Why are you gaining weight fast and what to do

Have you ever realised realized that you’ve suddenly gained a lot of weight without seemingly changing your lifestyle? It can be emotionally taxing as you try to figure out where the excess weight came from. If you’ve found yourself gaining weight fast, read on. This post’ll cover the potential reasons for your unexplained weight gain. 

Anastasia Kolesnikova
MRes, Biochemist, Scientific Officer

Reasons You’re Gaining Weight

How does weight gain happen? Typically, weight gain occurs when you increase your caloric intake, resulting in a surplus. If you don’t burn the calories you eat daily, the surplus will be stored as fat mass. Additionally, many individual physiological traits make certain people more or less likely to put on pounds. 

If you’re curious about why certain people cannot gain weight and others cannot lose weight, check out this post. 

However, that doesn’t cover the whole story. There are other causes of rapid weight gain. These don’t have to be connected to what you eat, as some arise due to changes in the body or may be caused by your intake of a particular substance. Let’s review them to understand how they contribute to faster weight gain. 

Lack of Sleep

Does sleep affect your weight? Absolutely. In fact, we covered some of the connections between sleep and weight in this post

Sleep is essential for our energy levels. When we don’t get enough sleep, our body sends signals promoting eating. This helps the body get the energy it didn’t get during sleep. This typically happens through increasing the hormones that make us feel hungry.

In addition, a tired body looks for the most accessible source of energy. This can lead us to overindulge in foods high in fats and sugars. In fact, people who don’t sleep enough tend to make poorer food choices than those who get enough sleep. 

If you’ve noticed that you haven’t been getting enough sleep, you may have increased your calorie intake without even noticing it. If you can’t fix your sleep schedule immediately, you may benefit from tracking your food consumption or being mindful of what you’re snacking on. 

However, improving your sleeping habits is the best way to address weight gain due to lack of sleep. Try to work out how you can incorporate sufficient sleep into your busy lifestyle. 

If you need help with supporting your sleep, check out the following posts: 


Stress is another factor that may play a role in sudden and unexplained weight gain. Having higher stress levels is associated with an increased likelihood of being overweight. It is probably related to multiple factors. Stress is connected to unhealthy eating patterns. 

You’re not alone if you’ve ever found yourself snacking on multiple packs of cookies when stressed. Stress-eating is a real thing. During continuous stress, our body releases cortisol, increasing our appetite and our motivation to eat. We also tend to prefer sugary and fatty foods during stressful times, as many of us associate them with comfort. Therefore, we might unknowingly consume more calories than usual when stressed, leading to weight gain.

Some people may turn to substances like alcohol to help them get through stress. Avoiding these strategies if you’re trying to stay in shape is best. Alcohol-related weight gain occurs due to its effects on our metabolism. It lowers how much fat we burn, can increase appetite and make us overeat. 

However, learning to cope with stress in healthy ways is possible. For example, we know that exercise can help deal with stress and can also help control weight. 


Weight gain can be associated with the use of certain medications. One class of such medications is corticosteroids, which are commonly known as steroids. These medications are used to treat a variety of conditions, from allergies to conditions like Chrohn’s disease and adrenal insufficiency. Unfortunately, weight gain is a common side effect of these medications, as around 70% of people taking them report weight gain. 

The weight gain occurs due to changes in our metabolism when we take these medications. They can lead to you feeling hungrier, piling on fat quicker, and changing how your body processes and stores fat and glucose. 


Our thyroid regulates our body’s metabolism. The thyroid produces thyroid hormone, which is the mastermind behind how the body spends its energy. When the thyroid is overactive, people tend to experience weight loss. Conversely, if the thyroid gland is producing insufficient thyroid hormone, we may experience weight gain. This is because our body spends less calories at rest in this case. 

If the thyroid becomes underactive, you may experience a small weight gain of about 5-10 pounds. The majority of this weight is water weight. This weight gain should stop if the condition is treated. If you suspect issues with your thyroid, it’s a good idea to consult with a medical professional. 


Many women think that menopause and weight gain go hand in hand. It is truly a very common occurrence, with at least half of women gaining weight during this time. On average, women gain about 1.5 kg every year during perimenopause. When menopause occurs, weight gain can accumulate to around 10 kg. 

Menopause and perimenopause bring with them a variety of challenging and frustrating symptoms. Weight gain, especially around the belly, is one of them. During this time, the body is producing less of the female sex hormones estrogen and progesterone. This, alongside ageing, can trigger changes in our metabolism. For example, a decrease in muscle mass will decrease how much energy your body spends at rest. 

In addition, the changes cause fat to be stored around your belly, likely making it noticeable to you. 

During this time, one of the best things you can do to help you with managing menopause is strength training. It benefits your basal energy expenditure, supports bone mass and can help you manage the weight gain. 

Certain medications

Taking some medications can lead to weight gain. This is common with steroids, as you’ve seen previously. Some medicines that support people’s mental health can also be associated with weight gain. If you’ve started piling on the pounds after taking a new drug, you may want to reach out to your medical practitioner. They will be able to advise you on whether you can change to a different medication or how to prevent weight gain. 

Unbalanced nutrition

The most common reason for people gaining weight is a slight change in their nutrition habits. We gain weight when we eat more calories than our body needs. If you’ve noticed weight piling on, chances are, you’ve unknowingly tweaked what you eat. Here are some things you may be doing without noticing: 

  • You have little time, so you start relying on pre-made meals or takeaways, which are typically high in fats, sugars, and salt 
  • You’re snacking more on foods that are easy to overeat 
  • You’re not getting enough protein during the day, resulting in feelings of hunger 
  • You’ve increased your portion sizes slightly, including cooking with more oil than usual 

Luckily, these can all be fixed pretty easily. 

Quitting smoking

If you have recently quit smoking, this may just be a cause of your weight gain. The majority of smokers tend to put on weight after quitting their habit. This weight gain, while frustrating, seems to be less harmful than continuing to smoke in terms of long-term health. 

There are a few reasons why quitting smoking may lead to weight gain. One is that nicotine affects our central nervous system, and its removal may lead to weight gain. Food consumption and smoking seem to activate similar reward mechanisms. Some people find that they replace the hand-to-mouth behavior found in smoking with eating. People who quit smoking may also be less able to perceive fat and sweetness in foods, leading to an increased food intake. 

Just because you’ve found yourself gaining weight quickly doesn’t mean that life is over. In many cases, you can manage the weight gain. It’s all about making minor changes to your lifestyle that will be able to help you prevent putting on pounds. 

If your weight gain is caused by things you can control, like stress or lack of sleep, try to address these things head-on. It will result in better overall well-being, and you may find that you can stop worrying about weight gain. If you’re gaining weight for other reasons, like medication, you may want to consult with a medical practitioner.

Your self-confidence, health and weight are in your hands.  

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