January 04, 2018

Trans fats:  A failure of logic?

Trans fats in food have long been a whipping boy for food faddists, Greenies and assorted attention-seekers. So the study below has been widely greeted with gladsome hearts.  It has been much-cited in the six months since it first appeared and seems to have won universal approval.

And for once I don't think there is any obvious problems with the statistics.  It does however have the logical problem that seems to bedevil most epidemiological research.  Despite all the warnings from logicians, it decides that correlation is causation.  It assumes that because the data was segregated according to its exposure to trans fats that therefore the effects observed reflected exposure to trans fats.  What else could you conclude? I can hear some angry epidemiologist ask.  Well, I will answer that.

You need some history.  Why did dietary trans-fats come into use in the first place?  Answer:  To replace saturated fats, which, courtesy of Ancel Keys, were for decades demonized as bad for your heart.  But a couple of years ago there was one of those big backflips that occur far too often in medical "wisdom". Saturated fats are now good for you!  So did the ban on transfats cause a mass reversion to saturated fats?    It is certainly possible but a more likely outcome is that transfats were replaced by some combination of [good] saturated fats and palm oil.  So it's perfectly possible that the decline heart attacks described below was not due to transfats being bad for you but rather because what replaced them is good for you.  The authors of the article have not pinpointed the cause of what they observed at all.


Hospital Admissions for Myocardial Infarction and Stroke Before and After the Trans-Fatty Acid Restrictions in New York

Abstract

Importance:  Trans-fatty acids (TFAs) have deleterious cardiovascular effects. Restrictions on their use were initiated in 11 New York State (NYS) counties between 2007 and 2011. The US Food and Drug Administration plans a nationwide restriction in 2018. Public health implications of TFA restrictions are not well understood.

Objective:  To determine whether TFA restrictions in NYS counties were associated with fewer hospital admissions for myocardial infarction (MI) and stroke compared with NYS counties without restrictions.

Design, Setting, and Participants:  We conducted a retrospective observational pre-post study of residents in counties with TFA restrictions vs counties without restrictions from 2002 to 2013 using NYS Department of Health’s Statewide Planning and Research Cooperative System and census population estimates. In this natural experiment, we included those residents who were hospitalized for MI or stroke. The data analysis was conducted from December 2014 through July 2016.

Exposure:  Residing in a county where TFAs were restricted.

Main Outcomes and Measures:  The primary outcome was a composite of MI and stroke events based on primary discharge diagnostic codes from hospital admissions in NYS. Admission rates were calculated by year, age, sex, and county of residence. A difference-in-differences regression design was used to compare admission rates in populations with and without TFA restrictions. Restrictions were only implemented in highly urban counties, based on US Department of Agriculture Economic Research Service Urban Influence Codes. Nonrestriction counties of similar urbanicity were chosen to make a comparison population. Temporal trends and county characteristics were accounted for using fixed effects by county and year, as well as linear time trends by county. We adjusted for age, sex, and commuting between restriction and nonrestriction counties.

Results:  In 2006, the year before the first restrictions were implemented, there were 8.4 million adults (53.6% female) in highly urban counties with TFA restrictions and 3.3 million adults (52.3% female) in highly urban counties without restrictions. Twenty-five counties were included in the nonrestriction population and 11 in the restriction population.

Three or more years after restriction implementation, the population with TFA restrictions experienced significant additional decline beyond temporal trends in MI and stroke events combined (−6.2%; 95% CI, −9.2% to −3.2%; P < .001) and MI (−7.8%; 95% CI, −12.7% to −2.8%; P = .002) and a nonsignificant decline in stroke (−3.6%; 95% CI, −7.6% to 0.4%; P = .08) compared with the nonrestriction populations.

Conclusions and Relevance:  The NYS populations with TFA restrictions experienced fewer cardiovascular events, beyond temporal trends, compared with those without restrictions.

JAMA Cardiol. 2017;2(6):627-634. doi:10.1001/jamacardio.2017.0491




Go to John Ray's Main academic menu
Go to Menu of longer writings
Go to John Ray's basic home page
Go to John Ray's pictorial Home Page
Go to Selected pictures from John Ray's blogs