The Dual Nature of Rhubarb: Diuretic and Laxative
For centuries, various rhubarb preparations have been recognized in traditional medicine for their impact on the digestive and urinary systems. However, it is crucial to differentiate between the mild diuretic properties and the more prominent laxative effects, especially when consumed as a stewed dish. The key to understanding this lies in the plant's bioactive compounds, primarily the anthraquinones found in the roots and stalks.
Anthraquinones and Their Effects
When you consume rhubarb, your gut bacteria convert certain anthraquinone glycosides into their active forms, which are anthrones. These compounds have a significant influence on your body, and their effect is largely dependent on the dosage:
- Laxative Effect: At higher concentrations, the anthraquinones stimulate the muscles of the large intestine, promoting stronger peristaltic contractions that speed up bowel movements. This purgative effect is what most people experience when consuming larger quantities of rhubarb. The resulting diarrhea or increased bowel movements can lead to a loss of fluids and electrolytes from the body.
- Diuretic Effect: While also present, the diuretic effect—the increase in urine output—is less pronounced in stewed rhubarb than the laxative action. Some studies suggest that specific compounds, like rhein, possess diuretic and kidney-protective properties, but research indicates that ethanol extracts show more significant diuretic activity than aqueous ones. This is a critical distinction, as stewing rhubarb involves an aqueous extraction method.
- Dose-Dependent Action: Herbalists have historically used different dosages to achieve specific outcomes. A smaller dose of rhubarb might have a tonic effect on the liver, while a larger dose acts as a powerful cathartic.
The Impact of Oxalic Acid
Another major consideration when eating stewed rhubarb is its oxalic acid content. While the leaves are toxic and should never be consumed due to extremely high levels of oxalic acid, the edible stalks also contain this compound.
Key facts about rhubarb and oxalic acid:
- Oxalic acid is a natural compound found in many plants.
- Rhubarb is particularly rich in oxalates.
- For individuals with a history of kidney stones, excessive intake of high-oxalate foods like rhubarb can increase the risk of forming calcium oxalate stones.
- Cooking methods can help reduce the soluble oxalate content. Boiling rhubarb in plenty of water and discarding the liquid can significantly lower oxalate levels.
- Eating calcium-rich foods, such as dairy products, alongside rhubarb can help bind the oxalic acid in the digestive tract, preventing its absorption.
Diuretic Effect vs. Laxative Effect: A Comparison
To clarify the primary action of stewed rhubarb, here is a breakdown of its two main physiological effects:
| Feature | Diuretic Effect | Laxative Effect |
|---|---|---|
| Primary Mechanism | Increases urine production in the kidneys. | Stimulates peristalsis in the large intestine. |
| Active Compounds | Primarily rhein, but effect varies based on extraction method. | Primarily anthraquinone glycosides, converted to anthrones. |
| Effect in Stewed Rhubarb | Minor or minimal, as aqueous extracts are less potent diuretics. | Prominent, as cooked rhubarb retains these laxative compounds. |
| Fluid Loss Pathway | Via urination. | Via bowel movements, potentially leading to dehydration. |
| Speed of Onset | Generally quicker acting than laxative effect if present. | Delayed, often taking around 8 hours post-ingestion. |
| Associated Concerns | Potential for electrolyte imbalance with excessive intake. | Dehydration and electrolyte depletion, especially with overuse. |
How to Safely Enjoy Stewed Rhubarb
While the laxative effect is the most likely outcome, you can still enjoy rhubarb safely by following these tips:
- Focus on the Stalks: Always use only the stalks for consumption and discard the leaves, which are toxic due to high oxalic acid.
- Prepare with Calcium: Consider pairing stewed rhubarb with a dairy product like yogurt, milk, or cream. The calcium helps bind the oxalic acid, reducing its absorption and the risk of kidney stone formation.
- Cook and Discard Water: For recipes where it's feasible, boil the rhubarb and discard the cooking water to remove some of the soluble oxalates.
- Consume in Moderation: As with many things, moderation is key. Regular, excessive intake of rhubarb can disrupt your electrolyte balance and potentially cause other health issues.
Conclusion
While some traditional herbal uses classify rhubarb as a diuretic, the more clinically significant effect of eating stewed rhubarb is its strong laxative action due to anthraquinones. This cathartic effect can cause increased fluid loss through the bowels, which is often misinterpreted as a diuretic function. The plant's high oxalic acid content poses a risk for individuals with kidney issues, but proper preparation and moderate consumption can mitigate this. For most people, enjoying stewed rhubarb in moderation is perfectly safe and a delicious seasonal treat. If you are taking diuretic medications or have kidney concerns, it is best to consult a healthcare provider before consuming significant amounts.
A note on the medicinal use of rhubarb
Historically, rhubarb root has been a staple in herbal remedies. For those interested in the broader traditional uses and pharmacological studies of rhubarb, more detailed information can be found via reputable sources detailing the plant's constituents and historical applications, which have often involved both diuretic and purgative actions.
Visit ScienceDirect for an overview of Rhubarb's traditional and scientific uses
What is the difference between a diuretic and a laxative?
- Diuretic: A substance that increases the production and excretion of urine from the body, typically by the kidneys.
- Laxative: A substance that stimulates bowel movements to facilitate the passage of stool, primarily affecting the digestive system.
How does rhubarb have both diuretic and laxative effects?
- The presence of anthraquinone derivatives in rhubarb is responsible for its dual action. At varying concentrations and with different extraction methods, these compounds can influence both kidney function (diuretic) and intestinal motility (laxative).
Is cooked rhubarb still a diuretic?
- The evidence suggests that cooked rhubarb's diuretic effect, caused by rhein, is less potent than its laxative effect. The laxative action, which causes fluid loss, is often more noticeable. Ethanol extracts, not aqueous ones from cooking, show a more remarkable diuretic effect.
What are the risks of consuming too much rhubarb?
- Excessive consumption of rhubarb can lead to dehydration and low potassium levels due to its strong laxative effect. For those with kidney issues, the high oxalic acid content increases the risk of kidney stones.
Can stewed rhubarb cause kidney stones?
- For individuals prone to calcium oxalate kidney stones, eating large amounts of rhubarb can be a risk factor due to its high oxalate content. However, cooking methods and pairing with calcium can reduce this risk significantly.
Is eating rhubarb leaves safe?
- No. Rhubarb leaves are toxic because they contain very high concentrations of oxalic acid. They must be removed and discarded before cooking or eating the stalks.
What is the best way to prepare rhubarb to reduce oxalic acid?
- To reduce the soluble oxalate content, you can boil the rhubarb stalks in plenty of water and then discard the cooking water. Additionally, consuming rhubarb with calcium-rich foods can help bind the oxalic acid in your gut.
