In his rebuke of Denise Minger Campbell makes a valid point that univariate analysis is fraught with danger.
What he means is analysing one variable to an effect can be misleading as other variables may be playing a part.
For example he cites that with wheat there is a predisposition for higher wheat consuming regions to be lower green plant eating regions. This would tilt the results somewhat if we accept that green plant is protective.
Indeed there are 23 regions where wheat exceeds grenn plant consumption and 41 where green plant exceeds wheat.
Looking at wheat alone and comparing it with average consumption of wheat across all regions, when it is above average heart disease stands at a high 23.24
But what would we expect to happen if wheat was greater than average wheat consumption but so too was green plant greater than average green plant consumption. Would we expect HD to be below 23.24 ?. Well it comes in at 26.33 from 7 regions
Wheat greater than average but plant less than average HD = 21.8 from 15 regions
Wheat less than average but plant greater than average HD = 8.91 from 19 regions