A study in the the February 2017 issue of Epidemiology discusses one of the untoward side effects of gluten free diet.

The downside is increased blood levels of heavy metal toxicity primarily arsenic and mercury.  An initial thought was increased intake of fish but the the hypothesized cause is thought to be increased rice which tends to absorb metals and particularly heavy metals from water and soil.

Researchers analyzed data on 7,471 participants in a larger national health study, of whom 73 reported being on a gluten-free diet. Concentrations of urinary arsenic in those on the diet were nearly twice as high as in those not on it. Blood levels of inorganic mercury were also significantly higher in gluten-free dieters.

People on gluten-free diets tend to increase their rice intake by eating special gluten-free products that contain rice, or rice syrup as a sweetener, though they tend to eat as much plain rice as others.

Arsenic and mercury are widely distributed throughout the environment, and everyone has some amount in their blood. But the levels of both elements among those on the gluten-free diet, while far from being toxic, were above those generally considered normal.

“The health impacts at this level of exposure are unknown,” Dr. Argos said. “But people should be aware of what they are eating. They are potentially consuming much more rice than they realize.”

A quick literature search found that in China, there is greater risk of toxic mercury from intake of rice rather than fish and that rice tends to absorb just about every heavy metal.

In an [April 2010] issue of Environmental Health Perspectives, the researchers report that although mercury exposures for these communities varied dramatically, in every one of them “rice accounted for 94 to 96 percent of the probable daily intake of methylmercury” — the most neurotoxic and readily absorbed form of mercury. Methylmercury poisoning has been linked with diminishing the IQ of children exposed in the womb and with raising blood pressure and other heart-disease risks among adults.

An April 2013 issue of Time Magazine also reported that imported rice (7% of all rice consumed in U.S.) also has elevated levels of lead.

Rice from Taiwan and China contained the highest levels of lead, although rice from Italy, India, Thailand, Bhutan and the Czech Republic also contained levels higher than the Food and Drug Administration’s (FDA) provisional total tolerable intake (PTTI).

The levels ranged from six milligrams/kilogram to 12 milligrams/kilogram; factoring in average consumption, that added up to estimated lead exposure levels 30 to 60 times greater than the Food and Drug Administration’s (FDA) provisional total tolerable intake (PTTI) levels for children and 20-40 times greater than the standard exposure levels for adults.

I guess it’s time to watch your rice as well.

Source: A Downside of Gluten Free – The New York Times