Obesity in adolescents with chronic fatigue syndrome: an observational study, 2016, Norris et al

I’m not an adolescent I was pretty healthy weight up to mid 30s. I have gradual onset ME and I struggle with beige carbs. If I eat them I want more.

 

This 2016 study was discussed quite extensively on PR.

As background - there were two data sources, the ALSPAC survey and specialist clinics. For both, data was obtained at ages 13 and 16.

Diagnosis of CFS in the ALSPAC survey was not done by a clinician. Young people whose mothers felt that the fatigue was caused by playing too much sport were excluded, which probably helped to skew the CFS sample towards young people with higher BMIs.

ALSPAC Age 13 years diagnosis method:

From what was written in the paper, it seemed as though only 15% of the data points from the specialist clinic had BMI information. Here's a post I made on PR:

There's something a bit weird with the imputation of missing data. If you look at the supplementary material on imputation, it appears that,
for specialist services data at both 13 and 16, only around 15% of the 1680 data points had BMI information;
for ALSPAC data at both 13 and 16, only around 40% of the data points had CFS data and only about 40% had BMI information.

The supplementary material says missing data was imputed using auxiliary variables due to, among other things, 'their strong hypothesised association with CFS/ME'. Auxiliary variables used included
Family Adversity Index
Life Difficulties
School Absences in Year 11
Academic attainment
Anxiety and depression measures

Different variables were used for the imputation in each data source (Alspac and Specialist).

(There was a mention of 99 data points created by imputation for each of data sources, but I'm not sure how that works as they would have had to create a lot more data points than 99 to make up for the missing data.)

But anyway, the supplementary material gives the results from the 'complete case analysis' which presumably is the analysis of the data points that had no missing data. Here's the complete case results (with the results that were reported in the main body of the paper in brackets for comparison).

...............................Alspac No CFS ........... Alspac CFS...............Specialist CFS
13 years
Mean BMI..................20....................................20..............................21...............
% obese....................3.57 (4.18).......................3.92 (3.72).................9.23 (9.28)

16 years
Mean BMI.......... .......21.....................................21..............................22.............
% obese...................3.94 (4.46).........................6.00 (5.46).................6.8 (16.43)

So, the differences between the three groups look a lot less impressive in the un-imputed data. Instead of an upward trend from 9% to 16% obese over three years in the specialist group, there is a downward trend from 9% to 7%.

That makes a big difference - there isn't evidence in the complete data points that the CFS children are growing more massive as each year passes.

The imputation process is not well explained. The raw data however is reported as being available - so that is something.

My conclusion: there may possibly be a very small difference between the BMI's and obesity prevalence of non-CFS and CFS adolescents but there's enough murkiness about what was actually done with the data that I would not be getting excited until someone without an agenda analysed the data afresh.
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If they’re so worried about links between obesity and CFS in adolescents maybe they should have a talk to themselves about prescribing amitryptiline......