Wednesday, April 21, 2010

Practically Paleo Perspective: Rice

A commenter asked me for my opinion on rice, so here you have it.

[Updated 4/20/12:  The original version of this post illustrates some of the poor reasoning I fell into as a result of reading books and blogs by people advocating paleo diet, while ignoring the bulk of research on diet and health.  My critiques and corrections of the original appear in brackets.]

Botany and Antinutrients

Rice is the seed of a monocotyledonous plant known to botanists as Oryza sativa. 

Like other seeds, whole (brown) rice contains chemical defenses against predation, primarily present in the hull and bran of the seed.  They include phytin (phytate), trypsin inhibitor, oryzacystatin and haemagglutinin-lectin.

Phytate binds minerals including calcium, zinc and iron; it also binds with protein.  Heat (cooking) does not denature phytate.  Studies have found that subjects fed brown rice diets have poorer mineral balance when compared to subjects fed milled rice diets.  On the other hand, phytate protects against dental caries, so white rice promotes dental decay more than brown rice.

[4/20/12:   Phytate fears are not founded on good science.  Science does not support claims that dietary phytate causes harm to humans.  Humans adapt to phytate ingestion, dietary vitamin C cancels the negative effect of phytate on mineral absorption, phytate adversely affects mineral balance only if the diet is deficient in minerals, and research has shown that dietary phytate has a strong health benefits for prevention and treatment of cardiovascular disease and cancer; it even inhibits the growth of malignant tumors.]

Trypsin inhibitor occurs in rice bran.  Steaming rice bran at 100 degrees C (212 F) inactivates trypsin inhibitor.  [4/20/12:  This means that boiled brown rice has no active trypsin inhibitor.] Polishing rice eliminates trypsin inhibitor.

Haemagglutinins  or lectins consist of globulins that agglutinate mammalian red blood cells and precipitate glycoconjugates or polysaccharides. Lectins bind to specific carbohydrate receptor sites on the intestinal mucosal cells and thus interfere with the absorption of nutrients across the intestinal wall.  Rice lectin agglutinates human A, B and O group erythrocytesAccording to the FAO, rice lectin sharply loses activity when heated to 100 degrees C. [4/20/12: Hence, since we boil rice at 100 degrees C before eating it, we don't have to worry about this lectin.]

Oryzacystatin is an inhibitor of protein-digesting enzymes.  Oryzacystatin remains 100% active after at least 30 minutes of boiling.

Rice also contains an allergenic protein that occurs primarily in the milled rice, not the bran, and remains stable (60%) even after boiling for 60 minutes at 100 C (212 F).

[4/20/12: Rice allergies occur in only 10% of atopic patients in Japan and less in Europeans and Americans.  Compare this to beef allergy:

"The prevalence of beef allergy is between 3% and 6.5% among children with atopic dermatitis and can be up to 20% in cow's milk allergic children. Several studies reported an incidence of 1-2% of food-induced anaphylactic reactions caused by ingestion of beef. In another study an even higher figure of 9% of anaphylactic events from foods were induced by beef."
These data appear to indicate a much greater incidence of anaphylactic events triggered by beef than by rice.]
 
Nutritional value

Rice has a very high carbohydrate content and low levels of micronutrients compared to vegetables or fruits.  The following table compares the levels of selected vitamins and minerals in 50-kcal portions of brown rice and a selection of vegetables and fruits.  Red numbers indicate items with the highest levels among the foods compared. Click on image to see larger version.



Notice that brown rice does not have the highest level of any of the nutrients listed.  White potatoes have twice as much riboflavin (B2), 2.5 times as much folate, vitamin C not present in rice, 10 times more potassium, more than 3 times as much iron, and 25% more calcium than brown rice.    Sweet potatoes supply carotenes (provitamin A) and vitamin C not present in brown rice, three times as much B2, 5.5 times as much folate, 9 times as much potassium, slightly more iron, and more than 3 times as much calcium.  Winter squash also makes brown rice pale in comparison.

Strawberries have 10 times as much B2, 12.5 times as much potassium, nearly 3 times as much iron, and more than 5 times as much calcium.

No matter which vegetable or fruit you compare to brown rice, you find the vegetable or fruit makes brown rice pale in comparison.

Then if you compare brown to white rice:


Brown Rice vs. White Rice

Nutrient
Brown Rice (1 cup)
White Rice (1 cup)
Energy (kcal)
218
241
Protein (g)
4.5
4.4
Carbohydrate (g)
46
53
Fat (g)
1.6
0.4
Fiber (g)
3.5
NA
Thiamin (mg)
0.2
0.3 (synthetic)
Riboflavin (mg)
0.02
0.03 (synthetic)
Niacin (mg)
2.6
2.8 (synthetic)
Pyridoxine (mg)
0.29
0.11
Folacin (mcg)
7.8
109.8 (synthetic)
Calcium (mg)
19.5
1.9
Iron
1.0
2.7 (fortified)
Magnesium
86
15
Phosphorus
150
61
Potassium
154
48
Zinc
1.2
0.74

Laying aside the synthetic fortification, brown rice supplies nearly 3 times as much pyridoxine, 10 times as much calcium, almost 6 times as much magnesium, more than 3 times as much phosphorus, more than 3 times as much potassium, and almost twice as much zinc.  Therefore, white rice doesn't hold a candle to brown rice, and brown rice doesn't hold a candle to white potatoes.

[4/20/12:  Turn this around, and judge by energy, protein, and carbohydrate delivery per unit volume, and you find that brown rice surpasses non-starchy vegetables and fruits.  We need some foods for energy and macronutrients, and some foods for micronutrients.  Brown rice is a nutrient-dense starch and energy source compared to white rice.]

White or brown, rice is basically filler with little nutritional value compared to vegetables and fruits.  If you eat rice, you crowd out more nutrient-dense sources of carbohydrate. 

[4/20/12:  Wow, what a ridiculous argument!  Both brown and white rice are much more nutrient-dense than fats like butter, lard, and olive oil, so I would have been more correct to state that fats are fillers compared to brown rice.  When I compared the micronutrient content of two equicaloric diets, one high in meat and supplying most of its energy from fat, and the other low in meat and supplying most of its energy from starches like brown rice, the starch-based diet won hands down.]

Ecology

Environmentalist vegetarians like to blame livestock for global warming, but according to Wikipedia:

In many countries where rice is the main cereal crop, rice cultivation is responsible for most of the methane emissions....Methane is twenty times more effective as a greenhouse gas than carbon dioxide.
[4/20/12:  This is an example of the half-truths used to support paleo perspectives.  How about taking a look at relative contributions of rice compared to animal products?  A study published in the American Journal of Clinical Nutrition calculated the amounts of greenhouse gases (carbon dioxide, nitrous oxide, and methane) emitted in the production of 22 different commonly consumed foods, in kg of CO2 equivalents per kg of final product:   Rice, 1.3;  eggs, 2.5; rapeseed oil, 3.0; chicken, 4.3; cod, 8.5; pork, 9.3; cheese, 11; beef, 30.  So the favored foods of low carb and paleo diets produce 2 to 23 times as much greenhouse gas emissions as rice.]

Further, rice fields are the principal breeding grounds for mosquitos that carry malaria.

So there you have my perspective on rice.   I do not recommend regular consumption of either brown or white rice. [Line through added on 4/20/12.]

[4/20/12:  I now highly recommend eating rice and other grains as staple foods, and I no longer recommend eating eggs, poultry, fish, pork, or beef or beef products.  Grains are far superior to meats and fats as human energy sources and for health support, and have much less deleterious effect on the environment.  Science has shown us that meat- and fat-based paleo dieting is not beneficial to human health, animal welfare, or for ecosystem preservation.]