Saturday, 5 July 2014

Lies, damned lies and statistics, part n+1. Riera-Crichton et al.

In Macronutrients and obesity: Revisiting the calories in, calories out framework, the conclusion is:-
"Our structural VAR results suggest that, on the margin, a 1% increase in carbohydrates intake yields a 1.01 point increase in obesity prevalence over 5 years while an equal percent increase in fat intake decreases obesity prevalence by 0.24 points."

So, carbohydrates are fattening but fat is slimming, eh? I declare shenanigans! Two can play at that game.

In Effect of Dietary Protein Content on Weight Gain, Energy Expenditure, and Body Composition During Overeating, Bray et al increased kcals by 40% by adding Fat grams. Carb grams didn't change. Protein grams changed a bit. ∴ Protein %E & Carb %E decreased by ~29%. %E means "as a percentage of total Energy".

Weight (lean body mass + body fat) increased as Fat kcals increased ± some interpersonal variation.
From Fig. 6.

_
 _Decreased P %E & C %E result in increased weight.
Increased P %E & C %E result in decreased weight.

Fat is fattening, but Protein & Carbohydrate is slimming! Q.E.D.

Do you see what's going on? Here's a summary:-

Diet contains A, B and C.
The amount of A increases, but the amounts of B and C remain constant.
A%E increases, but B%E and C%E decrease.  

In Riera-Crichton et al, A = Carbohydrate, B = Fat and C = Protein.
In Bray et al, A = Fat, B = Carbohydrate and C = Protein.

23 comments:

MacSmiley said...

So does the Riera-Crichton study "rise" to the level if junk science?

Nigel Kinbrum said...

I don't think that it even got that high.

I see that someone on Twitter has criticised my Bray analysis on the grounds that the P, C & F data are unrelated. Duh?

MacSmiley said...

How that? Like none of them are like, um, food?

Nigel Kinbrum said...

NVM. He emailed me. It was a misunderstanding. Twitter is useless for holding meaningful conversations, 140 characters at a time.

CynicalEng said...

Protein grams did change in the Bray study, only carbohydrate was constant at 330g per 2200 cals. It's in the supplementary docs as a table.

Nigel Kinbrum said...

Protein varied between groups. The protein in each group was held constant.

CynicalEng said...

but varied from baseline ?

Nigel Kinbrum said...

Whatever baseline P & C grams were for each subject was held constant during overfeed. Overfeed kcals came from Fat grams only.

CynicalEng said...

Not according to the tables in the supplementary materials. The main text says "participants were randomized to diets containing 5% of energy from protein (low protein), 15% (normal protein), or 25% (high protein), which they were overfed during the last 8 weeks of their 10- to 12-week stay in the inpatient metabolic unit. Compared with energy intake during the weight stabilization period, the protein diets provided approximately 40% more energy intake" and they were all on 15% to start with. Certainly not extra fat only.

See also the Protein g/day row in the Table in the body - one down, two up.

Nigel Kinbrum said...

It's in the text - twice.

Anyway, I'm out for the night, so I won't be responding again 'til tomorrow.

CynicalEng said...

That's why I look at data and not words, although 1) does not say *protein" it says absolute *carbohydrate* was the same, which I agree with. Protein varied, which is not what you said. See the Table. Here's the link, to make sure we're on the same page http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3777747/table/T1/

The comment 2) appears to be worded erroneously as it contradicts the table and the gory detail to be found in http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3777747/bin/NIHMS506388-supplement.doc

Nigel Kinbrum said...

That's interesting. The Table data suggests that the weight-stabilizing diets for all three groups were the same composition. From the text:-
"After consuming a weight-stabilizing diet for 13 to 25 days,
participants were randomized to diets containing 5% of energy from
protein (low protein), 15% (normal protein), or 25% (high protein),
which they were overfed during the last 8 weeks of their 10- to 12-week
stay in the inpatient metabolic unit."
So, although the energy surplus was from fat only, the number of fat grams varied as the number of protein grams varied. The low protein grams group had more fat grams than the high protein grams group. That explains why the high protein group had lower than expected fat mass gain vs kcal surplus. That's a bit naff.

I thought that the weight-stabilizing diets were 5%, 15% & 25%E from protein for the three groups. Realisation dawns. Cheers!

George said...

Riera-Crichton is free-living populations over long periods of time. Bray is a sall group of volunteers being overfed in a lab for a short time. There is no reason why the results of these two studies should correspond. Can you not find a closer analogy to what Riera-Crichton have done than the Bray paper?
Oh, I meant to say, "et al.".

Nigel Kinbrum said...

Irrelevant, George.

Riera-Crichton et al had increased carbs, which decreased %E from protein & fat.

Bray et al had increased fat, which decreased %E from protein & carbs.

George said...

Riera-Crichton et al also measures increased fat. And increased protein. Have you read the full-text?
Your comparison would be more meaningful if the two papers were heterogenous in some way, but they seem to be as far apart as diet papers can get. Overfeeding is an artificial state; of the multitudes included in Riera-Crichton et al., no-one was instructed by the authors to overeat.

CynicalEng said...

Indeed, so your maths might need a bit of a rework.

CynicalEng said...

R-C is just a massive maths exercise on long term trend data, it isn't an experiment. The examples given to explain the impenetrable maths may fix the calories. When they say "on the margin, a 1% increase in carbohydrates intake yields a 1.01 point increase in obesity prevalence over 5 years while an equal percent increase in fat intake decreases obesity prevalence by 0.24 points" do they mean 1% increase in grams per day per head or a shift from 45 to 46 E% - I think the former, possibly adjusted to constant calories. The lack of units in the paper makes it difficult to tell.

Nigel Kinbrum said...

R-C et al is a crock of shit - and you know it. The LC & VLC world is positively creaming themselves over it because it confirms their beliefs - that carbs are fattening and fat is slimming.



Bray et al showed a strong positive correlation between excess kcals of (virtually all) fat grams (depending on which protein group you're talking about) and fat mass.

Fat grams went up. ∴ Fat %E went up and fat mass went up. ∴ Fat is fattening.

Carb grams were constant. ∴ Carb %E went down and fat mass went up. ∴ Carbs are slimming.

Are you going to argue about irrelevances all night?

CynicalEng said...

Actually I'm busy reading how weight didn't go up with fat intake in another study you linked to - Kasper et al.

R-C is statistical epidemiology, it's as much use as any other statistical epidemiology - not seen any of it rationalise the obesity growth in a population yet. Bray appears to demonstrate that fat is fattening in the presence of high carbohydrates, don't have any problem with that. It isn't clear to me what R-C are using yet -grams or % or what.

George said...

Bray was an over-feeder. End of comparison.
Skip to the bit in R-C where they discuss correlation of protein with "overweight", i.e. BMI, vs. "Obesity", i.e fat mass. Does that seem wrong like the wrong conclusion to you?
If it's not, and it's derived by the same formula as the other results, why doubt those?
It is morning here, but some are still in the dark.

Nigel Kinbrum said...

Hardly. Some things went up a lot in grams. Other things stayed constant in grams and some things varied a little in grams. The rest remains the same.

Nigel Kinbrum said...

"Actually I'm busy reading how weight didn't go up with fat intake in another study you linked to - Kasper et al."
It went up eventually - after much "glowing". Please don't misquote.

Nigel Kinbrum said...

I don't care about protein. It's an irrelevance.

Any population study that shows that fat is slimming when it's not, is a crock of shit.



And, for that last sentence, welcome to my Black List.