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Causes of Decreased Appetite and Its Impact on Patient Care

Nutrition

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Causes of Decreased Appetite and Its Impact on Patient Care

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The physiology of appetite regulation is best explained as a coordinated effort between multiple hormones and chemical signals, the GI tract, and the hypothalamus. Part of appetite initiation involves the hypothalamus receiving signals from the GI tract that indicate whether the stomach is empty or full.1 

When the stomach is empty, ghrelin, an endogenous circulating hormone that enhances appetite (known as an orexigenic substance), is released by the stomach and small intestines.2 Ghrelin levels rise during fasting, peak just before eating, and decline after a meal. Further, ghrelin stimulates the release of growth hormone and insulin-like growth factor 1.1 Ghrelin’s mechanism of action is short-lived, but it plays a critical role in appetite initiation.2 

Anorexigenic signals, or appetite inhibitors, include both hormonal and mechanical factors. Hormonal signals such as insulin, cholecystokinin, and peptide YY are released in the GI tract during food intake as a feedback signal to the hypothalamus and satiety centers in the brain. As the stomach is filled, stretch receptors in the stomach wall are stimulated to inhibit further filling.1 As adipose cells grow, leptin is released and opposes the action of ghrelin by inhibiting appetite.2

Causes and Assessment

Assessment of a patient with decreased appetite will vary depending on the degree of appetite reduction. Inappetence is often referred to as anorexia, or a lack of appetite leading to no food intake. However, it is equally important to recognize and address hyporexia, or a decreased appetite leading to decreased food intake, and dysrexia, a change in appetite that results in an altered food intake.3 

There are many acute causes of inappetence, including3:

  • Short-term illnesses (eg, gastroenteritis)
  • Psychological stressors (eg, environmental changes, boarding)
  • Dietary changes (eg, improper transitioning, food aversion)
  • Localized and/or generalized pain 
  • Side effects of common medications (eg, antibiotics)1

Management and treatment of systemic and chronic diseases plays an important role in appetite assessment. Common conditions include3:

  • Kidney disease
    • Inappetence associated with chronic kidney disease is likely multifactorial, including an increase in inflammatory cytokines and uremic toxins that affect the CNS.
  • Heart disease
    • Inappetence associated with canine heart disease is likely attributed to an increase in inflammatory cytokines activated by systemic inflammation and adrenergic stimulation, thus resulting in azotemia and progressive kidney disease, pulmonary edema, ascites, and medication-related effects.5,6 
  • Cancer
    • Inappetence associated with cancer is likely attributed to secondary organ dysfunction and chemotherapy-induced nausea.7 
  • GI disorders
    • Inappetence associated with GI disorders is likely attributed to a variety of mechanisms, including persistent inflammation damaging the mucosal lining of the GI tract, changes in gastric acidity, and nonspecific abdominal pain.8
  • Respiratory disease
    • Inappetence associated with respiratory disease is likely attributed to significant pulmonary disease (eg, pneumonia, cancer) interfering with normal functions.

Consequences

Practitioners must remember that the consequences of prolonged inappetence may be more detrimental to patient status than the actual underlying condition, regardless of chronicity. Prolonged decreased nutritional intake leads to immune suppression with secondary organ dysfunction, poor wound healing, and overall increased morbidity and mortality.3,7 Ensuring proper caloric intake is critical to prevent a patient from entering a catabolic state, which could lead to cachexia or the loss of lean body mass and inappropriate protein metabolism.3,7,9 

Conclusion

To the client, inappetence (hyporexia, anorexia, dysrexia) can be the first—or only—sign that something is wrong with their pet.3 Early identification and intervention can help minimize the risk for continued inappetence that may further complicate underlying conditions. In selecting methods to correct an altered appetite, appetite physiology and underlying disease pathology should be viewed cohesively to create the best treatment plan and yield the most positive clinical outcome. 

IMPORTANT SAFETY INFORMATION: ENTYCE® (capromorelin oral solution) is for use in dogs only. Do not use in breeding, pregnant or lactating dogs. Use with caution in dogs with hepatic dysfunction or renal insufficiency. Adverse reactions in dogs may include Diarrhea, vomiting, polydipsia, and hypersalivation. Should not be used in dogs that have a hypersensitivity to capromorelin. Please see the full Prescribing Information for more detail.

References

For global readers, a calculator to convert laboratory values, dosages, and other measurements to SI units can be found here.

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