Seaweed may have health benefits, including improved thyroid function, blood sugar control, heart health, and weight management. However, eating too much seaweed can have potential risks and side effects.
Seaweed has many different flavors depending on how it’s prepared. Common varieties are often described as salty, umami (earthy), fishy, or briny. Seaweed can be eaten as a snack or used in various dishes, including soups, salads, stews, and smoothies.
1. Helps Control Blood Sugar with Diabetes
Research indicates seaweed may help with diabetes by improving blood sugar regulation. In one study of brown seaweed, participants saw a significant improvement in hemoglobin A1c (HbA1c) levels, an essential measurement of blood sugar control.
Multiple reviews also report that seaweed positively impacts blood sugar levels, especially in people with type 2 diabetes. The effect appears to happen soon after consumption. However, the longer-term impact is unknown.
2. Improves Blood Pressure Regulation
High blood pressure (hypertension) is a significant risk factor for heart disease and stroke. Research suggests seaweed may help lower blood pressure, possibly because of how the body processes sodium.
Excess sodium consumption is linked to high blood pressure. Alginate and other compounds in seaweed bind to sodium and excrete it, which prevents the body from absorbing the sodium and, in turn, prevents sodium from affecting blood pressure.
Other components in seaweed may have an effect similar to those of blood pressure medications called angiotensin-converting enzyme (ACE) inhibitors. Both the medications and seaweed inhibit angiotensin-converting enzyme—a key compound involved in blood pressure control.
Studies show that a dose of seaweed above 4 grams (g) daily for about a month is needed to see blood pressure benefits.
3. Manages BMI and Weight
Some research shows that seaweed may positively affect weight and waist circumference. It may also slightly impact body mass index (BMI), a risk factor for type 2 diabetes, heart disease, and premature death.
Consumption must be fairly high—more than 4 grams daily—and results are inconsistent across studies. For example, one study found positive effects only occurred in males.
4. Lowers Blood Lipid Levels
High cholesterol levels and other blood lipids (fats) increase your risk of heart disease and metabolic disorders. Seaweed is high in fiber, and high-fiber diets are known to lower lipid levels.
Studies are mixed as to seaweed’s actual effect on human lipid levels. Some research has found that seaweed consumption may:
However, another study reported increased triglycerides after four weeks of a high-seaweed diet.
5. Supports Gut Health
Seaweed may support the digestive system in three ways:
- The carbohydrates in seaweed act as prebiotics—food components that feed the healthy bacteria in your digestive tract.
- A type of sugar in seaweed (called sulfated polysaccharides) may increase the growth of “good” bacteria in the gut.
- In laboratory studies, sulfated polysaccharides have been shown to increase levels of short-chain fatty acids. These fatty acids help keep the cells lining the intestinal tract healthy.
6. Slows Down Appetite
Some research suggests eating seaweed may help you feel full faster, but the evidence is weak.
7. Supports Thyroid Function
The high iodine content in seaweed may support thyroid health, but studies suggest it may change thyroid levels too much and harm thyroid function.
8. Alleviates Oxidative Stress
Many diseases are linked to oxidative stress, and antioxidants in brown seaweed appear to help alleviate oxidative stress.
9. Increases Blood Mineral Levels
Despite seaweed’s high calcium levels and other minerals, studies have failed to show that the food can increase mineral levels in your blood.
10. Boosts Immune Health
Seaweed contains antioxidants and prebiotics that are known to support a healthy immune system. However, it’s unclear how well the body absorbs and uses these components.
Possible Links
Although more research is needed, some studies uncovered links between eating seaweed and a lower risk of:
Seaweed Nutrition
Nutritionally, seaweed has much to offer. It is nutrient-rich (a good source of vitamins, minerals, and fiber) and is low in sugar and fat. Seaweed also contains polyphenols, which offer antioxidant and anti-inflammatory properties.
If you’re not accustomed to eating seaweed, you may want to start with small amounts of dried seaweed and increase it as you get used to the flavor or find ways you like it. Even a single tablespoon offers some nutritional benefits.
| Dried Spirulina Seaweed Nutrition | ||
|---|---|---|
| 1 Tbsp. | 1 Cup | |
| Fiber | 0.25 g | 4.03 g |
| Calcium | 8.4 mg | 134 mg |
| Iron | 2 mg | 31.9 mg |
| Magnesium | 13.6 mg | 218 mg |
| Potassium | 95.2 mg | 1,520 mg |
| Sodium | 73.5 mg | 1,180 mg |
| Vitamin C | 0.707 mg | 11.3 mg |
| Folate | 6.58 mcg | 105 mcg |
| Vitamin A | 39.9 IU | 638 IU |
| Fatty Acids | 0.185 g | 2.97 g |
Iodine levels vary greatly by seaweed type. Nori, the most common type, has 58 mcg per tablespoon, or 928 mcg per cup.
Fresh, Roasted, vs Dried Seaweed
You can eat fresh seaweed right out of the ocean. However, not all types are edible; some may even be toxic. Fresh seaweed is commonly used in seaweed salads.
Dried seaweed has been dehydrated but will contain more moisture than roasted seaweed.
Most commercially available seaweed is roasted, which means it has undergone an additional heating process that makes it crisper than dried seaweed. This includes the variety called nori, which is the standard sushi seaweed. Nori comes in thin, dry strips often wrapped around a sushi roll.
How Much Is Too Much Seaweed?
While seaweed may offer some health benefits, eating too much may cause health risks due to its iodine and heavy metal content.
Iodine
Most people in the United States and other developed countries get enough iodine in their diets. Iodine intake over 1,100 micrograms (mcg) is considered dangerous. Although iodine is essential for thyroid health, getting too much can lead to goiter, elevated TSH levels, and hypothyroidism.
If you include seaweed in your diet, keep your total iodine consumption under 1,100 mcg.
Heavy Metals
Heavy metals, such as arsenic, mercury, cadmium, or lead, can contaminate seaweed in the water where it grows. Washing and cooking may not effectively remove them.
Heavy metals such as mercury can impair thyroid function. Your thyroid health may take a double hit from large amounts of seaweed.
While the amount of heavy metals in seaweed may be relatively low, regularly eating it can lead to heavy metal toxicity. One study showed healthy adults who ate large amounts of seaweed had elevated levels of arsenic.
Potential Side Effects
Side effects of excess dietary iodine may include:
- Burning in the mouth, throat, and stomach
- Coma
- Diarrhea
- Fever
- Nausea and vomiting
- Stomach pain
- Weak pulse
Symptoms of hypothyroidism (low thyroid function), which may result from eating too much iodine, may include:
Heavy metals may cause the following side effects:
- Cancer
- Congenital disabilities
- Damage to blood vessels
- Digestive problems
- Immune system dysfunction
- Kidney dysfunction
- Nervous system disorders
- Skin lesions
Research suggests that eating seaweed once or twice a week is likely safe. However, use caution when consuming it more often than that. If you are concerned, speak with a healthcare provider before consuming it.
Sourcing Reputable Seaweed
Many types of seaweed are available online and in stores, especially in Asian markets. These products are not required to list iodine or heavy metal content.
However, most commercial seaweed is farmed, not harvested from the sea, which should reduce the risk of heavy metal contamination. The label or the company’s website may provide information about the seaweed’s source.
When buying dried seaweed, be sure it’s in a sealed, air-tight container. It shouldn’t be especially crumbly or look gray. Properly packaged dry seaweed should last a long time.
Ways to Enjoy Seaweed
There are many ways to incorporate seaweed into your diet, such as:
- Use it to flavor broths and soups.
- Toss with sesame oil, rice wine vinegar, and cucumber for a quick seaweed salad.
- Sauté in garlic and oil.
- Make a sushi roll.
- Add to noodle dishes and casseroles.
- Add to stir-fry dishes.
- Sprinkle on top of salads.
- Add to smoothies.
- Eat by itself as a snack.
Summary
Although more research is needed, some evidence shows seaweed may benefit thyroid function, blood sugar, heart health, and more. Seaweed can be eaten raw, dried, or roasted.
While seaweed is nutrient-rich, too much may cause health risks due to the iodine and heavy metal content. Speak to a healthcare provider if you’re concerned before consuming seaweed.
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