Reasons for Unexplained Weight Gain & What To Do About It

Unexplained weight gain can be a perplexing, frustrating issue. You may gain weight for numerous reasons, but you may not always be able to pinpoint the exact reason. Learn about the possible reasons behind unexplained weight gain and what to do about it to make managing your weight easier and reach the fitness goals you aspire to.


Stress is surprisingly influential on weight gain, primarily due to the body’s response to stressful situations. When stressed, the body releases cortisol, a hormone that increases appetite and causes inflammation, potentially leading to weight gain. Chronic stress can cause long-term changes in eating behaviors and preferences, prompting an increased consumption of high-calorie foods.

Manage stress-induced weight gain by incorporating some stress-management techniques into your daily routine. These techniques could include mindfulness practices such as yoga and meditation, engaging in regular physical activity, or dedicating time to a hobby you enjoy. Exercise is also a great way to reduce stress.

Hormonal Imbalances

Various hormones, including thyroid hormones, insulin, sex hormones, and stress hormones, influence your hunger, metabolism, and body fat distribution. For instance, hypothyroidism, a condition where your body produces insufficient thyroid hormones, slows down your metabolism and causes weight gain. Similarly, insulin resistance, a characteristic of type 2 diabetes, can lead to weight gain by making your body store more fat. Polycystic ovary syndrome (PCOS), which is characterized by elevated levels of insulin and androgens, can also result in weight gain, particularly around the waist.

Correcting hormonal imbalances involves medical treatments or intervention. For hypothyroidism, thyroid hormone replacement therapy may restore normal thyroid function and manage weight. Lifestyle modifications, including regular physical activity and a balanced diet, are effective for conditions such as insulin resistance or PCOS.

Always consult a health-care provider for a complete diagnosis and treatment plan if you suspect a hormonal imbalance. Hormonal imbalances are complex, and addressing them with a comprehensive, individualized approach is important.

Lack of Quality Sleep

A lack of quality sleep is another significant factor that can cause weight gain. Various studies suggest that insufficient sleep may upset the balance of hormones that regulate hunger and satiety, leading to increased appetite and calorie consumption. Likewise, fatigue from poor sleep might deter you from physical activity.

Improve your sleep quality by establishing a regular sleep schedule: go to bed and wake up at the same time every day, even on weekends. Create a sleep-friendly environment with a cool room temperature, quiet surroundings, and a comfortable bed. Avoid large meals, caffeine, and alcohol close to bedtime. Regular exercise and stress-management techniques can also promote better sleep.

Side Effects of Certain Medications

Certain medications, including some forms of antidepressants, antipsychotics, and corticosteroids, may cause weight gain as a side effect. These drugs may increase your appetite, decrease your body’s rate of metabolism, or cause water retention, all possibly leading to weight gain.

If you suspect your medication is contributing to weight gain, don’t stop taking the medication without consulting your health-care provider. Instead, discuss your concerns with them. They may be able to adjust your dosage, switch you to a different medication, or suggest lifestyle changes to counter the weight gain. Additionally, regular physical activity and a balanced diet can help you manage weight gain associated with medication use.


Aging is a natural process that causes various changes in the body, including a slowdown in metabolism. As we age, we lose muscle mass, which causes us to burn fewer calories, leading to our body storing more fat. Additionally, we tend to become less active, further contributing to this issue and causing us to gain weight more quickly.

However, weight gain due to aging isn’t inevitable. Regular physical activity, particularly strength training, can help you maintain muscle mass and keep your metabolism active. Adjust your diet to match your body’s changing needs. As your metabolism slows, your body requires fewer calories, so focusing on nutrient-rich foods that provide necessary vitamins and minerals without adding excessive calories is important.


Water is crucial in many metabolic processes, including digestion and nutrient absorption. When you’re dehydrated, these processes might not function optimally, potentially becoming a reason for unexplained weight gain. Remember to consume plenty of fluids throughout the day to improve your body’s natural ability to lose weight.

The exact amount of water you should drink each day varies based on several factors, such as your weight and physical activity, but a range of 91 to 125 ounces of water a day should suffice. Be mindful of beverages that can lead to dehydration, such as those high in caffeine or alcohol, and balance their consumption with adequate water intake.

Lack of Adequate Protein in Diet

Proteins are essential macronutrients that keep you satiated, regulate your metabolism, and maintain muscle mass. When your diet is low in protein, you may feel hungrier and end up eating more, which may result in weight gain. Moreover, insufficient protein intake causes a loss of muscle mass, which slows down your metabolic rate.

Incorporate more protein-rich foods such as lean meats, fish, eggs, dairy products, legumes, and nuts into your diet. Plant-based protein sources such as tofu, lentils, chickpeas, and quinoa are excellent choices for vegetarians and vegans.

Overeating Healthy Foods

It may seem counterintuitive, but overeating healthy foods can contribute to weight gain. People often rationalize eating larger portions of healthy foods because they’re “good for you.” However, all foods—even the healthiest ones—contain calories, and consuming them in excess can lead to a calorie surplus, resulting in weight gain. For instance, foods such as avocados, nuts, and whole grains—while highly nutritious—are also calorie dense.

Rectify this by practicing portion control, even with healthy foods. Learn to recognize serving sizes, and use measuring tools if needed. While focusing on the quality of your food, also be mindful of the quantity; balance and moderation are the keys to a healthy diet.


Depression is a common mental health disorder that affects one’s mood and thoughts, leading to changes in one’s eating and sleeping habits—both factors that influence weight. The lethargy and lack of motivation associated with depression can also reduce motivation to perform physical activity. Even the most physically fit people may notice a subtle increase in their weight as they feel less inclined to work out with as much intensity and frequency.

Recognizing the link between depression and weight gain is the first step toward managing the latter. Implementing a balance of regular exercise, good sleep habits, and cognative-behavioral therapy is usually effective in avoiding the side effects of depression.

You may consider implementing at-home gym equipment such as a home spin bike to find a middle ground between wanting to stay at home and remaining physically active. Antidepressant medications may also be beneficial, but it’s important to consider their side effects.

Underlying Medical Conditions

Certain underlying medical conditions can also lead to weight gain. These include hypothyroidism and Cushing’s syndrome, among others. Such disorders affect your body’s metabolism and hormonal balance, leading to increased fat storage and, consequently, weight gain.

A health-care provider can diagnose any potential underlying conditions through a comprehensive evaluation and suggest appropriate treatment options to manage them and any weight gain they’ve cause.

Keeping your weight down can be challenging, especially when you encounter unexplained weight gain. Learn some possible reasons behind gain weight and use these solutions to achieve a healthier lifestyle and efficient weight loss.

Reasons for Unexplained Weight Gain & What To Do About It