(Originally posted January 10, 2018 on Medium: https://medium.com/@kevinnbass/the-data-do-not-support-the-idea-that-the-low-fat-dietary-guidelines-caused-the-obesity-epidemic-687e382894ed. Copied in full to Patreon September 21, 2018, with sporadic additional commentary as noted in the text.)

According to Dr. David Ludwig and many others endorsing the Low Fat Dietary Guidelines Caused Obesity Story (including Dr. Robert Lustig, journalists Gary Taubes and Nina Teicholz, and others), the Dietary Guidelines for Americans (1980) caused Americans to reduce fat consumption, increase carbohydrate to compensate for the reduction in fat, and become obese.

This occurred because, according to the story, carbohydrate is uniquely obesogenic: carbohydrate consumption is said to stimulate appetite and food intake. And, because carbohydrate consumption increased as a result of the dietary guidelines, the dietary guidelines can therefore be said to have caused the obesity epidemic. The conclusion: if we change the dietary guidelines Americans will eat fewer carbohydrates, and the obesity epidemic will be solved; in short, to regain our health, we must to return to the Lost Lower Carbohydrate Dietary Guidelines Golden Age.

I believe that a substantial range of data demonstrate that this story is incorrect and not even plausible from the point of view of a well-informed human behavioral ecology. However, for the time being, I will focus simply on refuting a core claim, namely that in response to the Dietary Guidelines for Americans, fat consumption was drastically reduced. I will demonstrate here that this claim is directly contradicted by the available evidence, namely that released by the Centers for Disease Control and Prevention (CDC) and United States Department of Agriculture (USDA). I know of no available evidence that supports this core claim of the story.

Although I have characterized the position that I will be providing evidence against, before proceeding let us focus on precisely the words used by the proponents of the story in question. I will focus on the claims of Dr. David Ludwig, in part because of his influence, in part because his statements are representative of the widely held narrative. But mostly, I will admit, because he told me I am wrong.

But unless I have made some fundamental error in my dozens of hours spent in front of Excel spreadsheets, poring through, organizing and re-organizing, and thinking about the data, then I am not wrong. I do not rule out the possibility that I have made such an error. Much stranger things have happened in science, to more gifted individuals.

Therefore I’ve no ego in this. But, I will argue against what I interpret as a popular myth, based upon a long and careful assessment of the data. I hope if someone has a different interpretation that they feel equally certain about, they will do the same in turn against me.


That’s a misleading statistic, Kevin. If we’re to look at trends, then total fat vs total carbs is more relevant — and that point is clear (it’s been the processed carbs). For a more complete review, see my pieces JAMA or CNN, linked here: https://t.co/GMriOyh8U7https://t.co/104Ap8D74H

 — @davidludwigmd

In providing these quotations, I will reference the above article, as well as the CNN and JAMA articles that Dr. Ludwig has provided as support for his claims in that original article.

Quotation from the original article that started this discussion:

Source: https://medium.com/@davidludwigmd/genetic-study-supports-carbohydrate-insulin-model-of-obesity-327d84be6d2b

(It is worth noting that Stephan Guyenet [Twitter: @whsource] has written an interesting rebuttal to this post of Dr. Ludwig’s, here: http://www.stephanguyenet.com/interesting-new-genetic-study-on-insulin-secretion-and-body-mass/. – KB 09/21/2018.)

It is worth noting here that Dr. Ludwig considers the “low-fat diet craze” a central point of contention, and indeed, as we shall soon see, the causal factor of the “flood” of processed carbohydrates that he believes is responsible for the obesity epidemic.

Now, let us take a look at the relevant quotation from the CNN article that Dr. Ludwig references in his tweet:

Source: https://www.cnn.com/2016/10/05/opinions/debate-low-fat-diet-ludwig/index.html

Here Ludwig cites unreferenced figures (>40% to ~30%) that I shall soon show are at odds with known facts. Perhaps more important, however, Ludwig causally links the replacement of fats with carbohydrates to “surging rates of obesity and diabetes”. Once again, we see how pivotal the notion of “low-fat” is to Dr. Ludwig’s explanatory schema — and how dramatic he considers the shift from the traditional American diet to the post-1980 low-fat diet to be. As we shall see, however, low-fat was neither causal in the increase in calories, nor was fat indeed reduced; fat increased after the guidelines were released.

Let us finally look at the relevant quotation from the Journal of the American Medical Association (JAMA) opinion piece that Ludwig referenced in his tweet:

Source: https://jamanetwork.com/journals/jama/article-abstract/2564564

Again, we find an unreferenced “30%” figure, as well as the claim that this 30% figure was caused by the dietary guidelines. The 30% figure is demonstrably untrue; the claim of causation by the guidelines is both unestablished and unreferenced, and I believe does not hold up to scrutiny when compared to the behavioral scholarship that is presently available to researchers.

What do the data say? We will begin by using USDA ERS data. USDA ERS data are obtained by USDA. USDA surveys food producers and compiles these records to estimate the total production in a country, county, city, etc. There are dozens of survey types, covering many types of food producers. USDA tries to capture data from all major food producers. USDA ERS supply data is considered a good proxy for consumption, though it cannot easily take into account waste. Because of this, calorie estimates per capita are often higher than what is actually the case. This is an important limitation of USDA data. However, USDA data are generally regarded as representative of food consumption trends, even as the number of absolute calories may be substantially lower.

With these caveats, let’s take a look at USDA supply data on fats and total calories.

As we can see, supplied calories from fat has consistently increased since 1910; they have not been decreasing relative to America’s traditional diet; they have been increasing; arguably, fat calories supplied increased at a faster rate post-1980 than before. This is not consistent with Ludwig’s claim that fat was reduced after the release of the Dietary Guidelines, nor with the claim that fat was higher before the guidelines.

Indeed, immediately after the guidelines were released, we actually see a small spike in fat calories supplied, the opposite of what we would expect if Ludwig’s hypothesis were true.

To remind ourselves of Ludwig’s claim that fat decreased, let us revisit his quotation from JAMA:

Note that Ludwig is correct that total calories have increased. Indeed, this increase, according to USDA and as we shall see, has largely been driven by an increase in fat calories — not carbohydrates.

Let us now take a look at the percent fat of total calories changes:

Although there is indeed a decline in fat calories as a total % of total calories, note how modest this decrease is, from 41% to 37%, or a 4% decline. Yet, this 4% decline in fat calories is claimed to account for the obesity epidemic.

Is this a plausible theory?

(Note, as a percentage of total calories, the increase in fat calories from 1980 to about 2000 (seen in the previous graphs) does not translate into an increase in fat %. This is because carbohydrate calories during the 1980–2000 period are increasing at an even faster rate than fat calories.)

Note, moreover, that by the year 2010, fat calories % was actually higher than in 1980. If Ludwig’s theory were true, we might therefore expect for carbohydrate intake to have decreased to levels below that of 1980. However, we can see that this is not the case:

Here we can see that carbohydrate intake in 2010 was still much higher than in 1980, and had only decreased modestly from its height in 2000 — despite a record high in fat intake (and, correspondingly, obesity).

Finally, let’s take a look at food categories and see what these have been doing over the past 40 years.

And here’s the whopper: over the past 20 years, fats have been the only major food category to increase. Everything else has gone down. Calories up, obesity up.

Perhaps most worrying for Ludwig’s thesis is that USDA reports a slow decline in calories since 1909, then a sudden sloping upward starting in the 60s and 70s.

The sloping downward makes sense: people are engaging in less physical activity and consume fewer calories. But the sudden increase in calories starting in the 60s and 70s needs to be explained. And it can’t be by Ludwig’s theory.

Now, it might be argued that food supply data do not adequately show real consumption trends. Let us therefore look at data from the CDC, obtained through the National Health and Nutrition Examination Survey (NHANES). NHANES, like USDA ERS, estimates food consumption, but through a different method: consumer surveys. I prefer USDA data, and I am not alone. It is objective. NHANES data reflect aspirations and what people believe they should be doing, rather than what they are doing. Multiple studies have shown that consumers underestimate total calories consumed — and especially fat. Obese people underestimate more than lean people.

Nonetheless, we will look at the NHANES data, and as we shall see, it too tells a different story than Ludwig’s. Let us start with total fat calories reported:

As we can see here, consumers actually reported an increase in fat calories just after the Dietary Guidelines were published. This contradicts Ludwig’s (and others’) claim that a decrease in fat calories caused people to eat more carbohydrates, becoming obese.

Moreover, if fat grams are increasing, then according to Ludwig, carbohydrates should be decreasing. Yet, according to NHANES data, carbohydrates went up dramatically:

Why carbohydrates went up is anyone’s guess. But it wasn’t driven by fat going down.

Now, what makes less sense is that even as fat in the food supply went up over 200 calories per capita according to USDA, reported fat only increased slightly. While this goes against Ludwig’s thesis, I don’t have a explanation that I am confident about for why this should be.

One possible explanation is that all of this added fat is in the form of cooking oils in restaurants. Because the cooking oils are thrown out after they are used, presto, consumers eat the same amount of fat, but more fat in the food supply is recorded. This is supported by the USDA data, if we take soybean oil to be the principal form of added oil in cooking oil.

For this explanation to work, we would need to see at least *some* decline in other sources of fat in USDA data to compensate. This is because if people are increasing their fat intake through restaurant-fried foods (if only modestly, i.e. much less dramatically than USDA would indicate), they would need to decrease their other sources of fat intake.

We see something like this in the USDA data. People consume less margarine, less tallow, less red meat, more chicken. Balanced out, people would seem to be consuming an uncertain amount more vegetable oils, and an uncertain amount of fat from other sources.

Another explanation is that as people get fatter, they progressively underreport their fat intake. This is supported by the findings of several papers. One, published in the International Journal of Obesity, reports particularly striking results, with an increase in underreporting as the obesity epidemic increases, with obese individuals underreporting more often than non-obese individuals. A screencap of the abstract:

This article may incidentally also explain why carbohydrate and calorie consumption seem to be going down in NHANES, even though the obesity rate continues upward only slightly slower than in previous years.

Finally, let’s look at the NHANES data reported as a % of fat — not total quantity.

From 38% to 34%, despite an increase in total fat. A far cry from >40% to nearly 30%, which is Dr. Ludwig’s charge. This change literally consists of a few grams of fat per day, causing the obesity epidemic. Again, note that the total fat calories are identical in 2010 to those in 1980. Only the total calories have changed.

Wrapping up. As food for thought, let’s look at China, perhaps one of the most dramatic cases of an explosive and sudden obesity epidemic in the known record. What does China teach us?

(Macronutrient figure adapted from Wan, 2017. Diabetes data from Shen et al, 2014; overweight/obesity data from WHO.)

(And to answer the pre-empt the question: no, it’s not because of an increase in sugar. Sugar consumption in China has remained incredibly low and stable for the past half century.)

To nutrition afficionados in these days, such graphs may strike some as confusing, even bizarre. In part, this is because a lot of us have been taught that carbohydrates cause obesity. But again, epidemiologists have known for generations that the nutrition transition accompanying industrialization classically looks like China’s — with the attendant diseases.

People deserve to know the truth. The truth goes deeper than anything presented by the low carbohydrate advocates. And it is much more complex than anything I have presented here. But only with the truth can we solve our present crisis of obesity and chronic disease.

The low-fat-caused-obesity story is a myth, and one that needs to die. Will Dr. Ludwig help us put this myth to rest? We can hope. The sooner we can come to an agreement, the sooner we can solve the present crisis — which is one of far greater significance than merely health, as Dr. Ludwig has written — and help the many people who struggle with their weight and their health.

In the meantime, for an in my opinion excellent overview of what many obesity researchers do think makes us fat, I recommend obesity researcher Kevin Hall’s recent article, “Did the Food Environment Cause the Obesity Epidemic?” http://onlinelibrary.wiley.com/doi/10.1002/oby.22073/full

I look forward to comments and criticisms.


As an MD/PhD student, my passion is for communicating the cutting edge of medical science and fighting misinformation. If this post is of use to you, please consider donating to my Patreon account. Your contribution will make a significant positive impact, and I will be greatly personally appreciative.

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