Could seaweed reduce greenhouse gas in the gut?
Could seaweed reduce greenhouse gas in the gut?

Could seaweed reduce greenhouse gas in the gut?

By Jordan Haworth, Clinical GI Physiologist

Climate change is an immediate global concern, and one of the major contributors is greenhouse gas production by animal agriculture. Specifically, methane, which is belched (not farted) by cows, has a warming effect around 30 times more potent than carbon dioxide.

Ruminants, such as cattle and sheep, have four stomachs with the capacity to harbour enormous amounts of methane-producing microorganisms.  These bugs, or methanogens, are also found in the guts of humans and can lead to digestive issues, including constipation and bloating.  However, one breed of sheep off the coast of Scotland are producing almost no methane thanks to a special diet of seaweed.

North Ronaldsay is the northernmost Orkney Island where the sheep have been penned to the shoreline since 1832.  In that time, they have adapted to a diet of consisting solely of seaweed washed up on the beaches.  Uniquely, the North Ronaldsay sheep produce substantially less methane in comparison to their grass-fed counterparts.  In addition, recent research has shown that incorporating seaweed into animal feed reduced methane emissions by up to 99%1.  These findings suggest not only a potential benefit for the environment, but a potential benefit for people with excessive methane production.

Methane is present in around 30 – 50% of the world’s population2.  In the human gut, methane is produced almost exclusively by archaea and the most abundant species is Methanobrevibacter smithii3.  However, excessive methane production in the gastrointestinal tract has been associated with functional bowel disease, such as constipation and bloating, as well as obesity and reduced weight loss following bariatric surgery.  Methane produced in the gut is transported to the lungs and exhaled in breath, so methane can easily be detected by performing a hydrogen and methane breath test.

Interestingly, the Japanese population has a low breath methane concentration compared to other countries4.  Also, they have significantly depleted levels of the archaeon Methanobrevibacter smithii5.  What makes this so unusual? Well, more than half of the Japanese population consumes seaweed regularly. Unlike most of the West, the Japanese have digestive enzymes that can break down the specific carbohydrates found in seaweed called porphyrans6.  In addition, one study found that eating fermented seaweed for 4 weeks promoted the growth of lactic acid bacteria in humans7.  Seaweeds are also rich in polyphenols and these compounds have been shown to modulate the gut microbiota by increasing beneficial bacteria, such as Bifidobacterium and Lactobacillus populations8.

Treating excessive methane production can be complicated because archaea are more closely related to us than bacteria, which renders most antibiotics as redundant.  Although, studies show that reducing breath methane levels with a combination of antibiotics, rifaximin and neomycin, also improved symptoms in IBS patients with constipation9.  The most favourable responses are seen when there is an eradication of methane to <10 ppm on hydrogen and methane breath testing.

Unfortunately, methanogens are hardy microbes and often grow back.  There are other researched ways to treat methane including herbal supplements and probiotics; however, there is currently no scientific evidence for the use of seaweed to treat excessive methane production in humans.

Seaweed appears to be a promising resource for reducing the environmental impact of methane whilst also highlighting new research opportunities for targeting methane production in humans. In the meantime, I’ll take the sushi rolls with a side of wakame, please.


  1. Roque BM, Brooke CG, Ladau J, Polley T, Marsh LJ, Najafi N et al. Effect of the macroalgae Asparagopsis taxiformis on methane production and rumen microbiome assemblage.  Animal Microbiome.  2019; 1 (1): 3.
  2. Triantafyllou K, Chang C, Pimentel M. Methanogens, methane and gastrointestinal motility.  Journal of Neurogastroenterology and Motility.  2014; 20 (1): 31 – 40.
  3. Kim G, Deepinder F, Morales W, Hwant L, Weitsman S, Chang C et al. Methanobrevibacter smithii is the predominant methanogen in patients with constipation-predominant IBS and methane on breath.  Digestive Diseases and Sciences.  2012; 57 (12): 3213-8.
  4. Morii H, Oda K, Suenaga Y, Nakamura T. Low methane concentration in the breath of Japanese.  Journal of UOEH.  2003; 25 (4): 397 – 407.
  5. Nishijima S, Suda W, Oshima K, Kim SW, Hirose Y, Morita H et al. The gut microbiome of healthy Japanese and its microbial and functional uniqueness.  DNA research: an international journal for rapid publication of reports on genes and genomes.
  6. Hehemann J-H, Correct G, Barbeyron T, Helbert W, Czjzek M, Michel G. Transfer of carbohydrate-active enzymes from marine bacteria to Japanese gut microbiota.    2010; 464 (7290): 908 – 12.
  7. Ko SJ, Kim J, Han G, Kim SK, Kim HG, Yeo I et al. Laminaria japonica combined with probiotics improves intestinal microbiota: a randomized clinical trial.  Journal of Medicinal Food.  2014; 17 (1): 76 – 82.
  8. Due #xfa, as M, Mu #xfa, oz-Gonz et al. A Survey of Modulation of Gut Microbiota by Dietary Polyphenols.  BioMed Research International.  2015; 2015: 15.
  9. Pimentel M, Chang C, Chua KS, Mirocha J, DiBaise J, Rao S et al. Antibiotic treatment of constipation-predominant irritable bowel syndrome.  Digestive Diseases and Sciences.  2014; 59 (6): 1278 – 85.