I hope this is going to be the last post on Bradley and Hunter. Once again Table 5, but now the HbA1c line.
An HbA1c of 5.2, 5.3, 5.4 or 5.5 is normal. Any variation within these limits is virtually irrelevant clinically. Moving a tenth of a percentage point in this region is utterly insignificant. The changes in HbA1c don't even get a mention in the discussion. But perhaps they should do.
The low fat group dropped their HbA1c from 5.4 to 5.3, shrug. The low carb group dropped their HbA1c from 5.3 to 5.2. Mega shrug. Sound just about identical, don't they?
There are two very strange things about this. The first is that the drop for the low fat group does not reach statistical significance. The p value is 0.4 for within LF group change.
But the drop from 5.3 to 5.2 in the low carbohydrate group is statistically very significant, p=0.01. How can this be?
The second strange thing is that, in the whole of Table 5, there is only one value expressed to three decimal places. That is the standard deviation of the HbA1c of the post diet low carbohydrate group. This sd has to use three decimal places because it is so small. Having zero would not look good.
What does an sd of +/- 0.003 mean? Because three standard deviations around a mean include 99% of the population we know that 99% of the values lie within the 5.2 +/- 0.009 range. But HbA1c is only reported to one decimal place and you can only ever deal with a whole number of people. So, by the end of the eight week study, 11/12 subjects on the low carbohydrate diet will have had an HbA1c of 5.2 and the 12th person will either have been 5.3 or 5.1, there is no other way of looking at the data.
This is what happens when you take a group of people eating anywhere between 190g/d and 275g/d of carbs and drop them all to close on 104g/d. Everyone's post prandial glucose drops and the range of HbA1c both drops and tightens up.
Not so the low fat diet people.
Before the study they started with carbohydrate intakes of about 120-240g/d and tightened in to a minimal spread round 226g/d on the low fat diet. So some individuals increased their carbs, some decreased them, some didn't change them that much.
The changes in glycaemia will have been all over the place following changes in individual carb intake. Some will have risen, some dropped. There was a spread to begin with and a spread at the end. The overall effect is a small and insignificant drop because the carb intake variation is blunted by a 500kcal energy deficit being made up of zero-carb butt fat!
Had this diet not included weight loss the low fat people would have really come out badly on an HbA1c basis as they would have been eating glucose instead of burning butt fat!
In terms of glycaemia, everyone benefited in the LC group. Some benefited and some were injured, ever so slightly, in the low fat group. This is hidden in the average but shows through the standard deviations!
Overall this aspect is more of interest for looking at how information gets buried, rather than any genuine clinical effect. Information gets buried all right. Luckily you can see the disturbed earth in the results tables.
That's it. I've had enough of Hunter and will give it a rest.