Gaining weight without eating more

The scale keeps creeping up. Your meals have not changed. Some weeks you eat less than before, and the number still climbs.

Weight can shift for many reasons. Age, sleep, stress, and some drugs all play a part. A slow thyroid can too, and that gland in your neck helps set the pace of your body.

When the thyroid runs slow, your body burns fuel at a lower rate. Part of the gain may be water and salt, not fat. Many people also notice dry skin, thin hair, low energy, and slow bowels.

When to see someone

See your doctor if the gain keeps on for months with no change in food. Book a visit sooner for a puffy face, a hoarse voice, a slow pulse, or a neck lump. Get same-day care for swollen legs, chest pain, or hard breathing.

Below are folk and natural remedies linked to a slow thyroid. Each one has a grade that shows how much research exists on it. A grade is not a promise of results, so talk your choices over with your doctor.

Hypothyroidism (Underactive Thyroid): natural remedies and the evidence behind them

8 options · 2 graded B · 2 graded C · 4 traditional or ungraded

How is your underactive thyroid affecting you, and where do you want to focus?

I feel stressed, foggy, and burned out, and want something to steady my energy and mood

Ashwagandha
Supported by smaller clinical studies· Centuries of traditional use (Evidence grade B · Traditional use long-standing)Long-standing traditional staple
Small RCT improved thyroid levels in mild (subclinical) cases
Why this matches
If low energy and a stress-driven, sluggish feeling are wearing you down, ashwagandha is an adaptogen traditionally used to steady energy and stress — dimensions that often ride along with an underactive thyroid.
Why try it
Ashwagandha is a traditional Ayurvedic adaptogen. In a small 8-week double-blind, placebo-controlled trial in adults with subclinical (mild) hypothyroidism, a standardized root extract significantly improved thyroid hormone levels (TSH, T3, T4) versus placebo, and it is also valued for steadying stress and energy. The trial was small and limited to mild cases, so treat this as promising support rather than a replacement for prescribed thyroid care.
Dose or use
Commonly 300–600 mg of a standardized root extract daily, taken with food; give it several weeks.
Time to results
Typically 6–8 weeks
Key study
Randomized controlled trial (2018, PMID 28829155): Efficacy and Safety of Ashwagandha Root Extract in Subclinical Hypothyroid Patients. In this 8-week double-blind, placebo-controlled pilot of 50 adults, 600 mg/day of ashwagandha root extract significantly improved serum TSH, T3, and T4 versus placebo. Encouraging but small and limited to subclinical hypothyroidism.
Caution
Avoid in pregnancy, and use caution if you have autoimmune (Hashimoto's) thyroid disease or take thyroid or sedative medication — talk to your doctor first, as it may raise thyroid hormone levels.
Exercise
Limited human trials so far· Most of the research is laboratory or animal work (Evidence grade C · No traditional record)
Supports metabolism; direct thyroid data is limited
Why this matches
If low energy, weight gain, and a sluggish metabolism are your main struggle, regular movement is one of the most reliable everyday ways to support your metabolism, mood, and weight while you address thyroid function.
Why try it
Everyday movement is well established for supporting metabolism, weight, and energy. Its direct effect on thyroid markers is less certain — the strongest thyroid-specific signal so far comes from a single mind-body exercise trial rather than from general cardio and strength work.
Dose or use
Aim for around 150 minutes of moderate activity per week, mixing cardio and strength; even gentle, consistent movement counts if fatigue is high.
Time to results
Typically 4–12 weeks of consistent effort
Key study
RCT (2025, PMID 40582060): a Baduanjin (mind-body) exercise program improved lipid profile, blood pressure, and TSH in elderly people with subclinical hypothyroidism. This is one specific mind-body trial; general cardio and strength work has not been shown to change thyroid markers directly.
Caution
Start gradually if fatigue is severe, and check with your doctor before beginning a new program if you have heart or joint concerns.

I'd rather support my thyroid directly with key nutrients and herbs

Ashwagandha
Supported by smaller clinical studies· Centuries of traditional use (Evidence grade B · Traditional use long-standing)Long-standing traditional staple
Small RCT improved thyroid levels in mild (subclinical) cases
Why this matches
If low energy and a stress-driven, sluggish feeling are wearing you down, ashwagandha is an adaptogen traditionally used to steady energy and stress — dimensions that often ride along with an underactive thyroid.
Why try it
Ashwagandha is a traditional Ayurvedic adaptogen. In a small 8-week double-blind, placebo-controlled trial in adults with subclinical (mild) hypothyroidism, a standardized root extract significantly improved thyroid hormone levels (TSH, T3, T4) versus placebo, and it is also valued for steadying stress and energy. The trial was small and limited to mild cases, so treat this as promising support rather than a replacement for prescribed thyroid care.
Dose or use
Commonly 300–600 mg of a standardized root extract daily, taken with food; give it several weeks.
Time to results
Typically 6–8 weeks
Key study
Randomized controlled trial (2018, PMID 28829155): Efficacy and Safety of Ashwagandha Root Extract in Subclinical Hypothyroid Patients. In this 8-week double-blind, placebo-controlled pilot of 50 adults, 600 mg/day of ashwagandha root extract significantly improved serum TSH, T3, and T4 versus placebo. Encouraging but small and limited to subclinical hypothyroidism.
Caution
Avoid in pregnancy, and use caution if you have autoimmune (Hashimoto's) thyroid disease or take thyroid or sedative medication — talk to your doctor first, as it may raise thyroid hormone levels.
Selenium
Supported by smaller clinical studies· Centuries of traditional use (Evidence grade B · Traditional use long-standing)Long-standing traditional staple
Trace mineral behind T4-to-T3 conversion
Why this matches
If you want to support your thyroid directly, selenium powers the enzymes that convert stored thyroid hormone (T4) into its active form (T3) and helps protect the gland from oxidative stress.
Why try it
Selenium powers the enzymes that activate thyroid hormone and help protect the gland from oxidative stress. In pooled randomized trials in autoimmune (Hashimoto's) thyroiditis — the most common cause of an underactive thyroid — selenium modestly lowered TSH and reduced thyroid antibodies, though it did not change thyroid hormone levels. It is a reasonable support, not a substitute for prescribed thyroid treatment.
Dose or use
Commonly around 100–200 mcg daily; a couple of Brazil nuts is a food source. Keep total intake under 400 mcg/day.
Time to results
Typically 8–12 weeks
Key study
Systematic review and meta-analysis of RCTs (2024, PMID 38243784): Selenium Supplementation in Patients with Hashimoto Thyroiditis. Across 35 trials, selenium modestly lowered TSH in people not on thyroid hormone and reduced thyroid peroxidase antibodies (TPOAb); it did not change free T4 or T3, so it supports autoimmune thyroid health rather than replacing thyroid treatment.
Caution
Selenium has a narrow safe range — too much can cause hair loss, brittle nails, and nerve problems. Don't stack multiple high-dose supplements.
Iodine
Centuries of traditional use across more than one tradition· Human evidence not yet assessed (Evidence grade not assigned · Traditional use classical)Classical use across multiple traditions
The raw material your thyroid needs to make hormone
Why this matches
If you want to support your thyroid directly, iodine is the building block your gland uses to make thyroid hormone — a genuine gap can leave it unable to keep up.
Why try it
Iodine is the direct precursor of thyroid hormones (T4 and T3), and its library entry lists hypothyroidism and goiter among its uses. Correcting a true iodine shortfall is well established; supplementing when you're not deficient is not, so this is best guided by testing.
Dose or use
Only supplement to correct a confirmed shortfall; the adult daily requirement is about 150 mcg. Ask your doctor before taking high-dose iodine.
Time to results
Varies; weeks to months when a true deficiency is corrected
Key study
Iodine is the established substrate for thyroid hormone; correcting a documented deficiency is a recognized approach, but routine supplementation without deficiency is not supported and can backfire.
Caution
More is not better: excess iodine can worsen thyroid function, and in autoimmune (Hashimoto's) hypothyroidism it can aggravate the condition. Do not take high doses without medical guidance.

I'm fighting low energy, weight gain, or a sluggish metabolism and want everyday habits that help

Exercise
Limited human trials so far· Most of the research is laboratory or animal work (Evidence grade C · No traditional record)
Supports metabolism; direct thyroid data is limited
Why this matches
If low energy, weight gain, and a sluggish metabolism are your main struggle, regular movement is one of the most reliable everyday ways to support your metabolism, mood, and weight while you address thyroid function.
Why try it
Everyday movement is well established for supporting metabolism, weight, and energy. Its direct effect on thyroid markers is less certain — the strongest thyroid-specific signal so far comes from a single mind-body exercise trial rather than from general cardio and strength work.
Dose or use
Aim for around 150 minutes of moderate activity per week, mixing cardio and strength; even gentle, consistent movement counts if fatigue is high.
Time to results
Typically 4–12 weeks of consistent effort
Key study
RCT (2025, PMID 40582060): a Baduanjin (mind-body) exercise program improved lipid profile, blood pressure, and TSH in elderly people with subclinical hypothyroidism. This is one specific mind-body trial; general cardio and strength work has not been shown to change thyroid markers directly.
Caution
Start gradually if fatigue is severe, and check with your doctor before beginning a new program if you have heart or joint concerns.
Vitamin D
Limited human trials so far· Most of the research is laboratory or animal work (Evidence grade C · No traditional record)
Preliminary single-trial signal on metabolic markers
Why this matches
For those managing weight and metabolic sluggishness, vitamin D supplementation has been studied specifically in women with subclinical hypothyroidism for its effect on metabolic health.
Why try it
Early evidence from a single trial suggests vitamin D may influence metabolic and body-composition markers in women with subclinical hypothyroidism. This is preliminary, based on surrogate measures rather than thyroid or clinical outcomes, and has not been confirmed by larger studies.
Dose or use
Typically 1,000–2,000 IU daily with a meal; follow your healthcare practitioner's guidance based on your blood levels.
Time to results
Typically 8–12 weeks
Key study
RCT (2023, PMID 38179303): Effects of vitamin D supplementation on metabolic parameters, serum irisin and obesity values in women with subclinical hypothyroidism: a double-blind randomized controlled trial.
Caution
High doses can cause toxicity; get your levels tested before supplementing long-term, especially if you have kidney issues.

I want to check whether a hidden nutrient gap is making things worse (get tested first)

Iodine Deficiency
Centuries of traditional use· Human evidence not yet assessed (Evidence grade not assigned · Traditional use long-standing)Long-standing traditional staple
Iodine gap is a classic, direct cause of low thyroid
Why this matches
If you're checking whether a nutrient gap is dragging your thyroid down, iodine is the most direct one to consider — it's the raw material your gland needs to make hormone.
Why try it
Iodine deficiency is a textbook, correctable cause of hypothyroidism and goiter. Confirming your status is a practical root-cause step rather than a treatment in itself.
Dose or use
Ask your provider about your iodine status (a dietary review or a urine iodine test) before supplementing.
Time to results
Correcting a true deficiency can take weeks to months
Key study
A documented iodine shortfall is a recognized, direct cause of an underactive thyroid; this is a root-cause check, not a treatment claim — ask your provider to assess your status.
Caution
Don't self-correct with high-dose iodine — excess can worsen thyroid function, especially in autoimmune (Hashimoto's) thyroid disease.
Selenium Deficiency
Centuries of traditional use· Human evidence not yet assessed (Evidence grade not assigned · Traditional use long-standing)Long-standing traditional staple
Low selenium can impair T4-to-T3 conversion
Why this matches
If you're looking for a hidden nutrient gap behind your symptoms, low selenium can impair how your body activates thyroid hormone and defends the gland from oxidative stress.
Why try it
Selenium's library entry notes its critical role in thyroid hormone metabolism; if you're low, correcting it may support how efficiently your body uses thyroid hormone.
Dose or use
Ask your provider whether checking or gently correcting selenium makes sense before adding supplements.
Time to results
Correction typically takes 8–16 weeks
Key study
Selenium is essential for the enzymes that activate thyroid hormone; this is a root-cause check, not a treatment claim — ask your provider before supplementing.
Caution
Selenium has a narrow safe range; don't take high-dose supplements to 'top up' without knowing your status.
Vitamin D Deficiency
Centuries of traditional use· Human evidence not yet assessed (Evidence grade not assigned · Traditional use long-standing)Long-standing traditional staple
Low vitamin D may compound thyroid-related symptoms
Why this matches
If you're wondering whether a hidden nutritional shortfall is making your hypothyroidism harder to manage, checking your vitamin D status is a practical first step.
Why try it
If you're low in vitamin D, correcting that deficiency may help support overall metabolic and immune function, which can be relevant when the thyroid is underperforming.
Dose or use
Ask your doctor for a 25-OH vitamin D blood test to know your baseline before supplementing.
Time to results
Deficiency correction typically takes 8–16 weeks
Key study
Correcting a documented shortfall can support recovery; this is a root-cause check, not a treatment claim — ask your provider to test your levels.
Caution
Do not self-prescribe high-dose vitamin D without testing; excess vitamin D accumulates and can cause harm.

Evidence grades describe the strength of published research for Hypothyroidism (Underactive Thyroid), not a promise of results. Nothing here is medical advice — talk to your clinician before starting anything, especially alongside prescription medication.