In response to my first post, Dr. Ludwig responded with his own. I have recopied it here in full, with his permission. Additionally, for illustration, I have added figures from several of the papers that he references in the appropriate places in the text.

(Originally posted January 10, 2018 on Medium: https://medium.com/@davidludwigmd/hi-kevin-appreciate-the-scholarly-debate-58a6b7df1bff. Copied in full, with added figures in the text.)

Dr. Ludwig:

Hi Kevin, appreciate the scholarly debate. Just a few brief comments. First, to be clear, I said your statistics were misleading, not that you’re wrong.

Ok, so what’s misleading? First, food availability data (see the bottom left caption in most of your figures) do not accurately reflect what is actually consumed. Nor do added oils, the focus of your comments elsewhere, reflect total fat intake. We know that the food supply contains about 3,900 kcal per person. Though actual calorie intake has gone way up, it’s nowhere near that level. Also, we need to be careful of self-report data, which has much selective bias.

Admittedly, data on dietary intakes can be problematic, but the long term trends are clear. Stephen and Wald summarize data in the US during the 20th century, estimating that in 1960 the proportion of calories as fat was about 40%.

The CDC has good data that proportion of dietary fat decreased to about 33% by 2000 (ie, near the government recommended level). The 2 figures in that report tell the story at a glance.

Yes, fat consumption in gram amount has remained about the same, but that’s just the point. We’re eating more of everything — arguably in part due to being hungrier from all the highly processed carbohydrates. As you say: “according to NHANES data, carbohydrates went up dramatically” from 1980 to 2000, consistent with the government advice to eat a high-carbohydrate, grain-based diet (those 6 to 11 servings a day!).

Of note, the “American Paradox” of decreasing proportion of fat as obesity rates rose was described by Heini and Weinsier 20 years ago — though it’s really no paradox at all considering the metabolic effects of processed carbohydrates.

Indeed, multiple recent meta-analyses show that high carbohydrate diets as actually consumed are demonstrably inferior to all higher fat diets for weight loss. Unfortunately, this high carbohydrate intake is also strongly linked to mortality among US cohorts. [Click here for the most relevant table from this paper. — KB]

So let’s certainly continue exploring this, but I don’t think that concerns about the low-fat diet recommendations are based on myths that need killing.

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Enjoy this article? Proceed to Part 3 of the macronutrient series, here [to be added].

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