The Core Difference: Lactic Acid vs. Oxalic Acid
To answer the question definitively: no, oxalic acid is not present in curd. The sour, tangy flavor of curd is a direct result of lactic acid, which is produced during the fermentation of milk. When milk is cultured with bacteria, these microorganisms convert the milk sugar (lactose) into lactic acid. This process thickens the milk and gives curd its characteristic taste and texture. Conversely, oxalic acid is a naturally occurring compound found primarily in plant-based foods, not dairy.
The Source of Oxalic Acid
Oxalic acid and its salt, oxalate, are found in significant quantities in a range of plants. Some common high-oxalate foods include:
- Green Leafy Vegetables: Spinach and rhubarb are notoriously high in oxalates.
- Nuts and Seeds: Almonds, cashews, and sesame seeds have high oxalate content.
- Fruits: Raspberries and some dried fruits contain notable amounts.
- Cereals and Grains: Buckwheat and bran can be high in oxalates.
For dairy products like curd, milk, and cheese, the oxalate content is generally negligible or nonexistent. The sourness is a biological byproduct of fermentation, not the presence of plant-based acids.
Unpacking the Curd and Spinach Myth
One of the most persistent food myths is the claim that combining curd and spinach (palak) is harmful because the oxalic acid in spinach reacts with the calcium in curd. The misconception suggests this combination leads to kidney stones or poor calcium absorption. While it is true that oxalic acid and calcium can bind together, forming calcium oxalate, the common understanding is often misconstrued.
Here’s the scientific perspective:
- Binding in the Gut: When high-oxalate foods like spinach are consumed with calcium-rich foods like curd, the calcium and oxalate bind together in the intestine.
- Prevents Absorption: This binding forms an insoluble compound that is then passed out of the body in stool, preventing the oxalate from being absorbed and reaching the kidneys.
- Protective Effect: Studies have shown that consuming adequate dietary calcium can actually be a protective measure against kidney stone formation, as it helps excrete oxalates before they can form stones in the kidneys.
- Nutrient Absorption: For iron, the presence of calcium can slightly inhibit its absorption, but this is a different nutritional consideration and not directly related to the oxalic acid myth.
Can you eat curd with spinach?
Yes, it is perfectly safe to eat curd with spinach. In fact, the calcium in curd may even have a beneficial effect by helping to excrete the oxalate from the spinach. Cooking spinach also significantly reduces its oxalate content, so preparing a cooked dish like 'Palak Raita' is a safe and traditional practice.
Lactic Acid vs. Oxalic Acid: A Comparison Table
| Feature | Lactic Acid | Oxalic Acid |
|---|---|---|
| Primary Source | Milk, Curd, Fermented Foods | Plants (Spinach, Rhubarb) |
| Chemical Formula | $C_3H_6O_3$ | $C_2H_2O_4$ |
| Formation | Fermentation of lactose by bacteria | Naturally occurs in certain plants |
| Metabolic Impact | Digested as a source of energy | Excreted by the body; can bind with calcium |
| Curd Content | High | Negligible or none |
| Safety in Curd | Safe for consumption | Not relevant, as it is not present |
Conclusion: Curd is Oxalic-Acid Free
It is clear that the belief that oxalic acid is present in curd is a widespread but inaccurate myth. The sourness comes from lactic acid, a beneficial compound created by natural fermentation. Curd and other dairy products are, in fact, low-oxalate foods. While oxalic acid is a real concern for individuals with a history of calcium oxalate kidney stones, combining calcium-rich dairy with high-oxalate foods is a scientifically sound practice for managing oxalate levels, not a dietary danger. For reliable information on managing oxalate intake, especially for kidney stone prevention, consulting trusted resources like the University of Chicago Kidney Stone Program is recommended.
How to Manage Dietary Oxalate
For those needing to watch their oxalate intake, here are some actionable tips:
- Consume adequate calcium: Ensure a daily intake of around 1000mg of calcium from food sources like dairy. This helps bind oxalates in the gut.
- Increase hydration: Drinking plenty of water is vital to dilute urine and flush out any potential stone-forming compounds.
- Cooking techniques: Boiling high-oxalate vegetables like spinach and discarding the water can remove a significant portion of their oxalate content.
- Pairing foods correctly: Combining a high-oxalate food with a high-calcium food in the same meal can be beneficial.
- Be mindful of supplements: Excessive vitamin C intake from supplements can increase the body's oxalate production.
- Seek personalized advice: For kidney stone patients, individualized dietary planning based on the specific stone type is essential.
Ultimately, enjoy your curd without fear of oxalic acid. Its nutritional benefits, from probiotics to calcium, make it a valuable part of a healthy and balanced diet.
Lists of High and Low Oxalate Foods
High Oxalate Foods:
- Spinach
- Rhubarb
- Almonds
- Baked Potatoes
- Beets
- Cocoa Powder
- Sesame Seeds
- Tofu
Low Oxalate Foods (safe to eat freely):
- Curd/Yogurt
- Milk
- Meat and Fish
- Eggs
- Apples
- Bananas
- Cabbage
- Cauliflower
