Loaded with vitamins and minerals, spinach has emerged as one of the healthiest foods on earth. It's low in calories, fills you up quickly and can be prepared in a multitude of ways. As with everything else, moderation is key. Eating too much spinach may cause digestive distress and promote the formation of kidney stones due to its high oxalate content. The fiber in spinach can lead to bloating and stomach pain.
Read more: Can I Eat Spinach Every Day?
Spinach and Kidney Health
Along with kale, beets and most nuts, spinach is a stone-forming food. This veggie boasts high levels of oxalates, which are waste products of metabolism. During digestion, oxalates bind to calcium in the GI tract, reducing its absorption. These compounds are naturally eliminated in the urine or stool.
A high intake of oxalates may cause kidney stones. According to a 2015 review published by the Korean Society of Clinical Nutrition, crystals start to form when oxalate concentration is four times above normal. Most calcium stones in the kidneys consist of calcium oxalate. Research shows that high-oxalate foods, such as spinach and rhubarb, promote stone formation. About half of the people who develop one stone tend to form another within 10 years.
Nuts, potatoes and spinach account for 44 percent of oxalate intake for most Americans, according to a 2014 study published by the Korean Urological Association. That's why health experts recommend eating these foods in moderation. The same study suggests that drinking more fluids may lower the risk of kidney stone formation.
Ideally, boil the spinach before consumption to reduce its oxalate levels. Cutting back on salt and meat may help too. These foods have been linked to a higher risk of kidney stones.
Effects of Spinach on Digestion
A bunch of raw spinach provides approximately 7.5 grams of fiber. That's about one-third of the daily recommended intake based on a 2,000-calorie diet. As noted by the Mayo Clinic, this nutrient promotes digestive health, prevents constipation and slows sugar absorption into your bloodstream.
Too much fiber, on the other hand, can have the opposite effect. According to an article published by Duke University, eating more than 70 grams of fiber per day may cause bloating, gas, diarrhea, constipation, stomach cramps and other gastrointestinal symptoms. Plus, it fills you up quickly and curbs appetite, which may lead to unintentional weight loss.
Read more: Spinach and Stomach Cramps
Some studies suggest that fiber may interfere with vitamin and mineral absorption. However, the research is mixed. Since this nutrient is considered safe, no upper level of intake has been set.
The fiber in spinach can help you maintain a healthy weight, suppress appetite and keep your digestive system running smoothly. Some individuals may experience gastrointestinal symptoms, but this may or may not happen to you.
Do a quick online search for "spinach gas," "spinach diarrhea" or "spinach digestion" and you'll see that the effects vary from one person to another. Increasing your fiber intake suddenly, for example, is more likely to cause digestive distress than gradually adding more fiber to your diet.
Read more: Spinach and Diarrhea
Other Potential Side Effects
Since this veggie is high in fiber, it may reduce your blood sugar levels. This may lower your risk of diabetes, insulin resistance, heart disease and other ailments. However, if you're taking anti-diabetes medications and eating high-fiber foods, you may experience hypoglycemia, or low blood sugar. Consult your doctor to determine whether spinach is safe for you.
If you're allergic to salicylates, you may not be able to eat certain fruits and veggies. As WedMD notes, these compounds occur naturally in spinach, eggplant, radishes, cruciferous vegetables, avocados, apples, peanuts and other foods. The most common allergic reactions include nasal congestion, swelling of the face and limbs, headaches, difficulty breathing, skin rash and itching.
- Harvard Medical School: 5 Steps for Preventing Kidney Stones
- K-State Research and Extension: Spinach and Kidney Stones
- Vegan Health: Calcium Absorption From Plant Foods
- Clinical Nutrition Research: Nutritional Management of Kidney Stones (Nephrolithiasis)
- The Korean Journal of Urology: Medical and Dietary Therapy for Kidney Stone Prevention
- Tufts University Health and Nutrition Letter: Should I Avoid Eating Spinach Because It Has Oxalate Found in Kidney Stones?
- SELF Nutrition Data: Raw Spinach
- Mayo Clinic: Dietary Fiber: Essential for a Healthy Diet
- Duke Student Health Nutrition Services: Fiber-How
- Australian Government Ministry of Health: Nutrient Reference Values: Dietary Fibre
- BioMed Research International: Hypoglycemic and Hypolipidemic Potential of a High Fiber Diet in Healthy versus Diabetic Rabbits
- WebMD: What Is a Salicylate Allergy?
- Fine Cooking; A Fresh Look at Spinach; Alan Tangren
- Jackson Siegelbaum Gastroenterology; Kidney Stone Diet; Frank W. Jackson, M.D.; 2008