What causes lack of appetite and fatigue?

October 2, 2025 •

4 min read

According to the CDC, millions of people suffer from chronic fatigue and low energy, which can often be linked to a lack of appetite. It's a debilitating combination of symptoms that profoundly impacts quality of life and makes daily tasks feel overwhelming. Unpacking the root cause is the first step toward regaining your energy and health, and it's essential to understand what causes lack of appetite and fatigue.

Quick Summary

The combined symptoms of reduced appetite and fatigue can be caused by a wide range of issues, from temporary conditions like infections and stress to more serious underlying medical problems such as chronic illness, nutritional deficiencies, or mental health disorders. The connection is often a vicious cycle, where not eating enough due to lack of appetite further worsens fatigue.

Key Points

Infections are common culprits: Viral and bacterial infections like the flu or gastroenteritis are frequent, but temporary, causes of both appetite loss and fatigue.
Chronic illness can be a factor: Persistent symptoms could indicate a chronic disease such as a thyroid disorder, heart disease, or Crohn's disease.
Mental health is a critical consideration: Depression, anxiety, and stress can significantly impact both energy levels and appetite, creating a vicious cycle.
Nutritional deficiencies contribute: A lack of essential vitamins and minerals, especially iron and B12, can directly lead to fatigue and a reduced desire to eat.
Medications may be to blame: Certain medications, including antibiotics and some antidepressants, can cause drowsiness and appetite changes as side effects.
Lifestyle matters: Poor sleep, dehydration, and excessive alcohol use are common lifestyle factors that can contribute to feelings of fatigue and a lack of hunger.

The Vicious Cycle of Lack of Appetite and Fatigue

Poor appetite and fatigue often occur together, creating a self-perpetuating cycle. When you don't eat enough, your body lacks the fuel it needs to produce energy, leading to fatigue. This tiredness can, in turn, reduce your motivation to cook and eat, suppressing your appetite even further. To understand the causes, it's helpful to categorize them into medical, psychological, and lifestyle factors.

Medical Conditions Affecting Appetite and Energy

Various underlying health issues can manifest with these dual symptoms. A medical professional can help diagnose and treat these conditions.

Acute Infections and Illnesses

Viral infections: Common colds and flu can leave you feeling weak and uninterested in food as your body prioritizes fighting off the virus.
Gastroenteritis: Often called a stomach bug, this viral or bacterial infection causes inflammation in the digestive tract, leading to nausea, diarrhea, and a subsequent loss of appetite and energy.
Respiratory infections: Conditions like pneumonia and bronchitis can cause chest discomfort and general malaise, suppressing hunger.

Chronic Diseases

Chronic Kidney or Liver Disease: These conditions can cause waste products to build up in the blood, leading to nausea and a loss of energy.
Hypothyroidism: An underactive thyroid gland slows down the body's metabolism, causing fatigue and sometimes a decreased desire to eat.
Diabetes: Poorly managed blood sugar levels, both high and low, can contribute to fatigue and can affect appetite.
Heart failure: When the heart is unable to pump blood efficiently, it can lead to fluid buildup and a reduced oxygen supply, resulting in tiredness and a poor appetite.
Crohn's Disease: This chronic inflammatory bowel disease affects the digestive tract, causing abdominal pain, cramping, and a loss of appetite, compounded by the body's increased energy expenditure to manage inflammation.

Nutritional Deficiencies

Iron-deficiency anemia: Iron is critical for producing hemoglobin, which carries oxygen in the blood. A deficiency leads to fatigue, weakness, and can affect appetite.
Vitamin B12 deficiency: Essential for nerve function and red blood cell production, a lack of B12 can cause significant fatigue and weakness.
Vitamin D deficiency: This is often linked to fatigue and mood changes, which can impact a person's desire to eat.

Psychological and Mental Health Factors

Emotional and mental states have a powerful impact on physical well-being. The mind-body connection can trigger physical symptoms like those of fatigue and low appetite.

Depression: A hallmark symptom of depression is a lack of interest in previously enjoyed activities, including eating. This can combine with low energy levels to create profound fatigue.
Anxiety and Stress: Chronic stress and anxiety can affect hormonal balance, particularly cortisol levels. High cortisol can suppress appetite in some individuals, while the mental exhaustion of anxiety drains energy.
Grief: Intense emotional distress from loss can profoundly impact eating patterns and lead to a lack of energy.
Eating Disorders: Conditions like anorexia nervosa are driven by psychological factors that fundamentally alter a person's relationship with food, resulting in significant fatigue and malnutrition.

Lifestyle and Environmental Causes

Daily habits and external factors can play a significant role in these symptoms.

Poor Sleep: A lack of restorative sleep is a major contributor to persistent fatigue. Poor sleep can also disrupt appetite-regulating hormones.
Medication Side Effects: Many common prescription and over-the-counter medications can cause drowsiness, nausea, or a metallic taste in the mouth, which in turn reduces appetite.
Dehydration: Simply not drinking enough water can lead to both decreased energy and a reduced sense of hunger, as the body's systems struggle to function correctly.
Excessive Alcohol or Drug Use: These substances can suppress appetite and disrupt sleep patterns, leading to a state of chronic fatigue.

How to Differentiate Between Causes

While many conditions cause these symptoms, the specific combination and duration of signs can offer clues. For instance, a fever and sore throat alongside appetite loss and fatigue often point to an infection, while persistent emotional distress suggests a psychological component. A comparison table can help to clarify some key differences.


Condition Category	Associated Symptoms	Key Differentiating Factors	Example
Infections	Fever, aches, nausea	Short-term, often resolves with recovery	Common cold, flu
Chronic Illness	Long-term fatigue, specific organ symptoms	Persistent, requires medical management	Hypothyroidism, Crohn's disease
Mental Health	Mood changes, loss of interest	Emotional component, psychological distress	Depression, anxiety
Nutritional Deficiency	Weakness, specific signs (e.g., pale skin)	Linked to dietary intake, diagnosed via blood tests	Iron-deficiency anemia
Medication Side Effects	Starts with new medication, resolves after discontinuation	Timing coincides with starting new drugs	Antibiotics, certain antidepressants

Seeking Professional Guidance

While short-term instances of fatigue and low appetite can be managed with rest and hydration, persistent symptoms warrant medical attention. A healthcare provider will perform a thorough evaluation, including a review of your medical history, a physical exam, and potentially blood tests to identify the root cause. For mental health-related issues, counseling or therapy can be a crucial part of the treatment plan.

Conclusion: Your Path to Recovery

Lack of appetite and fatigue are more than just inconvenient; they can signal a deeper issue affecting your health. Whether caused by a common illness, a nutritional deficit, or a chronic condition, addressing the underlying problem is key. By paying close attention to your body's signals and seeking professional help when needed, you can identify the cause and take steps toward feeling revitalized and well. For more information on general health and wellness, please visit the National Institutes of Health website.

Frequently Asked Questions

In many cases, a sudden onset of these symptoms is due to a short-term illness, such as a cold, flu, or stomach virus. These infections cause your body to divert energy to your immune system, leading to fatigue, while the illness and its symptoms can suppress your desire to eat.

You should see a doctor if your symptoms are persistent and last for more than a few days, or if they are accompanied by other worrying symptoms like significant weight loss, fever, or pain. It is especially important to seek medical advice if you have a known underlying health condition.

Yes, psychological factors like stress, anxiety, and depression can significantly affect your appetite and energy levels. Chronic stress can alter hormone levels, and the mental drain of anxiety can contribute to physical fatigue.

Yes. Deficiencies in key nutrients, such as iron, vitamin B12, and vitamin D, are well-known causes of fatigue. The resulting fatigue and overall malaise can also reduce your interest in food.

Yes. Many medications, including some antibiotics, blood pressure drugs, and antidepressants, list fatigue and appetite changes as potential side effects. If you suspect a new medication is the cause, speak to your doctor.

Try eating small, frequent, nutrient-dense meals and staying hydrated. Opt for foods that are easy to digest and appealing to you. Moderate, gentle exercise can also help stimulate your appetite and boost energy levels.

Chronic conditions such as heart, kidney, and liver disease can disrupt the body's normal functions and metabolism, causing both chronic fatigue and a reduced appetite. The body's energy is often spent on managing the illness, leaving less for other functions.