Rice, dietary staple or poison?

More rice is eaten pound for pound, than any other food on the planet. It has been estimated that more than 20% of all our calories worldwide come from rice. As such the nutritional qualities of rice are very important.

The most reliable evidence shows that rice was first domesticated over 10,000 years ago in China. From there it gradually spread westwards to Europe and eventually, in the middle of the last millenium, to the Americas.

Rice production

A rice grain is made up of an inner starchy endosperm, surrounded by several layers, collectively called the bran layer that contain more protein and fat. Outside this is the husk (hull) which contains mostly indigestible elements.

In most cases the indigestible husks of the rice are removed. This used to be done by winnowing, chucking the rice grains up in the air from a sieve and letting the lightest hulls or chaff blow away. Mortar and pestle was also used to remove more of the outer layers. Nowadays rice hulling machines do this by compressing the rice seeds between cylindrical steel rollers.

Brown and white rice

After the chaff has been removed the result rice is brown rice. This is the clump to the right of the diagram. The freshly harvested seeds are shown to the left. Above them both is polished white rice. The process of polishing removes any remnants of the husk, the bran layer and the germ. The germ is pictured as the embryo in the picture above.

White rice lasts better than brown rice as it does not contain the fats that are present in the bran and germ. Fats can easily go rancid if left for any time in the presence of air, heat or light.

The polishing of white rice leads to the loss of many vitamins and minerals as well as the nourishing fats, present in brown rice. As such there are various techniques occasionally employed to restore some of these nutrients. One of these is parboiling, which involves boiling brown rice to move thiamine (vitamin B1) and some other nutrients into the endosperm. This was done primarily to prevent the thiamin deficiency condition, beri-beri, in populations for whom rice was the predominant dietary staple.

Long grain and short grain

Long grain rice generally retains its form after cooking. It is formed predominantly from a starch called amylose, which takes a linear form and is more resistant to digestion. This makes it lower GI, which means it has a less disruptive effect on your blood sugar than other types of rice. There are forms of long grain rice which contain more starch in the form of amylopectin. This is easily degraded in the gut, and means that rice containing a lot of it is higher GI a nd is more disruptive to blood sugar levels. Thai sticky rice is an example.

Medium grain rice, like Thai sticky rice, contains more amylopectin and is commonly used in risotto, sushi and sweet dishes.

Short grain rice is again high in amylopectin and is often used for rice pudding.

Cooking methods

Most rice is boiled in just enough water that it absorbs it all when cooked. Some cooking methods involve rice being fried briefly before cooking. Biryani, pilaf, saffron and risotto rice are commony produced in this way. One tasty recipe using rice is paella. Here is a recipe adapted from Felicity Cloakes perfect paella(1).

Paella recipe

SEAFOOD: 4 unshelled tiger prawns; 150g monkfish cut into chunks; 150g squid cut into rings; 150g mussels

VEGETABLES: 150g broad beans; 3 cloves garlic chopped; 1 onion diced; 200g chopped tomatoes

RICE, OIL & STOCK: 200g Short-grain rice; 90ml olive oil; 500ml fish stock

FLAVOURS: 1 tsp paprika; 50ml dry white wine; Pinch of saffron; Handful of flat-leaf parsley to garnish; lemon wedges

  1. Shell the prawns and put the flesh aside. Heat 1 tsbp olive oil in a large pan and gently sauté one clove of chopped garlic for 2 minutes. Add the prawn heads and tails and sauté, stirring to break them up, for three minutes. Pour in the stock and simmer gently for 30 minutes, then strain, season to taste and keep warm.
  2. Heat the remaining oil in a 26cm paella or other wide, thin-based pan and add the monkfish. Sauté for five minutes until slightly browned, then remove and set aside. Add the onion and garlic and cook until softened, then stir in the paprika and cook for one minute. Tip in the tomatoes and wine, turn up the heat and simmer for 10 minutes. Add the squid and beans.
  3. Stir in the rice to coat well so it forms an even layer, then add 400ml stock and the saffron and soaking water. Simmer vigorously for 10 minutes then arrange the monkfish, mussels and prawns on the top of the dish, pushing them well into the rice. Cook for about 8 minutes, add stock if the dish looks very dry.
  4. Cover the dish with foil and take off the heat. Allow to rest for 10 minutes then garnish with flat-leaf parsley and wedges of lemon.
 

Health issues

Beri-beri

In some East Asian countries, where polished white rice is the main dietary staple, the deficiency disease, beri-beri has been common, as a result of the removal of thiamin (vitamin B1) during processing. 

Arsenic poisoning

More recently there has been concern that rice and rice products contain dangerous amounts of the toxic element arsenic. Arsenic comes in many forms, some of which are non-toxic. 

For instance many shell fish contain large amounts in the form of an organic arsenic compound called arsenobetaine. For instance prawns can contain as much as 175ppm (parts per million) of arsenic. Arsenobetaine is non-toxic however, as after it is absorbed from our guts it is rapidly removed via our kidneys.

On the other hand some inorganic forms of arsenic such as arsenopyrite and arsenic trioxide are normally toxic in low doses. Arsenic trioxide has been used over the centuries as a poison, and was once known as succession powder, after its use in poisoning kings and princes and leading to a swift succession! Arsenic trioxide is also used in insecticides and herbicides. Notably it has been used in the US to eliminate the boll weevil from rice fields. The result has been rice with more than recomended maximum amounts 5 ppb (parts per billion) of arsenic in them. 

Brown rice is more problematic than white rice as much of the arsenic is contained in the bran that is removed during the processing of white rice. A recent report in the US showed levels of betwen 30-200ppb of arsenic in a number of common brands of rice, rice cakes and rice based cereals(2).

Is brown rice better than white rice?

On balance I'd prefer white rice for the following reasons:

  1. Brown rice contains roughly 3-6 times more arsenic than white rice.
  2. Brown rice contains more phytate than white rice. Phytate reduces absorption of valuable minerals from the gut. When you are eating a complete meal, with rice and plenty of vegetables, white rice makes a more sensible complement, as it will allow for more mineral absorption from the vegetables.
  3. Brown rice can also reduce the amount of protein that you can absorb from food(3).
  4. Brown rice contains more beneficial nutrients, but these can be got from elsewhere if you have access to a varied diet.

References

(1) http://www.guardian.co.uk/lifeandstyle/2011/aug/18/how-to-cook-perfect-paella

2) http://www.consumerreports.org/content/dam/cro/magazine-articles/2012/November/Consumer%20Reports%20Arsenic%20in%20Food%20November%202012_1.pdf

(3) http://www.ncbi.nlm.nih.gov/pubmed/2822877