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Unexpected Weight Gain: Causes & Exactly How to Handle It

Beyond being frustrating, unexpected weight gain can leave you questioning your health habits. Join us as we reveal potential culprits and how to recalibrate your weight.  

Unexpected Weight Gain: Causes & Exactly How to Handle It

For much of the population, unexpected weight gain is a reality of life. In certain seasons of life, it’s normal to wonder about the cause of sudden weight gain and what you can do to address it. 

Fortunately, identifying barriers is becoming easier, and solutions exist for getting back on track. Read on for common causes of unexpected weight gain, including answers to common questions like “How do you deal with unexpected weight gain?” 

What Is Unexpected Weight Gain?

Although there isn’t necessarily a universal definition for unexpected weight gain, it’s typically described as body weight gained without an individual trying to do so. In other words, food intake, hydration habits, and exercise haven’t been altered. However, the number on the scale continues to rise. 

Another name for this phenomenon is unexplained weight gain, and (as the name suggests) this sudden weight gain doesn’t seem to have an explanation. Whether unintentional or intentional, rapid weight gain reflects what’s happening under the surface. And even if only a modest amount of weight is gained in the short term, metabolism, gut health, and heart health can be affected in the long term. 

Keep in mind that there are periods of life where an increase in body weight or body fat is normal. For example, for growing children, teens, or pregnant women, an increase in weight may actually be a sign of good health. However, gaining too much weight can be linked with symptoms that worsen health in the long run. 

It’s also important to remember that weight fluctuations from day to day, year to year, and sometimes from hour to hour are normal. Some of the factors affecting weight gain listed below explain why weight may fluctuate from time to time without actually having anything to do with changes in body fat. In other words, a slight increase in body weight according to the scale may have more to do with the time of day than with a diagnosed disorder. 

In any case, tracking trends can help decipher whether unexpected weight gain is due to situational factors or more serious causes. Remember, if at any point your journey feels overwhelming, you can choose to involve qualified healthcare professionals to help you shoulder the load. 

What Can Cause Sudden Weight Gain?

Wondering what might be causing a sudden increase in weight and how you can overcome it? Read on for the top 10 causes of unexpected weight gain, including reasons that may surprise you.

Chronic or Underlying Medical Conditions 

When working with a healthcare team to determine the cause of unexpected weight gain, it’s likely clinicians will first try to rule out underlying conditions. Some of these may be obvious, such as chronic conditions you already know about. 

However, it’s sometimes necessary to dig deeper into the diagnostic process for another disorder or disease before weight gain can be resolved. For example, conditions like heart disease and kidney disease are known to cause weight gain. This is due to their effect on fluid retention in the body and fluid buildup in certain tissues.

Some other underlying conditions known to cause weight gain include: 

•Cushing syndrome
•Hypothyroidism (underactive thyroid)
•Polycystic ovarian syndrome (PCOS)

Hormonal Changes

Speaking of sneaky, underlying causes of weight gain, hormonal disorders rank at the top of the list. Hormonal shifts or imbalances, where levels of certain hormones are higher or lower than normal, can chemically affect how the body stores fat. 

Two prime examples of this phenomenon occur in women. During the menstrual cycle of a woman, fluid can build up in certain tissues and cause temporary weight gain. Phasing into menopause is also linked with weight gain in midlife, thanks to a decrease in the hormone estrogen. In general, women tend to carry more fat on their bodies than men, especially around their hips and buttocks. 

Endocrine disorders, which affect hormone functions, can impact everything from metabolism to sleep. The most common endocrine disorder is diabetes, but other endocrine conditions that can affect weight include: 

•Addison’s disease
•Graves’ disease
•Hashimoto’s disease 
•Hypogonadism (low testosterone) 

The way your body experiences stress is also impacted by an important hormone called cortisol. It’s affectionately, and sometimes non-affectionately, called “the stress hormone” since it helps to control the body’s stress response. 

In acute or short-term stress, such as swerving to avoid a car accident when driving, this hormone is considered helpful in focusing the body’s resources to prevent an imminent threat.

On the other hand, chronic stress, such as from an intense career, is thought to put the body in a suspended state of fight-or-flight—a sort of “survival mode” that encourages the body to store more fat. 


For reasons researchers are still struggling to understand, being overweight or obese runs in families. Genetic material transferred to you through your parents can affect not only the amount of fat your body is primed to store but where your body fat may accumulate. 

Many people with a genetic propensity to gain weight experience increased body fat as a “slow burn” over time. For others, it may seem like a switch is flipped, and certain genes are suddenly turned “on” which causes a sudden increase in weight. This may make maintaining a healthy weight more difficult than before. 

Eating Patterns 

As you might have guessed, eating patterns play a pretty significant role in weight gain—but probably not in the ways you would suspect. It’s not just foods or beverages high in calories, sugar, or saturated fats that cause weight gain, although those items are associated with weight gain. 

In particular, foods high in salt can also pose a problem. Sodium (salt) has an interesting relationship with the body’s fluids and can cause fluid retention and even high blood pressure. Luckily, simple hacks like switching from salt to other herbs or seasonings may make a big difference in blood pressure and weight. 

It may seem counterintuitive, but regularly following fad (trendy) diets, “yo-yo” dieting, or repeatedly cycling through very low-calorie diets can cause weight gain. Similar to the chronic stress described above, dangerous dieting tactics put the body into survival mode—which can prompt the body to bank more fat instead of burn it. 

Surprisingly, the healthy habit of quitting smoking can ultimately lead to sudden weight gain. Since smoking interferes with the body’s appetite hormones, you can expect to eat more or change your appetite during the cessation process. While most experts would agree this risk is worth it in the long run, it’s important to know that quitting smoking may cause weight gain up to about 30 pounds. 

A shift in environmental cues can also cause you to gain weight quickly. Switching where you work, live, go to school, or worship may affect food availability. For example, relying on vending machine meals or breakroom breakfast pastries when you didn’t before may cause a noticeable change. Family habits and immersing yourself in a cultural expectation for food may also affect weight. 

Hydration Status 

As mentioned previously, the amount of water stored in the body also affects weight. The body needs plenty of fluids to lubricate and facilitate life processes. You may notice that staying hydrated or drinking a lot of water may cause your weight to increase temporarily. 

During periods of fluid retention or if you have a disorder that causes you to retain water, your healthcare provider may suggest monitoring salt intake or even prescribe “water pills” (diuretics) to help your kidneys move excess fluid and salt out of your body. As a byproduct, these measures may affect your weight. 

Bathroom Patterns 

It may not be considered a polite dinner conversation, but it’s important to discuss bathroom patterns regarding fluctuating weight status. In particular, bloating or constipation can cause a temporary increase in weight since both cases involve the body hanging on to fluid or waste products.

So if you’re constantly dealing with these digestive issues, it can affect your weight dishearteningly. 

Side Effects from Medication 

While medications can be necessary to improve quality of life, a frustrating side effect of certain medications can be weight gain. The following classes of drugs are known to have weight-influencing interactions: 

Anti-hypertensives: some ꞵ-blockers (ꞵ-andrenergic receptor blockers)
Contraceptives: such as birth control pills
Corticosteroids: local or systemic 
Psychiatric drugs: including antidepressants, antipsychotics, and antiepileptics 
Some anti-diabetics: such as insulin 

Poor Mental Health

Mental health can also play a role in unexpected weight gain. In addition to being on medication for mental disorders like depression, eating or exercise patterns during periods of poor mental health also play a part.

Plus, eating disorders like binge eating disorder or bulimia nervosa may alter gut health and body chemistry in the long run in a way that makes weight management difficult. 

Metabolism Slows

There are many pervasive myths about metabolism out there, but one does ring true. As you age, metabolism slows, making proper diet and exercise habits even more important.

Moreover, it's even considered “normal” for adults to gain about 1-2 pounds per year until they reach 60 or 65 years old.

Sleep, Interrupted 

Lack of sleep may also cause a swift rise in the number on the scale, and sleep habits and quality can affect weight gain. Research hints that people who don’t get enough sleep are more prone to eating excessive amounts of calories and indulging in late-night snacking (nocturnal eating) more often. 

Moreover, having the energy to be active is limited when tired. All of these factors can compound the risk of weight gain. 

How Do You Deal with Unexpected Weight Gain? 

If you’ve gained weight suddenly and unexpectedly, there’s no need to panic! Although the situation may seem urgent, slow and simple tactics are known to create more sustainable habits in the long run. In other words, instead of engaging in dangerous dieting or over-exercising, try these tactics. 

Address Family History 

Just because obesity or being overweight runs in your family doesn’t mean it’s inevitable. Being aware of a genetic tendency can help you focus on aspects of health you can control, such as diet and exercise.

Genetic testing may provide further information to help you make informed choices regarding your weight. 

Focus on Non-Scale Victories 

It may sound counterintuitive to weight loss, but avoid the scale for a while. Non-scale victories are a great way to measure your progress, primarily because they go beyond the scale to celebrate healthy ways in which you honor your health. 

Pay Attention to Daily Practices 

Habits are powerful routines, especially when it comes to health and wellness. From eating to sleeping to exercise, it’s helpful to monitor your habits.

For example, after tracking your regimens, you may find that you’re skipping meals or routinely getting less than the recommended 7-9 hours of sleep adults need. Highlighting areas of improvement can give you a great place to start! 

Kick Bad Habits to the Curb 

As mentioned above, using substances like alcohol or tobacco can make weight control more complicated. Health experts recommend quitting smoking and moderating drinking in order to stay well and maintain a healthy weight.

Working with a dietitian while weaning off of certain substances can help you monitor your nutritional or weight status. 

Lead an Active Life

You don’t have to be a natural born athlete to enjoy exercise. If introducing movement into your routine seems difficult, start with a method of movement you enjoy or excites you. For example, if HIIT sounds too intense, try a goat yoga class!

Thanks to the internet, there are a plethora of exercise options available at the push of a button. The key is to find a type of exercise you like regardless of whether or not it seems to be “making a difference” according to the number on the scale.

Professional Care for Unexpected Weight Gain

The good news about addressing unexpected weight gain? You don’t have to do it on your own! 

Choosing the right members for your healthcare team will be absolutely crucial to your success during your weight loss journey. They can provide valuable insight and guidance along the way, particularly at times when you feel stuck. 

As mentioned above, it’s important to talk to your doctor in the case of underlying diseases or conditions. Doctors and specialists may be able to recommend medications that can help with weight loss or maintenance. For example, during menopause, a doctor may be able to prescribe hormone replacement therapy. As a byproduct, weight may stabilize when hormones become more balanced. 

Working with a health expert, like a dietitian, can help you identify factors leading to weight gain. They can also provide more comprehensive body composition analysis, including information that illuminates whether a rise in weight is due to muscle or fat. 

Experts like dietitians or physical therapists may also come into play when you’re having difficulty navigating certain phases of life, such as weight gain during pregnancy. They can also help if you are having a difficult time tolerating a type of food or exercise.

Unexpected Weight Gain: Final Takeaways

From startling, underlying diagnosis to addressing barriers to healthy eating, unexpected weight gain can be frustrating and even feel hopeless at times. Working with qualified healthcare experts, such as a dietitian or doctor, can help the journey feel a lot less lonely. 

Despite the cause of unexplained weight gain, the solution is often the same— address causes, examine habits, and make meaningful changes designed to last for the long term. 

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