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A Functional Medicine approach to Giardia

So you’ve had a stool test and it looks like you have a Giardia infection. In this article we are going to review what giardia is, how you might have contracted this parasite, commonly associated symptoms, the difference between chronic vs acute infections and then review some nutrition considerations.

Giardia is a common human parasite that was first described back in 1681. It can cause significant morbidity; however, natural medicine has great potential to influence the course of Giardia infection, particularly those that are chronic in nature.

It is a microscopic protozoan parasite that is considered to be the most common cause of diarrheal disease worldwide. Humans infected with Giardia may have diarrhea, vitamin and mineral deficiencies, weight loss and failure to thrive.

Giardia has a teardrop shape. It has four thin filaments protruding from its body. These structures are known as flagella and they help Giardia to move. Giardia also has a disc that allows it to attach to the lining of the small intestine.

In chronic cases of Giardia, a blend of nutrition intervention with specific plant based therapeutics should be the first line of therapy and antibiotics saved for more acute or stubborn cases because of the known potential side effects of antibiotic therapy.

Giardia Lifecycle

Unlike some other parasites, Giardia’s lifecycle is very simple. There are only two forms of the organism, active trophozoites and inactive cysts.

The cysts are passed out in the stool and are picked up by humans or animals that eat or drink from contaminated sources.

When Giardia cysts are ingested, the cysts are exposed to stomach acid and digestive enzymes. This process is called excystation and results in Giardia becoming the active trophozoite form.

Giardia Transmission

Giardia is usually transmitted through contaminated water. However person-to-person transmission and food contamination are also possible.

Summary of possible transmission routes:

  • Water
  • Person-to person in areas of poor hygiene
  • Children in day care centers
  • Food

Giardia occurs in both humans and animals, which allows for frequent contamination of surface water supplies.

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Symptoms of Giardia

Giardia gained notoriety because of its ability to cause diarrhea, but it can also cause many other symptoms. Because the organisms attach to the intestinal lining, they can cause a blanketing effect where large areas of intestine are covered. This leads to the inability to digest and absorb food properly, inevitably leading to malnutrition, even in people who are eating a healthy diet.

Some of the most common symptoms include diarrhea, fatigue, gas and bloating, abdominal cramping, nausea, weight loss, fever, constipation and general irritable bowel syndrome type symptoms. In some cases it has also been linked with urticarial and reactive arthritis (Hill, 2001).

Notice how Giardia can cause general symptoms of malaise, as well as seemingly unrelated symptoms such as nausea, urticaria (a skin condition) & arthritis. In my experience, any unwanted visitor to our digestive system – be it a parasite, fungus or bacteria – has the ability to cause pretty much any symptom you can think of because once the digestive system is put into a state of imbalance this resonates throughout other systems in the body.

Chronic Giardia Infections

Initially, Giardia tends to cause acute diarrhea. Studies have shown that these acute infections can be severe enough to lead to hospitalisation. However, most doctors do not acknowledge that the infection can become chronic.

Because Giardia attaches to the wall of the intestine, it can cause damage to the delicate structures that help in the digestion and absorption of nutrients, known as the villi. This can make it hard for the digestive system to absorb fat, vitamins such as A, D, E, K and B12, protein, iron and lactose.

A person who has vitamin A, B12, fat, protein and iron deficiency may develop symptoms consistent with those deficiencies. So even if there are only very mild digestive symptoms, fatigue, skin problems, neural problems and other symptoms can quickly develop simply because the Giardia prevents adequate nutrition reaching the body.

Giardia Nutrition Considerations

The main aims of dietary modification in giardiasis should be to reduce the acute symptomatology, promote immune function, and inhibit growth and replication of Giardia. These aims can be achieved by consuming a whole-food, high fibre, low simple-carbohydrate and lower-fat diet along with some targeted supplementation.

Consuming foods low in simple carbohydrates limits the amount of sugars available in the intestinal lumen, which may lessen the osmotic draw of water into the intestinal lumen, and reduce diarrhea if that is a symptom.

Reducing the intake of fat might reduce nausea and diarrhea symptoms. Dietary fat stimulates the release of bile acids, something giardia depends upon for their survival in the small intestine.

As well as the above changes utilising functional pre and probiotic foods and wheat germ in some individuals appears to be beneficial in giardia clearance.

Dairy Removal

Studies have shown Giardia infection, whether symptomatic or asymptomatic, can reduce the production of lactase in the small intestine, resulting in lactose malabsorption and its resultant diarrhea.

Dr. David R. Hill recommends that:

“All patients should be instructed to avoid lactose-containing products, so that any recurrent diarrhea will not be confused with relapse of infection”.

Prebiotic Foods

Prebiotics are the compounds and fibers in foods that feed beneficial bacteria. In terms of giardia, prebiotics can increase short chain fatty acids which helps support the integrity of the intestinal lining and increase mucin production which can assist in giardia clearing.

In some instances bloating, pain and flatulence can increase, thus start low and take it slow when introducing in prebiotic foods, especially if other digestive imbalances are present.You can learn more in my article – What are the best prebiotic and priobiotic foods.

Some specific dietary recommendations

Functional foods include:

  • Probiotic foods minus the dairy based probiotic food options, in particular sauerkraut and Kimchee because of their good content of the probiotic strain L.plantarum. This particular strain has been shown to have specific giardia inhibition qualities.
  • 2tbsp of wheatgerm 3 x per day may be beneficial in those who are gluten tolerant, although it has to be said many people with such an infection often have issues with gluten that have developed.
  • Choose lean proteins and minimise the amount of fat added to meals to help reduce bile acid production.
  • Avoid the consumption of refined sugar and grains.
  • If tolerated, consume some whole grain, beans and lentils as your carbohydrate foods.
  • Emphasis on good quality protein.

Specialist support

As well as nutritional adjustments, specialist support is often required. As mentioned there are natural therapies that have been shown to be useful against Giardia. These should be implemented under the eye of a professional to ensure it is the right therapy at the right time.

I have found broad-spectrum antimicrobial herbal blends alongside high dose oregano oil to be particularly useful and research has indicated that oregano oil especially can have anti-giardia effects.

I would also typically recommend some level of intestinal barrier support.

Animal studies have indicated that cinnamon and ginger appear to have suppressive effects on Giardia.

 If you follow the 5R approach to gastrointestinal health, emphasis on the removal and repair followed by or alongside repopulation (pro & prebiotic therapy) is typically very supportive.

Learn how using the Functional Medicine 5R approach can help address your digestive issues in my article How to imrove your digestive health – the 5R approach.


  • Hill, 2001, in Principles & Practice of Clinical Parasitology, edited by Gillespie & Pearson).
  • Vega-Franco L, Meza C, Romero JL, et al. Breath hydrogen test in children with giardiasis. J Pediatr Gastroenterol Nutr 1987;6:365-368 Vesy CJ, Peterson WL. Review article: the management of Giardiasis. Aliment Pharmacol Ther 1999;13:843-850.
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  • Sakata T. Influence of short chain fatty acids on intestinal growth and functions. In: Kritchevsky D, Bonfield C, eds. Dietary Fiber in Health and Disease. New York, NY: Plenum Press; 1997:191-199.
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  • Abdel Gadir AM, Mohamed M, Abd-el-Malek Y, et al. Indigenous fermented foods involving an acid fermentation. In: Steinkraus KH, ed. Handbook of Indigenous Fermented Foods. New York, NY: Marcel Dekker; 1996:111-148.
  • Cheigh HS, Park KY. Biochemical, microbio- logical, and nutritional aspects of kimchi (Korean fermented vegetable prod
  • Altern Med Rev 2003;8(2):129-142

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