Tuesday, July 8, 2008

Wheat in China

Dr. Michael Eades linked to an interesting study yesterday on his Health and Nutrition blog. It's entitled "Vegetable-Rich Food Pattern is Related to Obesity in China."

It's one of these epidemiological studies where they try to divide subjects into different categories of eating patterns and see how health problems associate with each one. They identified four patterns: the 'macho' diet high in meat and alcohol; the 'traditional' diet high in rice and vegetables; the 'sweet tooth' pattern high in cake, dairy and various drinks; and the 'vegetable rich' diet high in wheat, vegetables, fruit and tofu. The only pattern that associated with obesity was the vegetable-rich diet. The 25% of people eating closest to the vegetable-rich pattern were more than twice as likely to be obese as the 25% adhering the least.

The authors of the paper try to blame the increased obesity on a higher intake of vegetable oil from stir-frying the vegetables, but that explanation is misleading. A cursory glance at table 3 reveals that the vegetable-eaters weren't eating any more fat than their thinner neighbors. Dr. Eades suggests that their higher carbohydrate intake (+10%) was partially responsible for the weight gain, but I wasn't satisfied with that explanation so I took a closer look.  Dr. Eades also pointed to their higher calorie intake (+120 kcal/day), which makes sense to me.

One of the most striking elements of the 'vegetable-rich' food pattern is its replacement of rice with wheat flour. The 25% of the study population that adhered the least to the vegetable-rich food pattern ate 7.3 times more rice than wheat, whereas the 25% sticking most closely to the vegetable-rich pattern ate 1.2 times more wheat than rice! In other words, wheat flour rather than rice was their single largest source of calories. This association was much stronger than the increase in vegetable consumption itself!

All of a sudden, the data make more sense. Wheat seems to associate with health problems in many contexts. Perhaps the reason we don't see the same type of association in American epidemiological studies is that everyone eats wheat. Only in a culture that has a true diversity of diet can you find a robust association like this. The replacement of rice with wheat may have caused the increase in calorie intake as well. Clinical trials of low-carbohydrate diets as well as 'paleolithic diets' have shown good metabolic outcomes from wheat avoidance, although one can't be sure what role wheat plays from those data.

I don't think the vegetables had anything to do with the weight gain, they were just incidentally associated with wheat consumption. But I do think these data are difficult to reconcile with the idea that vegetables protect against overweight.

16 comments:

Debs said...

I'm surprised that the sweets/cake diet didn't have an effect on obesity. Was the cake flour wheat-based or rice-based?

That conclusion about the use of oil for stir-frying does seem pretty inane. Sadly unsurprising, though.

Stephan said...

I don't know what the cake was made of, but I wouldn't necessarily assume it was wheat. They make cakes out of rice flour. I also thought it was curious that there was no association with weight gain there.

reid said...

Rice has traditionally had such a strong association with most asian cultures. I wonder what the reason is for the recent shift towards wheat? Perhaps an economic or media influence?

Stephan said...

I don't know. I suspect it has something to do with the fact that wheat is the food of affluent Western nations.

John said...

"Dr. Eades suggests that their higher carbohydrate intake (+10%) and higher calorie intake (+120 kcal/day) are responsible for the weight gain..."

+120 kcal/day seems like a reasonable and adequate explanation for why this group showed more obesity. Am I missing something?

Stephan said...

John,

Absolutely. But the big question is "why were they eating 120 more kcal per day"?

I believe wheat causes overeating, among other problems. This study is consistent with that.

John said...

Ah,yes, and so you plainly said, Stephan. Sorry.

"The replacement of rice with wheat may have caused the increase in calorie intake as well, subsequent to metabolic dysfunction."

Cynthia said...

I think that you can literally "pack more in" when you are eating flour as opposed to grain. Also when the grain is pre-digested (milled) the absorption rate is likely to be faster. I agree that it is odd that the cake and sugar diet didn't result in weight gain.

Karn said...

I think I am guilty of eating the "Macho Diet"!

Nico said...

Actually, a large part of China- the north- always had a wheat-based diet, mostly in the form of noodles, steamed buns, and flat bread. Rice is the staple in the south of China. I don't know how the paper addresses this, as I haven't read it.

Pavitar said...

"Wheat is the food of affluent Western nations"... I beg to differ. My ancestors in the north of India have been eating wheat based breads like chapati, and naans for centuries, as have many people in the middle east. Leavened and unleavened bread are wheat based.

Stephan said...

Hi Pavitar,

Yes, of course other cultures eat wheat as well. That does not contradict my statement.

Peter said...

I've read that there is much more heart disease in Southern India where they eat rice than in Northern India where they eat wheat. I would have thought it would be the other way around.

Peter said...

Do the starches the Africans eat in their traditional diets raise their blood sugar even though they don't seem to cause heart disease and diabetes? I' trying to figure out why their starches are ok and ours aren't.

lori pickering said...

If rice remains in the digestive track longer, it may relay satiation messages to the brain for a longer length of time. This would account for a greater length of time between feeding for the rice population, which may also contribute to a lower overall calorie intake.

Additionally, if wheat supplies the body with a quicker, more readily absorbed source of glucose then blood glucose levels will spike higher than they would for the rice. The body will respond with a higher output of insulin to absorb the glucose. Then, the "glucose crash" following the transitory hyperinsulmia, will result in a greater drop in blood glucose levels for the wheat eaters than for the rice eaters. This will cause the wheat eaters to "feel" hungrier sooner and more intensely than the rice eaters. The result is a tendency to eat more often, and consequently more calories.

r l love said...

lori,

I read somewhere that processed flours are being recognized as simple sugars instead of complex sugars and thereby causing insulin spikes. Is that what you are referring to in your comment?