April 09, 2019

Is fast food bad for you?

A big study in France set out to answer that and did find a slightly higher rate of death among enthusiastic fast food eaters.  It did however also find that fast food eaters were younger, poorer, less educated etc.  Even after controlling for such factors, however, some effect of fast food itself remained.

There were however two problems with the study.  The first is easy.  The subjects were food freaks. As the study says:  "the participants are more health conscious than the general population". So how well the findings would generalize to the overall population is unknown.  Food freaks may be generally less healthy. I rather wonder why the study was done  with such a severe sampling problem but I guess some information was better than none

The second problem was "when excluding prevalent CVDs and cancer cases, the associations were no longer statistically significant".  Deleting the two main causes of death from the analysis seems wildly hilarious to me.  The "bad" effects of fast food were only shown if you didn't have heart disease and cancer. Remove the heart and cancer patients and you remove a lot of the deaths.

I am struggling with the logic of that but it seems to me that you are "fiddling" your sample and that it is only in your fiddled sample that bad effects are found.  Putting it another way, it looks like heart disease and cancer had a protective effect -- protecting you from death due to bad food.  Which is surely borderline insane.  Or maybe not.  Maybe fast food is good for you.

However you look at it, however, the problem is the non-representativeess of the sample.  You take a population of health nuts (at least some of whom may be health nuts because of health problems) and then make the sample even less reprsentative by subtracting from it the more ill component (people with heart and cancer symptoms) and then use that as your study sample. It's a parody of good survey research that may tell you nothing about the whole national population.

Poor sampling is endemic throughout the social science and medical literature but that does not mean that we should treat it as better than it is

Anyway, it seems that the bad effects of fast food are still at this stage "not proven', to use the old Scottish verdict. Journal abstract below.

Association Between Ultraprocessed Food Consumption and Risk of Mortality Among Middle-aged Adults in France

Laure Schnabel et al.

Abstract

Importance  Growing evidence indicates that higher intake of ultraprocessed foods is associated with higher incidence of noncommunicable diseases. However, to date, the association between ultraprocessed foods consumption and mortality risk has never been investigated.

Objective  To assess the association between ultraprocessed foods consumption and all-cause mortality risk.

Design, Setting, and Participants  This observational prospective cohort study selected adults, 45 years or older, from the French NutriNet-Santé Study, an ongoing cohort study that launched on May 11, 2009, and performed a follow-up through December 15, 2017 (a median of 7.1 years). Participants were selected if they completed at least 1 set of 3 web-based 24-hour dietary records during their first 2 years of follow-up. Self-reported data were collected at baseline, including sociodemographic, lifestyle, physical activity, weight and height, and anthropometrics.

Exposures  The ultraprocessed foods group (from the NOVA food classification system), characterized as ready-to-eat or -heat formulations made mostly from ingredients usually combined with additives. Proportion (in weight) of ultraprocessed foods in the diet was computed for each participant.

Main Outcomes and Measures  The association between proportion of ultraprocessed foods and overall mortality was the main outcome. Mean dietary intakes from all of the 24-hour dietary records available during the first 2 years of follow-up were calculated and considered as the baseline usual food-and-drink intakes. Mortality was assessed using CépiDC, the French national registry of specific mortality causes. Hazard ratios (HRs) and 95% CIs were determined for all-cause mortality, using multivariable Cox proportional hazards regression models, with age as the underlying time metric.

Results  A total of 44 551 participants were included, of whom 32 549 (73.1%) were women, with a mean (SD) age at baseline of 56.7 (7.5) years. Ultraprocessed foods accounted for a mean (SD) proportion of 14.4% (7.6%) of the weight of total food consumed, corresponding to a mean (SD) proportion of 29.1% (10.9%) of total energy intake. Ultraprocessed foods consumption was associated with younger age (45-64 years, mean [SE] proportion of food in weight, 14.50% [0.04%]; P < .001), lower income (<€1200/mo, 15.58% [0.11%]; P < .001), lower educational level (no diploma or primary school, 15.50% [0.16%]; P < .001), living alone (15.02% [0.07%]; P < .001), higher body mass index (calculated as weight in kilograms divided by height in meters squared; ≥30, 15.98% [0.11%]; P < .001), and lower physical activity level (15.56% [0.08%]; P < .001). A total of 602 deaths (1.4%) occurred during follow-up. After adjustment for a range of confounding factors, an increase in the proportion of ultraprocessed foods consumed was associated with a higher risk of all-cause mortality (HR per 10% increment, 1.14; 95% CI, 1.04-1.27; P = .008).

Conclusions and Relevance  An increase in ultraprocessed foods consumption appears to be associated with an overall higher mortality risk among this adult population; further prospective studies are needed to confirm these findings and to disentangle the various mechanisms by which ultraprocessed foods may affect health.

JAMA Intern Med. 2019;179(4):490-498. doi:10.1001/jamainternmed.2018.7289 





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