This thread was originally posted here.

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Let’s be clear Zoe. This is an hypothesis that has all available evidence against it.

USDA and FAO data both show fat going up since the dietary guidelines were released–and more than carbohydrates.

I will show this in the following, comprehensive article.

Here are USDA and FAO dietary trend data in the attached graphs:

As we can see, the “gap” between carbohydrates and fats narrows over time, indicating a faster rise of fats compared to carbohydrates.

Below is the above data, but with a breakdown for each nutrient class:

These observations suggests that the claim that reduced fat caused carbohydrates to go up is wrong.

In addition, obesity trends also seem to contradict the claim that dietary guidelines caused the obesity epidemic. As we can see below, obesity has been steadily increasing since at least the 1880s–a century before the Dietary Guidelines:

Not unimportantly, USDA does have a food availability dataset that goes back almost this far, using a different methodology to document years prior to 1970. The parallels between the increase in obesity and this dataset are striking. (Look at the two graphs side-by-side.)

Here, we can see that the macronutrient that consistently and inexorably increases is fat, not carbohydrate.

Possibly deadly in our case, however, is the spike in carbohydrates starting in 1980, which we will return to later. 6/nNext, we can turn to the acceleration in the increase of obesity. This can be seen by taking the derivative (a mathematical operation) of the Komlos & Brabec graphic:

(The above graphic is for white men. The patterns for other genders and ethnicities are different and worth exploring at length some other time. But all show the same basic trend: gradual increase.)

The graphic shows that while those at the higher end of the BMI scale are gaining weight at an accelerating rate, the present acceleration did not start after the Dietary Guidelines for Americans were released, but 30 years earlier–around 1950.

What’s more, the above graph is roughly consistent with the food availability data. If we look closer (below), we see that calories also inflect at roughly 1960–20 years before the Dietary Guidelines:

It is likely that many factors account for the recent explosion in obesity, but whatever they are, the above evidence suggests that the seeds were planted in the 1950s or 60s or even the 1870s or 80s–not the 1980s. So, neither of these datasets, which do not rely on subjective self-reports, are consistent with is the hypothesis that the Dietary Guidelines caused the obesity epidemic.

There is however one other major dataset to look at: NHANES, the national health survey that tracks food consumption not by looking at the food supply, but by surveying a selection of the general population. And it is certainly conceivable that NHANES might be more representative than food availability data. This is perhaps why David Ludwig, possibly the most highly qualified defender of the carbohydrate-obesity hypothesis, chose to include NHANES but not FAO or USDA in his recent article defending the carbohydrate-insulin model of obesity:

To support this, Ludwig cites the paper by Ford & Dietz, which shows the following graph:

Here, we can see a spike in % calories from carbohydrates and a drop in % calories from fat between NHANES II and NHANES III. This is thought by the low-carbohydrate camp to have been the result of the 1980 Dietary Guidelines for Americans. This interpretation certainly would fit the temporal picture of recent rapidly increasing obesity, prior increases and other caveats notwithstanding. Upon closer examination, however, we see a small problem: the increase in carbohydrate % and decrease in fat % is driven entirely by an increase in carbohydrate intake of approximately 60g/d or 240cal/d:

This doesn’t undermine @davidludwigmd’s case, since Dr. Ludwig is only saying that carbohydrate and insulin drive obesity in article, not necessarily that low-fat drove carbohydrate intake.

Still, one wonders how this increase in carbohydrate should have occurred without a drop in fat intake, if fat reduction was major driver of the uptick in intake. Could it have been A.) that “low-fat” foods, lacking fat, caused people to eat more of them to get “sufficient” fat? There is no evidence that appetite is driven in this way and ample evidence against it. I do not believe this is a plausible hypothesis. If someone believes that evidence does support this, I am eager to hear how they come to this conclusion.

Another explanation. Could it have been that B.) people used “low-fat” health-washing to self-justify increasing their intake of simple sugars and other refined carbohydrates? According to this hypothesis, people did not limit fats and increase carbohydrates, but simply increased carbohydrates in accordance with “low-fat” marketing, i.e. industry colluded with the consumer in a circle of mutually deceptive consumption. This has some face validity: it is after all difficult to forget discussions by some prominent low-carbohydrate that one might be able to eat as many fat calories as one wishes, so long as one does not consume carbohydrate.

Were similar sorts of claims made about low-fat diets during the low-fat heyday? Were such things implied in the popular media? If it could be shown that this did occur, this might explain why carbohydrate intake might have increased. To be sure, this explanation and narrative would implicate both industry and the consumer–and possibly government for idly sitting by while this took place–and is very different than the anti-Dietary Guidelines narrative.

To return to our analysis.

Bear in mind that this increase in carbohydrate was also an increase in calories. Therefore, the hypothesis that carbohydrate increase might have caused the uptick in obesity is confounded by the calorie increase. One would need to show that carbohydrates have special obesogenic properties, beyond that of their calorie content. However, it is not clear why we should focus on the carbohydrate rather than the calorie component of the increased intake in the NHANES data, given Kevin Hall’s experiments over the past few years showing no metabolic advantage of carbohydrate-restricted diets.

Two of these classic papers can be found here and here.

To complicate matters, the NHANES data themselves are questionable, as made clear by Edward Archer and colleagues in a 2013 paper. In this paper, Archer notes that the methodology of NHANES II and III was entirely different, leading to an artifactual increase in reported calories. Please read the highlighted portion below:

Since the only source of additional calories was carbohydrates, this suggests that the spike in carbohydrate consumption was “merely an artifact”.

This explanation however does not square with the food availability data, which show a very clear increase in carbohydrate consumption during approximately the same period as the transition from NHANES II to NHANES III:

(It is worth noting that the spike in carbohydrate consumption starts before 1980, as we can see below. On the other hand, the argument might be made that low-fat recommendations from official organizations were being made for years prior to the release of DGA. So…)

This implies perhaps that at least a part of the increase from NHANES II to NHANES III was not in fact artifactual. However inasmuch as carbs were increasing before 1980, it is still not possible to fully square the USDA data with the NHANES data.

To evaluate this further, it would be necessary to carefully examine Dr. Archer’s analysis.

Finally, in NHANES, carbohydrate consumption is generally increased or fat consumption decreased among the lean:

This suggests that even if carbohydrate consumption did increase and/or fat consumption decrease (as suggested by the probably deeply flawed NHANES data), this pattern was protective against obesity. This is at odds with the overall macronutrient trend. This is evidence that the correlation between the macronutrient trend in NHANES and obesity is not a causal relationship. This would suggest to us the interpretation that obesity happened in spite of such macronutrient ratio changes, not because of them. If this is so, this is a good example of correlation ≠ causation, which we know from our study of epidemiology.

To continue along this line of thinking, another group, looking at all NHANES wave data, concluded that replacing fat with carbohydrate was actually associated with a decreased energy intake:

Earlier research has suggested similarly (I do not mean to imply that all research says this.)

In any case, while NHANES did show a per capita increase in carbohydrate intake, this pattern either A.) did not actually occur on a population level, or B.) is not, according to NHANES, associated with higher BMI, but in fact a lower BMI on an individual level. These facts seriously qualify or possibly compromise conclusions about macronutrient trends that might be drawn from the NHANES dataset.

It is worth pointing out that other studies of the food intake from NHANES show that the carbohydrate intake pattern appears exceedingly unhealthy:

I suggest because these data indicate unhealthy eating patterns, they’re less likely to be the result of misreporting and thus more likely to be trustworthy. In fact, evidence suggests that they probably underestimate the unhealthfulness of typical American intake. This is suggested by research summarized and presented in Archer et al’s above 2013 paper:

If we therefore assume that *these* NHANES data are more reliable than the macronutrient trend data, we may conclude that American carbohydrate intake is unhealthy and likely to include lots of simple sugars and added fats, which research shows are easy to overconsume. And perhaps this gets to the heart of the matter.

It does not seem like a stretch therefore to propose that success on a low-carbohydrate diet may in fact in large part if not entirely result from eliminating such hyperpalatable, low-quality, highly calorie dense foods. This would suggest that attributing success from carbohydrate restriction to carb restriction as such is possibly confounded by restrictions in calorie density, palatability, food diversity (the latter leading to the well-known phenomenon of sensory-specific satiety), etc. This interpretation, and probably other related explanations (recommended: Stephan Guyenet’s book), helps explain the real-world success of carbohydrate restriction, despite a lack of evidence from the dietary trend data showing carbohydrate intake to be the *cause*.

And despite the possibility that carbohydrate restriction as such may not account for the weight loss results of carbohydrate-restricted diets (given some, but not all, human experimental data). I would also like to cite one major, and in my opinion definitive, piece of evidence that places the macronutrient trend data in context: Most if not all developed countries have over the past century demonstrated similar reductions in carbohydrate %, coincident with increases in fat intake, obesity, and metabolic disease. The case of China is just one of many examples of what may be considered an almost iron-clad trend of reduced carbohydrate and increased fat in the course of modernization.

These macronutrient and disease trends seem to be continuing even currently in most if not all developed countries, including the United States. I do not have the space to demonstrate this here, but this is my belief based on looking at the data from dozens of countries; a more formal analysis of the currently available data updating this line of thought using the available national statistics may be warranted, if other investigators have not already done this.

Broadly speaking, these trends are known as the nutritional and epidemiological transitions. They accompany modernization and have been universally accepted phenomena in the research literature for the past 50 years. 

Awareness of this literature is one of the main reasons that I find the “low-fat caused obesity” narrative so strange. It goes against universally accepted historical trends, where increased fat, decreased carbs coincides with increased obesity in virtually every society. Interestingly, it may be that the United States is one interesting exception to this trend, in a way, in that it has not successfully reduced carbohydrate intake coincident with increased fat intake; I suggest that this may explain the severity of America’s obesity epidemic: carbohydrate and fat calories have rapidly increased at the same time, again, unlike in other countries, where, while many are experiencing worsening epidemics of metabolic disease, carbohydrate calories have often decreased while fat has increased.

This may lend partial credence to the Dietary Guidelines iz Evilz people, but only really indirectly and not for the reasons they think. This hypothesis is at least indirectly testable, as is the proposal that health-washing may have led to this increase in carbohydrate intake (as I’ve discussed above), albeit not immediately by hard science.

Finally, it is worth pointing out, in response to Zoe’s claim that she cannot think of anything else that can account for the increase in obesity over the past 50 years:

1. Directly after WW2, the promise of pristine suburban life was a prominent cultural feature and may have coincided with reduced physical activity; we know that physical activity is an extremely important component of weight management, as Kevin Hall has recently shown data for in presentations.

2. Post-WW2 women’s rights movements and the movement of women from the home to the workforce, reducing availability of home-cooked meals. We know that countries that seem to have successfully maintained traditional food cultures and fended off rapid increases in obesity—Japan, Korea, Singapore—have very traditional cultural arrangements around gender. On the other hand, other countries that are even more traditional have seen a rapid increase in obesity, and this discrepancy must be accounted for.

3. The rapid rise of hyperpalatable food design, processing, and availability. (David Kessler’s End of Overeating, Michael Moss’s Salt Sugar Fat are a good start here.) Many other explanations may help to explain the rise of the modern food environment, which is probably the final, upstream outcome of all these social forces that really took off in the post-WW2 period. This is introduced in Kevin Hall’s article. These factors are widely known and discussed. It is surprising that, given her long involvement in this field, Zoe seems to be unaware of them and focuses so much on carbohydrates.



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