An exchange of half bricks

I would guess that everyone is aware of the study by Ebbeling et al, Ludwig's group, looking at the metabolic effect of low carbohydrate diets on total energy expenditure (TEE, all graphs show kcal/d) in the aftermath of weight loss on a conventional diet.

Effects of a low carbohydrate diet on energy expenditure during weight loss maintenance: randomized trial

I'd like to summarise their data using numbers taken from Tables 2 and 3 which, with a little arithmetic, allows me to produce this graph of TEE at various time points. These are as follows: when the subjects walk off the street (Pre on the graph), after a period of semi-starvation on a conventional diet (Start) and then during weight stability on a high, medium or low carbohydrate diet (End). The plot looks like this:

In the study they compared the change from the Start TEE to the End TEE, ie they used these data points:

They took the absolute changes from Start to End thus and got a resultant p of less than 0.05

This, obviously, is completely unacceptable. Well, it is if you are Kevin Hall. So now we have this

No Significant Effect of Dietary Carbohydrate versus Fat on the Reduction in Total Energy Expenditure During Maintenance of Lost Weight

What Ludwig's group did wrong (amongst the many other things pointed out by Hall and Guo) is that they used the wrong data points.

Recall the original graph:

According to Hall: If you want to ask about the effect of low carbohydrate diets on the depression in TEE produced by conventional semi-starvation you should NOT compare the semi-starved TEE (as in Start) to the TEE on a high, medium or low carbohydrate diet (End). You should instead use the TEE expenditure at randomisation (Pre on the graph). Like this:

Using Pre as your anchor point you can draw the same data thus:

Which obviously gives us p greater than 0.05 and all of the benefits of low carbohydrate diets are lost. Phew. Happy Hall. But why should anyone use the Pre values as an anchor point?

Now, no one is an unbiased researcher. Hall is, surprisingly, no exception. Hence the current exchange of half bricks in the BMJ.

As I see it the Ebbeling paper looks at the effect of LC eating on the damage done to TEE by conventional dieting.

What Hall wants the analysis to do instead is to look at the overall effect of damage done to TEE by conventional semi-starvation combined with partial rescue during weight-stable LC eating vs the combined damage done by conventional semi-starvation followed by maintained damage done by HC weight-stable eating. As he writes:

"However, the final analysis plan was modified to make the diet comparisons with the TEE measurements collected in the immediate post-weight loss period rather than at the pre-weight loss baseline"

To me Hall is stating that Ebbeling et al almost did make the "Hall" mistake of using the "Pre" TTE as anchor point but corrected this at the 11th hour, still before blinding was unmasked. What puzzles me is how Ebbeling could have ever even considered using the "pre weight loss baseline" as the anchor point in the original study design.

The massive benefit to Hall of including the conventional semi-starvation active weight loss period along with the intervention weight stability period is to dilute the remedial biological effect of LC eating out of statistical significance.

The core information which the study provides is about the remedial effect of LC eating on correcting the damage done by a conventional semi-starvation period. That effect only happens between "Start" and "End", which is when carbohydrate restriction is applied.

That's one of the MASSIVE problems with carbohydrate restricted eating. It only provides benefit when you don't eat carbohydrate!

Including data from "Pre" right through to "End" dilutes the clearly demonstrable biological effect of carbohydrate restriction on reduced TEE post conventional dieting.

So what doe the title and text of Hall's rebuttal tell us? Either about Hall or about TEE? Don't over think it!

I would also declare that my own biases are a conflict of interest but if you need me to say that then you have probably arrived here by accident, you know where the back button is.

However I would say that I am ambivalent about the importance of the TEE changes, though I suspect they do happen. What really matters to me is what happened in Aberdeen over a decade ago.

Peter

Edit

More excellent half bricks here

End edit.