Key takeaways:
Hypothyroidism is caused by an underactive thyroid. It can cause weight gain, among other symptoms.
Untreated hypothyroidism can lead to weight gain of around 5 to 10 pounds.
Treating hypothyroidism may not be enough to lose the extra weight. You may also need to make other changes in your diet, exercise, or medications.
If you’ve recently gained weight and you’re not sure why, an underactive thyroid might be the cause. Hypothyroidism affects up to 5% of people, but probably more people have it without realizing it. In this common condition, the thyroid gland doesn’t produce enough thyroid hormones. The body needs thyroid hormones to maintain different systems, including a normal weight and a healthy metabolism.
Can hypothyroidism cause weight gain?
Yes, hypothyroidism often causes weight gain. Your thyroid gland and thyroid hormones play important roles in regulating your metabolism and weight. If you’ve recently gained weight without explanation, consider talking with a healthcare professional about having your thyroid hormone levels checked through blood work.
How much weight can you gain with hypothyroidism?
There’s no clear data on how much weight people gain with hypothyroidism or how much weight they lose after treating the condition. Estimates suggest that half of people with hypothyroidism experience some weight gain. And most people usually gain 5 to 10 pounds. But some women can gain more — especially if their thyroid hormone levels are very low for a long period of time.
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Weight gain is a common symptom of an underactive thyroid. But if you’ve gained more than 10 pounds, something else may be at play. Beyond checking your thyroid health, take a look at your:
Stress levels
Diet
Sleep patterns
Physical activity levels
Why does hypothyroidism cause weight gain?
Researchers don’t know exactly how low thyroid levels cause weight gain. The cause of most weight gain in hypothyroidism is increased retention (holding onto) of salt and water. But some weight gain can be from increased fat due to a slower metabolism. But it likely involves several processes:
Slowing of your metabolism: Your thyroid helps control your metabolism. When thyroid levels are low, your metabolism slows down and you burn less energy, even when you’re resting. You’re also less likely to burn fat for energy, which can cause weight gain.
Changes in appetite: Your thyroid regulates your appetite. It may lead to food cravings, increased appetite, and an increase in calories.
Fluid retention: Hypothyroidism may increase how much salt and water your body holds onto (retains), and this can lead to an increase in weight.
Decreased physical activity: About 4 in 10 people with an underactive thyroid feel more tired than normal. This may lead to less physical activity, which can contribute to weight gain.
Will I lose weight on thyroid medication?
Hypothyroidism treatment may help keep you from gaining more weight. But it may not help you lose the weight you’ve already gained. Other factors may be contributing, such as hormonal changes, poor sleep and nutrition, and low levels of physical activity.
Treating your low thyroid means taking a thyroid-replacement medication like levothyroxine (Synthroid). The amount you take can change depending on your blood work and symptoms, so it may take a few months to find the right dose for you. If you’re still having difficulty losing the extra weight, you may need to make other diet and lifestyle changes (more on those below).
How to stop weight gain with hypothyroidism
In addition to treating hypothyroidism, there are ways to lose weight that you may have gained with hypothyroidism. Strategies include making healthy and sustainable changes to what and how you eat and drink, as well as how often you’re physically active.
There’s no specific diet or food that’ll reverse hypothyroidism. Still, let’s review some tips that will help you lose weight with hypothyroidism and maximize your thyroid health.
Cut out sugars and refined carbohydrates
Studies show that eating a diet of low-glycemic foods — those that are least likely to spike your blood sugar — help with weight loss. Examples of low-glycemic foods include:
Non-starchy vegetables
Beans
Whole grains
Berries
Fish
Meat
It’s also a good idea to avoid processed food as much as possible.
Focus on nutrient-dense whole foods
It’s important to get the recommended amounts of vitamins and minerals in your diet. Making sure you have enough healthy nutrients in your diet can also contribute to a healthy thyroid. Low levels of iodine can also contribute to hypothyroidism. So be sure to use iodine-enriched salt (most table salts) and to eat iodine-rich food like cod and yogurt.
Studies have also shown that zinc and selenium can help improve hypothyroidism. And improving thyroid function may help restore your metabolism and ideal weight.
Check your fasting blood sugar (glucose)
Hypothyroidism has been linked to metabolic syndrome — a group of health conditions that increase your risk for diabetes and heart disease. It includes:
High blood sugar (diabetes)
Abnormal fat and cholesterol levels
A larger waist circumference
Because of this, it’s worth bearing in mind that extra weight may also be a sign of something else — not just hypothyroidism. So, if you have hypothyroidism and you’re having a hard time losing weight, talk with your primary care provider about screening tests for diabetes (or prediabetes) and these other health conditions.
Get plenty of sleep and exercise
It’s very clear that not getting enough regular, good-quality sleep is linked with weight gain. It can also keep you from losing excess weight. The American Academy of Sleep Medicine recommends at least 7 hours of sleep each night as well as keeping a consistent sleep schedule.
Exercise is important for mental and physical health, and not getting enough can affect your ability to sleep well and keep excess weight off. It’s recommended to get at least 150 minutes of moderate-intensity aerobic activity, or 75 minutes of vigorous aerobic activity, each week.
Watch how much alcohol you drink
Alcohol can add a lot of calories to your diet. For some people, drinking too much is associated with weight gain. Cutting back how much you drink is often a good way to help lose weight. It’ll improve your sleep quality and energy levels too.
Try eliminating gluten
Autoimmune hypothyroidism has been linked with celiac disease, another autoimmune condition in which the immune system reacts abnormally to gluten. Gluten is a protein found in many different grains, including wheat. A gluten-free diet may help improve hypothyroid symptoms in some women, and it may help with weight loss.
Gluten is in many foods, like:
Bread products, including bagels and English muffins
Traditional pastas, doughs, and crusts
Crackers and cookies
Frequently asked questions
Signs of hypothyroidism can sometimes be subtle. Common early signs include:
Weight changes
Mood changes
Fatigue
Changes in your bowel habits
Hair, skin, or nail changes
Talk to a healthcare professional if you develop new or unexplained symptoms.
Yes, hypothyroidism can cause belly fat. An underactive thyroid can slow your metabolism and affect the way your body stores fat. This can lead to weight gain and excess belly fat.
Because hypothyroidism can cause nonspecific symptoms, it can be mistaken for generalized conditions like:
Fibromyalgia
Hormonal changes (like perimenopause or menopause)
Sleep apnea
A healthcare professional can help you figure out what’s causing your symptoms and the best way to treat it.
Signs of hypothyroidism can sometimes be subtle. Common early signs include:
Weight changes
Mood changes
Fatigue
Changes in your bowel habits
Hair, skin, or nail changes
Talk to a healthcare professional if you develop new or unexplained symptoms.
Yes, hypothyroidism can cause belly fat. An underactive thyroid can slow your metabolism and affect the way your body stores fat. This can lead to weight gain and excess belly fat.
Because hypothyroidism can cause nonspecific symptoms, it can be mistaken for generalized conditions like:
Fibromyalgia
Hormonal changes (like perimenopause or menopause)
Sleep apnea
A healthcare professional can help you figure out what’s causing your symptoms and the best way to treat it.
The bottom line
If you’ve gained weight unexpectedly, an underactive thyroid — or hypothyroidism — could be the cause. Treating hypothyroidism with thyroid medication can help get rid of the extra weight, but it may not be enough. You may also have to focus on some lifestyle changes, such as getting enough sleep and exercise, limiting sugar and alcohol, and sticking to nutrient-dense whole foods. If you’re still not at your weight goal, be sure to talk with your primary care provider about the best next steps.
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References
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American Thyroid Association. (2024). Thyroid & weight.
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