It’s perfectly normal for your weight to fluctuate over time — the body is supposed to change and you may experience periods of both weight gain and weight loss. 

If you’re experiencing sudden and unexplained weight loss, you’re probably wondering what’s causing it and in turn, this can impact both your physical and mental health.

Let’s explore why this might be happening and ways you can approach sustainable weight loss.

Causes of sudden weight gain

There are many reasons why you might be experiencing sudden and unexpected weight gain — here are some of the most common. 

#1 Underactive thyroid 

Your thyroid is responsible for producing metabolic-regulating hormones but if you have an underactive thyroid (which is known as hypothyroidism), it can slow down your metabolism and in turn, may lead to weight gain [1]. 

Hypothyroidism affects an estimated 6-10% of women and it tends to increase with age — up to a quarter of women over the age of 65 may be affected [1]. If you’re experiencing unexplained weight gain, you might want to ask your doctor if it could be linked to your thyroid. 


Polycystic ovary syndrome (PCOS) is an endocrine disorder that is caused by imbalanced reproductive hormones, which can impact your menstrual cycle and cause heavy or irregular periods [2]. 

Many women who have PCOS usually also tend to have insulin resistance, which means the body struggles to pull glucose from the bloodstream and use it for energy. As a result, it will begin overproducing insulin.

This can lead to insulin resistance and weight gain. In fact, it’s estimated that more than half of women with PCOS are overweight [3]. 

#3 Sleep deprivation

Your brain produces appetite-regulating hormones called ghrelin, which promotes hunger, and leptin, which promotes fullness. Sleep deprivation can impact your body’s ability to regulate these hormones and may lead to weight gain [4]. 

One study of men found that those who got 4 hours of sleep had increased levels of ghrelin and decreased levels of leptin compared to those who got 10 hours of sleep [4].

#4 Stress

It’s something we’re all familiar with but you might not realise how big of a role stress can play in your weight. Chronic stress can cause your body to experience fight or flight mode regularly, which in turn, releases hormones like cortisol and adrenaline. 

Cortisol can slow down your metabolism and both cause weight gain and make it more difficult to lose weight [5].

What to do if you’ve experienced sudden weight gain

While sudden weight gain can be confronting, there are ways you can approach it. Here are 3 next steps to consider.

Talk to your doctor

The first thing to do if you’re experiencing sudden weight gain is visit your doctor as they will be able to pinpoint what could possibly be behind it. Your doctor may request a blood test or ultrasound to rule out things like a thyroid disorder or PCOS. 

Try a holistic weight loss program

If there doesn’t seem to be a medical reason behind your unexpected weight gain, you might want to try a holistic health program that takes a multipronged approach to weight loss.

Designed by doctors, dietitians and health coaches, Juniper’s Weight Reset Program can help you achieve your weight goals through a combination of medication, support and lifestyle and habit changes. 

Juniper’s Weight Reset Program includes:

  • Clinically-proven medication, which suppresses appetite and increases the feeling of being full
  • Unlimited access to weight loss experts, including GPs, nurses, dietitians, health coaches and pharmacists 
  • Free smart scales to measure biometric health improvements and check in on your goals
  • Members-only app, so you can benefit from progress tracking and guides to health and nutrition, or speak directly to a health coach
  • Free and discreet home delivery, so you can skip waiting rooms and pharmacy visits 
  • Access to a private online community where you can find support and advice from women on the same journey

Juniper has helped thousands of Australian women find new confidence, change their habits and improve their health. 

Make lifestyle changes 

Your lifestyle plays an important role in your weight and everything from poor sleep to increased stress can contribute to sudden weight gain. 

It might be helpful to survey your current habits and see if these could be playing a role — are you sleeping enough? Are you moving your body a few times per week? What do your stress levels look like? 

If you’re not sure where to start, you might want to try the following:

  • If you find it difficult to prioritise nourishing meals, meal replacement shakes can be helpful. Juniper’s Nourish Shakes contain 20 vitamins and minerals, 29.4g of high-quality protein and 205 calories per shake, which helps support your weight loss journey and stay fuller for longer
  • Ensure you’re carving out time in the evening to engage in a wind down routine in order to set yourself up for a good night of sleep
  • Move your body when you can — it can be as simple as heading out for a walk around your neighbourhood a few times per week