Why Am I Gaining Weight When I Barely Eat?

Updated on March 29, 2026 by Rachel Conklin. Medically reviewed by Jordan Stachel, MS, 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.

---

Table of contents

• Inconsistent Eating Habits
• Sedentary Lifestyle
• Medical Conditions or Medications
• Stress
• Manage Your Weight via Everlywell
• Related Content

---

When losing weight, it’s considered good practice to create a calorie deficit. That is, eating fewer calories than your body needs so that it burns fat for energy instead. [1] However, this strategy isn’t always effective. Restrictive eating and dieting can actually lead to weight gain.

Particularly, inconsistent eating habits can disrupt your physiological responses, and your body may adapt by holding onto weight rather than losing it. [2] Additionally, many dieters find that even if they do lose weight, they quickly gain it back within five years. [3]

So, what’s the reason for this? What are the causes of weight gain? The reality is numerous factors can contribute to weight gain when dieting. Let’s explore four common factors below.

1. Inconsistent Eating Habits

Oftentimes, dieters take a restrictive approach to their food intake for weight management purposes. However, a low-calorie diet can cause your body to respond differently to food availability.

This all comes back to evolution. When humans were hunters and gathers, the body learned to sustain its energy sources over long periods of time, particularly in times of food scarcity. So, when long-term food availability is uncertain, the body holds onto fat deposits in an effort to maintain its energy storage. [2]

Many people who lose weight through dieting find it difficult to maintain that weight loss long term, a pattern often referred to as weight cycling or “yo-yo dieting”. [2]

Dieting can also impact your metabolism—the chemical processes that break down the food you consume into energy. Essentially, lowering your calorie intake can also lower your metabolic rate, meaning you’ll burn fewer calories in general. [4]

2. Sedentary Lifestyle

Staying active is another way your body burns calories and use the energy you consume. It’s generally recommended that adults participate in at least 150 minutes of physical activity a week to maintain optimal health. More activity is recommended for those who are looking to lose weight. [5]

Those who are sedentary, however, may be more at risk of [6]:

• Weight gain
• Chronic diseases
• Cardiovascular problems

A sedentary lifestyle is typically one that’s characterized by any waking behavior, such as sitting or leaning, with an energy expenditure of 1.5 metabolic equivalent task (MET) or less. In other words, you spend most of your day sitting at your desk or couch, with very limited physical activity, such as walking or running. [7]

Sedentary behavior can put your health at risk and increase abdominal fat and your chances of being overweight, even if you restrict calories. [8]

To counteract, say, an eight-hour workday at your desk, consider spending your free time engaging in moderate-to-vigorous activities that promote calorie and fat burning, such as cycling, jogging, or swimming.

3. Medical Conditions or Medications

Certain medical conditions can also contribute to sudden weight gain. For example, hypothyroidism—a condition characterized by the thyroid’s inability to make enough hormones—can cause unexplained weight gain, as well as other symptoms that may affect your activity levels, such as [9]:

• Fatigue
• Joint and muscle pain
• Heavy or irregular menstrual cycles
• Depression

Additional conditions that may lead to obesity or weight gain include [10]:

• Cushing’s disease – A noncancerous tumor forms on the pituitary gland, triggering an overproduction of cortisol. This hormone imbalance can impact the body in numerous ways, including weight gain.
• Polycystic ovary syndrome – Similarly, polycystic ovary syndrome (PCOS) can impact the hormones of women and people assigned female at birth (AFAB). In addition to weight gain, PCOS may cause irregular menstrual periods, excess hair growth, acne, or infertility.

Certain medications can also lead to sudden weight gain, such as antidepressant and antipsychotic drugs.

4. Stress

No matter your diet, long-term stress can contribute to weight gain. When stressed, cortisol levels spike, flooding the body with urgency, anxiety, and panic. In effect, elevated cortisol levels can lower your metabolic rate and increase your cravings for fatty or sugary foods. [11]

Short sleep duration has been associated with higher body weight in some studies. In one study, women who received less than six hours of sleep a night had higher BMIs than women who slept for six hours or more a night. [12]

To mitigate these effects, try implementing relaxation techniques into your daily routine to help calm your body and mind, such as:

• Meditation
• Yoga
• Walking
• Journaling
• Listening to calming music

Manage Your Weight via Everlywell

If you’re asking yourself, “Why am I gaining weight when I barely eat,” several factors may be at play. Your body may be holding onto fat stores if your eating habits are inconsistent or restricted. Or, your weight gain may be the effect of a sedentary lifestyle, medical condition, or long-term stress.

To help you understand what’s going on within your body and what may be disrupting your weight loss efforts, Everlywell provides a number of insightful, at-home tests. For instance, our at-home Thyroid Test measures your thyroid hormone levels to assess how effectively your body is converting food into energy.

References

1. Calorie Deficit: What To Know. Cleveland Clinic. Published December 21, 2022. https://health.clevelandclinic.org/calorie-deficit. Accessed June 9, 2023.
2. Higginson A, McNamara J. An adaptive response to uncertainty can lead to weight gain during dieting attempts. Evolution, Medicine, and Public Health. doi: 10.1093/emph/eow031. https://pmc.ncbi.nlm.nih.gov/articles/PMC5139007/. Accessed June 9, 2023.
3. Duloo A, Montani J. Pathways from dieting to weight regain, to obesity and to the metabolic syndrome: an overview. Obesity Reviews. doi: 10.1111/obr.12250. https://pubmed.ncbi.nlm.nih.gov/25614198. Accessed June 9, 2023.
4. Contreras R. Physiological and Epigenetic Features of Yoyo Dieting and Weight Control. Frontiers in Genetics. doi: 10.3389/fgene.2019.01015. https://pmc.ncbi.nlm.nih.gov/articles/PMC6917653/. Accessed June 9, 2023.
5. Website N. Physical activity guidelines for adults aged 19 to 64. nhs.uk. Published October 6, 2025. https://www.nhs.uk/live-well/exercise/physical-activity-guidelines-for-adults-aged-19-to-64/. Accessed March 2, 2026.
6. Heinonen I. Sedentary behaviours and obesity in adults: the Cardiovascular Risk in Young Finns Study. BMJ Open. doi: 10.1136/bmjopen-2013-002901. https://pmc.ncbi.nlm.nih.gov/articles/PMC3669715/. Accessed June 9, 2023.
7. Park J. Sedentary Lifestyle: Overview of Updated Evidence of Potential Health Risks. Korean Journal of Family Medicine. doi: 10.4082/kjfm.20.0165. https://pmc.ncbi.nlm.nih.gov/articles/PMC7700832/. Accessed June 9, 2023.
8. Gonzalez K. Physical Inactivity, Sedentary Behavior and Chronic Diseases. Korean Journal of Family Medicine. doi: 10.4082/kjfm.2017.38.3.111. https://pmc.ncbi.nlm.nih.gov/articles/PMC5451443/. Accessed June 9, 2023.
9. Hypothyroidism (Underactive Thyroid). National Institute of Diabetes and Digestive and Kidney Diseases. https://www.niddk.nih.gov/health-information/endocrine-diseases/hypothyroidism. Accessed June 9, 2023.
10. Risk factors for obesity. CDC. Published November 14, 2025. https://www.cdc.gov/obesity/risk-factors/risk-factors.html. Accessed March 2, 2026.
11. You Guessed It: Long-Term Stress Can Make You Gain Weight. Cleveland Clinic. Published March 1, 2023. https://health.clevelandclinic.org/stress-and-weight-gain. Accessed June 9, 2023.
12. Kazem Y. Sleep Deficiency is a Modifiable Risk Factor for Obesity and Cognitive Impairment and Associated with Elevated Visfatin. Open Access Macedonian Journal of Medical Sciences. doi: 10.3889/oamjms.2015.063. https://pmc.ncbi.nlm.nih.gov/articles/PMC4877875/. Accessed June 9, 2023.