Most stone advice starts with the food. But for a subgroup of people with calcium oxalate stones, the plate is not where the problem begins — the gut is. A condition called enteric hyperoxaluria changes how much oxalate the intestine lets through, and the newest data puts a number on just how wide that gate swings open.
The word "enteric" points to the intestine. It shows up in bowel conditions where fat is not absorbed properly — Crohn's disease, short bowel syndrome, exocrine pancreatic insufficiency, and weight-loss (bariatric) surgery. When fat is not taken up in the gut, it binds calcium instead of letting calcium bind oxalate. With calcium occupied, free oxalate is absorbed in larger amounts and ends up in the urine, where it can crystallize.
The 2026 study measured this directly with a labeled-oxalate absorption test and confirmed what the mechanism predicts: the enteric group pulls in far more oxalate from the same meal. Under a balanced, standardized diet, urinary oxalate fell in both groups, but the drop was larger in the enteric group — a useful signal that diet still matters even when the underlying problem is intestinal.
For someone with this gut pattern, the same high-oxalate foods that are a moderate concern for most people become a sharper one. The measured values:
| Food | Oxalate (mg) | Serving | Rating |
|---|---|---|---|
| Spinach, raw | 590 mg | 1 serving | Avoid |
| Rhubarb, raw | 1,293 mg | 1 cup diced | Avoid |
| Almonds | 107 mg | 1/4 cup | Avoid |
| Dark chocolate | 65 mg | 1 oz | Caution |
| Tea, black, brewed | 14 mg | 1 cup | Safe |
The hierarchy is unchanged — spinach and rhubarb sit at the top — but the clinical weight shifts. A person whose gut already over-absorbs oxalate gets more urinary oxalate per gram of these foods than someone with normal absorption, which is why the standard advice to pair oxalate with calcium lands harder here.
The actionable piece is not "eat fewer oxalate foods" in isolation — it is "take calcium with the meal that contains oxalate," because in enteric hyperoxaluria the calcium is being stolen by unabsorbed fat. A clinician may also test for fat malabsorption and look at the underlying bowel condition. For everyone else, the takeaway is narrower but still useful: a stone workup that keeps showing high urine oxalate despite a normal diet may be pointing at the gut, not the grocery list.
See how oxalate values are measured and verified on our data methodology page.