The diagnostic workup typically includes complete medical and psychosocial history and follows a rational and formulaic approach to the diagnosis. Neuroimaging using fMRI, MRI, PET and SPECT scans have been used to detect cases in which a lesion, tumor or other organic condition has been either the sole causative or contributory factor in an eating disorder. "Right frontal intracerebral lesions with their close relationship to the limbic system could be causative for eating disorders, we therefore recommend performing a cranial MRI in all patients with suspected eating disorders" (Trummer M "et al." 2002), "intracranial pathology should also be considered however certain is the diagnosis of early-onset anorexia nervosa. Second, neuroimaging plays an important part in diagnosing early-onset anorexia nervosa, both from a clinical and a research prospective".(O'Brien "et al." 2001).

After ruling out organic causes and the initial diagnosis of an eating disorder being made by a medical professional, a trained mental health professional aids in the assessment and treatment of the underlying psychological components of the eating disorder and any comorbid psychological conditions. The clinician conducts a clinical interview and may employ various psychometric tests. Some are general in nature while others were devised specifically for use in the assessment of eating disorders. Some of the general tests that may be used are the Hamilton Depression Rating Scale and the Beck Depression Inventory. longitudinal research showed that there is an increase in chance that a young adult female would develop bulimia due to their current psychological pressure and as the person ages and matures, their emotional problems change or are resolved and then the symptoms decline.

Medical tests to check for signs of physical deterioration in anorexia nervosa may be performed by a general physician or psychiatrist, including:

- Complete Blood Count (CBC): a test of the white blood cells, red blood cells and platelets used to assess the presence of various disorders such as leukocytosis, leukopenia, thrombocytosis and anemia which may result from malnutrition.

- Urinalysis: a variety of tests performed on the urine used in the diagnosis of medical disorders, to test for substance abuse, and as an indicator of overall health

- Chem-20: Chem-20 also known as SMA-20 a group of twenty separate chemical tests performed on blood serum. Tests include cholesterol, protein and electrolytes such as potassium, chlorine and sodium and tests specific to liver and kidney function.

- Glucose tolerance test: Oral glucose tolerance test (OGTT) used to assess the body's ability to metabolize glucose. Can be useful in detecting various disorders such as diabetes, an insulinoma, Cushing's Syndrome, hypoglycemia and polycystic ovary syndrome.

- Serum cholinesterase test: a test of liver enzymes (acetylcholinesterase and pseudocholinesterase) useful as a test of liver function and to assess the effects of malnutrition.

- Liver Function Test: A series of tests used to assess liver function some of the tests are also used in the assessment of malnutrition, protein deficiency, kidney function, bleeding disorders, and Crohn's Disease.

- Lh response to GnRH: Luteinizing hormone (Lh) response to gonadotropin-releasing hormone (GnRH): Tests the pituitary glands' response to GnRh a hormone produced in the hypothalamus. Hypogonadism is often seen in anorexia nervosa cases.

- Creatine Kinase Test (CK-Test): measures the circulating blood levels of creatine kinase an enzyme found in the heart (CK-MB), brain (CK-BB) and skeletal muscle (CK-MM).

- Blood urea nitrogen (BUN) test: urea nitrogen is the byproduct of protein metabolism first formed in the liver then removed from the body by the kidneys. The BUN test is primarily used to test kidney function. A low BUN level may indicate the effects of malnutrition.

- BUN-to-creatinine ratio: A BUN to creatinine ratio is used to predict various conditions. A high BUN/creatinine ratio can occur in severe hydration, acute kidney failure, congestive heart failure, and intestinal bleeding. A low BUN/creatinine ratio can indicate a low protein diet, celiac disease, rhabdomyolysis, or cirrhosis of the liver.

- Electrocardiogram (EKG or ECG): measures electrical activity of the heart. It can be used to detect various disorders such as hyperkalemia

- Electroencephalogram (EEG): measures the electrical activity of the brain. It can be used to detect abnormalities such as those associated with pituitary tumors.

- Thyroid Screen TSH, t4, t3 :test used to assess thyroid functioning by checking levels of thyroid-stimulating hormone (TSH), thyroxine (T4), and triiodothyronine (T3)

A variety of medical and psychological conditions have been misdiagnosed as anorexia nervosa; in some cases the correct diagnosis was not made for more than ten years.

The distinction between the diagnoses of anorexia nervosa, bulimia nervosa and eating disorder not otherwise specified (EDNOS) is often difficult to make as there is considerable overlap between people diagnosed with these conditions. Seemingly minor changes in a people's overall behavior or attitude can change a diagnosis from anorexia: binge-eating type to bulimia nervosa. A main factor differentiating binge-purge anorexia from bulimia is the gap in physical weight. Someone with bulimia nervosa is ordinarily at a healthy weight, or slightly overweight. Someone with binge-purge anorexia is commonly underweight. People with the binge-purging subtype of AN may be significantly underweight and typically do not binge-eat large amounts of food, yet they purge the small amount of food they eat. In contrast, those with bulimia nervosa tend to be at normal weight or overweight and binge large amounts of food. It is not unusual for a person with an eating disorder to "move through" various diagnoses as their behavior and beliefs change over time.

Previously considered a topic for further research exploration, binge eating disorder was included in the "Diagnostic and Statistical Manual of Mental Disorders" in 2013. Until 2013, binge eating disorder was categorized as an Eating Disorder Not Otherwise Specified, an umbrella category for eating disorders that don't fall under the categories for anorexia nervosa or bulimia nervosa. Because it was not a recognized psychiatric disorder in the "DSM-IV" until 2013, it has been difficult to obtain insurance reimbursement for treatments. The disorder now has its own category under "DSM-5", which outlines the signs and symptoms that must be present to classify a person's behavior as binge eating disorder. Studies have confirmed the high predictive value of these criteria for diagnosing BED.

According to DSM-5, the following criteria must be present to make a diagnosis of binge eating disorder. Studies have confirmed the high predictive value of these criteria for diagnosing BED.

A. Recurrent episodes of binge eating. An episode of binge eating is characterized by both of the following:

1. Eating, in a discrete period of time (e.g., within any 2-hour period), an amount of food that is definitely larger than what most people would eat in a similar period of time under similar circumstances.

2. A sense of lack of control over eating during the episode (e.g., a feeling that one cannot stop eating or control what or how much one is eating).

B. The binge-eating episodes are associated with three (or more) of the following:

1. Eating much more rapidly than normal.

2. Eating until feeling uncomfortably full.

3. Eating large amounts of food when not feeling physically hungry.

4. Eating alone because of feeling embarrassed by how much one is eating.

5. Feeling disgusted with oneself, depressed, or very guilty afterward.

C. Marked distress regarding binge eating is present.

D. The binge eating occurs, on average, at least once a week for 3 months.

E. The binge eating is not associated with the recurrent use of inappropriate compensatory behavior as in bulimia nervosa and does not occur exclusively during the course of bulimia nervosa or anorexia nervosa.

Individuals suffering from BED often have a lower overall quality of life and commonly experience social difficulties.

Early behavior change is an accurate prediction of remission of symptoms later.

Individuals who have BED commonly have other comorbidities such as major depressive disorder, personality disorder, bipolar disorder, substance abuse, body dysmorphic disorder, kleptomania, irritable bowel syndrome, fibromyalgia, or an anxiety disorder. There may also be panic attacks and a history of attempted suicide.

While people of a healthy weight may overeat occasionally, an ongoing habit of consuming large amounts of food in a short period of time may ultimately lead to weight gain and obesity. Binging episodes usually include foods that are high in fat, sugar, and/or salt, but low in vitamins and minerals, as these types of foods tend to trigger greatest emotional reward. The main physical health consequences of this type of eating disorder are brought on by the weight gain resulting from the binging episodes. Up to 70% of individuals with BED may also be obese, and therefore obesity-associated morbidities such as high blood pressure and coronary artery disease type 2 diabetes mellitus gastrointestinal issues (e.g., gallbladder disease), high cholesterol levels, musculoskeletal problems and obstructive sleep apnea may also be present.

There are two main types of treatment given to those suffering with bulimia nervosa; psychopharmacological and psychosocial treatments.

Some researchers have also claimed positive outcomes in hypnotherapy.

Few studies to date have examined OSFED prevalence. The largest community study is by Stice (2013), who examined 496 adolescent females who completed annual diagnostic interviews over 8 years. Lifetime prevalence by age 20 for OSFED overall was 11.5%. 2.8% had atypical AN, 4.4% had subthreshold BN, 3.6% had subthreshold BED, and 3.4% had purging disorder. Peak age of onset for OSFED was 18–20 years. NES was not assessed in this study, but estimates from other studies suggest that it presents in 1% of the general population.

A few studies have compared the prevalence of EDNOS and OSFED and found that though the prevalence of atypical eating disorders decreased with the new classification system, the prevalence still remains high. For example, in a population of 215 young patients presenting for ED treatment, the diagnosis of EDNOS to OSFED decreased from 62.3% to 32.6%. In another study of 240 females in the U.S. with a lifetime history of an eating disorder, the prevalence changed from 67.9% EDNOS to 53.3% OSFED. Although the prevalence appears to reduce when using the categorizations of EDNOS vs. OSFED, a high proportion of cases still receive diagnoses of atypical eating disorders, which creates difficulties in communication, treatment planning, and basic research.

Few studies guide the treatment of individuals with OSFED. However, cognitive behavioral therapy (CBT), which focuses on the interplay between thoughts, feelings, and behaviors, has been shown to be the leading evidence-based treatment for the eating disorders of BN and BED. For OSFED, a particular cognitive behavioral treatment can be used called CBT-Enhanced (CBT-E), which was designed to treat all forms of eating disorders. This method focuses not only what is thought to be the central cognitive disturbance in eating disorders (i.e., over-evaluation of eating, shape, and weight), but also on modifying the mechanisms that sustain eating disorder psychopathology, such as perfectionism, core low self-esteem, mood intolerance, and interpersonal difficulties. CBT-E showed effectiveness in two studies (total N = 219) and well maintained over 60-week follow-up periods. CBT-E is not specific to individual types of eating disorders but is based on the concept that common mechanisms are involved in the persistence of atypical eating disorders, AN, and BN.

Rather than providing specific diagnostic criteria for EDNOS, the fourth revision of the "Diagnostic and Statistical Manual of Mental Disorders" ("DSM-IV") listed six non-exhaustive example presentations, including individuals who:

1. Meet all criteria for anorexia nervosa except their weight falls within the normal range

2. Meet all criteria for bulimia nervosa except they engage in binge eating or purging behaviors less than twice per week or for fewer than three months

3. Purge after eating small amounts of food while retaining a normal body weight

4. Repeatedly chew and spit out large amounts of food without swallowing

5. Do not meet criteria for binge eating disorder

Despite its subclinical status in "DSM-IV", available data suggest that EDNOS is no less severe than the officially recognized "DSM-IV" eating disorders. In a comprehensive meta-analysis of 125 studies, individuals with EDNOS exhibited similar levels of eating pathology and general psychopathology to those with anorexia nervosa and binge eating disorder, and similar levels of physical health problems as those with anorexia nervosa. Although individuals with bulimia nervosa scored significantly higher than those with EDNOS on measures of eating pathology and general psychopathology, those with EDNOS exhibited more physical health problems than those with bulimia nervosa.

Although EDNOS (formerly called atypical eating disorder) was originally introduced in "DSM-III" to capture unusual cases, it accounts for up to 60% of cases in eating disorder specialty clinics. EDNOS is an especially prevalent category in populations that have received inadequate research attention such as young children, males, ethnic minorities, and non-Western groups.

Food addiction impacts relationships, especially those within the family. This is because the person with the addiction is vastly more involved with food than with people – it becomes their safest, most important and meaningful relationship. Other connections to friends and family take a back seat. This often leads to a deep sense of isolation from others.

Drunkorexia is not a medically diagnosed disorder therefore there is no specific treatment. However, as drunkorexia is a combination of two different disorders, binge drinking and eating disorders such as anorexia and bulimia the treatment will need to address both.

Purging disorder is an eating disorder characterized by recurrent purging (self-induced vomiting, misuse of laxatives, diuretics, or enemas) to control weight or shape in the absence of binge eating episodes.

Purging disorder differs from bulimia nervosa (BN) because individuals with purging disorder do not consume a large amount of food before they purge. In current diagnostic systems, purging disorder is a form of Other specified feeding or eating disorder (OSFED). Research indicates that purging disorder may be as common as bulimia nervosa or anorexia nervosa in women, that the syndrome is associated with clinically significant levels of distress, and that it appears to be distinct from bulimia nervosa on measures of hunger and ability to control food intake. Some of the signs of purging disorder are frequent trips to the bathroom directly after a meal, frequent use of laxatives, and obsession over one's appearance and weight. Other signs include swollen cheeks, popped blood vessels in the eyes, and clear teeth which are all signs of excessive vomiting.

Compulsive overeating is treatable with nutritional assistance and medication. Psychotherapy may also be required, but recent research has proven this to be useful only as a complementary resource, with short-term effectiveness in middle to severe cases.

Lisdexamfetamine is an FDA-approved appetite suppressant drug that is indicated for the treatment of binge eating disorder. The antidepressant fluoxetine is a medication that is approved by the Food and Drug Administration (FDA) for the treatment of an eating disorder, specifically bulimia nervosa. This medication has been prescribed off-label for the treatment of binge eating disorder (BED). Off-label medications, such as other selective serotonin reuptake inhibitors (SSRIs), have shown some efficacy, as have several atypical agents, such as mianserin, trazodone and bupropion. Anti-obesity medications have also proven very effective. Studies suggest that anti-obesity drugs, or moderate appetite suppressants, may be key to controlling binge eating.

Many eating disorders are thought to be behavioral patterns that stem from emotional struggles; for the individual to develop lasting improvement and a healthy relationship with food, these affective obstacles need to be resolved. Individuals can overcome compulsive overeating through treatment, which should include talk therapy and medical and nutritional counseling. Such counseling has been recently sanctioned by the American Dental Association in their journal article cover-story for the first time in history in 2012: Given "the continued increase in obesity in the United States and the willingness of dentists to assist in prevention and interventional effort, experts in obesity intervention in conjunction with dental educators should develop models of intervention within the scope of dental practice". Moreover, dental appliances such as conventional jaw wiring and orthodontic wiring for controlling compulsive overeating have been shown to be “efficient ways in terms of weight control in properly selected obese patients and usually no serious complications could be encountered through the treatment course.

As well, several twelve-step programs exist to help members recover from compulsive overeating and food addiction, such as Overeaters Anonymous and others.

Drunkorexia consists of 3 major aspects: alcohol use/abuse, food intake restriction, and excessive physical activity. It is commonly summarised in the following activities:

- Counting daily calorie intake (commonly known as "calorie counting") to ensure no weight will be gained when consuming alcohol.

- Missing or skipping meals to conserve calories for consumption of alcoholic beverages.

- Over exercising to counterweigh for calories consumed from alcoholic beverages.

- Consuming an extreme amount of alcohol to vomit previously digested food.

Disordered eating describes a variety of abnormal eating behaviors that, by themselves, do not warrant diagnosis of an eating disorder.

Disordered eating includes behaviors that are common features of eating disorders, such as:

- Chronic restrained eating.

- Compulsive eating.

- Binge eating, with associated loss of control.

- Self-induced vomiting.

Disordered eating also includes behaviors that are not characteristic of any eating disorder, such as:

- Irregular, chaotic eating patterns.

- Ignoring physical feelings of hunger and satiety (fullness).

- Use of diet pills.

- Emotional eating.

- Night eating.

- "Secretive food concocting": the consumption of embarrassing food combinations, such as mashed potatoes mixed with sandwich cookies. See also Food craving § Pregnancy and Nocturnal sleep-related eating disorder § Symptoms and behaviors.

Disordered eating can represent a change in eating patterns caused by other mental disorders (e.g. clinical depression), or by factors that are generally considered to be unrelated to mental disorders (e.g. extreme homesickness).

Certain factors among adolescents tend to be associated with disordered eating, including perceived pressure from parents and peers, nuclear family dynamic, body mass index, negative affect (mood), self-esteem, perfectionism, drug use, and participation in sports that focus on leanness. These factors are similar among boys and girls alike. However, the reported incidence rates of are consistently and significantly higher in female than male participants, with 61% of females and 28% of males reporting disordered eating behaviors in a study of over 1600 adolescents.

Rumination syndrome is diagnosed based on a complete history of the individual. Costly and invasive studies such as gastroduodenal manometry and esophageal Ph testing are unnecessary and will often aid in misdiagnosis. Based on typical observed features, several criteria have been suggested for diagnosing rumination syndrome. The primary symptom, the regurgitation of recently ingested food, must be consistent, occurring for at least six weeks of the past twelve months. The regurgitation must begin within 30 minutes of the completion of a meal. Patients may either chew the regurgitated matter or expel it. The symptoms must stop within 90 minutes, or when the regurgitated matter becomes acidic. The symptoms must not be the result of a mechanical obstruction, and should not respond to the standard treatment for gastroesophageal reflux disease.

In adults, the diagnosis is supported by the absence of classical or structural diseases of the gastrointestinal system. Supportive criteria include a regurgitant that does not taste sour or acidic, is generally odourless, is effortless, or at most preceded by a belching sensation, that there is no retching preceding the regurgitation, and that the act is not associated with nausea or heartburn.

Patients visit an average of five physicians over 2.75 years before being correctly diagnosed with rumination syndrome.

There is presently no known cure for rumination. Proton pump inhibitors and other medications have been used to little or no effect.

Treatment is different for infants and the mentally handicapped than for adults and adolescents of normal intelligence. For adults and adolescents,Biofeedback and relaxation techniques, to be practice after eating or whenever regurgitation occurs, has proven to be most effective.

Among infants and the mentally handicapped, behavioral and mild aversive training has been shown to cause improvement in most cases. Aversive training involves associating the ruminating behavior with negative results, and rewarding good behavior and eating. Placing a sour or bitter taste on the tongue when the individual begins the movements or breathing patterns typical of his or her ruminating behavior is the generally accepted method for aversive training,

although some older studies advocate the use of pinching.

In patients of normal intelligence, rumination is not an intentional behavior and is habitually reversed using diaphragmatic breathing to counter the urge to regurgitate. Alongside reassurance, explanation and habit reversal, patients are shown how to breathe using their diaphragms prior to and during the normal rumination period. A similar breathing pattern can be used to prevent normal vomiting. Breathing in this method works by physically preventing the abdominal contractions required to expel stomach contents.

Supportive therapy and diaphragmatic breathing has shown to cause improvement in 56% of cases, and total cessation of symptoms in an additional 30% in one study of 54 adolescent patients who were followed up 10 months after initial treatments. Patients who successfully use the technique often notice an immediate change in health for the better. Individuals who have had bulimia or who intentionally induced vomiting in the past have a reduced chance for improvement due to the reinforced behavior. The technique is not used with infants or young children due to the complex timing and concentration required for it to be successful. Most infants grow out of the disorder within a year or with aversive training.

Accurately assessing for a specific Depressive Disorder diagnosis requires an expenditure of time that is deemed unreasonable for most primary care physicians. For this reason, physicians often use this code as a proxy for a more thorough diagnosis. There is concern that this may lead to a "wastebasket" mindset for certain disorders. In addition reimbursement through Medicare may be lower for certain non specific diagnosis.

The DSM-IV-TR diagnostic criteria for panic disorder require unexpected, recurrent panic attacks, followed in at least one instance by at least a month of a significant and related behavior change, a persistent concern of more attacks, or a worry about the attack's consequences. There are two types, one with and one without agoraphobia. Diagnosis is excluded by attacks due to a drug or medical condition, or by panic attacks that are better accounted for by other mental disorders.

The diagnostic criteria:

The essential feature is recurrent attacks of severe anxiety (panic), which are not restricted to any particular situation or set of circumstances and are therefore unpredictable.

The dominant symptoms include:

- sudden onset of palpitations

- chest pain

- choking sensations

- dizziness

- feelings of unreality (depersonalization or derealization)

- secondary fear of dying, losing control, or going mad

Panic disorder should not be given as the main diagnosis if the person has a depressive disorder at the time the attacks start; in these circumstances, the panic attacks are probably secondary to depression.

The Panic Disorder Severity Scale (PDSS) is a questionnaire for measuring the severity of panic disorder.

Panic disorder typically begins during early adulthood; roughly half of all people who have panic disorder develop the condition before age 24, especially those subjected to traumatic experiences. However, some sources say that the majority of young people affected for the first time are between the ages of 25 and 30. Women are twice as likely as men to develop panic disorder and it occurs more often in people with above average intelligence.

Panic disorder can continue for months or years, depending on how and when treatment is sought. If left untreated, it may worsen to the point where one's life is seriously affected by panic attacks and by attempts to avoid or conceal the condition. In fact, many people have had problems with personal relationships or employment while struggling to cope with panic disorder. Some people with panic disorder may conceal their condition because of the stigma of mental illness. In some individuals, symptoms may occur frequently for a period of months or years, then many years may pass without symptoms. In some cases, the symptoms persist at the same level indefinitely. There is also some evidence that many individuals (especially those who develop symptoms at an early age) may experience symptom cessation later in life (e.g. past age 50).

In 2000, the World Health Organization found prevalence and incidence rates for panic disorder to be very similar across the globe. Age-standardized prevalence per 100,000 ranged from 309 in Africa to 330 in East Asia for men and from 613 in Africa to 649 in North America, Oceania, and Europe for women.

Conduct disorder is classified in the fourth edition of "Diagnostic and Statistical Manual of Mental Disorders" (DSM). It is diagnosed based on a prolonged pattern of antisocial behaviour such as serious violation of laws and social norms and rules in people younger than the age of 18. Similar criteria are used in those over the age of 18 for the diagnosis of antisocial personality disorder. No proposed revisions for the main criteria of conduct disorder exist in the "DSM-5"; there is a recommendation by the work group to add an additional specifier for callous and unemotional traits. According to DSM-5 criteria for conduct disorder, there are four categories that could be present in the child's behavior: aggression to people and animals, destruction of property, deceitfulness or theft, and serious violation of rules.

Almost all adolescents who have a substance use disorder have conduct disorder-like traits, but after successful treatment of the substance use disorder, about half of these adolescents no longer display conduct disorder-like symptoms. Therefore, it is important to exclude a substance-induced cause and instead address the substance use disorder prior to making a psychiatric diagnosis of conduct disorder.