Seaweeds are among the most ancient and chemically complex organisms on Earth, living in one of the most dynamic environments on the planet: the intertidal zone, where land meets sea. In this constantly shifting landscape of wave force, tidal change, and exposure, seaweeds have evolved remarkable adaptations—using the very elements that challenge their existence to thrive. In this way, seaweeds are profoundly shaped by the environments in which they grow. Dynamic marine conditions influence their growth, chemistry, and even their appearance. In many cases, environmental factors can outweigh genetics in shaping a seaweed’s appearance—individuals of the same species may look strikingly different from one location to another, sometimes requiring genetic analysis for accurate identification—a visible reminder of how profoundly seaweeds interact with their world.

Because seaweeds are so deeply shaped by the environments in which they live, working with them as foods and medicines asks us to expand how we think about the herbal repertoire. The seaweeds that we use in our home kitchens continually point us back to the places from which they come. While all medicinal plants are shaped by place, the chemistry of seaweeds is so directly influenced by dynamic marine environments that their ecological context remains especially important to how we understand and work with them. In many cases, these environmental influences can be observed directly in home preparations. Differences in mucilage content, flavor, and extraction characteristics between seasonal harvests are often readily experienced in home uses of seaweeds in a way that is less visible with many terrestrial herbs.

This is where the practice of Marine Herbalism lives—at the intersection of ecology, chemistry, nourishment, and relationship. Seaweeds are shaped by their environments, and in turn, this shaping directly influences how they interact with our bodies when we eat them. Working with seaweeds is therefore not just a study of their chemistry, but also a practice of building relationships with the ecosystems that give rise to these unique and fascinating organisms.

What Makes Seaweeds Unique

Unlike terrestrial plants, which absorb nutrients primarily through their roots, seaweeds absorb nutrients directly across their tissues from surrounding seawater. Seaweeds also experience a broader and more rapidly changing suite of environmental conditions that continually influence their growth, physiology, and chemistry. Intertidal seaweeds are exposed to both terrestrial and marine environmental stressors: during low tide they may experience drying, freezing, UV exposure, and rain or other weather patterns; while submerged they experience changing salinity, nutrient availability, ocean chemistry, and wave forces. Because these environmental influences exert such a strong effect on seaweed biology, the nutrient and bioactive composition of seaweeds can vary significantly across species, seasons, locations, growth stages, and changing environmental conditions. In this sense, wild seaweeds behave less like standardized crops and more like highly dynamic organisms, and this variability is one of the reasons they are both powerful and complex as foods and medicines.

While generalizations can be made about different seaweed groups and species, in many cases it is impossible to know the precise nutrient or phytochemical content of an individual seaweed sample without directly testing that sample. For instance, product testing has in some cases revealed dramatic differences between the nutrient levels indicated on the label and those found in the seaweed itself. What’s more, the chemistry of seaweeds continues to change after harvest—preparation methods, drying, storage, and other handling practices can all influence nutrient composition and bioavailability.

Living predominantly in nutrient-rich marine ecosystems, seaweeds also have access to a wider range of minerals and trace elements than most terrestrial plants, and they possess biological mechanisms that allow them to accumulate and concentrate certain elements in amounts far greater than those typically found in land plants. As a result, seaweeds contain a number of nutrients and compounds that are either unique to them or occur only in relatively small amounts in terrestrial herbs, notably concentrated iodine and diverse trace elements that may be limited in terrestrial soils.

Their unusual chemistry, distinctive phytochemicals, and remarkable capacity to concentrate minerals and trace elements help explain why seaweeds occupy such a unique place in the herbal repertoire.

Nutrients and Bioactive Compounds in Seaweeds

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(If you’d like a broader overview of seaweeds as food and medicine—including iodine nuance, polysaccharide actions, and species selection—you may also enjoy my earlier overview essay Seaweeds in the Herbal Kitchen.)

Food as Medicine: Eating Seaweeds as a Foundational Practice in Marine Herbalism

Seaweeds are one of our greatest food-based medicines; in fact, they could be considered one of our lesser-known “superfoods.” They contain a wide range of nutrients and phytochemicals—often in significantly higher concentrations than most land-based foods. The following simple guidelines offer a clear framework for incorporating seaweeds safely and effectively into your daily diet.

Eat small amounts of seaweed daily.

As a food-based medicine, eating seaweeds is the best way to use them for general nutritive and health-supportive purposes—they don’t require complicated extraction techniques for you to receive their benefits. Using them in a water-based or rehydrated form allows access to most of their nutrients and medicinal compounds. And because these nutrients are so concentrated, you only need small amounts—eating a little every day is one of the best ways to build a relationship with seaweeds and steadily replenish the body with their dense and diverse nutrients.1 Small amounts daily can also help folks who are new to eating seaweeds cultivate specific seaweed-digesting gut bacteria that support digestion and absorption of seaweed constituents.

What is a small daily amount? The generally recommended dosage for adults (approx. 175 lbs) is 3–5 g dry weight (DW) daily or 1–1.5 oz per week—a standard established by my mentor, Ryan Drum, and confirmed in various other international resources about seaweed intake. About 5 g equals roughly 1 teaspoon of powdered seaweed, depending on the fineness of the powder (see image below). The average intake of seaweeds globally ranges from 2.6–8.5 g/day DW and is higher in Asian countries that have a culinary tradition steeped in seaweed use. While most sources recommend the lower end of this typical consumption range, some experts have observed notable benefits from the higher end (8.5g/day DW).

Eating small amounts daily also generally keeps consumption within safe limits for contaminants as established by international food safety organizations. Seaweed contamination and nutrient levels vary widely by growing conditions, location, and species. Contamination and consumption safety are also complex and highly contextual topics: just because a contaminant is present in the water does not mean the seaweed will absorb it—and just because a contaminant is present in the seaweed does not mean it is bioavailable to the human body. This topic is explored in more detail in my ongoing Seaweed Detox series. Regardless, generally speaking, 3–5 g daily is a good balance nutrient-wise for most people and low-risk with regard to safety concerns. A lower, more cautious dosage of 3–7 g once or twice per week is recommended by some researchers for certain health conditions or low-iodine or other therapeutic diets (Vogliano et al., 2024).

With these standards in mind, I also want to emphasize that optimal seaweed consumption amounts are highly individual. Some of the reasons for this include:

• The iodine threshold varies significantly from person to person and some people may respond to iodine differently due to gut health or nutrient status.

• Everyone is unique in their health and lifestyle picture, in the foods that they eat on a daily basis, and in herb and nutrient needs.

• There are also several situations where seaweeds may best be used in limited amounts or not at all (see Storage, Stability, and Safety section).

Eat the seaweed rainbow (reds, greens, and browns).

Since nutrient and phytochemical profiles of seaweeds are highly variable—perhaps more so than land plants—depending on season and growing conditions, among other factors, mixing and matching seaweeds is one of the best ways to get a more balanced complex of nutrients and bioactive compounds into your diet. Because seaweeds from each class tend to have similar nutrient and phytochemical profiles, mixing from the three main classes—red (e.g., Irish Moss/Chondrus crispus, Dulse/Palmaria palmata), green (Sea Lettuce/Ulva spp.), and brown (kelps such as Nereocystis luetkeana and Laminaria/Saccharina spp.; Bladderwrack/Fucus spp.)—ensures a diversity of nutrients and phytochemicals.

Recommendations for proportions from each seaweed class are variable. While Ryan Drum has recommended eating brown to red seaweeds in a ratio of 2:1 because of the generally higher mineral profile of brown seaweeds, other folks recommend eating brown seaweeds such as kelp, kombu, and bladderwrack only 1-2 times a week. Certainly this lower brown seaweed consumption rate may be more appropriate for some folks if the seaweeds are uncooked and there is concern about too much iodine consumption. There are few green seaweeds commonly available or used in food-based preparations—the main one is Sea Lettuce (Ulva spp.), a lower iodine-containing seaweed with a mild flavor that is good for daily use.

Eat a variety of seaweed species.

Varying the species you eat within each class is also a way to diversify the nutritional compounds you are getting from seaweeds. Despite similarities in nutrient and phytochemical content amongst seaweeds of the same class, each species tends to accumulate more of certain minerals and less of others and has its own unique polysaccharide profile and content (more on seaweed polysaccharides in a moment). For instance, Bullwhip Kelp (Nereocystis luetkeana) is especially high in minerals (up to 40% dry weight), particularly potassium and magnesium salts, compared to other brown seaweeds, and kombu (Laminaria/Saccharina spp.) has a significantly higher iodine content (up to 5000 µg/g) compared to other brown seaweeds such as Wakame (Alaria spp./Undaria pinnatifida) (295 µg/g).

Eat cooked and uncooked seaweeds.

Varying your use of cooked and uncooked seaweeds as an integrated part of your diet helps to provide a balance of seaweed nutrients and phytochemicals, which can be are more or less available, depending on the type of preparation. Soaking and discarding soak water—or cooking and allowing steam to evaporate—can significantly reduce the iodine content of seaweeds if that’s a concern. Cooking or decocting seaweeds in water can also enhance bioavailability of certain nutrients such as minerals, polysaccharides, amino acids, and some vitamins (Mabeau & Fleurence, 1993; Holdt & Kraan, 2011) while uncooked (but usually dried) or gently rehydrated seaweeds retain the more heat-sensitive compounds such as essential fatty acids and vitamins (such as Vitamin C), carotenoids, and polyphenols.

From Food to Formulation: Extracting Seaweeds as Herbal Medicine

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This article series explores the complex relationship between seaweeds, minerals, metals, and digestion. While seaweeds offer incredible nutritional benefits and are celebrated for their detox potential, they also absorb contaminants from the environment. What does that mean for us—and for how we use seaweeds in our homes or with clients?

This multi-part series draws on a wide range of research, offering grounded insights into how seaweeds interact with both toxic and essential elements—such as heavy metals and minerals—from ocean to gut. Because research integrity is central to my work with seaweeds—and because some of these questions don’t yet have clear answers in the literature—this series will be released gradually over the coming months.

Here’s an overview of what’s to come in this article series:

📚 The Series

Part I – Seaweeds: Detoxifiers or Toxic Risk? (Free)
An introduction to the complexities and considerations around seaweeds and chelation—in the environment and in the digestive tract. Why this conversation matters.

Part II – Meet the Binders: Seaweed Compounds with an Affinity for Metals and Minerals
This section introduces the major bioactive compounds in seaweeds that give them their metal-binding powers. We’ll examine how the molecular structure and chelation behavior of various seaweed compounds—like polysaccharides—shape their unique interactions with metals and minerals.

Part III – Chelation and Digestion: Seaweeds in the GI Tract
How seaweed polysaccharides and chelated metals move through the digestive system. What happens to bound metals along the way?

Part IV – What Influences Heavy Metal Bioavailability?
How seaweed constituents may affect the body’s uptake of heavy metals and their impact on tissues.

Part V – Radioactive Isotopes in Seaweed
How radioactive elements like cesium and iodine-131 interact with seaweeds and the body.

Part VI – What About Extracts and Home Preparations?
Teas, tinctures, powders, and more: how preparation affects metal release and absorption.

🧭 Who This Article Series Is For

* Herbalists, nutritionists, and seaweed enthusiasts seeking clarity.

* People who eat seaweed and want to understand risks and benefits.

* Anyone curious about the science behind “detox” claims.

🔓 Part I is free to read—just click this link.

To access the full series, become a paid subscriber.

Part I: Seaweeds—Detoxifiers or Toxic Risk?

Seaweeds have long been valued for their ability to cleanse and create movement in the body, particularly in the digestive tract—and in recent years, they’ve gained popularity as a “natural detox” food and supplement. From Traditional Chinese Medicine, where seaweeds are used to disperse stagnation and clear toxins, to the enduring practice of seaweed bathing in Ireland, seaweeds have been used across cultures to support elimination, healing, and internal cleansing.

But what gives seaweeds this potential? What molecular tools allow seaweeds to bind—or compete with—metals and minerals in their environment, and possibly in your body when you ingest them?

Seaweeds are known as detoxifiers, not just for humans, but also in environmental applications—which is why there is concern among seaweed-consuming folks and some regulatory agencies about contaminants in seaweed. Contaminants are pervasive, though often dilute, in our ocean ecosystems, and many seaweeds have powerful mechanisms through which they can accumulate and concentrate some of these toxins, sometimes several times the concentration found in seawater.

However, the ways seaweeds interact with toxins—whether in the water or in our guts—is complex and not fully understood. We know that seaweed uptake of contaminants such as heavy metals in their ocean environment is highly variable by species and season. Depending on the form of a heavy metal and the conditions in which the seaweed is growing, it may not absorb contaminants immediately—or at all—even if they are present in the water for weeks. While concern about heavy metal contamination in seaweeds is well-founded, it’s important to remember these key points: just because a contaminant is present in the water does not mean the seaweed will absorb it—and just because a contaminant is present in the seaweed does not mean it is bioavailable to the human body.

Though seaweeds themselves may contain toxic heavy metals, some of the same compounds that allow them to bind heavy metals in the ocean may also help sequester toxins in the digestive tract and support their safe elimination from the body. But what’s actually happening in the growing seaweed’s environment—and in your digestive tract when you eat it—is not a black-and-white story, but a nuanced, ongoing exploration. Through this article series, I hope to begin unraveling this story. To date, I haven’t found any study that fully addresses all the intricacies involved—and because human trials involving contaminants are often ethically or financially unfeasible, much of what we do know comes from in vitro models or animal studies. In addition, most research focuses on isolated seaweed compounds, with relatively few studies examining whole-form seaweeds.

This article series will dive into the complex science behind seaweeds and chelation. Over the course of these articles, we’ll explore:

• seaweeds’ relationship to heavy metals, minerals, and radioactive elements in their environments;

• how seaweed phytochemicals bind to or interact with these elements in the human digestive tract;

• bioavailability—an informed look, based on available in vitro and animal studies, at how whole seaweeds and the elements they contain may be transformed or eliminated through digestion;

• how different preparation methods affect the bioavailability of toxins and may enhance seaweeds’ detox capabilities;

• how antioxidant compounds in seaweeds may mitigate oxidative stress caused by metal contaminants;

• the dynamics of seaweed–contaminant interactions in ocean environments—when and why uptake occurs, how it happens, and what it means for seaweed food safety.

The focus of this article series is mainly on seaweeds’ interactions with heavy metals, radioactive isotopes, and minerals, which are chemically similar. Other environmental contaminants, like PCBs, are also a concern, though they behave quite differently. This topic may be discussed in a future article.

Selected References

Besada, V., Andrade, J. M., Schultze, F., and González, J. J. 2009. “Heavy Metals in Edible Seaweeds Commercialised for Human Consumption.” Journal of Marine Systems 75(1–2): 305–313. https://doi.org/10.1016/j.jmarsys.2008.10.010

Circuncisão, A. R., Catarino, M. D., Cardoso, S. M., and Silva, A. M. S. 2018. “Minerals from Macroalgae Origin: Health Benefits and Risks for Consumers.” Marine Drugs 16(11): 400. https://doi.org/10.3390/md16110400

Davis, T. A., Volesky, B., and Mucci, A. 2003. “A Review of the Biochemistry of Heavy Metal Biosorption by Brown Algae.” Water Research 37(18): 4311–4330. https://doi.org/10.1016/S0043-1354(03)00293-8

García-Sartal, C., Barciela-Alonso, M. C., and Bermejo-Barrera, P. 2013. “Study of Cooking on the Bioavailability of As, Co, Cr, Cu, Fe, Ni, Se and Zn from Edible Seaweed.” Microchemical Journal 108: 92–99. https://doi.org/10.1016/j.microc.2012.10.003

Holdt, S. L., and Kraan, S. 2011. “Bioactive Compounds in Seaweed: Functional Food Applications and Legislation.” Journal of Applied Phycology 23(3): 543–597. https://doi.org/10.1007/s10811-010-9632-5

Huang, L., Lee, J.-Y., Park, Y.-K., and Lee, J. 2025. “Heavy Metals in Seaweed: Implications for Health Benefits, Risks, and Safety Regulations.” Journal of Agriculture and Food Research 21: 101830. https://doi.org/10.1016/j.jafr.2025.101830

Mac Monagail, M., Cornish, L., Morrison, L., Araújo, R., and Critchley, A. T. 2017. “Sustainable Harvesting of Wild Seaweed Resources.” European Journal of Phycology 52(4): 371–390. https://doi.org/10.1080/09670262.2017.1365273

Shanmugam, S., Shakila, R. J., Shalini, R., Aanand, S., Jayakumar, N., Arisekar, U., and Manikandan, B. 2024. “Bioaccessibility of Toxic Heavy Metals/Metalloids in Edible Seaweeds: Exposure and Health Risk Assessment.” Food Research International 182: 114135. https://doi.org/10.1016/j.foodres.2024.114135

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Seaweeds live in one of the most challenging environments on earth, where they are exposed to both excess sun, rain, and freezing temperatures at low tide and the incredible oceanic forces of currents and waves pounding the shore every 5-10 seconds: “because the density of seawater is ˜800 times greater than that of air, large waves can exert almost 100 times the force as hurricane winds on the same object” {Glenn 2013}. And yet, as a microscopic sporophyte or zygote, seaweeds are able to create secure attachment within minutes of settling on a rocky substrate. Through a small but mighty structure called a “holdfast,” almost all seaweeds hold themselves in place for their entire life cycle in this mechanically-challenging environment, rife with potential for detachment and death: “Seaweeds are exposed to a range of forces that could potentially dislodge them—drag, lift, buoyancy, and an accelerational force” {Friedland and Denny 1995}.

The study of seaweed holdfast adhesion at its core is the study of seaweeds’ constant interaction with and response to these dynamic oceanic conditions.

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Working with bitter plants as food and medicine has been integral to human culture for our whole existence. These plants remain important supportive health foods, but they are no longer pervasive in our modern American diets. The historical dietary and medicinal importance of bitter herbs is highlighted by fact that bitters formulas—ancient recipes featuring bitter herbs—and special uses of bitter plants developed independently among European, Asian, and South American cultures over 2000 years ago. Some of these secret proprietary formulas have been passed down for generations and are still available today as medicinal formulas or synergists for the perfect cocktail.1

The 1850s was the heyday of bitters in the U.S. with a vast array of hundreds of formulas marketed as cure-alls (before the FDA began to regulate product claims) and listed as a defining element in the original “cocktail,” which originated around this time. There are lots of awesome old bitters advertisements and artfully-designed original bottle labels that you can find images of online; I highly recommend taking a jaunt down “bitters memory lane” with a google search for these items. (In my last search I came across some bitters bottles from the late 1800s for sale on Ebay still containing their original liquid! Needless to say, I was tempted to buy and try them, but thought it wisest not drink a 150-year-old concoction, even if preserved in alcohol.) Many commercial bitters that originated in this boom time did not survive prohibition, and around that same time the rise of the American Medical Association and resulting decline to near extinction of home folk medicine and herbalism practices in the U.S. likely further contributed to the demise of these formulas.2 With the revival of American herbalism for several decades now and the trend toward interesting and innovative cocktail development over the past 20+ years, American bitters have been resurrected—in new specialty formulas in the cocktail and herbal product industry, as well as in the kitchens of foodies and home herbalists. In fact, some companies have even resurrected lost historical formulas and are producing them commercially again.3

I love bitters formulas—many of the common cocktail bitters, such as Campari—are some of my favorite stand-alone sipping beverages, and I often enjoy smaller amounts of bitters in soda water for a flavorful, low-alcohol beverage treat. For me, playing with bitters recipes is largely for the pure pursuit of delighting in herbaceous and interesting flavor combinations. I am also a firm believer in the incredible medicinal value that bitters formulas provide for folks as well—when done right, bitters help to stimulate and coordinate the digestive process, and good digestion is foundational for the health of many systems of the body and the basis for healing numerous conditions.

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Seaweeds are unique and important food offerings of the sea. It’s true, seaweeds contain a diversity and concentration of nutrients beyond that of their land-based counterparts, most notably minerals and micronutrients. You might even call them “superfoods”! While individual seaweeds contain unique nutrient profiles—determined by species and highly variable growing conditions—seaweeds contain a diversity of vitamins, antioxidants, essential fatty and amino acids, and notable quantities of mineral and trace elements not commonly found in land-based food sources. Most seaweeds contain iodine in significantly larger quantities than land plants and in a form that is more bioavailable than the iodine in other foods. Iodine content of seaweeds is highly variable by species—some seaweeds contain significantly more iodine than others, and some in the form of thyroid hormone precursors (MIT and DIT).2

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