Why am I gaining weight?

Many of us gain weight at some point in our lives. A range of factors can play a part, including our diets and different lifestyle factors, health conditions, and medications. 

Below, we’ll look at 13 factors that can contribute to weight gain and give you ideas about how to tackle them.

1. Ultra-processed foods

Fast foods, microwave dinners, cookies, chips, breakfast cereals, and many other packaged foods are ultra-processed

They often contain high levels of fat, sugar, salt, and other additives. And if you have these foods regularly, they can lead to weight gain. 

For instance, a large study found that participants who ate the most ultra-processed foods were 32% more likely to have obesity than those who ate the least. And many other studies have reached similar conclusions.

So, it’s best to enjoy these products just once in a while. When possible, opt for meals made with whole foods and fresh ingredients instead.

2. Unsustainable dieting

Many people try fad diets and lose some weight, then quickly put on that weight again. 

According to some scientists, so-called yo-yo dieting might actually increase weight gain in the long term.

The reason might be that recurrent dieting signals to the body that there isn’t enough food around. In turn, the body signals that it needs more food, just in case.

At ZOE, we know that restrictive diets don’t work. It’s not about calorie counting or focusing on one particular diet plan.

Instead, adding in a variety of fresh foods, such as fruits, vegetables, legumes, pulses, nuts, and seeds can help you maintain a moderate weight. Making sustainable lifestyle changes is the way forward.

3. Blood sugar 

After a meal, your body breaks down carbs into sugar. This sugar then travels from your gut into your bloodstream, causing your blood sugar levels to rise. This is normal and healthy.

But all bodies are different, and some people have a more pronounced response: larger spikes and dips in blood sugar.

According to ZOE’s own research, people with larger blood sugar dips are more likely to feel hungrier and consume more calories throughout the day.

This is one reason why understanding how your body works is important. If you’d like to learn about your personal blood sugar responses, you can start by taking our free quiz

And for advice about how to manage blood sugar spikes, listen to our ZOE Science & Nutrition podcast episode on the topic.

4. Sleep

Research has consistently shown links between sleeping habits and the risk of weight gain and obesity. 

People who don’t sleep enough or have poor quality sleep are more likely to gain weight.

Good quality sleep is essential for a healthy lifestyle. Experts recommend getting 7–9 hours a night for adults, but what’s best for you may be a little more or less. 

It’s not always easy, what with busy schedules, stress, family obligations, and the sounds and bright lights of modern life, but it’s worth trying. 

Getting enough quality sleep could go a long way toward helping you maintain a healthy weight.

Interestingly, there’s evidence of links between gut health and better sleep. So, improving your gut health might be a good place to start.

5. Stress

Studies have shown that stress can also lead to weight gain. Whatever the cause, stress can increase the likelihood of developing obesity. 

Learning how to deal effectively with stress might help you maintain a moderate body weight. 

6. Lack of exercise

Research suggests that simply getting more exercise only has a minimal impact on weight loss. However, scientists have shown that exercise can help prevent weight gain. 

To reap the most benefits, improving your exercise routine should accompany other lifestyle changes.

Physical activity of any type is linked with multiple health benefits beyond weight management. 

Plus, exercise can help some people get better sleep, and as we’ve seen, better sleep can help you maintain a moderate weight.

7. Quitting smoking 

Quitting smoking is another common cause of weight gain. One review found that people who gave up smoking put on an average of around 9 pounds (4.1 kilograms) over the following 3 months or longer. 

This may be because nicotine is an appetite suppressant. Recent evidence also suggests that changes in the gut microbiome after the end of smoke exposure could contribute to weight gain. However, that study was conducted in mice.

Trying to quit smoking can also lead to higher stress levels, which can increase the risk of weight gain, as we’ve seen above.

Still, giving up smoking remains one of the best things you can do for your long-term health.

8. Menopause

On average, people gain 6 pounds during menopause and the years leading up to it, which are known as perimenopause. 

There are several possible reasons for weight gain during menopause, though they aren’t clear-cut.

Hormonal changes can directly contribute to weight change, but other factors are involved. For instance, many women have difficulty sleeping during menopause and may exercise less. Both can play a part in weight gain.

These factors interact, too: If you aren’t sleeping well, you’ll likely have less motivation for exercise, and if you’re not exercising, this can make it harder to drift off at night. 

The good news is, dietary and lifestyle changes can reduce weight gain during menopause.

9. Medication 

Certain medications can lead to weight gain. For instance, some schizophrenia medications are strongly associated with this effect.

Similarly, doctors often prescribe lithium for people with bipolar disorder, and this drug can also result in weight gain, as can antidepressants.

And corticosteroids, which help treat asthma and other inflammatory conditions, may influence weight when you take them for more than 3 months.

If you’re concerned about weight gain and are using any of these medications, speak with a doctor. There may be alternatives, in some cases.

If no other treatments are available, some of the strategies in this article might help offset any weight gain. 

10. Thyroid issues 

Your thyroid gland produces hormones that regulate your metabolism. An underactive thyroid gland may cause weight gain, among other symptoms. This issue is called hypothyroidism.

If you think you might have a thyroid condition, speak with a doctor.

11. PCOS

Polycystic ovary syndrome (PCOS) also has links with weight gain and obesity. 

It’s common, and it has wide-ranging effects, including some that involve your metabolism. 

Experts think that obesity increases the risk of developing PCOS — and PCOS can increase the risk of obesity.

If you think you might have PCOS, talk with a doctor.

12. Depression

Depression is a mental health disorder that affects about 5% of people in the world. Weight gain is one possible effect, possibly due to changes in appetite

These changes might involve undereating, overeating, or binge eating. And having an eating disorder can increase the risk of depression.

Interestingly, evidence suggests that making positive diet changes can help alleviate depression for some people.

Meanwhile, as we mentioned earlier, some antidepressant medications may cause weight gain.

If you’re living with depression, speak with a doctor to make sure you’re getting the support you need.

13. Fluid retention 

Some health conditions keep your body from getting rid of fluids correctly. This excess fluid leads to swelling, which causes an increase in weight. 

Heart failure and kidney and liver diseases are just some of the conditions that can have this effect.

If you notice any rapid changes that may stem from fluid retention, speak with a doctor.


Beyond eating habits and nutrition, various lifestyle factors and health conditions can lead to weight gain.

Getting regular exercise and good quality sleep — and having a balanced diet with limited processed foods — can help you reduce weight gain.

If you’re doing all these things and continue to gain weight, it might be a good idea to visit a doctor.


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