Clinically important weight loss is generally defined as loss of more than 5 percent of usual body weight over 6 to 12 months.
Differential Diagnosis of unintentional weight loss
Psychiatric disorders: particularly depression; eating disorders
Advanced chronic disease: eg, cardiac cachexia from heart failure, pulmonary cachexia (e.g. from advanced COPD), renal failure)
Drugs / Medications/substances (see below)
Neurologic diseases: Dementia, Parkinson disease, amyotrophic lateral sclerosis, stroke.
Neoplasm: gastrointestinal, lung, lymphoma, renal, and prostate cancers, etc.
Nonmalignant gastrointestinal diseases: peptic ulcer disease; Liver disease; celiac disease, inflammatory bowel disease, Malabsorption)
Endocrine: Hyperthyroidism, diabetes, adrenal insufficiency; Hypopituitarism
Infection: HIV, viral hepatitis, tuberculosis, chronic fungal or bacterial disease, chronic helminth infection, Valley fever (Coccidiomycosis); Intestinal parasites;
Msk and Rheumatologic diseases: severe rheumatoid arthritis, giant cell vasculitis
Autoimmune: Lupus, etc.
Inflammation: Inflammatory bowel disease, hepatitis (non-infectious),
Poor oral intake: Social factors (isolation, no money); Swallowing disorders
Poor absorption
Increased metabolism – e.g.Chronic vigorous exercise (eg, distance runners, ballet dancers, gymnasts)
Anorexia of aging
Uremia
Wegener’s granulomatosis
Polyarteritis nodosa
Whipple’s disease
Drugs/ Medication/substances associated with weight loss
Alcohol
Illicit drugs (below)
Cocaine
Amphetamines
Drug withdrawal syndromes (withdrawal after chronic high-dose psychotropic medications or cannabis)
Tobacco
Adverse effects of prescription drugs (eg, anticonvulsants diabetes medications, thyroid medication)
Herbal and other nonprescription drugs (5-hydroxytryptophan, aloe, caffeine, cascara, chitosan, chromium, dandelion, ephedra, garcinia, glucomannan, guarana, guar gum, herbal diuretics, nicotine, pyruvate, St. John’s wort)
References / Further Reading
CMAJ. 2005 Mar 15; 172(6): 773–780. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC552892/ (This is an excellent article)
Am Fam Physician. 2014 May 1;89(9):718-722. http://www.aafp.org/afp/2014/0501/p718.html
https://www.uptodate.com/contents/approach-to-the-patient-with-unintentional-weight-loss