Spinach is often touted as a superfood – an extremely healthy food that provides significant health benefits. It’s packed with vitamins, minerals, antioxidants and various bioactive compounds that can boost health. However, like most foods, spinach also has some potential downsides. This article will examine the main disadvantages and downsides of eating spinach regularly.
One potential disadvantage of spinach is the bioavailability of some of its nutrients. Bioavailability refers to the proportion of a nutrient that is actually absorbed and utilized by the body. Some of the nutrients in spinach have relatively low bioavailability:
- Iron: Spinach contains high levels of iron, but this iron has low bioavailability due to the presence of oxalic acid which binds to the iron. The absorption rate of iron from spinach is estimated to be between 2-15%.
- Calcium: The calcium in spinach also has low bioavailability, with only about 5% being absorbed.
- Vitamin A: A significant amount of vitamin A in spinach is in the form of carotenoids like beta-carotene. The conversion process from these carotenoids to active vitamin A is not very efficient.
So while spinach contains decent absolute amounts of these nutrients, the actual usable quantities that make it into the body may be much lower.
Oxalic Acid Content
Spinach contains moderate amounts of oxalic acid, an antinutrient which can bind to minerals like calcium and iron in the digestive tract and prevent their absorption. It can also accumulate in the body over time when foods high in oxalic acid are regularly consumed.
In most people this is not an issue as the oxalic acid and mineral complexes are simply excreted out of the body. But in some individuals with a genetic tendency towards high oxalate levels, excess oxalates can contribute to kidney stone formation.
For most people spinach oxalates do not pose problems, but for those prone to kidney stones a high spinach intake may need to be avoided.
Spinach contains moderate amounts of nitrates, compounds which have both benefits and drawbacks when it comes to health:
- Benefits: Inside the body dietary nitrates can convert to nitric oxide, which dilates blood vessels and improves circulation.
- Drawbacks: High intakes of nitrates have been associated with an increased risk of certain cancers like gastric cancer when converted to nitrosamines.
For most people the nitrate content of spinach is not an issue. But some individuals may want to limit intake if concerned about cancer risk or have been advised to restrict nitrates for medical reasons.
Spinach plants typically require high use of pesticides and herbicides during commercial growing. Studies have found spinach often has detectable levels of pesticide residues:
- A report by the USDA found that over 70% of spinach samples contained pesticide residues. This was one of the highest rates among fruits and vegetables tested.
- The Environmental Working Group lists spinach on its “Dirty Dozen” guide to the most pesticide-contaminated produce.
Washing spinach thoroughly can help remove some topical pesticide residues but not all. Choosing organic spinach can reduce exposure to pesticide residues.
Purines are natural compounds found in some foods that can contribute to high uric acid levels in the body. This is an issue for those with gout or kidney stone tendencies, who need to restrict purine-containing foods. Spinach contains moderate amounts of purines.
For most people purines in spinach are not a concern. But those with gout or prone to uric acid kidney stones may want to moderate intake.
FODMAPs refers to fermentable oligo-, di-, mono-saccharides and polyols. These are carbohydrates that some people have difficulty digesting. Spinach contains moderate amounts of FODMAPs.
For most people this is not an issue. But for those with irritable bowel syndrome (IBS) or other digestive conditions, limiting high FODMAP foods like spinach may help improve symptoms.
Like other leafy greens, spinach is vulnerable to contamination from bacteria like Salmonella and E. coli. Outbreaks of foodborne illness from contaminated spinach have occurred in the past:
- In 2006, a major E. coli outbreak in the US from spinach resulted in over 200 illnesses and 3 deaths.
- In 2021, a Salmonella outbreak linked to spinach affected dozens across 10 states.
Proper handling and washing of spinach reduces this risk. But contamination can still occasionally occur.
Spinach allergies do occur, although more commonly in individuals who are sensitive to other related foods like swiss chard and amaranth. Children are more prone to developing spinach allergy. Symptoms can include itching, hives, swelling and anaphylaxis in severe cases.
Those with confirmed spinach allergy need to avoid it entirely. For others, spinach allergies are very rare.
Certain nutrients and compounds in spinach can negatively impact the absorption of other nutrients:
- Oxalic acid can bind calcium and iron, preventing absorption.
- Spinach contains vitamin C and iron, but vitamin C can actually inhibit iron absorption.
- The calcium in spinach can inhibit the absorption of manganese.
However, these interactions are usually not a major concern as spinach is rarely relied on as the sole source of these micronutrients in the diet.
Here is a summary of the main disadvantages and downsides to spinach consumption:
|Low nutrient bioavailability||The iron, calcium and vitamin A in spinach have relatively low bioavailability.|
|Oxalic acid content||May impair mineral absorption and contribute to kidney stones in prone individuals.|
|Nitrate content||High intakes have been linked to increased cancer risk, although spinach nitrates are generally not a concern.|
|Pesticide residues||Spinach tends to have high amounts of pesticide residues compared to other produce.|
|Purine content||Moderately high levels may exacerbate gout or kidney stones in prone individuals.|
|FODMAPs||Fermentable carbohydrates in spinach can exacerbate IBS and digestive issues in some people.|
|Bacterial contamination||Outbreaks of food poisoning have been linked to contaminated spinach.|
|Allergies||Spinach allergies occur in a small number of people.|
|Nutrient antagonists||Compounds in spinach can impair absorption of some nutrients like iron, calcium and manganese.|
In conclusion, spinach does contain some antinutrients and compounds that may cause issues for some people when consumed in excess. This includes reduced nutrient bioavailability, kidney stone risks from oxalates, and problems digesting FODMAP carbs.
However, for most people these concerns do not outweigh the many health benefits of spinach. Unless you have confirmed kidney issues, gout, digestive conditions or other health concerns, spinach can be enjoyed moderately as part of a healthy diet.