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  #1   ^
Old Tue, Mar-23-21, 11:46
Grav Grav is offline
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Default David Ludwig: Does low carb help speed up energy metabolism?

Does low carb help speed up energy metabolism?

Turns out the answer is no... for the first 2.5 weeks or so, while the body adjusts. Beyond that, yes, by an average of around 135 kcal/day, according to a new meta-analysis of feeding studies by David Ludwig and his team.

Quote:
Do Lower-Carbohydrate Diets Increase Total Energy Expenditure? An Updated and Reanalyzed Meta-Analysis of 29 Controlled-Feeding Studies

ABSTRACT

Background

The effect of macronutrient composition on total energy expenditure (TEE) remains controversial, with divergent findings among studies. One source of heterogeneity may be study duration, as physiological adaptation to lower carbohydrate intake may require 2 to 3 wk.

Objective

We tested the hypothesis that the effects of carbohydrate [expressed as % of energy intake (EI)] on TEE vary with time.

Methods

The sample included trials from a previous meta-analysis and new trials identified in a PubMed search through 9 March 2020 comparing lower- and higher-carbohydrate diets, controlled for EI or body weight. Three reviewers independently extracted data and reconciled discrepancies. Effects on TEE were pooled using inverse-variance-weighted meta-analysis, with between-study heterogeneity assessed using the I2 statistic. Meta-regression was used to quantify the influence of study duration, dichotomized at 2.5 wk.
Results

The 29 trials ranged in duration from 1 to 140 d (median: 4 d) and included 617 participants. Difference in carbohydrate between intervention arms ranged from 8% to 77% EI (median: 30%). Compared with reported findings in the prior analysis (I2 = 32.2%), we found greater heterogeneity (I2 = 90.9% in the reanalysis, 81.6% in the updated analysis). Study duration modified the diet effect on TEE (P < 0.001). Among 23 shorter trials, TEE was reduced on lower-carbohydrate diets (−50.0 kcal/d; 95% CI: −77.4, −22.6 kcal/d) with substantial heterogeneity (I2 = 69.8). Among 6 longer trials, TEE was increased on low-carbohydrate diets (135.4 kcal/d; 95% CI: 72.0, 198.7 kcal/d) with low heterogeneity (I2 = 26.4). Expressed per 10% decrease in carbohydrate as %EI, the TEE effects in shorter and longer trials were −14.5 kcal/d and 50.4 kcal/d, respectively. Findings were materially unchanged in sensitivity analyses.

Conclusions

Lower-carbohydrate diets transiently reduce TEE, with a larger increase after ∼2.5 wk. These findings highlight the importance of longer trials to understand chronic macronutrient effects and suggest a mechanism whereby lower-carbohydrate diets may facilitate weight loss.

Link: https://doi.org/10.1093/jn/nxaa350
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  #2   ^
Old Tue, Mar-23-21, 14:17
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Ms Arielle Ms Arielle is offline
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I need to read this in detail when my brain is fresh.

Very interested to see how thi s study compares to the severe drop in BMR among the Biggest Loser participants.
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  #3   ^
Old Tue, Mar-23-21, 14:44
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wbahn wbahn is online now
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Note that, even here, half of the studies were four days or less and in half of them 30% or more calories were from carbs (for a 2000 kcal diet that's 150 g of carbs a day). If you are holding to 40 g of carbs on a 2000 kcal diet you are right at the 8% mark which is the lowest-carb diet in the entire study. Many low carbers are below that.

It's nice to see the evidence that there is a metabolic advantage to low carb (just as Atkins and others said two or three decades ago) and also good that they are recognizing that longer-term studies are needed because shorter-term results simply don't apply.

But it is still bothersome that all of these "researchers" that "debunk" the low-carb approach rely on "evidence" that is not from low-carb lifestyles. They either use what can best be described as slightly-lower-carb diets (I saw one study where the lowest carb diet they considered was 200 g/day) and most of them are based on a few days to at most thirty days.

It's not like they don't know better, either. Look at nearly any study about most other things and they don't consider anything less than three to six months as providing meaningful data because it is well known that the body needs at least that long to materially adapt to most significant changes -- and changing the very basis of the fuel the body is burning should certainly count as significant.
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  #4   ^
Old Wed, Mar-24-21, 12:40
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Quote:
Originally Posted by wbahn
But it is still bothersome that all of these "researchers" that "debunk" the low-carb approach rely on "evidence" that is not from low-carb lifestyles. They either use what can best be described as slightly-lower-carb diets (I saw one study where the lowest carb diet they considered was 200 g/day) and most of them are based on a few days to at most thirty days.

It's not like they don't know better, either. Look at nearly any study about most other things and they don't consider anything less than three to six months as providing meaningful data because it is well known that the body needs at least that long to materially adapt to most significant changes -- and changing the very basis of the fuel the body is burning should certainly count as significant.

I did a little research into this particular angle last year. In some circles, the definition of "low carb" seems to originate from a 2005 NASEM report (free PDF at https://doi.org/10.17226/10490), which set the recommended range for carb consumption as being anywhere from 45-65% of total energy intake. This 45% minimum is used by both the 2015 and 2020 systematic reviews that underpinned the respective editions of the US dietary guidelines, as well as by the last dietary survey conducted here in NZ, during 2008/09. By this interpretation, anything that tracks for <45% carbs is technically considered to be "low carb".
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  #5   ^
Old Wed, Mar-24-21, 16:11
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Dodger Dodger is online now
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There seems to be a lot of statistical mumbo jumbo with this study.
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  #6   ^
Old Wed, Mar-24-21, 18:22
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wbahn wbahn is online now
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Quote:
Originally Posted by Grav
I did a little research into this particular angle last year. In some circles, the definition of "low carb" seems to originate from a 2005 NASEM report (free PDF at https://doi.org/10.17226/10490), which set the recommended range for carb consumption as being anywhere from 45-65% of total energy intake. This 45% minimum is used by both the 2015 and 2020 systematic reviews that underpinned the respective editions of the US dietary guidelines, as well as by the last dietary survey conducted here in NZ, during 2008/09. By this interpretation, anything that tracks for <45% carbs is technically considered to be "low carb".


Thanks for the info. Not surprising. Still seems a bit disingenuous of them to call 44% "low carb" and then infer sweeping conclusions about all "low carb" diets, even ones that are 4%. Is it laziness? Or an agenda? Or just poor science?
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  #7   ^
Old Wed, Mar-24-21, 19:07
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GRB5111 GRB5111 is offline
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Quote:
Originally Posted by wbahn
Thanks for the info. Not surprising. Still seems a bit disingenuous of them to call 44% "low carb" and then infer sweeping conclusions about all "low carb" diets, even ones that are 4%. Is it laziness? Or an agenda? Or just poor science?

Possibly all of the above as these types of "studies" using a very loose definition of what constitutes low carb have been commonplace over the past 15 years of so. Started with Atkins and now seems to be continuing today. Of course, the term "low carb" is relative and if not rigorously applied as below 50 grams per day. Therefore, the study's design is disingenuous to say the least. Relative to those eating SAD means they can peg low carb at 44% and still be correct. Important to read between the lines, as you're doing, but most don't.
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  #8   ^
Old Wed, Mar-24-21, 23:03
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wbahn wbahn is online now
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This is also an endemic problem with the "meta-analysis" studies that are becoming the norm instead of doing an actual study to address the specific question at hand. It is almost impossible to properly account for all of the various differences and diverging definitions between the various studies that are included -- which is not to say that a lot of quality effort hasn't gone into trying to do so.
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  #9   ^
Old Thu, Mar-25-21, 00:53
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Quote:
Originally Posted by GRB5111
Possibly all of the above as these types of "studies" using a very loose definition of what constitutes low carb have been commonplace over the past 15 years of so. Started with Atkins and now seems to be continuing today. Of course, the term "low carb" is relative and if not rigorously applied as below 50 grams per day. Therefore, the study's design is disingenuous to say the least. Relative to those eating SAD means they can peg low carb at 44% and still be correct. Important to read between the lines, as you're doing, but most don't.

I wouldn't call it disingenuous at all, it just helps to make one particular point without also complicating the picture with various other factors.

Many who argue against low carb on the grounds of "keto flu" style symptoms will often cite those shorter studies as the basis for their arguments. What this study demonstrates is that yes, there can often be side effects when first getting underway with low carb, but also that those symptoms are temporary. Past the first 2-3 weeks, things tend to work out much better in terms of TEE in the long run. That's the real point behind this study as I see it.

Yes, this may well have incorporated some studies where the definition of low carb might not quite agree with ours. But think about this: if a study like this had been done by assessing only those studies where carbs made up a maximum of say 20% of energy intake for example, the results may very well have turned out even better from our point of view, but at the same time, would also have given detractors an opportunity to argue the point, that not all "low carb" studies were considered, that the data was "cherry-picked" or whatever. And by their definition, they would be right. By including more liberal low carb studies in the mix, to actually meet their definition anyway and still demonstrate successful outcomes, that really leaves opponents with no room whatsoever to argue that particular point.

Could the results have turned out even better if eligible studies were limited to only those with even greater carb restriction? Probably, but that's not the purpose of this study as I understand it. That would be the subject of another study for another day.
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  #10   ^
Old Thu, Mar-25-21, 00:58
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Quote:
Originally Posted by wbahn
This is also an endemic problem with the "meta-analysis" studies that are becoming the norm instead of doing an actual study to address the specific question at hand. It is almost impossible to properly account for all of the various differences and diverging definitions between the various studies that are included -- which is not to say that a lot of quality effort hasn't gone into trying to do so.

One possible reason for lots of meta-analyses as of late could also be Covid? I imagine it would be a lot harder trying to conduct "original research" under pandemic-induced restrictions, than it would be under more normal circumstances.
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  #11   ^
Old Thu, Mar-25-21, 03:16
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WereBear WereBear is offline
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Quote:
Originally Posted by wbahn
But it is still bothersome that all of these "researchers" that "debunk" the low-carb approach rely on "evidence" that is not from low-carb lifestyles. They either use what can best be described as slightly-lower-carb diets (I saw one study where the lowest carb diet they considered was 200 g/day) and most of them are based on a few days to at most thirty days.

It's not like they don't know better, either.


But it's sure a way to get headlines that say new study shows low carb doesn't work or whatever.

The sugar industry paid for years to keep evidence away from people. I'm sure they still are.
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  #12   ^
Old Thu, Mar-25-21, 06:10
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thud123 thud123 is online now
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135 cal a day can easily be over come by adding extra fat into ones coffee. Be careful out there about what you choose to believe
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  #13   ^
Old Thu, Mar-25-21, 09:34
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GRB5111 GRB5111 is offline
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Quote:
Originally Posted by Grav
I wouldn't call it disingenuous at all, it just helps to make one particular point without also complicating the picture with various other factors.

Many who argue against low carb on the grounds of "keto flu" style symptoms will often cite those shorter studies as the basis for their arguments. What this study demonstrates is that yes, there can often be side effects when first getting underway with low carb, but also that those symptoms are temporary. Past the first 2-3 weeks, things tend to work out much better in terms of TEE in the long run. That's the real point behind this study as I see it.

Yes, this may well have incorporated some studies where the definition of low carb might not quite agree with ours. But think about this: if a study like this had been done by assessing only those studies where carbs made up a maximum of say 20% of energy intake for example, the results may very well have turned out even better from our point of view, but at the same time, would also have given detractors an opportunity to argue the point, that not all "low carb" studies were considered, that the data was "cherry-picked" or whatever. And by their definition, they would be right. By including more liberal low carb studies in the mix, to actually meet their definition anyway and still demonstrate successful outcomes, that really leaves opponents with no room whatsoever to argue that particular point.

Could the results have turned out even better if eligible studies were limited to only those with even greater carb restriction? Probably, but that's not the purpose of this study as I understand it. That would be the subject of another study for another day.

Grav, thanks for clarifying. "Disingenuous" is not the correct word in this case, as I don't believe any of the referenced studies were that. I like the fact that Ludwig observed that issues with low carb (reduced TEE) resolved after a few weeks (~2.5 wks), citing the importance of study duration, to your point. He also found increased TEE in other studies. This Ludwig meta-analysis appears to be a direct response to the Kevin Hall study of a few years ago among others.

However, I would like to see future studies designed to report on more discrete consumption of carbs by several levels of percentages with weights referenced, say 250, 200, 150, 100, 50 grams per day, etc, on a continuum. Given the variables at play among the macros, being able to identify how a low carb group is defined in a particular study would be helpful in producing reliable results and enabling accurate claims. Agree that isn't the purpose of Ludwig's analysis, but I'm curious to discover what the "sweet spot" would be for participants using these conditions.

Consuming fewer carbs than a SAD does not necessarily mean it was actually low carb depending on the definition; yet, some will take it as gospel and some will immediately discount it based on subjective interpretation. It would be nice to see that subjective interpretation eliminated. I believe this is one of the issues that stimulated conducting this meta-analysis.

Last edited by GRB5111 : Thu, Mar-25-21 at 12:07.
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  #14   ^
Old Sat, Mar-27-21, 04:29
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WereBear WereBear is offline
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I can state, from constantly repeated personal experience, that I spend months at low calorie intake, plus exercising. And lost no more than ten pounds.

Since fat retention is far more about hormones than it is calories, this makes sense to me now.
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  #15   ^
Old Tue, Mar-30-21, 23:56
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CMCM CMCM is offline
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Quote:
Originally Posted by WereBear
But it's sure a way to get headlines that say new study shows low carb doesn't work or whatever.

The sugar industry paid for years to keep evidence away from people. I'm sure they still are.


And the grain industry succeeded in getting a food pyramid that told people to eat 11+ servings of grain a day! That's a real ticket to obesity.

I believe virtually nothing that I read in popular media any more. Beware of anything that begins "Studies show...."
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