When I first heard Professor Christine Thompson from the Department of Human Nutrition, Otago University tell us that eating just two Brazil nuts a day provides us with all the selenium we need, I was excited. So simple, so natural, so perfect for us New Zealanders who err on the side of selenium deficiency due to our selenium deficient soil.

So if a couple of Brazil nuts are good, more must be better, right? Wrong!! This is one food that we definitely DO NOT want to overdose on. Why?

First, we can get selenium poisoning. We need a little selenium – it acts as an anti-oxidant and has potential anti-cancer effects – but eat too much and it will build up in the body to toxic levels. If you’ve over-embraced the ‘Brazil nuts are good for you’ message and have noticed you’re fatigued, irritable, feel nauseous, have a horrible garlic breath even when you haven’t been near garlic or, horror of horrors, your nails look bad and brittle and you’re losing hair, chances are you’ve overdosed on selenium.

Second, Brazil nuts naturally contain barium and thorium. Barium is a metal and thorium is a naturally occurring radioactive metal. Yes – radioactive! Eating Brazil nuts is not like having an x-ray but it has to be said that they are one of the most naturally radioactive foods around! Before you panic and vehemently cross Brazil nuts off your shopping list, remember that we are exposed to radioactivity every day – in our water, our food, sunlight, and every time you take an overseas plane trip. Like most things in life, a little is fine but too much is not.

As selenium expert, Professor Christine Thompson says, “People should be careful to limit themselves to no more than a few Brazil nuts a day otherwise selenium could potentially accumulate to toxic levels in body tissues. Also, as the nuts can contain relatively high amounts of the elements barium and thorium, people should avoid eating too many as it is still unclear what intake of these elements might be harmful.”

So when you follow the health experts’ advice to eat a small handful of unsalted nuts each day, make sure it’s a variety and not all Brazils!