Restrictive diets, the most common being the low oxalate diet, are widely reported in the lay press and on-line for vulvodynia (a chronic pain condition of the vulva). In one study, 41% of women with chronic vulvar pain reported trying a low-oxalate diet.
The only problem? The low oxalate diet doesn’t work.
How this diet became almost main stream is a testimony to lack of evidence, desperation of patients, inadequate evidence-based therapies, and snake oil. A perfect storm.
The whole idea that oxalate could potentially have a role in vulvodynia stemmed from a single case report published in 1991 in which a woman with refractory vulvodynia was found to have periodic hyperoxaluria. For this one patient, the addition of calcium citrate alleviated symptoms. Calcium citrate binds oxalate, therefore preventing it from irritating the skin/nerves during urination – the mechanism of cause and effect proposed in the case report.
A single case report and somehow it gets recommended. Initially by word of mouth, by both patients and providers and then later on web sites and chat rooms. Someone writes a cookbook about the diet and someone offers 24-hour urinary oxalate testing. You know, for a price.
However, we know that dietary oxalate consumption appears to be the same among women with vulvodynia as compared with controls and a prospective study of urinary oxalate levels in 130 women with vulvar pain and 23 controls found a similar distribution of oxalate levels between the two groups. In studies looking at a low-oxalate diet, improvement in pain ranges from 2.5% to 24%, which is equivalent or worse than the placebo response rate in other vulvodynia studies. In addition, women with kidney stones (and have high levels of oxalate in the urine) do not have appear to have a higher incidence of vulvodynia.
I would guess at least 50% of my patients with vulvodynia have tried the calcium oxalate diet and perhaps 5-10% felt it helped. A far worse outcome than placebo effect. Many of my patients spent money on the cookbook and others spent even more money sending 24-hour urine samples to “a special lab in Colorado for oxalate testing.”
Well, you might think. What’s the harm in trying the diet without wasting money on the testing? After all, if it works, it works, right?
The low oxalate diet is very restrictive and many patients get stressed about it (stress is bad for pain). Others feel inadequate because they just can’t do it (also not good for pain, most people with chronic pain don’t need an additional reason to feel bad). It is also better to focus energies and resources on proven therapies, not on a diet where there is a mountain of evidence to disprove both the theory of causation and the effectiveness of the intervention.
Are there any diets that can help women with vulvar pain? None that have been specifically studied. However, women with vulvodynia who have either painful bladder syndrome or irritable bowel syndrome may find relief of bladder or bowel symptoms with specific dietary measures aimed at eliminating bladder or gastrointestinal triggers. Pain in one area of the body makes pain elsewhere worse. So, getting bladder or bowel symptoms under control may help reduce vulvar pain.
But the low oxalate diet and vulvodynia is a cautionary tale about jumping on the results of a single case report. Not much different from Andrew Wakefield’s now retracted and debunked case series on the MMR vaccine and autism. Two things may co-exist, that’s all a case report or a case series tells us. We need prospective studies to guide treatment recommendations.