Hormones & Weight Gain: What’s the Link?

There are powerful relationships between our hormones and weight gain. Learn about the different ways your body’s chemical messengers influence your eating.

Our hormones — the chemical messengers in our bodies — have a powerful effect on our behaviour, including around food. 

That pang of hunger you get at 11am? Hormones. The sudden rush of saliva in your mouth when you smell something tasty? Hormones. That urge to binge on comfort food after a stressful day? Hormones again. 

Whether you’re trying to shed a few pounds, or have noticed a sudden increase or decrease in body fat, it’s really valuable to know about hormonal weight gain and weight loss. In this article, you’ll learn about:

• What hormones are
• How hormones affect how you eat and process food
• Conditions that affect hormones and weight gain and weight loss
• The role of lifestyle

What are hormones?

Hormones are chemical messengers your body releases that tell parts of your body to do certain things. There are glands all around your body (known as the endocrine system) which release hormones into your blood. These then travel into your muscles and organs and affect how they behave.

There are over 50 hormones we know about, and they affect all manner of things, from growth to sexual function to metabolism, to tiredness, mood and much more.

To illustrate how it works, let’s take the example of cortisol, which is known as the ‘stress hormone’. Iit plays a critical role in the ‘fight or flight’ response.

• You’re walking through the woods, then a bear suddenly steps into the path in front of you
• You see the bear, and this information gets sent to a part of your brain called the hypothalamus which registers it as a threat
• The hypothalamus sends a signal to your pituitary gland, which sends another signal to your adrenal glands
• Your adrenal glands release cortisol into your bloodstream
• The cortisol tells your liver to release sugar into your bloodstream, which will provide more energy to your muscles 
• That means you can run faster

This is, of course, a simplified description. 

How do hormones affect your weight?

Our hormones are incredibly powerful and complex and they can influence weight in many ways. 

It’s important to be aware that the relationship between specific hormones and weight gain isn’t always straightforward. 

For example, high levels of oestrogen can encourage the body to store fat. So, you might assume low levels of oestrogen would do the opposite. Not so. Low levels of this hormone may make your body burn calories more slowly, so you still put on weight. 

But, to help you get an understanding, we’ve described some of the hormones that can influence weight gain and loss. 

• Ghrelin: This is the ‘hunger hormone’ and is produced in the stomach. Among other things, it sends signals to your brain that stimulate hunger (medical source).
• Motilin: This hormone is produced in the small intestine. It makes the intestine contract when the small intestine is empty (those stomach rumbles we all get when we’re hungry) and signals to your brain that you need food (medical source).
• Leptin: This hormone is produced by our fat cells, and is known as the ‘fullness hormone’. This tells your brain that you’re full up (medical source).
• Insulin: Produced by your pancreas, insulin helps move sugar from your blood into your cells. It helps regulate blood sugar levels and ‘tells’ your brain about nutrient levels in your body and whether or not you need more (medical source).
• Thyroid hormones: The thyroid is a gland that produces hormones which regulate metabolism (the way your body converts food into energy). 
• Cortisol: As we’ve already seen, cortisol is released when you’re stressed, and triggers an increase in blood sugar levels. 
• Oestrogen: This sex hormone regulates where in your body fat is distributed (both women and men use oestrogen, but women have more). 
• Testosterone: This sex hormone maintains muscle mass. Lower levels of testosterone can increase fat storage (both women and men use testosterone, but men tend to have more).

There are many other hormones that can also influence people’s weight.

Related: How do you gain weight?

Relationships between hormones and weight loss or gain

The ways that hormones can affect our weight are often super complex. But let’s look at a couple of examples to see how they influence things. 

One place to start is with the hormone cortisol and weight gain. As we saw earlier, when you encounter stressful situations, cortisol releases sugar into your bloodstream to help with fight or flight. However, in modern society, where many of us face chronic stress, cortisol hormone weight gain can happen because the hormone tells our brains that the body needs more energy, meaning we eat more. Research has shown that increased cortisol levels can stimulate people to reach for more sweet food and that can contribute to weight gain.

Or take leptin, the hormone that tells your brain that you feel full. Leptin is mainly produced by our fat cells, and so obese people often have higher levels of leptin. But here’s the rub. Researchers have shown that obese people tend to develop leptin resistance, so they’re less likely to feel full, even after they’ve just eaten. 

Another common issue relates to thyroid disorders. Some people have an underactive thyroid, affecting the hormones that convert food into energy. This slows down their metabolism, meaning their bodies don’t burn as many calories, and they gain weight. On the flipside, an overactive thyroid can cause hormone weight loss, by telling the body to burn more calories than it needs to.

One of the most common kinds of hormonal weight gain happens during menopause. During menopause, changes to oestrogen (estrogen) levels can affect your metabolism and even change where in your body you store fat. Many women notice the changes happening quickly. Sometimes, fat gets stored around their stomach and waist more than before.

There are several other causes of hormonal weight loss or gain, including: 

• Cushing’s syndrome
• Polycystic ovaries
• Endometriosis

Side effects of medication, hormones, and weight gain

If you’re taking a new medicine, you might notice that you’ve suddenly put on, or lost, a few pounds. Some medications can disrupt your hormones and therefore affect your weight. These include things like:

• Antidepressants
• Blood pressure medications
• Diabetes medication
• Steroids
• Birth control
• Migraine medication
• Certain epilepsy medications

If you notice any sudden increase or decrease in weight after starting on a new medication, talk to your doctor. 

Could hormonal weight loss diets help?

You might have heard about hormone weight loss diets. These diets are designed to help give your immune system the food it needs to manage hormone levels effectively. However, there’s not much evidence that you can reset your hormones to reduce fat levels. 

Does a hormonal imbalance cause weight gain?

Gaining weight is a complex process with several causes. However, certain symptoms indicate a hormonal problem could be contributing to it. Here are some of the common signs of hormonal weight gain:

• Rapid weight gain or loss: Sometimes, people with a hormonal imbalance notice they’ve gained or lost weight rapidly with no obvious explanation (such as a change in diet or activity level). 
• Increase in abdominal fat: People often notice a significant increase in the amount of abdominal (tummy) fat — especially if they haven't previously put weight on there.
• Fatigue: Many people with hormonal imbalances notice they feel much more tired than usual.
• Changes in face shape: This is a rare symptom of a hormonal disorder called Cushing’s syndrome. It causes fat to be stored around the face, which is sometimes called ‘moon face’. This is quite uncommon. 

Besides weight changes, there are many other symptoms of hormonal imbalances. If you believe your weight gain or loss might be related to your hormones, book an appointment with your GP. They might recommend doing blood tests to check if changes in your weight could be caused by a hormonal imbalance. 

Any unexpected and rapid change in weight could be a cause of concern, so it’s best to see your doctor to get to the bottom of it.

Lifestyle changes to manage hormonal weight gain

In the last few years, the science around how we gain and lose weight has progressed quite a lot. The traditional idea that it is just about inputs and outputs is increasingly being questioned, and researchers are developing more nuanced ideas about why some people seem to gain weight more than others. And there’s a lot of research going on into hormones and weight gain too. 

Related: Why does your weight fluctuate so much?

Nonetheless, the basic recommendations about managing weight — including hormonal weight gain — haven’t changed that much. 

• Get it checked: If you’ve noticed unusual changes in your weight or have tried lots of dieting to no avail, it could be worth getting this checked by your GP or an endocrinologist (a hormone specialist).
• Think about what you eat: A healthy balanced diet involves:

1. Eating at least five portions of fruit and veg a day
2. Consuming lots of fibre, such as from whole grains
3. Getting protein from beans, peas, lentils, as well as meat or fish
4. Consuming some dairy or fortified plant milks
5. Choose ‘healthy’ unsaturated fats
6. Reduce alcohol consumption
7. Limit the amount of sugary or highly processed foods you eat

• Know how much you need: Try to consume the right amount of calories for your sex, age and activity level (you can use calorie calculators to estimate how much you personally need).
• Exercise: If you can, aim for at least five, 30-minute exercise sessions per week. These don’t have to be super hard, a fast-paced walk is a good start. 
• Rest: Sleep is also super important and studies show it can help with hormone regulation. Read our guide to better sleep.
• Relax: Stress management is also critical since stress affects your hormones. If you often feel stressed, try to find ways to manage the issue. Check out our guide to stress.
• Manage it with others: Many people find that weight loss groups or courses can give them the motivation they need. 

Ask a nutritionist: What should I eat for energy without weight gain?

Understanding hormones and weight gain

Hormonal weight gain is a common issue and it affects millions of people around the world. While there are no easy answers to this issue, learning about the relationship between hormones and weight loss or gain is a helpful place to start, and it can give you a better understanding of what’s happening in your own body.