Unexpected weight loss can result from muscle loss or muscular atrophy. Muscle weakness is the main symptom. Even so, one of your limbs can seem smaller than the other. Your body is composed of water, muscle, bone, and fat-free mass, which comprises these components. You'll lose weight if your muscle mass decreases. If your muscles aren't used for a while, this may occur. People who are bedridden, desk-job workers, or non-exercisers are more likely to experience it. Muscle loss may typically be prevented with exercise and a healthy diet.

Additional potential reasons for muscle loss include:

• Injuries, such as broken bones
• Aging
• Burns
• Stroke
• Osteoarthritis
• Rheumatoid arthritis
  
• Osteoporosis
• Multiple sclerosis
• Nerve damage
• ...

Your thyroid gland produces too much thyroid hormone, which leads to hyperthyroidism, or an overactive thyroid. Numerous bodily processes, including metabolism, are regulated by these hormones. Even if you have a good appetite, an overactive thyroid will cause you to burn calories very quickly. Hyperthyroidism can accelerate your body's metabolism, causing unintentional weight loss and a rapid or irregular heartbeat.

Additional signs include:

• Fast, irregular heart rate
• Anxiety
• Fatigue
• Heat intolerance
• Sleep troubles
• Hand tremors
• Light periods in women
• ...

Possible causes of hyperthyroidism include:

• Graves’ disease
• Thyroiditis
• Eating too much iodine
• Taking too much thyroid medicine
• ...

An autoimmune condition called rheumatoid arthritis (RA) causes your immune system to attack the lining of your joints, which results in inflammation. In some people, the condition can damage various body systems, including the skin, eyes, lungs, heart and blood vessels. Chronic inflammation can boost metabolism and help people lose weight overall.

Joint discomfort and swelling are RA symptoms. On both sides of your body, the same joints are typically affected. If you don't move for an hour or more and have RA, your joints could feel stiff.

There is no known cause for RA. It might be related to the following:

• Age
• Genes
• Hormonal changes
• Smoking
• Secondhand smoking
• Obesity
• ...

Diabetes patients' bodies are unable to use the glucose in their blood as energy because their insulin levels are insufficient. This results in the body beginning to burn fat and muscle for energy, resulting in a decrease in total body weight. Before being diagnosed with type 1 diabetes, persons frequently experience unexpected weight loss, although type 2 diabetics can also experience it. When you have type 1 diabetes, your immune system attacks the insulin-producing cells in your pancreas. Your body cannot use glucose as fuel without insulin. This results in elevated blood sugar. Unused glucose is eliminated by your kidneys through urine. Calories also leave your body as sugar does.

Diabetes type 1 also results in:

• Frequent urination
• Dehydration
• Fatigue
• Blurry vision
• Excessive thirst
• Excessive hunger
• ...

Although depression mostly affects your mood and mental state of mind, it can also result in physical symptoms. You may have aches and pains, a decline in energy, fatigue, unusual stomach and digestive problems, or changes in appetite. When you experience depression, feeling lost, or feeling empty for at least two weeks, you may experience weight loss as a side effect of depression. Going to work or school or other regular duties is made more difficult by these emotions. The areas of the brain that regulate hunger are also impacted by depression. This may result in decreased appetite and, ultimately, weight reduction. Depression may boost appetite in some people. Each person experiences different symptoms.

Additional indications of depression include:

• Constant sadness
• Loss of interest in hobbies
• Low energy
• Poor concentration
• Sleeping too little or too much
• Thoughts of death or suicide
• Irritability
  ...

Inflammatory bowel disease (IBD) may have symptoms, including unexpected weight loss. IBD refers to a variety of gastrointestinal tract inflammatory diseases that are chronic in nature. Crohn's disease and ulcerative colitis are the two most prevalent varieties. Your body enters a catabolic condition as a result of the chronic inflammation caused by IBD, which causes it to constantly burn through energy. The appetite and satiety hormones ghrelin and leptin are both disturbed by IBD. Reduced appetite and weight reduction follow from this; It’s hard to eat well with symptoms like nausea and belly pain. When you have no appetite, you may eat fewer of the calories and nutrients that you need to maintain your weight.

Additional symptoms include:

• Diarrhea
• Stomach pain
• Bloating
• Bloody stools
• Fatigue
• ...

A lung condition that worsens over time is a chronic obstructive pulmonary disease (COPD). Emphysema and chronic bronchitis fall under this category. Both are common among COPD patients. Emphysema slowly deteriorates the lungs' air sacs, making breathing difficult. The airways that transport air to your lungs become inflamed as a result of chronic bronchitis. As a result, you cough up mucus and have breathing problems. Early COPD is not severe.

Although some people may not show symptoms, those that might do so include:

• Shortness of breath
• Wheezing
• Chest tightness
• Mild coughing, with or without mucus
• ...

COPD might result in weight loss in its later stages. Calorie burn is high during breathing difficulties. A person with COPD may require 10 times more calories to breathe than someone without COPD, according to Cleveland Clinic. In addition, breathing while eating might be painful. Additional signs of severe COPD include:

• Swelling of legs, ankles, or feet
• Low muscle endurance
• Fatigue
• ...

The endocardium, or inner lining of your heart, becomes inflamed as a result of endocarditis. It develops when bacteria, which are typically germs, enter the bloodstream and accumulate in the heart. Fever is typically present in endocarditis patients. A poor appetite could accompany this. Increased metabolism and fat burning from elevated body temperature result in weight loss. Visit your doctor as soon as you can if you have symptoms of endocarditis, especially if you have a congenital heart defect or a history of endocarditis. Similar signs and symptoms may be brought on by less serious illnesses. The diagnosis can only be made after a qualifying examination by a healthcare professional.

Additional signs include:

• Heart murmur
• Coughing, with or without blood
• Abdominal pain
• Chest pain
• Difficulty breathing
• Night sweats
• Back pain
• Headache
• Red or purple spots on the skin
• ...

A contagious disease that typically affects the lungs, tuberculosis (TB) is another reason for unexplained weight loss. Mycobacterium tuberculosis bacteria are to blame. Major TB symptoms include weight loss and decreased appetite, but the causes are not entirely known. TB spreads through air droplets. You can get TB even if you feel healthy. The bacteria will stop reproducing if your immune system is able to combat it. Latent TB is the name for this. It may develop into active TB over time.

These signs include:

• Bad cough that lasts 3 weeks or more
• Chest pain
• Coughing up blood or phlegm
• Fatigue
• Night sweats
• Chills
• Fever
• ...

Some people are vulnerable to having active TB. This includes those with weakened immune systems, particularly those who:

• Low body weight
• Substance use disorder
• Diabetes
• Silicosis
• Leukemia
• Hodgkin’s disease
• HIV
• Organ transplant
• ...

Cancer is the general term for conditions that cause abnormal cells to spread and divide quickly. One of the early warning symptoms of cancer, according to the American Cancer Society, could be an unexplained weight loss of 10 pounds or more. Pancreatic, lung, stomach, and esophagus cancers usually show this. Inflammation rises in cancer. This encourages muscle wasting and interferes with the hormones that control hunger. Your resting energy expenditure (REE), or the amount of energy your body uses when at rest, may also rise as a result of a growing tumor.

Early symptoms of cancer also include:

• Fever
• Fatigue
• Pain
• Skin changes
• ...