Woman standing on bathroom scale while wondering, "Why does my weight fluctuate so much?"

Why Does My Weight Fluctuate So Much?

Medically reviewed on January 4, 2024 by Jordan Stachel, M.S., RDN, CPT. To give you technically accurate, evidence-based information, content published on the Everlywell blog is reviewed by credentialed professionals with expertise in medical and bioscience fields.

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It’s perfectly normal for your weight to differ from what it was yesterday. On average, adult weights fluctuate from five to six pounds a day. Maybe you ate a large dinner the night before and woke up a few pounds heavier, or maybe a busy day interrupted meal times, causing you to drop a few pounds overnight.

Body weight fluctuation may also arise as a result of long-term lifestyle changes, hormonal imbalances, or health problems.[1]

All that said, you may be asking yourself, why does my weight fluctuate so much? Let’s explore.

The Drivers Behind Weight Gain

In the United States, nearly one in three adults is overweight, and over 40 percent of adults are obese.[2] Healthcare providers most often use body mass index (BMI)—a person’s weight divided by their height—to diagnose overweight and obesity in patients. However, some research suggests that this unit of measurement may be a poor metric when measuring a person’s health.[3]

Nevertheless, weight gain is fairly common in the United States, and there are multiple reasons as to why the number on the scale continues to rise.

1. Hormone Imbalance

In many cases, high stress levels can cause hormonal weight gain. When bodies perceive a threat—whether physical or psychological—a hormone called cortisol spikes. Chronic stress can lead to long-term elevations, which can trigger physiological changes, such as an increase in appetite. Accordingly, people who are chronically stressed are more likely to eat more than their body needs. This increase in calorie intake can lead to a buildup of fat and body weight fluctuation or weight gain.[4,5]

In women and people assigned female at birth (AFAB), changes in the sex hormone estrogen can disrupt the metabolism and body weight, specifically around the hips and thighs.[4]

In addition to cortisol excess and estrogen dominance, several additional hormonal conditions may lead to weight gain including [4]:

  • Thyroid hormone deficiency
  • Androgen imbalance
  • Insulin resistance
  • Metabolic syndrome
  • Polycystic ovary syndrome (PCOS)
  • Growth hormone deficiency
  • Leptin resistance
  • Prolactin excess
  • Pituitary insufficiency

Oftentimes, healthcare providers can treat weight change brought on by hormonal imbalances by prescribing lifestyle changes, hormone replacement therapies, and certain medications.[4]

2. Lack of Sleep

The National Sleep Foundation recommends that adults aged 18 to 64 should get anywhere from seven to nine hours of sleep nightly. For older individuals, those numbers decrease slightly to seven to eight hours a night.[1]

That said, daily responsibilities, anxiety, and unsatisfactory sleeping conditions can interrupt nightly rest, leaving the body in need of energy. Thus, you may eat more and increase your calorie intake, leading to weight gain.[1] To combat restless nights, consider removing electronic devices from the bedroom, creating a dark and comfortable environment, and avoiding large meals before bedtime.[1,6]

3. Health Problems and Medications

Several medical conditions can lead to weight gain. These include, but are not limited to [1]:

  • Endocrine diseases
  • Genetic conditions
  • Depression
  • Long-term stress
  • Damage to the hypothalamus
  • Eating disorders

Some medications may also affect weight gain, such as [1]:

  • Corticosteroids
  • Diabetes medications
  • Beta-blockers, alpha-blockers, and calcium channel blockers
  • Antihistamine medications
  • Depression medications
  • Epilepsy medications
  • Medications to treat psychotic disorders

Reasons For Weight Loss

For some, weight loss is intentional. For others, weight loss can occur without altering diet, physical activity, or lifestyle habits. This can point to several potential medical reasons that might cause one to lose weight, which is explored below.[7,8] It’s also important to note that understanding the stages of weight loss may help identify if it’s being caused by one of the following medical conditions.

1. Hyperthyroidism

Hyperthyroidism occurs when the thyroid—an endocrine gland in the neck—releases too much of the thyroid hormone. It impacts about one percent of the United States population.[9]

Among its many symptoms is unexplained weight loss. That said, there are multiple possible causes of hyperthyroidism, including [9]:

  • Graves’ disease
  • Thyroid nodules
  • Thyroiditis
  • A high-iodine diet

Treatments for an overactive thyroid include antithyroid drugs, radioactive iodine medication, surgery, and beta blockers.[9]

2. Mental Health Issues

Mental health conditions, such as anxiety, depression, eating disorders, and obsessive-compulsive disorder (OCD) may cause one to lose weight, as patients may become disinterested in food and/or experience a decrease in appetite.[8]

3. Digestive Disorders or Gastrointestinal Problems

Disorders, like celiac disease or irritable bowel syndrome (IBS), can impact the digestive system and potentially lead to weight loss. People with celiac disease have an immune system that attacks gluten when ingested. This can damage the gut and inhibit the body’s ability to absorb nutrients. Conversely, IBS can cause bloating, nausea, and stomach pain that can impair appetite.[8]

Certain gastrointestinal problems, like peptic ulcers and ulcerative colitis, can cause nausea that may also lead to weight loss.[7]

Maintain a Healthy Weight With Everlywell

There are numerous reasons as to why you may be gaining or losing weight. To best understand your health and body composition, make an appointment with a healthcare provider to discuss your symptoms and possible treatment plans for healthy weight management.

The Everlywell online weight management option provides virtual weight management support from the comfort of your home. When you enroll, you’ll have access to regular one-on-one visits, quarterly at-home lab tests, lifestyle recommendations, and medical prescriptions for patients who qualify.

At Everlywell, we don’t fluctuate when it comes to consistent, quality care.

3 Stages Of Weight Loss

Fat Loss vs. Weight Loss: What Is the Difference?

Where Does Fat Go When You Lose Weight?


  1. Factors Affecting Weight & Health. National Institute of Diabetes and Digestive and Kidney Diseases. Published August 11, 2023. URL. Accessed January 2, 2024.
  2. Overweight & Obesity Statistics. National Institute of Diabetes and Digestive and Kidney Diseases. Published June 8, 2023. URL. Accessed January 2, 2024.
  3. BMI a poor metric for measuring people’s health, say experts. Harvard School of Public Health. Published October 28, 2022. URL. Accessed January 2, 2024.
  4. Endocrinology Associates. Hormonal Weight Gain - Endocrinology Consultants, P.C. Endocrinology Consultants, P.C. Published September 28, 2023. URL. Accessed January 2, 2024.
  5. Harvard Health. Understanding the stress response. Harvard Health. Published July 6, 2020. URL. Accessed January 2, 2024.
  6. Good sleep habits. Centers for Disease Control and Prevention. Published September 13, 2022. URL. Accessed January 2, 2024.
  7. Professional CCM. Unexplained weight loss. Cleveland Clinic. Last reviewed August 31, 2018. URL. Accessed January 2, 2024.
  8. Website N. Unintentional weight loss. Nhs.uk. Published December 23, 2022. URL. Accessed January 2, 2024.
  9. Professional CCM. Hyperthyroidism. Cleveland Clinic. Last reviewed October 19, 2021. URL. Accessed January 2, 2024.

Jordan Stachel, M.S., RDN, CPT is most fulfilled when guiding others towards making stepwise, sustainable changes that add up to big results over time. Jordan works with a wide variety of individuals, ranging in age from children to the elderly, with an assortment of concerns and clinical conditions, and has written for publications such as Innerbody. She helps individuals optimize overall health and/or manage disease states using personalized medical nutrition therapy techniques.
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