This is part one of two blogs regarding two recent studies, both of which are being touted in the media as proof that fat people are dumber than not-fat people.
The first study has to do with cognitive decline in old(er) people, and whether being fat speeds up that process.
And the headlines are screaming that fat makes you dumber
The results of the study actually says:
Among the obese, the global cognitive score at baseline (p = 0.82) and decline (p = 0.19) over 10 years was similar in the metabolically normal and abnormal groups. In the metabolically normal group, the 10-year decline in the global cognitive score was similar (p for trend = 0.36) in the normal weight (−0.40; 95% confidence interval [CI] −0.42 to −0.38), overweight (−0.42; 95% CI −0.45 to −0.39), and obese (−0.42; 95% CI −0.50 to −0.34) groups. However, in the metabolically abnormal group, the decline on the global score was faster among obese (−0.49; 95% CI −0.55 to −0.42) than among normal weight individuals (−0.42; 95% CI −0.50 to −0.34), (p = 0.03).
Say what? I really had to stop and wrap my brain around this. This seems to be what the results actually say (based on the foregoing):
Obese participants’ decline stayed about the same whether or not they were metabolically normal or abnormal.
The decline for metabolically normal participants (fat and non-fat) decline was similar.
The obese and metabolically abnormal participants had a faster decline than average sized participants; but looking at the numbers (-0.49 for obese versus -0.42 for average weight), it doesn’t look like there is all that much difference.
Also, this study is over 10 years; starting with the youngest participants at 39 and the oldest 63 and we don’t know how the age group versus metabolic status was spread – were most of the younger people metabolically normal and most of the older participants metabolically abnormal? Nor do we know what other medical issues may be arising (particularly for the older participants who were going from age 63 to 73 during the study).
Serious medical issues could skew the results significantly as well, since hospitalization substantially speeds up cognitive decline, even after controlling for illness severity and pre-hospital cognitive decline.
Based on a 10-year study in England, cognitive decline is estimated to begin at age 45 with older people having greater and faster cognitive decline. Also almost 2/3 of the participants were men and older men have faster cognitive decline than women.
So depending on how the deck was “stacked” (and I use that phrase advisedly), it would be pretty easy to come up with the results – and those “results” don’t stack up to a whole lot of difference between fat and non-fat people.