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Fatigue with low appetite happens for many medical reasons. It can be temporary or last a long time. Here are clear causes, based on medical data, clinical studies, and recent research.
Common Medical Reasons
Most cases start with infection. Viral illnesses like influenza or COVID-19 can reduce appetite and cause tiredness. When the body fights these infections, it releases chemicals that interfere with hunger cues and drain energy. For some, especially after COVID, fatigue and appetite problems may last weeks or longer. These ongoing symptoms also appear in conditions like tuberculosis, where inflammation and tissue breakdown lead to ongoing muscle loss and tiredness.
Cancer is known to strip appetite, prompted by treatments and by the disease itself. Chemotherapy and radiation not only bring nausea but also change how the body uses nutrients. In cancer patients, extreme weight and muscle loss, called cachexia, accounts for up to 20 percent of deaths. Both the illness and its treatment put strain on the body’s energy balance, which helps explain ongoing fatigue.
Thyroid levels play a part. Low thyroid (hypothyroidism) drives low energy and sometimes causes weight gain; high thyroid (hyperthyroidism) has the opposite effect, with restless energy and weight loss despite strong hunger. Diabetes can slow stomach movement after meals, making people feel full quickly or lose interest in eating.
Nutritional Deficits and Hormones
Lack of iron, B12, or folate slows down how blood carries oxygen. This leaves people tired, pale, dizzy, and sometimes craving odd things like ice or dirt, a sign called pica. Simple blood tests can detect most nutrient shortfalls, and correcting them with diet or supplements reduces symptoms in many cases.
Hormones that control hunger and fullness, like leptin and ghrelin, can get out of balance from poor sleep or excess weight. When sleep is poor, hunger and fullness signals become unreliable, making fatigue worse and food choices less healthy. These hormone changes partly explain why sleep disorders such as sleep apnea leave people both tired and more likely to skip meals.
Psychological and Chronic Illness Factors
Mental health matters. Depression is a common cause of fatigue and reduced appetite. It changes brain chemicals and can make food preparation or eating seem pointless. Medicines used to treat depression sometimes make this worse, causing side effects like nausea or sedation. Chronic pain conditions, such as fibromyalgia, migraines, or arthritis, also sap energy and interfere with meals, especially in settings where pain flares up during eating.
Digestive conditions, including celiac disease and inflammatory bowel disorders, irritate the gut and can make eating uncomfortable. These diseases reduce the absorption of nutrients and lead to both low energy and lower desire for food.
Medications for pain, blood pressure, mental illness, or infections can trigger both fatigue and poor appetite through their side effects. Some drugs work best when taken with food or at specific times of day. Adjusting the dose, meal timing, or the prescription itself can cut down on these complaints.
Uncommon Triggers in Daily Life
Less typical causes of fatigue and appetite loss can include unexpected changes in routine, exposure to high altitude, and variations in sleep schedules. Extended travel or shift work disrupts circadian rhythms, leading to both tiredness and lower interest in food.
Dietary supplements and cannabis-infused edibles sometimes have side effects that include tiredness or reduced appetite. For example, products like melatonin gummies, magnesium powders, or Delta 9 Gummies may affect how energized or hungry you feel. Other products containing cannabinoids, sleep aids, or even herbal blends can produce similar results, especially when combined with other factors like dehydration or stress.
Aging, Special Populations, and Cancer
Older adults can experience natural changes in taste, smell, and hormones that blunt appetite. Anorexia of aging is common and increases the risk of illness and malnutrition if ignored. For patients facing advanced conditions such as heart failure, about 40 percent report persistent loss of appetite, which can spiral into further fatigue, muscle loss, and a reduced ability to recover from other illnesses.
Cachexia is a medical term for severe weight and muscle loss, often seen in late-stage cancer, advanced infections, or chronic heart and lung diseases. In these cases, both fatigue and appetite loss are hard to treat, but nutritional support, exercise, and symptom care can help.
Gut Health, the Microbiome, and Special Cases
There is growing study of how gut bacteria impact appetite and tiredness. Changes in the type or amount of bacteria, from illness, antibiotics, or diet, can interfere with gut-brain hormones that control hunger. People with rare disorders like Ehlers-Danlos syndrome or mast cell activation syndrome often have chronic fatigue with digestive complaints, which make eating more difficult.
Pregnancy causes hormone changes that can lead to temporary loss of interest in food, nausea, or odd cravings. Morning sickness and food aversions often pass after the first trimester.
When fatigue and low appetite persist, it is best to check with a healthcare professional who can review your symptoms, order basic tests, and help identify the cause. Early evaluation is important, especially when symptoms quickly worsen, result in weight loss, or occur with new pain.