Yes, infections can absolutely cause weight loss, often due to decreased appetite, increased metabolic demands from fighting the infection, inflammation, nutrient malabsorption, or stress, affecting various pathogens from viruses to bacteria and parasites. This "wasting" can involve losing fat and muscle as the body mobilizes energy, which can be a mechanism to help manage severe illness but also impact quality of life, so unexplained weight loss warrants seeing a doctor.

When should you worry about weight loss?

You should worry about weight loss when it's unintentional and significant, typically more than 10 pounds or 5% of your body weight over 6-12 months, without dieting or exercise, especially when accompanied by symptoms like fatigue, appetite changes, or altered bowel habits. This can signal underlying conditions such as diabetes, cancer, digestive issues, or mental health disorders, warranting a doctor's visit for proper diagnosis and treatment, say experts from Mayo Clinic and UCLA Health.
 

What can make you lose weight?

A lifestyle with good nutrition, regular physical activity, stress management, and enough sleep supports a healthy weight. People who lose weight at a gradual, steady pace—about 1 to 2 pounds a week—are more likely to keep the weight off than people who lose weight quicker.

What bacteria causes weight loss?

Gut bacteria and weight loss

People who had more bacteria that belonged to a group called Prevotella compared with those that belonged to the Bacteroides group lost weight and body fat more easily than people who had equal amounts of these bacteria.

What are the symptoms of a bacterial infection in the stomach?

Symptoms include nausea, vomiting, fever, diarrhea, abdominal cramping, and pain. In severe cases, you may become dehydrated and have an electrolyte imbalance. Bacterial gastroenteritis is sometimes treated with antibiotics.

Expert explains when unintended weight loss should be cause for concern

What are the worst bacterial infections?

The most deadly bacterial disease contracted by human beings is mycobacterium tuberculosis, the world's leading infectious disease with more than 1,700,000 deaths per year.

What counts as unexplained weight loss?

Unexplained weight loss is concerning if you lose more than 5% of your body weight or 10 pounds over six to 12 months, especially if you're over age 65.

What is the main reason to lose weight?

Improving health

Many people are motivated to lose weight to improve their overall health and reduce the risk of obesity-related health conditions such as type 2 diabetes, hypertension, heart disease, stroke, certain cancers, and sleep apnea.

What tests are done for unexplained weight loss?

When the Scale Drops Without Trying: Essential Tests for Weight Loss

• Initial Laboratory Testing. ...
• Cancer Screening Tests. ...
• Digestive System Evaluation. ...
• Hormonal and Metabolic Testing. ...
• Cardiovascular and Pulmonary Assessment. ...
• Infectious Disease Screening. ...
• Next Step.

What is an alarming amount of weight loss?

Your body weight can regularly fluctuate. But the persistent, unintentional loss of more than 5 per cent of your weight over 6 to 12 months is usually a cause for concern. Losing this much weight can be a sign of malnutrition. This is when a person's diet doesn't contain the right amount of nutrients.

When are doctors concerned about weight loss?

There isn't an exact number for when weight loss becomes a medical concern. In general, see your healthcare professional if you lose more than 5% of your weight in 6 to 12 months when you aren't trying to lose weight. For example, a 5% weight loss in someone who is 160 pounds (72 kilograms) is 8 pounds (3.6 kilograms).

Can dehydration cause weight loss?

A 2025 review published in Physiology & Behavior suggests that drinking enough water does not cause weight loss on its own, instead being under-hydrated can make weight loss harder than it needs to be.

What illness causes weight loss?

While cancer and GI issues and mental health cause most unintentional weight loss, there are many other reasons you might suddenly lose weight, including: Dementia, due to changes in mealtime habits. Endocrine issues, including thyroid disorders and diabetes.

What is considered suspicious weight loss?

Contact your provider if: You or a family member loses more weight than is considered healthy for their age and height. You have lost more than 10 pounds (4.5 kilograms) or 5% of your normal body weight over 6 to 12 months or less, and you do not know the reason. You have other symptoms in addition to the weight loss.

Can unintentional weight loss be harmless?

Unintentional weight loss is when you lose weight without changing your diet or exercise routine. It can be a sign of stress or a serious illness. It's important to get it checked if you're losing weight without trying.

What autoimmune disease causes weight loss?

The signs and symptoms of autoimmune Addison disease can begin at any time, although they most commonly begin between ages 30 and 50. Common features of this condition include extreme tiredness (fatigue), nausea, decreased appetite, and weight loss.

What medications cause weight loss?

• Anticonvulsants (e.g. Topiramate)
• Appetite Suppressants (e.g. Phentermine)
• Bupropion (Wellbutrin)
• Levodopa.
• Metformin (Glucophage)
• Antipsychotic Medication (Neuroleptics)
• Opioid Analgesics.
• Stimulant Medications (e.g. Methylphenidate, Dextroamphetamine)

Which cancers cause loss of appetite?

Ovarian, lung, stomach and pancreatic cancers also commonly cause loss of appetite. Tumors release hormones that may distort your body's perception of hunger, making you feel full when you're not. The cancer may cause appetite-reducing symptoms such as nausea, pain, stress, depression and dehydration.

How do you know if you have a serious bacterial infection?

Signs and Symptoms of a Bacterial Infection:

1. Fever and chills.
2. Fatigue and weakness.
3. Redness, swelling or pus (for skin infections)
4. Cough, difficulty breathing (for respiratory infections)
5. Painful urination, cloudy urine (for urinary tract infections)
6. Nausea, vomiting, diarrhea (for gastrointestinal infections)

What is the king of all bacteria?

E. coli, King Of All Bacteria | The New York Sun.

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