Why Do We Lose Our Appetite When We Are Sick? The Science Explained

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The bowl of khichdi sits untouched on the bedside table, going cold. Two spoonfuls in, the plate is pushed away. Anyone who has had a fever or a bad bout of flu knows the feeling: the body is clearly working overtime, yet the very thought of food is unbearable.

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It seems illogical. So why does loss of appetite when sick happen at the exact moment the body needs fuel the most? We spoke to Dr Arun P, Associate Consultant, Department of Gastroenterology, KIMSHEALTH, Thiruvananthapuram, who explained that the answer lies in a tightly coordinated conversation between the immune system, the hormones and the gut.

How The Immune System Switches Off Hunger

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During an infection, the immune system releases inflammatory chemicals called cytokines, such as IL-1β and TNF-α. Dr Arun explained that these cytokines influence the hypothalamic-pituitary-adrenal axis, the body's central stress-response system, at every level. That, in turn, triggers the release of stress hormones including cortisol and catecholamines.

The effect is a rise in the resting metabolic rate. In simple terms, the body starts burning more energy even when the person is lying still in bed.

The Gut Hormone Connection

There is another player in the story. "Hormones known as incretins, particularly glucagon-like peptide-1 (GLP-1), which is released directly from gut tissue, may be important in the development of anorexia - in the medical sense, a loss of appetite," said Dr Arun.

Recent evidence has found a cross-talk between inflammatory cytokines, mainly IL-6 and IL-1β, and GLP-1 and its analogues. This interaction reduces food intake and can eventually lead to weight loss in the systemic inflammatory response that accompanies acute illnesses.

Why The Body Eats Less When It Needs More Energy

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Here lies the real paradox. Fighting an infection demands enormous amounts of energy - for the fever, for making antibodies, for producing cytokines and for multiplying immune cells. And yet the patient eats less.

The explanation, Dr Arun said, is that the body increasingly draws nutrients from its own stores rather than from food. Inflammation produces insulin resistance, which raises the level of glucose circulating in the blood. Fat stores undergo lipolysis, a process that breaks fat down and releases fatty acids. Protein in the skeletal muscles is broken down to provide amino acids.

The result is a clever workaround. Activated immune cells keep receiving the important fuel they need, even when oral intake drops.

When The Stomach Joins In

The immune system and hormones are not acting alone. "Depending on the illness, gastrointestinal symptoms can push appetite down even further. Nausea, delayed gastric emptying (when food leaves the stomach more slowly than usual), abdominal discomfort, and changes in taste and smell can all make eating unappealing," added Dr Arun.

He noted that all these factors together contribute to the loss of appetite seen during acute illness.

Bottomline

The next time a sick family member turns away from a lovingly prepared meal, it is worth remembering that this is not fussiness. Loss of appetite when sick is the body's own strategy at work: redirecting its resources, drawing on internal reserves and keeping the immune system fuelled while the infection is fought off.

Disclaimer: The information provided in this article is for general informational and educational purposes only and is not intended as a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or a qualified healthcare provider with any questions you may have regarding a medical condition.