Kelp

Studies in people

• Benefit

  Gut bacteria balance⁶

  In people, eating kelp with lactic acid bacteria raised four of seven helpful gut bacteria types.

• Concern

  Thyroid hormone levels⁸

  In healthy people, taking kelp for four weeks raised thyroid-stimulating hormone and, at higher doses, lowered total triiodothyronine.

• Benefit

  Body fat in overweight men⁹

  In overweight Japanese men, kelp powder tablets lowered body fat percentage over 8 weeks, but not in women.

• Benefit

  Short-term memory in older adults¹¹

  In older people, taking fermented kelp daily improved memory test scores and walking speed.

Found in some samples or products

These come from where it was grown, how it was processed or cooked, or what it was made into. They are not about the ingredient itself, so the signal does not count them.

• Pollutants in seaweed³

  Kelp from China can carry flame-retardant chemicals and PCBs, though risk levels were judged acceptable.

• Supplement contamination and poisoning⁵

  Eight of nine kelp supplements tested contained arsenic, and one woman's hair loss and memory loss improved after she stopped taking kelp.

Single cases of misuse or overdose

One person or one incident, such as an accidental overdose or a mistake in a kitchen or factory. They are real, but a single case does not show what happens at normal amounts, so the signal does not count them.

• Thyroid health⁴

  A woman's thyroid went overactive then underactive after a kelp diet, but it is not known if kelp causes this in everyone.

How it’s made and used

• How the body handles it⁷

  In people, fucoxanthin from kelp turned into fucoxanthinol in the blood, peaking after about four hours.

• Blood fat levels¹⁰

  In people with high blood fats, eating kelp for 4 weeks changed the types of fats in their blood.

• Gut bacteria and digestion¹²

  In lab studies, kelp's galactofucan survived digestion and changed gut bacteria without feeding them.

The signal at the top counts the findings in people and in animal and lab studies. A concern in studies of people outranks animal and lab studies, and “No concerns” needs at least one finding in people. When most findings in people point one way, the page leans that way (“Mostly”), and every finding is still shown. Findings whose study type is not stated are shown but not counted. This page is a reference, not medical advice. It describes what regulators and published research say. Talk to a doctor or dietitian about your own diet.