Downside of spinach
Leafy greens are an important part of healthy diet. They contain high levels of fiber, iron, magnesium, calcium, potassium, very little carbohydrates, sodium and cholesterol. The dark greens supply a significant amount of folate, a B vitamin that promotes heart health and helps prevent certain birth defects.
Beta-carotene, the plant pigment is not only in carrots and yellow-orange veggies, it is also hiding in leafy greens. This is revealed to our eyes only when you see the bright multicolored leaves during fall when they lose chlorophyll, the pigment that makes them green. This protects us from sun’s harmful UV rays, it is a Natural sun screen. Chlorophyll is also a detoxifier, which means it binds to toxins and help liver in cleansing process.
Spinach is a nutrient-dense, dark green leafy vegetable. It’s tender texture and mild taste make it a favorite addition to smoothies, soups, and stir-fries. Spinach comes from the same family as beets and swiss chard. These superfoods are known for reducing inflammation and slowing the aging process.
Then what is the downside of spinach?
This is because spinach contains substances that inhibit certain nutrients from being properly absorbed. Spinach contains a substance called oxalic acid or oxalates which can bind to calcium and iron in the body and prevent the body from being able to absorb them. Oxalic acid is a natural substance found in several different plant based foods including rhubarb (its leaves contain very high amounts of oxalic acid), chard, and beet greens.
Oxalic acid binds to some minerals, making them unavailable for the body to absorb. So it is a good idea to rotate the green leaves rather than just sticking to one green leaf such as spinach. Consuming large quantities of foods containing lots of oxalic acid on a daily basis, you probably will end up with some nutritional deficiencies over a period of time. This may take weeks to months, not just a meal or two.
Oxalates can accumulate in the body, especially the kidneys. When the oxalates combine with calcium, kidney stones can form. Calcium oxalate is responsible for about 80% of kidney stones as a matter of fact.
The amount of dietary calcium in the diet has a significant effect on urinary oxalate excretion, which increases when calcium intake is low and decreases when calcium ingestion is elevated (2). This effect of dietary calcium is hypothesized to be due to the genesis of crystalline calcium oxalate in the intestinal lumen as dietary calcium increases, thus limiting intestinal oxalate absorption and reducing its urinary excretion. In contrast, more oxalate will be soluble with diminished calcium intake, thus augmenting net oxalate gastrointestinal absorption and urinary oxalate excretion.
Gut Bacteria and oxalate stone formation
Gut bacteria are thought to play an important role in oxalate absorption, since some types of gut bacteria break down oxalate, especially oxalobacter formigenes, lactobacillus, and bifidobacteria (1).
Oxalobacter formigenes is an intestinal organism that is unique in relying on oxalate as a carbon source for energy and growth. In Western societies it appears to colonize the gut of 30–40 % of the population. Stone formers are colonized at approximately half of this rate and those not colonized are 70 % more likely to develop a kidney stone. It’s mode of action appears to be twofold. Firstly, the degradation of oxalate in the intestine decreases its absorption particularly when calcium intake is low. Secondly, it may promote oxalate secretion into the gut. (3, 4, 5, 6)
Increasing the intake of magnesium to bind oxalate in the gut has also been considered as a way to decrease oxalate absorption. Magnesium does decrease the absorption of oxalate provided as a soluble oxalate load, but a randomized clinical trial in stone patients did not see any effect of supplemental magnesium on stone formation. (7)
- Rotate the greens leafy vegetables, not just stick to one variety. When you add spinach to smoothies limit the amount, do not use this for more than once or twice a week, add less oxalate containing greens the other days.
- Food combining: Ensure that a calcium-rich food is consumed with a meal known or suspected to contain significant amounts of oxalate. For example on the day you eat spinach, consume calcium rich foods such as cheese, milk or yogurt. And do not consume several oxalate rich foods the same day, especially in the same meal.
- Increase the intake of water, this decreases oxalate concentration in urine.
- Keep you gut healthy. Increase microbial richness and diversity in the gastrointestinal tract.
3. Oxalate degrading anaerobes in the gut: Allison MJ, Dawson KA, Mayberry WR, Foss JG. Oxalobacter formigenes gen. nov., sp. nov.: oxalate-degrading anaerobes that inhabit the gastrointestinal tract. Arch Microbiol. 1985 Feb;141(1):1-7. doi: 10.1007/BF00446731. PMID: 3994481.
4. Oxalobacter Formigenes and its relation to colonization and calcium oxalate stones. Knight J, Deora R, Assimos DG, Holmes RP. The genetic composition of Oxalobacter formigenes and its relationship to colonization and calcium oxalate stone disease. Urolithiasis. 2013 Jun;41(3):187-96. doi: 10.1007/s00240-013-0566-7. Epub 2013 Apr 30. PMID: 23632911; PMCID: PMC3713771.
5. Oxalobacter Formigenes may reduce risk of oxalate stones.Kaufman DW, Kelly JP, Curhan GC, Anderson TE, Dretler SP, Preminger GM, Cave DR. Oxalobacter formigenes may reduce the risk of calcium oxalate kidney stones. J Am Soc Nephrol. 2008 Jun;19(6):1197-203. doi: 10.1681/ASN.2007101058. Epub 2008 Mar 5. PMID: 18322162; PMCID: PMC2396938.
6. Jiang J, Knight J, Easter LH, Neiberg R, Holmes RP, Assimos DG. Impact of dietary calcium and oxalate, and Oxalobacter formigenes colonization on urinary oxalate excretion. J Urol. 2011;186(1):135–139.
7. Liebman M, Costa G. Effects of calcium and magnesium on urinary oxalate excretion after oxalate loads. J Urol. 2000;163(5):1565–1569.