Not often (once every month at most).
Supposedly rice really loves to absorb pesticides, and it also contrains arsenic (a poison).
If you eat rice alot, your body is accumulating these things. (heart disease, diabetes and cancer, as well as development problems)
The right way to eat rice (safest way):
"Scientists claim rice should be steeped in water overnight to flush out the poison, and then it can be rinsed and cooked the next day."
No one I know does this, so its not really healthy to eat too often.
If you love rice remember these two:
1) Basically dont feed kids rice.
2) Remember to steep in water overnight, before useing it the next day.
This post is full of both correct information and incorrect conclusions.
Firstly, rice does like to absorb arsenic. But whole plant foods help your body detoxify. Add turmeric and black pepper (even in small amounts) to your food and it will especially amp up your body's detoxifying function.
To the degree you're worried about toxins in food, don't worry about rice, worry about meat that is full of estrogen and other mammalian hormones, pesticides (they eat huge amounts of non-organic plant foods before being slaughtered), antibiotics, heavy metals (they're near the top of the food chain and toxins bioaccumulate up the food chain), etc. Whereas whole plant are lower down the food chain so generally contain fewer toxins, and whole plant foods help the body detoxify, food animals are higher up the food chain so have more toxins and consuming animal products actually works towards inhibiting the body's ability to detoxify.
Fun fact: in most parts of North America, the majority of the aresenic in our soil comes from chicken manure used as fertilizer (with the arsenic itself having come from arsenic-laced antibiotics the chickens were given for decades).
So unless you're on a whole food plant-based diet (and if you add turmeric to your food, even if you are), rice is probably the least of your dietary worries.
Citations for all of the above available upon request (I have them handy, just not on this PC).