Low oxalate diet Practice, Theory, and Evidence

safety

A qualified healthcare provider should be consulted before making decisions about diets and/or health conditions.
Foods with only low levels of oxalate may not need to be completely eliminated because dietary oxalate is not efficiently absorbed into the body. Low level dietary consumption of oxalate may not have a significant effect on the amount of dietary oxalate consumed.
Constipation may occur with a low oxalate diet. Most experts recommend eating and selecting foods (e.g. whole grains, legumes, fruits, and vegetables) with good sources of fiber to aid in regularity. An excellent source of fiber would be any food that provides at least 3-4g of fiber per serving. The National Academies' Institute of Medicine recommends a total intake of dietary fiber to be 21-38g per day.
Weight gain is a possibility if a significantly larger quantity of animal products (e.g. meat, fish, poultry, eggs, dairy products) as compared to fruits and vegetables, whole grains, and legumes are consumed. Otherwise, the low oxalate diet typically does not lead to weight gain.
Weight loss may occur because some of the foods listed on the diet are not calorically dense (not high in fat). Generally, omitting high oxalate foods should not lead to a reduction in caloric intake and weight loss. However, evidence suggests that some people may typically consume fewer calories when put on a restrictive diet.
A low oxalate diet may be nutritionally inadequate because it may provide lower levels of nutrients, such as vitamin C and folate. However, with careful and wise food selections, an individual may maintain a low oxalate diet and still consume recommended levels of all key nutrients.

theory/evidence

There are two types of oxalates: calcium oxalate and oxalic acid. Oxalic acid is a strong organic acid, which is commonly found in both plants and animals. In the animal kingdom oxalate and its salts are present in the urine and blood of mammals. The oxalate in humans and animals comes from the oxalate ingested with plant material, although through the oxidation of glyoxalate and ascorbate they synthesize tiny amounts. Both sodium and potassium oxalate salts are water soluble; however, calcium oxalate is insoluble. Therefore, if calcium oxalate is present in high enough concentrations, it has a tendency to precipitate in the kidneys or in the urinary tract to form calcium oxalate crystals. It is not clear why women have a much lower frequency of kidney stones than men. Both men and women synthesize oxalate from a number of compounds that are precursors to oxalate.
Scientists once thought that the higher the oxalate concentration in food, the higher the risk of forming kidney stones. However, they have found that consuming certain foods and/or beverages containing oxalate are more likely to increase urinary oxalate. There remains no universal consensus on which oxalate-containing foods belong on high oxalate food lists. Nonetheless, there is growing awareness that people with a history of kidney stones should avoid certain high oxalate foods that are most responsible for increasing urinary concentrations of oxalate. The majority of the urinary oxalate obtained from food may appear in the urine 2 to 6 hours after the consumption of the food containing oxalate.
Oxalate is in many foods and binds to calcium in the body. Often they will they bind together in the stomach or intestines and then they will pass through the body and not get into the kidneys. But if oxalate does not find calcium to bind with in the stomach, it will get into the kidneys, find calcium to bind with there, and form stones.
Vitamin C metabolizes to oxalate and intake is often reduced during this diet. However, a Nurses' Health Study, Intake of vitamins B6 and C and the risk of kidney stones in women, analyzed over 85,000 women and found no increased risk of kidney stone formation with vitamin C intake.
People suffering from vulvodynia (lasting pain in the area around the opening of the vagina (vulva) or chronic vulvar pain) may often adhere to a low oxalate diet. Many patients typically combine this diet with treatments such as surgeries; antibiotics, antidepressants, antifungals, anti-inflammatory drugs; or most topical preparations. In one study, 31 women with vulval vestibulitis were evaluated for evidence of abnormal dietary oxalate intake and a wide range of dietary intakes was recorded. No woman was found to have abnormal urinary excretion. Sixteen women agreed to undertake a low oxalate diet and there was an apparent response in six (37%).
The American Society for Parenteral and Enteral Nutrition Clinical Guidelines states that a low oxalate diet may be appropriate for patients with short bowel syndrome (malabsorption resulting from anatomical or functional loss of a significant length of the small intestine) and an intact colon. Calcium oxalate kidney stones are a potential complication of short bowel syndrome. Dietary calcium in the stool normally binds to oxalate, not allowing it to be absorbed in the colon. Because of fat malabsorption, the calcium binds better to the free fatty acids in the stool. This leaves the oxalate free to be absorbed by the colon and may lead to hyperoxaluria and kidney stones. Nutritional management is thought to be the key factor in achieving an optimal outcome in short bowel syndrome. Patients with a short bowel and colon are often advised to follow a diet low in oxalate because 25% of the oxalate may develop as calcium oxalate kidney stones.