Calories in Seaweed: Nutrition Facts & Serving Sizes
Per 2 tbsp (1/8 cup) (10g)
Per 100g
Source: USDA FoodData Central, SR Legacy, March 2026.
A 2 tbsp serving of seaweed (10g) contains just 2.6 calories, making it one of the most nutrient-dense, calorie-free foods available. Per 100g, seaweed provides 26 calories with 6.8g of carbs, 0.5g of protein, and 0g of fat. Despite the negligible calorie count, seaweed contains 67mg of magnesium per 100g (about 16% of the daily value), 54mg of calcium, and 85mcg of folate. The magnesium content is the standout: seaweed provides more magnesium per gram than most vegetables. Seaweed is also one of the best food sources of iodine, which supports thyroid function. The vitamin K content of 2.3mcg per 100g contributes to blood clotting and bone metabolism. Common edible seaweeds include nori (used in sushi), wakame (used in miso soup), and kelp. For anyone cutting calories, seaweed is essentially free food that adds minerals and umami flavor.
Nutrition Highlights
Calories by Serving Size
| Serving | Cal | Protein | Carbs | Fat | Fiber |
|---|---|---|---|---|---|
| 2 tbsp (1/8 cup) (10g) | 2.6 | 0.1g | 0.7g | 0g | 0.1g |
| 100g | 26 | 0.5g | 6.8g | 0g | 0.5g |
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Full Nutrition Facts (per 100g)
| Nutrient | Amount | % Daily Value |
|---|---|---|
| Calories | 26 | 1% |
| Protein | 0.5g | 1% |
| Total Fat | 0g | |
| Total Carbohydrates | 6.8g | 2% |
| Dietary Fiber | 0.5g | 2% |
| Sugars | 0.3g | 1% |
| Sodium | 9mg |
Vitamins & Minerals (per 100g)
| Nutrient | Amount | % Daily Value |
|---|---|---|
| Calcium | 54mg | 4% |
| Iron | 1.9mg | 11% |
| Potassium | 226mg | 5% |
| Magnesium | 67mg | 16% |
| Phosphorus | 5mg | 0% |
| Zinc | 0.6mg | 5% |
| Selenium | 0.7mcg | 1% |
| Folate | 85mcg | 21% |
| Niacin (B3) | 0.1mg | 1% |
% Daily Values based on a 2,000 calorie diet (FDA reference).
Health Benefits of Seaweed
Seaweed is a nutrient-dense, ultra-low-calorie food that provides minerals most land vegetables cannot. The 67mg of magnesium per 100g supports muscle contraction, sleep quality, and energy production. Many people who train regularly are low in magnesium, and seaweed is an easy dietary source alongside nuts and seeds.
Seaweed is one of the few food sources of iodine, a mineral critical for proper thyroid function. The thyroid regulates metabolism, energy levels, and hormone production. Adequate iodine intake is essential for anyone managing body composition. Kelp in particular is very high in iodine, though overconsumption can cause thyroid issues, so moderation matters.
The 85mcg of folate per 100g is significant. Folate supports DNA synthesis, red blood cell production, and cellular repair, all of which matter for anyone doing heavy resistance training. Seaweed also contains 54mg of calcium per 100g, which contributes to the daily calcium target alongside dairy and fortified foods.
Seaweed has been studied for its fiber content, specifically soluble fiber (like fucoidan and alginic acid) that may support gut health and slow digestion. It is a versatile ingredient that can be added to soups, salads, or eaten as a snack in dried form.
Dietary Considerations
Seaweed is naturally gluten-free, vegan, and keto-friendly at only 6.8g of carbs per 100g. It is excellent for weight loss given its near-zero calorie count. The main concern with seaweed is iodine overconsumption if eaten in large quantities daily, particularly with kelp varieties. Nori sheets used for sushi are lower in iodine and safe for frequent use. Sodium is very low at 9mg per 100g, making seaweed a sodium-friendly food.
Daily Intake (100g)
100g of seaweed provides 1% of a 2,000-calorie diet.
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Frequently Asked Questions
How many calories in seaweed?
A 2 tbsp serving of seaweed (10g) has about 2.6 calories. Per 100g, seaweed contains 26 calories. It is one of the lowest-calorie foods you can eat.
Is seaweed good for weight loss?
Yes, seaweed is excellent for weight loss. With just 2.6 calories per serving, it adds virtually no calories while providing minerals and fiber. It works well as a low-calorie side dish or snack.
How much protein in seaweed?
Seaweed contains 0.5g of protein per 100g. A 2 tbsp serving has only 0.05g of protein. Seaweed is not a meaningful protein source and should be used as a mineral-rich side dish.
Is seaweed high in iodine?
Yes, seaweed is one of the richest food sources of iodine, especially kelp. Iodine supports thyroid function and metabolism. However, excessive iodine from kelp can actually disrupt thyroid function, so variety matters. Nori is a safer, lower-iodine option for daily use.
Is seaweed keto-friendly?
Yes, seaweed is keto-friendly with only 6.8g of carbs per 100g and almost no calories per serving. A typical serving of nori sheets or dried seaweed adds minimal carbs to your daily total.
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