dietary oxalates and hyperoxaluria

Introduction

calcium oxalate stones account for 75-80% of urolithiasis / renal stones / renal calculi

excessive amounts of oxalates in the urine (“hyperoxaluria”) is a significant risk factor in the formation of calcium oxalate kidney stones as urinary calcium concentrations are typically 10 times higher than oxalate, thus, even minor changes in urinary oxalate concentrations can significantly impact the saturation of calcium oxalate crystals
urine contains oxalate from two main sources in approx. equal proportions (although pathologically elevated urinary oxalate concentrations may be more associated with increased gastrointestinal oxalate absorption):
- endogenous oxalate produced during liver metabolism
- dietary oxalate absorbed in the intestine
  - enteric hyperoxaluria (excessive absorption of oxalates from the gut) is a significant risk factor for calcium oxalate stone formation and is related to oxalate intakes, calcium levels, and, to a much lesser extent the the GIT microbiome
    - diets very low in calcium will result in higher oxalate absorption from the gut
    - high fibre diets reduce oxalate absorption from the gut
    - the GIT microbiome some bacteria may metabolize oxalates and reduce risk while others may increase risk
      - oxalate-degrading bacteria, such as Oxalobacter formigenes, which require a strictly anaerobic environment to survive, tend to colonise in the colon however, much of the dietary oxalate is absorbed in the proximal parts of the intestine before it gets to this organism ¹⁾

ensure you drink enough water (eg. 2.5L/day including 250mL each hour and a large glass before bed and one glass overnight if you wake up) to avoid concentrated dark orange urine as this is a major factor for all stone types - adequate water intake helps reduce stone formation and helps to flush microcrystals out before they get bigger
have high calcium foods/drinks at the same time as oxalate intake
- this may result in reduced oxalate absorption from the gut as the calcium will bind to the oxalate
reduce salt intake to less than 1 teaspoon a day
- high sodium intakes increase calcium excretion in kidneys
lemon juice is a good source of citrate which helps to prevent stones forming. Drink 100ml of lemon juice daily (could be added to water)
caffeinated drinks (except black tea which has high oxalate levels) have been shown to prevent kidney stones, but limit to 3 cups per day.

although not related to oxalate stones and are much less common, one should ensure diet is moderated in this regard as well
limit intake of purines such as red meat
- these not only result in higher urate levels but also increase acidity of urine which encourages urate stone formation
limit alcohol intake
see also hyperuricaemia

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