Fish Oil Supplementation and Urinary Oxalate Excretion in Normal Subjects on a Low-oxalate Diet

Abstract

OBJECTIVE To determine if fish oil supplementation reduces endogenous oxalate synthesis in healthy subjects. MATERIALS AND METHODS Fifteen healthy non–stone-forming adults participated in this study. Subjects first abstained from using vitamins, medications, or foods enriched in omega-3 fatty acids for 30 days. Next, they collected two 24-hour urine specimens while consuming a self-selected diet. Subjects consumed an extremely low-oxalate and normal-calcium diet for 5 days and collected 24-hour urine specimens on the last 3 days of this diet. Next, the subjects took 2 fish oil capsules containing 650-mg eicosapentaenoic acid and 450-mg docosahexaenoic acid twice daily for 30 days. They consumed a self-selected diet on days 1–25 and the controlled diet on days 26–30. Twenty-four-hour urine samples were collected on days 28–30. Excretion levels of urinary analytes including oxalate and glycolate were analyzed. RESULTS Although there was a significant reduction in urinary oxalate, magnesium, and potassium excretions and an increase in uric acid excretion during the controlled dietary phases compared with the self-selected diet, there were no significant differences in their excretion during controlled diet phases with and without fish oil supplementation. CONCLUSION These results suggest that fish oil supplementation does not reduce endogenous oxalate synthesis or urinary oxalate excretion in normal adults during periods of extremely low oxalate intake. However, these results do not challenge the previously described reduction in urinary oxalate excretion demonstrated in normal subjects consuming a moderate amount of oxalate in conjunction with fish oil.

The Efficacy of Polyunsaturated Fatty Acids as Protectors against Calcium Oxalate Renal Stone Formation: A Review

“…They suggested that this inconsistency might be due to differences in their respective patient cohorts as their earlier study involved hypercalciuric patients while their subsequent study did not [5]. Interestingly, Table 1 shows that four of the other studies in which no decrease in urinary Ca occurred used healthy subjects as their test group as opposed to stone-formers [6,10,14,25] lending support to the notion that PUFA-induced reduction of Ca excretion is possibly restricted to stone-forming patients. Indeed, Buck and co-workers commented in an earlier paper that the normalizing effect of fish oil with respect to urinary calcium and oxalate levels was more pronounced in patients in whom these parameters were markedly raised [1].…”

“…We note that a total of 16 studies is listed. PUFAs which were tested are EPA (2 studies) [1,5], EPA+DHA (8 studies) [1,2,[6][7][8][9]11,14], LA+GLA (5 studies) [2,10,25], and EPA+DHA+GLA+LA (one study) [2]. These have been delivered as fish oil or as isolated supplements (EPA, GLA, evening primrose oil).…”

“…Studies that have suggested a protective effect for n-3 fatty acids have demonstrated reductions in important stone risk factors such as hypercalciuria [2,4,[8][9][10], hyperoxaluria [6], or both [1,7,11]. On the other hand, other studies have questioned the veracity of this association [8,[12][13][14][15]. For example, the study by Taylor and co-workers involving over 230,000 subjects in 3 three large national US cohorts showed that an increased intake of dietary n-3 PUFAs is highly unlikely to reduce the risk for kidney stone formation [13].…”

Lowering urinary oxalate excretion to decrease calcium oxalate stone disease

“…One study demonstrated that the administration of a lactic acid bacterial probiotic reduced oxalate excretion in patients with idiopathic hyperoxaluria [31]; although this has not been substantiated by others [24]. The administration of fish oil should be further explored to confirm its effects and mode of action [32]. Pyridoxine therapy has been recommended for patients with hyperoxaluria.…”

Metabolism oxalic acid: failure causes and consequences of molecular-biochemical factors for the formation of oxalate-induced diseases

“…Споживання оксалатів у поєднання з жирами, наприклад риб'ячим жиром, не впливає на рівень їх екскреції. Проте викликає жваву дискусію у науковій спільноті, оскільки не підтверджує і не спростовує попередні результати досліджень, які описують підвищення ексретованого оксалату за умов високожирової дієти [17].…”