Lyme Disease Weight Gain and Weight Loss: Why Both Happen
Lyme disease weight gain and weight loss can both occur—and often confuse patients.
Some people lose weight rapidly without trying. Others gain weight despite eating the same or less. Many notice appetite swings that range from nonexistent to unusually strong.
These changes are not random. They reflect how Lyme disease affects metabolism, inflammation, hormones, gut function, sleep, and the autonomic nervous system.
Patients often describe similar patterns in different ways. Some say, “I keep losing weight and I’m not dieting.” Others report, “I’ve gained weight since getting Lyme, and nothing else changed.”
These shifts are common in Lyme disease and arise from physiologic mechanisms—not lifestyle choices or lack of willpower.
For a broader overview, see the Lyme disease symptoms guide.
Why Lyme Disease Causes Weight Changes
Lyme disease can drive metabolic changes in both directions.
Early in the illness, inflammation and infection-related stress may push weight downward. As the disease evolves, autonomic instability, hormonal disruption, gut changes, sleep disturbance, and reduced activity may shift the body toward weight gain.
These patterns reflect how the body adapts to ongoing physiologic stress and are consistent with broader mechanisms of chronic Lyme disease.
Coinfections and chronic inflammatory responses may further influence appetite, metabolism, and energy balance.
Why Lyme Causes Weight Loss
Some patients experience unintentional weight loss early in infection or during flares because several mechanisms converge.
Inflammatory Metabolism
Inflammation increases metabolic demand and alters fuel use, making it harder to maintain weight.
Loss of Appetite
Inflammation affects appetite-regulating hormones and gut function, leading to nausea, early fullness, altered taste, or reduced intake.
Increased Energy Expenditure
Immune activation and sympathetic overdrive increase calorie use even without increased activity.
Gut Dysfunction
Lyme disease may impair digestion and nutrient absorption. Bloating, diarrhea, constipation, or gastroparesis-like symptoms can reduce both intake and nutrient utilization.
Autonomic dysfunction affecting the gastrointestinal tract may contribute to bloating, altered motility, and symptoms resembling gastroparesis or small intestinal bacterial overgrowth.
Can Lyme Disease Cause Loss of Appetite?
Yes. Many patients experience loss of appetite during acute infection or flares. Inflammation, nausea, altered taste, autonomic dysfunction, and gastrointestinal symptoms may all reduce food intake.
Some patients report early fullness, bloating, or nausea that makes maintaining weight difficult. Others alternate between periods of reduced appetite and increased hunger.
Reduced appetite may also reflect gastrointestinal dysmotility and autonomic dysfunction. Case reports of Lyme neuroborreliosis have described nausea, constipation, decreased appetite, and significant weight loss that improved following treatment.
Lyme Disease Weight Gain: Why It Happens
Not all patients lose weight. As illness evolves, some individuals experience the opposite pattern.
Many patients develop gradual—or sometimes sudden—weight gain as the illness progresses.
Autonomic Nervous System Dysfunction
Autonomic disruption can slow metabolic rate and alter how the body stores and uses energy.
Inflammation and Hormonal Effects
Inflammation may affect insulin sensitivity, cortisol rhythms, and fat distribution, promoting weight gain and fluid retention.
Some patients notice rapid increases in weight due to fluid retention rather than changes in body fat.
Thyroid and Hormonal Disruption
Subtle hormonal changes can slow metabolism even when laboratory values remain within reference ranges.
Reduced Physical Activity
Fatigue, pain, dizziness, and post-exertional worsening often reduce movement and overall energy expenditure.
Sleep Disturbance
Poor sleep affects appetite hormones and glucose regulation. Lyme-related insomnia or circadian disruption may increase hunger while reducing satiety.
Why Weight Can Swing in Both Directions
Many patients experience early weight loss followed later by weight gain—or the reverse.
Early infection may accelerate metabolism and suppress appetite. Later, autonomic dysfunction, hormonal shifts, reduced activity, sleep disruption, and gut dysfunction may alter metabolism in the opposite direction.
Weight changes often reflect the body’s attempt to adapt to shifting physiologic stress.
Why These Symptoms Are Often Missed
Weight changes are frequently dismissed as stress, aging, inactivity, diet, or lifestyle-related problems.
Standard blood tests—including thyroid panels, glucose levels, and cortisol studies—may appear normal even when the body is under substantial metabolic and autonomic strain.
Normal laboratory findings do not exclude infection-related metabolic dysfunction or autonomic involvement.
Can Medications Affect Weight?
Changes in weight may not always be due to Lyme disease itself. Reduced activity, antidepressants, sleep medications, steroids, and other treatments may also influence appetite and metabolism.
Weight changes often reflect several factors acting together rather than a single cause.
What We Still Don’t Know
Although weight gain and weight loss are commonly reported in Lyme disease, formal research examining these metabolic shifts remains limited.
Much of what clinicians understand comes from broader research involving inflammation, autonomic dysfunction, hormonal disruption, sleep disturbance, and observed clinical patterns.
More research is needed to better understand why these changes occur and which patients are most affected.
Frequently Asked Questions
Can Lyme disease cause weight gain?
Yes. Some patients develop gradual or sudden weight gain related to inflammation, hormonal changes, reduced activity, sleep disruption, and autonomic dysfunction.
Can Lyme disease cause weight loss?
Yes. Inflammation, appetite changes, increased energy expenditure, and gastrointestinal dysfunction may contribute to unintentional weight loss.
Is weight loss a symptom of Lyme disease?
Yes. Some patients experience unintentional weight loss due to inflammation, loss of appetite, gastrointestinal symptoms, and increased energy expenditure.
Why do some patients experience both weight gain and weight loss?
Weight changes may shift over time. Early infection may favor weight loss, while later autonomic dysfunction, hormonal changes, reduced activity, and sleep disruption may contribute to weight gain.
Can Lyme disease affect appetite?
Yes. Lyme disease may affect appetite through inflammation, gastrointestinal symptoms, autonomic dysfunction, and sleep disturbance. Some patients lose their appetite, while others experience increased hunger.
Clinical Perspective
Weight changes in Lyme disease are often misunderstood because they may fluctuate over time and occur despite relatively stable eating habits.
Inflammation, autonomic dysfunction, sleep disruption, hormonal effects, reduced activity, and gut dysfunction may all contribute to metabolic instability.
Emerging evidence suggests that dysautonomia and gastrointestinal dysfunction may contribute to some of these symptoms, although additional research is needed.
Clinical Takeaway
Lyme disease may contribute to both weight loss and weight gain through inflammation, autonomic dysfunction, hormonal effects, sleep disruption, gut dysfunction, and altered metabolism.
Unexpected weight changes should be interpreted within the broader context of multisystem illness rather than lifestyle factors alone.
Related Articles
Autonomic Dysfunction in Lyme Disease
Mechanisms of Chronic Lyme Disease
Gut Symptoms in Lyme Disease
Recovery From Lyme Disease
References
- Zlotnikov N, et al. Infection with the Lyme disease pathogen suppresses innate immunity in mice with diet-induced obesity. Cell Microbiol. 2017.
- D’Adamo CR, et al. Supervised resistance exercise for patients with persistent symptoms of Lyme disease. Med Sci Sports Exerc. 2015.
- Adler BL, Chung T, Rowe PC, Aucott J. Dysautonomia following Lyme disease: a key component of post-treatment Lyme disease syndrome? Front Neurol. 2024;15:1344862.
- Hansen BA, Finjord T, Bruserud Ø. Autonomous dysfunction in Lyme neuroborreliosis: a case report. Clin Case Rep. 2018;6(5):901-903.
Dr. Daniel Cameron, MD, MPH
Lyme disease clinician with over 30 years of experience and past president of ILADS.
Symptoms • Testing • Coinfections • Recovery • Pediatric • Prevention
I have gained over 30 pounds (rapidly) since I was diagnosed with lyme and mold illness. My diet hasn’t changed but I am working out less now, because of severe fatigue. I used to practice hot yoga for many years until this illness slowed me down. Has anyone gotten better and been able to lose the weight?