterized as “obese” according to BMI classifications.

Participants were randomly assigned to two treatment groups: a “diet” group and “health at every size” group. In both conditions, women were asked to attend 24 sessions, each with a 1.5 hour duration. Participants had the option of attending periodically after this predetermined number as well.

With the guidance of a registered dietitian and aided by the LEARN Program for Weight Control instructions, participants assigned to the diet group were encouraged to engage in behavior change, “monitoring,” and self-regulation all oriented towards weight loss. The health at every size group was trained according to the core tenets of the “weight-neutral” approach, including the practice of intuitive eating principles such as honoring hunger and fullness and integrating the desire for satisfaction with nutritional considerations for optimal functioning.

The researchers measured various aspects of participants’ health and wellbeing at baseline and around 3 months (mid-treatment), 6 months (post-treatment), 12 months (post aftercare), and 24 months (follow-up). Regarding physiological outcomes, researchers measured participants’ body mass index (BMI) as well as total cholesterol, low-density lipoprotein cholesterol (LDL), high-density lipoprotein cholesterol (HDL), systolic blood pressure, and diastolic blood pressure. They estimated participants’ “energy expenditure” using information acquired through the Stanford Seven Day Physical Activity Recall, which was given by a team of two interviewers per participant. The researchers administered the Eating Inventory at each time point to evaluate participants’ cognitive restraint, disinhibition, and hunger. Likewise, they used the Eating Disorder Inventory-2 (EDI-2) to measure participants’ drive for thinness, bulimia, body dissatisfaction, ineffectiveness, perfectionism, interpersonal distrust, interoceptive awareness, and maturity fears. The Beck Depression Inventory (BDI), Rosenberg Self Esteem Measure, and Body Image Avoidance Questionnaire were used to evaluate the females’ psychological wellbeing.

In communicating and interpreting their results, the researchers noted that 42% of the diet group dropped out of the study before its completion, which may have had bearing on their results collected at later time points.

A detailed depiction of all the researchers’ results can be found in their tables 2-4 (pages 933-934).

When comparing scores at baseline and follow-up (104 weeks), neither the diet group nor the health at every size group demonstrated a significant change in BMI.

With regards to cholesterol, the health at every size group demonstrated a significant decrease from baseline to follow-up. The diet group demonstrated no significant change. HDL cholesterol had significantly decreased for both groups at follow-up, while LDL had only significantly decreased in the health at every size group.

Systolic blood pressure had significantly decreased at follow up in the health at every size group. Though it decreased in the diet group for much of the study, this drop was not sustained through 104 weeks. Diastolic blood pressure did not change significantly for either group.

Considering all physiological measures, no significant between-group differences were found.

With regards to physical activity and energy expenditure, the health at every size group demonstrated a significant increase, which held at 26 and 104 weeks. This increase encompassed “moderate,” “hard,” and “very hard” activities. The diet group showed a significant increase in energy expenditure at 52 weeks, but this was not sustained at 24 months.

With regards to eating behavior, the health at every size group demonstrated a significant decrease in cognitive restraint, hunger, and disinhibition at follow-up two years after baseline measurement. The diet group showed this same lasting improvement in disinhibition, but not in hunger or cognitive restraint. There was only a significant between-group difference in cognitive restraint. Significant between-group differences were found only in drive for thinness and body dissatisfaction.

Measured by the EDI-2, the HAES group demonstrated a significant decrease in drive for thinness, bulimia, and body dissatisfaction as well as an increase in interoceptive awareness at 104 weeks. Though the diet group demonstrated sporadic improvements in bulimia and body dissatisfaction, they did not demonstrate any significant change in scores on either of these measurements, nor on interoceptive awareness or drive for thinness, at follow-up.

Regarding psychological wellbeing, the diet group originally demonstrated a decrease in BDI scores, but there was no significant change assessed at 104 weeks, while the health at every size group did demonstrate a significant decrease at this time point. Similarly, the health at every size group showed a significant increase in self-esteem two years after their baseline measurement. Conversely, the diet group demonstrated a significant decrease in self-esteem even though it had initially increased. The diet group demonstrated no sustained significant change in body image avoidance, while the health at every size group showed a significant decrease. Differences in self esteem were the only significant between-group differences.

The researchers also collected participants’ feedback. All participants in the health at every size group reported the program “made them feel better about [themselves]” and envisioned the program would have a “lifelong impact,” while only 47% and 37%, respectively, of the diet group agreed to these statements. The vast majority of the health at every size group reported they did not “feel like [they] have failed,” while 53% of the diet group did. 89% of the health at every size group reported using skills they had acquired in the program “regularly” or “often,” while 11% of the diet group agreed to the same.

The researchers interpreted their results as evidence suggesting that substantial changes in health can be prompted without significant changes in weight by adopting a health at every size approach, which heavily incorporates the principles of intuitive eating.

Limitations
Much of the research on intuitive eating and its correlates is cross-sectional, meaning variables of interest are measured within a population at the same point in time. Neither causality nor temporal precedence can be inferred from research employing this correlational design. For example, numerous studies have identified an inverse relationship between intuitive eating and BMI. However, due to the studies' correlational nature, one cannot determine whether eating intuitively leads to low BMI or whether low BMI leads to a high degree of intuitive eating. This unclear directionality is highlighted in multiple experimental investigations in which the adoption of intuitive eating did not prompt weight loss. This could suggest that the relationship between intuitive eating and BMI runs in a direction counter to that which is assumed, or perhaps yet undiscovered variables explain the observed link.

Additionally, a considerable portion of the research specific to intuitive eating, particularly early theoretical work, has been conducted by psychologist Tracy Tylka. Other scientists’ replication of her findings would support the credibility of theory and results published thus far.