Monday, February 21, 2011

The China Study II: Wheat, dietary fat, and mortality

In this post on the China Study II data we have seen that wheat apparently displaces dietary fat a lot, primarily fat from animal sources. We have also seen in that post that wheat is strongly and positively associated with mortality in both the 35-69 and 70-79 age ranges, whereas dietary fat is strongly and negatively associated with mortality in those ranges.

This opens the door for the hypothesis that wheat increased mortality in the China Study II sample mainly by displacing dietary fat, and not necessarily by being a primary cause of health problems. In fact, given the strong displacement effect discussed in the previous post, I thought that this hypothesis was quite compelling. I was partly wrong, as you’ll see below.

A counterintuitive hypothesis no doubt, given that wheat is unlikely to have been part of the diet of our Paleolithic ancestors, and thus the modern human digestive tract may be maladapted to it. Moreover, wheat’s main protein (gluten) is implicated in celiac disease, and wheat contains plant toxins such as wheat germ agglutinin.

Still, we cannot completely ignore this hypothesis because: (a) the data points in its general direction; and (b) wheat-based foods are found in way more than trivial amounts in the diets of populations that have relatively high longevity, such as the French.

Testing the hypothesis essentially amounts to testing the significance of two mediating effects; of fat as a mediator of the effects of wheat on mortality, in both the 35-69 and 70-79 age ranges. There are two main approaches for doing this. One is the classic test discussed by Baron & Kenny (1986). The other is the modern test discussed by Preacher & Hayes (2004), and extended by Hayes & Preacher (2010) for nonlinear relationships.

I tested the meditating effects using both approaches, including the nonlinear variation. I used the software WarpPLS for this; the results below are from WarpPLS outputs. Other analyses of the China Study data using WarpPLS can be found here (calorie restriction and longevity), and here (wheat, rice, and cardiovascular disease). For yet other studies, click here.

The graphs below show the path coefficients and chance probabilities of two models. The one at the top-left suggests that wheat flour consumption seems to be associated with a statistically significant increase in mortality in the 70-79 age range (beta=0.23; P=0.04). The effect in the 35-69 age range is almost statistically significant (beta=0.22; P=0.09); the likelihood that it is due to chance is 9 percent (this is the meaning of the P=0.09=9/100=9%).


The graph at the bottom-right suggests that the variable “FatCal”, which is the percentage of calories coming from dietary fat, is indeed a significant mediator of the relationships above between wheat and mortality, in both ranges. But “FatCal” is only a partial mediator.

The reason why “FatCal” is not a “perfect” mediator is that the direct effects of wheat on mortality in both ranges are still relatively strong after “FatCal” is added to the model (i.e., controlled for). In fact, the effects of wheat on mortality don’t change that much with the introduction of the variable “FatCal”.

This analysis suggests that, in the China Study II sample, one of wheat’s main sins might indeed have been to displace dietary fat from animal sources. Wheat consumption is strongly and negatively associated with dietary fat (beta=-0.37; P<0.01), and dietary fat is relatively strongly and negatively associated with mortality in both ranges (more in the 70-79 age range).

Why is dietary fat more protective in the 70-79 than in the 35-69 age range, with the latter effect only being significant at the P=0.10 level (a 10 percent chance probability)? My interpretation is that, as with almost any dietary habit, it takes years for a chronically low fat diet to lead to problems. See graph below; fat was not a huge contributor to the total calorie intake in this sample.


The analysis suggests that wheat also caused problems via other paths. What are them? We can’t say for sure based on this dataset. Perhaps the paths involve lectins and/or gluten. One way or another, the relationship is complex. As you can see from the graph below, the relationship between wheat consumption and mortality is nonlinear for the 70-79 age range, most likely due to confounding factors. The effect size is small for the 35-69 age range, even though it looks linear or quasi-linear in that range.


As you might recall from this post, rice does NOT displace dietary fat, and it seems to be associated with increased longevity. Carbohydrate content per se does not appear to be the problem here. Both rice and wheat foods are rich in them, and have a high glycemic index. Wheat products tend to have a higher glycemic load though.

And why is dietary fat so important as to be significantly associated with increased longevity? This is not a trivial question, because if too much of that fat is stored as body fat it will actually decrease longevity. Dietary fat is very calorie-dense, and can be easily stored as body fat.

Dietary fat is important for various reasons, and probably some that we don’t know about yet. It leads to the formation of body fat, which is not only found in adipocytes or used only as a store of energy. Fat is a key component of a number of important tissues, including 60 percent of our brain. Since fat in the human body undergoes constant turnover, more in some areas than others, lack of dietary fat may compromise the proper functioning of various organs.

Without dietary fat, the very important fat-soluble vitamins (A, D, E and K) cannot be properly absorbed. Taking these vitamins in supplemental form will not work if you don’t consume fat as well. A very low fat diet is almost by definition a diet deficient in fat-soluble vitamins, even if those vitamins are consumed in large amounts via supplements.

Moreover, animals store fat-soluble vitamins in their body fat (as well as in organs), so we get these vitamins in one of their most natural and potent forms when we consume animal fat. Consuming copious amounts of olive and/or coconut oil will not have just the same effect.

References

Baron, R. M., & Kenny, D. A. (1986). The moderator–mediator variable distinction in social psychological research: Conceptual, strategic, and statistical considerations. Journal of Personality & Social Psychology, 51(6), 1173-1182.

Preacher, K.J., & Hayes, A.F. (2004). SPSS and SAS procedures for estimating indirect effects in simple mediation models. Behavior Research Methods, Instruments, & Computers, 36 (4), 717-731.

Hayes, A. F., & Preacher, K. J. (2010). Quantifying and testing indirect effects in simple mediation models when the constituent paths are nonlinear. Multivariate Behavioral Research, 45(4), 627-660.

29 comments:

1leone said...

Execuse my ignorance but could you explain what exactly means "one of wheat’s main sins was indeed to displace dietary fat from animal sources" or point me towards an article where you may have discussed this.

Many thanks for your work,
Leonardo

Ned Kock said...

Hi Leonardo. A link to a previous post discussing relevant evidence (from HCE) is right at the top of this post.

anonymoose said...

For vegetarians, if consuming copious amount of olive/coconut oil isn't enough to provide the fats needed for vitamin a/d/k absorption... what about fat from dairy?

And since milk already contains vitamins d (and k?) perhaps no need for supplementation.

My mother used to make us drink a glass of warm whole milk with a tablespoon of cod liver oil every night.. yech!

Peter said...

I've read that in Southern India, where they favor rice, they have far more heart disease than in northern India where they eat a lot wheat.

bee said...

peter,
punjab has the most obesity in india and also produces and consumes the most wheat in india.

http://en.wikipedia.org/wiki/Obesity_in_India

Ned Kock said...

Hi anonymoose. Those oils would indeed provide the fat needed for absorption of fat-soluble vitamins. They simply wouldn’t provide the same vitamin content, methinks. The fat from milk seems like a better choice over oils to me; from, e.g., butter, ghee, cream, and aged cheese.

Ned Kock said...

If you look at the states in India and the incidence of obesity, the numbers are all over the place. For example, the two top states in terms of overweight and obesity are Punjab and Kerala, which are at the very top and bottom of the map, respectively.

Tuck said...

Fascinating post, as always.

Two observations: One, why do you say that eating fat leads to storing fat? From what I've been reading lately, eating fat does not lead to storing fat, at least not to more than a small amount of fat. In animals similar to man, you can't induce obesity by over-feeding animal fats (note the qualifier).

Second, as to why fat may be protective in the older population, Peter at the Hyperlipid blog has pointed to studies where high blood cholesterol is protective in elder people. High HDL cholesterol seems to be correlated with high consumption of saturated fat.

My own anecdote is that wheat's ill effects on me occur even now that I'm on a high-fat diet. Given that these ill effects led to one surgery already, I have no trouble doubting your hypothesis that wheat is linked with mortality. It was nearly linked with my mortality. :)

Stargazey said...

Tuck, I was one of the people who (sort of) fell for Charles Washington's version of the Zero-Carb Path. Some people recommended adding fat trimmings to the meat. I did and *bingo* love handles for the first time since I reached my goal weight on low-carb. I stopped the extra fat and the love handles disappeared.

Ned, as far as eating animal fat, yes vitamins could be stored in the fat. But so can hormones, antibiotics, pesticides and herbicides. Just something to think about.

Ned Kock said...

Hi Tuck. Indeed, there are associations between things like moderately high BMI (around 25) as well as lipids and health in older folks. Those associations may due to other factors; it is a bit hard to rule out confounders.

Dietary fat becomes body fat very easily, and under normal circumstances it is also released very easily. Abnormally high insulin levels tend to prevent body fat from being released.

If one’s glycogen stores are depleted, normally carbs will not become body fat; nor will protein. But dietary fat will, as it cannot be used to replenish glycogen.

In the end, the three macronutrients (plus alcohol, for those who drink) will contribute to meeting the caloric needs of the person consuming them. Calories count, even though they are not everything.

One of the big problems that modern humans face seems to be not releasing the stored fat when it is needed, in which case a person will be getting fat and feeling hungry at the same time.

Ned Kock said...

Hi Stargazey. Good point, toxins are also stored in animal fat. And the higher in the food chain the animal is, the more concentrated they are. A good reason to stay away from top predators as a source of food, on both land and water. And to consume organic animal foods.

Ravi said...

Hi Ned - thanks yet again for another great post -

i'm searching - to no avail - for SPECIFIC data on the actual reduction of gluten, phytates and (and WGA for wheat) when the grains are treated and soured in the "traditional" way (as per weston price) my personal feeling is that it's still a toss-up as to whether there is ultimately a net-positive nutritional benefit eating a properly soured rye bread (for example) as we really don't know if there is still enough of the less-desirables to make the nutritional gains of the grains worth it. My suspicion is that Weston Price erroneously assumed that the soured rye breads being consumed by the Swiss were net-beneficial - however when you look at the tooth decay data - the swiss mountain people, although very low in caries compared to modern-refined food eaters, were still considerably higher than cultures consuming NO grains at all (an exception being the Gaelic people who had their fermented oats but loads of seafood) -

waddya think?

Ravi

Anonymous said...

@Peter

It is actually the other way around.. or at least used to be. Kerela used to have the least cases of CHD until seed/vegetable oils replaced use of coconut oils ..I think in 70s. Northern India (and also central and western) have the highest rate of obesity and CHD since they consume mostly wheat based products.
Even in Northern India and also all other states where wheat was consumed at a higher rate the CHD cases rose only after seed/vegetable oils were introduced. These oils replaced use of Ghee (clarified butter) or palm oil (among lower middle class and below).
Still it seems wheat was the major cause of obesity and CHD.

Ned Kock said...

Hi Ravi. There is good evidence suggesting that traditional methods, such as soaking and fermentation, significantly reduce phytate content:

http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=909168

Crazy as it may sound, there are some researches who believe, also based on reasonable empirical evidence, that phytates can also be health-promoting:

http://linkinghub.elsevier.com/retrieve/pii/027153179500040P

Perhaps traditional methods don’t complete eliminate the toxins, but I don’t think that was the main reason for the differences in tooth decay unveiled by Price. I am talking, like you, about differences among the isolated groups. The modernized ones were uniformly disastrous.

The isolated Loetschental folks had an interesting diet, with most of their nutrition coming from raw milk and cheese made from raw milk. That was apparently plenty. They also had an active lifestyle. It is difficult to tell whether the rye bread helped or hindered.

The Eskimos and other big meat-eaters studied by Price had many fewer cavities, but that may have been due to them having to chew their food a lot more. Chewing tough foods seems to make a whole lot of difference.

For example, there is research showing that chewing sugar cane leads to many fewer cavities than eating refined sugar, even if you consume more sugar via the sugar cane route.

thhq said...

Thank you for the analysis and musings, Ned. I find this post more interesting for portraying the macros of the study group: average weight 116 pounds, consuming 2500 calories per day of a very high GI diet by western standards for optimal health.

These people are by implication VERY active. 700 cslories per day is a huge amount of activity - at that weight something equivalent to a 20 mile hike. Forget about lectins, Taubes and neandratals for a moment and look at what the billboard is screaming. Be your own ox! Shovel in the carbs!

For this kind of life they are essential fuel. Rice and wheat are not junk foods.

Ned Kock said...

Hi thhq. You may be referring to numbers on a different post, covering the same China Study dataset.

But your point that physical activity may make a huge difference is a very good one.

One can burn an extra 700 calories relatively easily through work-related physical activity throughout the day. If you are a top-level athlete in some sports, like swimming, you’ll burn a lot more than that.

Doing some 20-50 minutes of strength training 2-3 times a week may also work, because it may significantly increase your caloric expenditure from nonexercise activity thermogenesis (NEAT). The same amount of aerobic exercise will not likely have the same effect.

thhq said...

I'm wondering how far you can take these conclusions Ned. First, this is not 3-4 times a week and voluntary but every day for your whole life. I have noticed that some paleo bloggers downplay activity to promote diet purity. Yet the activity is more definitive than the food - what part of hunter/gatherer aren't they getting - and in a less powered transportation driven culture like China perhaps the same is true. Second, a dietary breakdown would be helpful. Simplistically I associate wheat with buns and noodles - city food - and rice with farmers. If correct wheat vs rice implies major lifestyle differences which could also help to explain mortality differences.

I'm not a member of the wheat lobby. I'm just a dietary inclusionist. Based on personal experience I rank overeating and inactivity to be of much higher importance for CV health compared to dietary choices. Your statistics on CV health (wheat vs rice diets) support this too, though things may change after I reach age 70.

David Isaak said...

Actually, I think our Paleo ancestors probably DID eat wheat (Neanderthals ate grains), but not in anything like the quantities before the advent of farming.

Whether or not our digestive systems are intolerant of wheat is an interesting question. There is some research in Europe that suggests intolerance to gluten is not caused by gluten per se, but instead caused by major yeast infections. The yeast express some proteins that share sequences with the gliadins in wheat, and those happen to be the same proteins the immune system uses as templates for the antibodies.

So the body may not have problems with wheat until it has had an intestinal yeast problem.

The plot thickens!

David Isaak said...

I'm a big fan of physical activity. But I've known people who worked at hard physical labor pretty much every day and still had massive beer bellies (and developed Type II diabetes). So activity alone is insufficient to preserve health.

thhq said...

Inactivity AND overeating David. My Norwegian grandpa was built like a barrel and worked hard as a mechanic, but he overate dairy products and died from CV problems in his mid 70s. But people that emigrated away from starvation didn't give much thought to calorie restriction. They just took their nitroglycerin tabs and went on eating.

The China study interests me because the participants are small, active, healthy (? I'm assuming) and eating way outside the American plan, be it paleo, vegan or USDA pyramid. No one recommends a diet consisting of 80% high GI grain products that I've ever heard of. They should write a book and go on TV.

Ned Kock said...

I think both of you, thhq and David, make very good points. Making diet and lifestyle changes for health improvement is a multi-factorial “game”, whose stakes and obstacles get increasingly higher as we get older.

The analysis in this post tries to make the best out of a limited dataset, and essentially shows that wheat’s negative effect is not completely subsumed by dietary fat displacement.

But the point that wheat flour consumption is too generic a variable is absolutely true. It is quite possible that the problem is not with wheat itself, but with engineered foods that are wheat-based.

As consumption of those foods goes up, so does consumption of wheat, and hence the strong associations. As I said here before – it is not hard to lie with statistics.

Humans are very good engineers. And engineered foods are designed to increase consumption, thus increasing profits, not to make people healthy.

thhq said...

Ned, being an engineer maybe I'm biased, but I don't see anything sinister about a bun or a noodle. I'm not disagreeing with the idea of putting the grain directly into a cooker to maximize the health benefits. However cooking itself is the ultimate engineering feat: converting indigestible starch into food. Should one quit milling, or adding spices (the original food additives, which still mask bad ingredients) which are also engineering?

Here in WA they're building new silos. China wants more wheat.

Ned Kock said...

I’m also an engineer. There is nothing sinister with good food engineering. But it doesn’t, in its current state, maximize long-term health.

If we were able to transport a few or our ancestors from 500 thousand years ago to a big city today, my guess is that they would want to eat nothing else after trying engineered food products.

They would develop the diseases of civilization, but might well live longer than they would 500 thousand years ago ;-)

thhq said...

Ned you have fired me up for one of my favorite rants. I'll do the short form:

Why would you want to go back 500,000 years? For whatever reason paleo didn't work out the first time and the human race has moved on to eating grain.

To get back to your original Aryan you'd have to deselect for maybe 50 generations using a huge gene pool. Fat chance of that happening unless several billion of us suddenly die from eating wheat. Even then it would fail. We got here linearly by selection - through random famines, wars and other catastrophes - and we wouldn't trace the line backwards to paleo even if the only thing we had to eat was steak.

I've pretty much had it with these humorless spouters of anti-wheat, anti-milk venom.

William said...

Hi Ned, great post. Where did you find information about wheat consumption and the French?

Thanks,
Bill

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