Diagnostic reasoning in rehabilitation nutrition: Position paper by the Japanese Association of Rehabilitation Nutrition (secondary publication)

Abstract Diagnostic reasoning is the thought process used to arrive at a diagnosis based on symptoms, examination findings, and laboratory values. Diagnosis is categorized as nonanalytic reasoning (intuition) and analytic reasoning (analysis). Rehabilitation nutrition involves the diagnosis of nutritional disorders, sarcopenia, and excess or deficient nutrient intake. There is usually only one correct answer for the presence or absence of these. On the other hand, there may be no single correct answer for the causes of anorexia, weight loss, or sarcopenia, and analytical reasoning is required. In this case, diagnostic reasoning involves hypotheses. Simply using nutritional supplements without performing diagnostic reasoning about these causes is like prescribing antipyretic analgesics to a patient with a headache without diagnosing the cause of the headache. To maximize function and quality of life in rehabilitation nutrition, it is necessary to suspect the common causes of anorexia, weight loss, and sarcopenia in all cases.


| INTRODUC TION: WHAT IS DIAG NOS TIC RE A SONING?
The rehabilitation nutrition care process includes a rehabilitation nutrition assessment and diagnostic reasoning. 1 The rehabilitation nutrition assessment and diagnostic reasoning involves a holistic assessment using the International Classification of Functioning, Disability and Health, medical history, evaluation of nutritional status and activity level, and assessment of sarcopenia/frailty to inform diagnostic reasoning about nutritional status, sarcopenia, excess or deficiency in nutrient intake, and their causes. Insufficient diagnostic reasoning naturally leads to inadequate rehabilitation nutrition care processes after the diagnosis, making it difficult to provide interventions that maximize function and quality of life. Therefore, it is necessary to master diagnostic reasoning to practice rehabilitation nutrition effectively.
Diagnostic reasoning is the thought process used to arrive at a diagnosis based on symptoms, examination findings, and laboratory values. The thought process is classified into nonanalytic reasoning (intuition, system 1) and analytic reasoning (analytic, system 2).
Nonanalytic reasoning is a diagnostic method in which the characteristic patterns of disease are understood and recognized subconsciously and intuitively in a short period of time. On the other hand, analytic reasoning is a diagnostic method in which a list of etiologies is created in the process of hypothesis formation, and prioritization is determined by frequency and severity. For example, a patient with a BMI of 14 would be intuitively diagnosed with undernutrition using primarily nonanalytic reasoning. In contrast, a patient with a BMI of 20 would not be intuitively diagnosed with undernutrition but would go through a series of hypotheses and their testing to arrive at a diagnosis. Both nonanalytic and analytic reasoning should be used in a well-balanced manner in both cases.
The causes of anorexia, weight loss, and sarcopenia are particularly important for diagnostic reasoning in rehabilitation nutrition.
Although these causes can sometimes be adequately diagnosed by nonanalytic reasoning alone, they often require analytic reasoning.
Adopting a small, high-energy, high-protein diet or using oral nutritional supplements without applying diagnostic reasoning about the causes is like prescribing only antipyretic analgesics to a patient suffering from chronic headache without diagnosing the cause of the headache. It may work, but it does not solve the underlying problem.
Diagnosing whether a patient has undernutrition, sarcopenia, or frailty is not difficult because the criteria can be simply applied.
However, analytic reasoning to examine multiple possible differential diagnoses and make a reasoned choice is required. In addition, multiple iatrogenic and noniatrogenic causes may be recognized. Therefore, mastering rehabilitation nutrition diagnostic reasoning requires daily case review and experience. In this position paper, we clarified our position, as the Japanese Association of Rehabilitation Nutrition, on the existing knowledge on undernutrition, overnutrition, causes of weight loss, sarcopenia, nutrient under-intake, causes of anorexia, and nutrient over-intake, together with diagnostic reasoning processes in cases, individual differences in diagnostic reasoning, and the process of learning diagnostic reasoning.

| D IAG NOS TI C RE A SONING FOR UNDERNUTRITION
By nonanalytic reasoning, we can diagnose undernutrition when we see a person who is extremely thin. However, there are some individuals who are not diagnosed with undernutrition by the Global Leadership Initiative on Malnutrition (GLIM) criteria 2 because they are thin, but healthy and have no etiologies such as decreased food intake, malabsorption, or inflammation. In addition, it is difficult to intuitively diagnose undernutrition in obese patients with a BMI of 25 or more who have complications of undernutrition.
In analytic reasoning, the following steps using the GLIM criteria are applied.
Step (1) A validated nutrition screening tool determines that the patient is at risk for undernutrition.
Step (2) A diagnosis of undernutrition is made when one or more of the following applies to the phenotypic criteria and etiologic criteria, respectively.

| Phenotypic criteria
a. Unintentional weight loss: This applies to weight loss of 5% or more within the past 6 months and 10% or more beyond 6 months.
b. Low body mass index (BMI): BMI is less than 18.5 for Asian patients under 70 years of age, and BMI is less than 20 for those over 70 years of age. For non-Asians, BMI is less than 20 for those under 70 years of age and BMI less than 22 for those over 70 years old.
c. Low muscle mass: The Asian Working Group for Sarcopenia (AWGS) 2019 criteria 3 are used for Asians. In the case of calf circumference, low muscle mass is defined as less than 34 cm in men and less than 33 cm in women.

| Etiologic criteria
a. Reduced food intake or assimilation: A decrease in food intake of 50% or less for more than 1 week, any decrease in food intake for more than 2 weeks, or any chronic gastrointestinal malabsorption.
b. Inflammation related to acute disease, trauma, or chronic disease.
Step (3) The severity of low nutrition (whether it is moderate or severe) is determined.
The causes of undernutrition are classified as follows: chronic disease with inflammation, acute disease or trauma with severe inflammation, chronic disease with little or no inflammation, and starvation without inflammation (due to a food shortage caused by socioeconomic or environmental factors). When multiple causes are identified, the most influential cause is considered. In the case of starvation, the clinician should move on to search for the cause of nutrient under-intake.

| D IAG NOS TI C RE A SONING FOR OVERN UTRITI ON
Overnutrition in the rehabilitation nutrition diagnosis is a condition in which the patient is at risk of developing health problems or declining activities of daily living (ADLs) due to excessive fat accumulation. By nonanalytic reasoning, we can diagnose overnutrition if we see a person who is extremely obese. However, overnutrition is not diagnosed in athletes with high skeletal muscle mass and low body fat mass, even if they have a BMI of 25 or higher. In addition, it is difficult to diagnose overnutrition by intuition if the patient has a standard body type with a BMI in the normal range.
Using analytic reasoning, the clinician should evaluate body fat mass to identify excessive fat accumulation. If the visceral fat area is greater than 100 cm 2 on an abdominal computed tomography (CT) image at the umbilical region, a diagnosis of overnutrition can be made. Bioelectrical impedance analysis (BIA) or dual-energy x-ray absorptiometry (DXA) can be employed to diagnose overnutrition when an individual's body fat percentage is greater than 25% in men and 32% in women, depending on age. Physical measurements may also be used: overnutrition can be diagnosed when the abdominal circumference is 85 cm or more for men and 90 cm or more for women.
Causes of overnutrition are categorized as excessive energy intake, insufficient energy expenditure, decreased basal metabolic rate due to aging or other causes, and diseases (endocrine disorders such as Cushing syndrome and hypothyroidism, and hereditary diseases such as Prader-Willi syndrome). When multiple causes are present, the most influential cause should be considered.

| D IAG NOS TI C RE A SONING FOR C AUS E S OF WEI G HT LOSS
Weight loss is often diagnosed when an individual loses more than 5% of their body mass in 6-12 months, or more than 2 kg in 6 months.
Nonanalytic reasoning is more likely to diagnose decreased food intake due to anorexia as the cause. In patients with advanced cancer, it is easy to intuitively diagnose cancer cachexia. However, weight loss may occur without anorexia or decreased food intake. Multiple causes may be present.  Table 3. Common causes should be suspected in all cases. Multiple causes and drugs may be recognized for weight loss.

| D IAG NOS TI C RE A SONING FOR SARCOPENIA
By nonanalytic reasoning, sarcopenia can be diagnosed if the patient is thin, requires assistance with ADLs, and has low skeletal muscle mass and low physical function. However, the cause of low skeletal muscle mass and low physical function may be an undiagnosed neuromuscular disorder rather than sarcopenia.
Analytic reasoning uses the AWGS 2019 criteria. 3 The diagnostic process in primary health care or community settings includes case finding, evaluation, and intervention, in that order. Case finding includes three items: the calf circumference measurement, the strength, assistance walking, rise from a chair, climbing stairs, and falls (SARC-F) questionnaire, and the SARC-F combined with calf circumference (SARC-CalF). For the evaluation of sarcopenia, the individual's handgrip strength is measured as a muscle strength assessment, and a five-chair stand test is performed as a physical function assessment. If the handgrip strength is less than 28 kg in men and less than 18 kg in women, the patient is considered to have low muscle strength, and if the five-chair stand test is longer than 12 s, the patient is considered to have a low physical function. Low muscle strength or low physical function is diagnosed as possible sarcopenia. The causes of sarcopenia are categorized as aging, activity, nutrition, disease, and iatrogenic. All causes are common in rehabilitation nutrition, and while multiple causes are often present, the cause with the greatest impact is considered. In the case of activity, clinicians should assess the duration and extent of low activity. In the case of nutrition, they should move to the diagnostic reasoning of nutrient under-intake. In the case of disease, clinicians should assess the presence and extent of acute or chronic inflammation. In the case of an iatrogenic cause, they should assess the possibility of low activity due to inappropriate bed rest or food abstinence, undernutrition due to inappropriate nutritional care management, and illness or adverse drug events 1 .

TA B L E 1 The OPQRST mnemonic of weight loss
Onset: "When did weight loss begin?" Palliative & Provoke: "Has weight loss continued/improved?" Quality & Quantity: "How much weight loss?" Region: "Where did you lose weight?" Symptoms: "What other symptoms do you have? Is there anorexia, nausea/vomiting, dysphagia, constipation, diarrhea, taste disorder, olfactory disorder, general fatigue, dyspnea, pain, fever, depression, anxiety, muscle weakness, or decreased ADLs?" Time course: "How is the progress after weight loss?" Abbreviation: ADL, activities of daily living.

| D IAG NOS TI C RE A SONING FOR N UTRIENT UNDER-INTAK E
In rehabilitation nutrition, a deficit of carbohydrates and fats is not diagnosed as nutrient under-intake when the energy intake has been intentionally reduced by aggressive nutrition therapy aimed at weight loss. However, protein and micronutrient under-intake should be noted. Nonanalytic reasoning would diagnose nutrient under-intake in inpatients and facility residents who consistently leave more than half of their provided diet. On the other hand, nutrient under-intake may be due to insufficient energy in the meal provided or too much physical activity, even if the patient consumes the entire meal provided.
In analytical reasoning, nutrient intake is calculated as the sum of diet plus enteral nutrition plus parenteral nutrition. Energy consumption is calculated using the Dietary Reference Intakes for Japanese, medical guidelines, and with the following formula: basic energy consumption multiplied by the activity coefficient multiplied by the stress coefficient. Next, intake minus consumption is used to diagnose the presence and degree of nutrient under-intake. At that time, the presence or absence of an accumulated amount (deficient amount) due to aggressive nutritional therapy is checked.
The causes of nutrient under-intake can be categorized as inadequate energy intake, impaired absorption due to disease or drugs, or increased energy consumption. Multiple causes may be present.
In the case of energy under-intake, clinicians should consider the presence or absence of anorexia and its cause if food intake is inadequate. If enteral nutrition or parenteral nutrition is deficient, they should consider whether it is intentional or unintentional. If absorption is impaired due to disease or drugs, clinicians should consider the exact causative disease and drug. In the case of increased energy expenditure, they should consider whether it is due to too much physical activity, involuntary movements, increased muscle tone, acute or chronic inflammation, etc.

| D IAG NOS TI C RE A SONING FOR ANORE XIA
For the assessment of anorexia, the Simplified Nutritional Appetite Questionnaire (SNAQ) 6,7 can be used. Nonanalytic reasoning often leads clinicians to believe that an older person's inability to eat adequately is inevitable due to aging. Although aging is one cause of anorexia 8 , rehabilitation nutrition often recognizes causes of anorexia other than aging, some of which can be improved.
Analytic reasoning confirms the OPQRST mnemonic of anorexia ( Table 4). The causes of anorexia in rehabilitation nutrition are listed in Table 5.

| D IAG NOS TI C RE A SONING FOR N UTRIENT OVER-INTAK E
In rehabilitation nutrition, nutrient over-intake is not diagnosed when energy intake is intentionally increased by aggressive nutrition therapy aimed at weight gain. Based on nonanalytic reasoning, clinicians suspect nutrient over-intake when inpatients and facility residents consume a large amount of food brought in, in addition to consuming a full provided meal. On the other hand, even if the patients do not consume the entire meal provided, they may have nutrient over-intake due to excessive energy in the meal provided or too little physical activity. Analytic reasoning of nutrient over-intake is similar to that for nutrient under-intake.

| REHAB ILITATION NUTRITION D IAG NOS TI C RE A SONING IN PR AC TI CE
As an example of applying diagnostic reasoning, we describe the case of an 83-year-old woman with a fracture of the proximal femur. Discontinue if on a lowsodium diet.

How should clinicians intervene for the third cause of anorexia and weight loss?
Please suggest nutrition goals after 1 month.

Please recommend rehabilitation intervention methods.
Use antidepressants (e.g., mirtazapine). Prescribe occupational therapy and add psychological occupational therapy. Increase or decrease activity levels to match nutritional intake. Individualized review of necessary activities in the home for rehabilitation intervention. Conduct a multidisciplinary case conference including a dietitian every 2 weeks. Share information on nutrition goals and rehabilitation goals.

Independent in walking and
ADLs.
Consider snacking and oral nutritional supplements.
Adjust the amount of gait training according to nutritional status.
Withdrawal or change of tramadol dose. Providing meals that meet the preferences, oral environment, and assisting swallowing function.

TA B L E 6 (Continued)
How should clinicians intervene for the third cause of anorexia and weight loss?
Please suggest nutrition goals after 1 month.

Please suggest rehabilitation goals after 1 month.
Please recommend nutrition intervention methods.

Please recommend rehabilitation intervention methods.
Search for causes of dementia and depression and treat if possible. Nutritional administration should be set up with an activity coefficient of 1.3, a stress coefficient of 1.0, and an energy accumulation of 500 kcal. The target energy intake should be 1720 kcal and 65 g protein (protein energy ratio 15%). Three meals should be provided and supplemented with additional oral nutritional supplements after rehabilitation and exercise.
Defecation is performed by guiding the patient to the toilet. Since improvement in nutritional status cannot be expected while the nutritional intake is low, resistance training should be avoided, and basic ADL training and walking training should be implemented. Once nutritional intake is sufficient, nutritional status is expected to improve, so the amount of gait training in rehabilitation should be increased, stair climbing training should be added, and resistance training (chair stand training) should be performed in the hospital ward.
Snacking with oral nutritional supplements, nutrient loading with a high-energy diet such as power rice (added medium chain triglyceride oil and protein powder) or tube feeding.
Continuation of nutritional administration of at least 2000 kcal and 60 g of protein per day with a target body weight of 45 kg.

Extended standing retention time, target Barthel Index 70-80 points
The patient should be placed on a nasogastric tube, and enteral nutrition should be administered combined with oral intake. The patient should be transitioned to a highenergy diet as she gains strength.
First, reduce supine time by using wheelchair rides and other activities during the day, and second, implement high-load rehabilitation when the patient has increased endurance through extended rehabilitation time.

| INDIVIDUAL DIFFEREN CE S IN REHAB ILITATI ON N UTRITI ON D IAG NOS TIC RE A SONING
The cause of anorexia and weight loss in this case is most likely to be drug-related. In addition, oral, denture, and swallowing problems, inappropriate eating patterns, food preferences, and depression may be complicating factors. Since these are common causes of anorexia  for these, the significance of the discussion among multidisciplinary staff members is minimal. The ability to make diagnostic reasoning can be gradually improved through case studies in which the causes of anorexia, weight loss, and sarcopenia are discussed by multidisciplinary staff members. It is important to pursue these causes further by discussion, and appropriate diagnostic reasoning will lead to higher quality rehabilitation nutrition goal setting and rehabilitation nutrition intervention.

| CON CLUS ION
Some rehabilitation nutrition questions have a single correct answer, while others may have multiple correct answers. There is usually a single correct answer for the diagnostic reasoning regarding the presence or absence of undernutrition, overnutrition, sarcopenia, and excess or deficiency in nutrient intake. However, when diagnostic criteria are updated, the updated diagnostic criteria should be used. On the other hand, there may not be a single correct answer for the causes of anorexia, weight loss, or sarcopenia. In this case, diagnostic reasoning includes creating hypotheses and rehabilitation nutrition goal setting. 9 However, to maximize function and quality of life, the most likely hypothesis should be considered from the outset. Therefore, the clinician must suspect the common causes of anorexia and weight loss as hypotheses in all rehabilitation nutrition cases. In that case, not only nonanalytical reasoning but also analytical reasoning should be used while collecting information related to the causes. If clinicians' ability of nonanalytical reasoning can also be improved by repeating analytical reasoning with multidisciplinary colleagues through case reviews, they will achieve more appropriate rehabilitation nutrition goal setting and rehabilitation nutrition intervention skills. This is the secondary English version of the original Japanese manuscript for "Diagnostic reasoning in rehabilitation nutrition: position paper by the Japanese Association of Rehabilitation Nutrition." 10

ACK N OWLED G M ENTS
We solicited public comments from members of the Japanese Association of Rehabilitation Nutrition from March 12 to 25, 2022.
Two respondents provided valuable comments that we incorporated into the manuscript. We would like to express our deepest gratitude to all those who provided public comments.

CO N FLI C T O F I NTE R E S T
The authors have stated explicitly that there are no conflicts of interest in connection with this article.