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I've repeatedly heard the claim, often from anti-fructose advocates, that there is a skyrocketing prevalence of two formerly rare disorders: non-alcoholic fatty liver disease (NAFLD) and juvenile type 2 diabetes:

I don't know if the historical data on these conditions is comparable to the data we're getting today. If screening methods became more sensitive, testing became more frequent, or diagnostic criteria changed, you could see more cases even if the underlying health conditions hadn't changed. This would be similar to the ostensible "autism epidemic" which turned out to mostly reflect change in diagnostic practices. It seems especially possible for NAFLD, since it is mostly asymptomatic. Type 2 diabetes, while it has more effects on health, can also be missed during the early stages if doctors don't think to look for it.

There's plenty of primary source material on these claims, but I haven't reviewed enough to know whether the methods used are reliable. I'd like to know if there's solid evidence for these four claims:

  1. Incidence of juvenile type 2 diabetes is increasing.
  2. Incidence of NAFLD is increasing.
  3. Juvenile type 2 diabetes was, until recently, very rare.
  4. NAFL was, until recently, very rare.

(these are logically distinct claims, but I'm putting them in the same question because I expect much of the same evidence to apply.)

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As a partial answer, I found this journal article: Increasing Prevalence of Nonalcoholic Fatty Liver Disease Among United States Adolescents, 1988-1994 to 2007-2010. The authors diagnosed NAFLD using weight and liver enzymes that were recorded as part of a study on a large, representative sample of adolescents (NHANES). Since they made the diagnosis based on archival data that was collected for other purposes, there's no concern about changes in sampling or diagnosis between the two timepoints. They found that "Suspected NAFLD prevalence (SE) rose from 3.9% (0.5) in 1988-1994 to 10.7% (0.9) in 2007-2010 (P < .0001)".

It's only a single study but it had a very large sample, a standard diagnostic method, and strong, medically significant findings. I consider it good evidence that NAFLD is increasing dramatically, at least in adolescents. It doesn't prove that NAFLD was previously very rare -- 3.9% is a fairly high prevalence, but we don't know whether it was already rapidly increasing prior to 1988.

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