This is actually my favorite sort of post to do; more so, even, than the rants here and there. I find it interesting to get two or more perspectives on some issue or controversy, then synthesize them into what I always hope will be a broader context of understanding and in particular, highly accessible to those less interested in the nitty-gritty of the science.
It's a dialectic of sorts, but in this case, doesn't involve any material antithesis. Here, it's actually two pretty compatible theses: one put forth by Anthony Colpo (quantitative); the other by Dr. Stephan Guyenet (quantitative and qualitative). This is a follow-on to my post of yesterday, JAMA: Effects of Dietary Composition on Energy Expenditure During Weight-Loss Maintenance (access the full text of the study here).
I do find this study highly fascinating. I suppose because it has a number of elements that are ripe for debate, and open debate tends to get more people more closer to more truth. I read the thing from start to finish a couple of times, including all the figures and tables. Something just didn't add up for me. I quote from the Comment section (emphasis mine):
The results of our study challenge the notion that a calorie is a calorie from a metabolic perspective. During isocaloric feeding following weight loss, REE was 67 kcal/d higher with the very low-carbohydrate diet compared with the low-fat diet. TEE differed by approximately 300 kcal/d between these 2 diets, an effect corresponding with the amount of energy typically expended in 1 hour of moderate-intensity physical activity.
OK, but then there's this from the Results section (emphasis mine):
Body weight did not differ significantly among the 3 diets.
So I popped off an email to David Ludwig, MD, PhD, one of the researchers. Here's the relevant part:
I was interested in the study just published yesterday [...]
However, I have a glaring question I have been unable to answer after reading the study and looking at the figures and tables:
Where did the 300 calories go LC vs. LF? As I understand it, participants ate isocalorically in crossover fashion, so the only change was the macro ratios. It's also stated that physical activity did not change. So if they ate the same calories, had the same physical activity, maintained the same weight loss throughout, then how are the 300 daily calories accounted for if not in additional weight loss beyond the initial loss?
Perhaps I could learn more from the eMethods supplement as cited in the article. However, the link to the PDF is broken. If you have that PDF I'd appreciate it, and of course any light you could shed on my question so I can pass it on to my readers and commenters.
Anticipating that the answer might be something like: increased bodily metabolism (higher heart rate, respiration, etc, etc), then my follow on question might be what's the point, the advantage?
I got back a very quick response.
The point is that 4 weeks isn't long enough to translate a 300 kcal/d difference into statistically significant weight change, especially when one considers that body weight normally fluctuates by a kilogram or two through the course of a week, based on differences in hydration status, the time of the last bowel movement, etc. We'd need 6 months to reliably see this effect. Nevertheless, there was a slight, and not statistically significant difference in the hypothesized direction, with body weight highest on the low fat diet (data included in the results section).
I've informed the journal about the web site problem with the eMethods. Hopefully they will correct that soon.
OK, now here's the two posts by Guyenet and Colpo.
- New Study: Is a Calorie a Calorie? (Guyenet)
- Finally, a Study that Proves a Low-Carb Metabolic Advantage? Yeah, Right… (Colpo)
Hmmm...now comes the hard part, which is where to begin, what to highlight, what to say about it (actually, I worked that latter part all out in the shower this morning). Suffice to say that I like both of these posts for their mutual injection of sanity into what seemed initially to be a lot of attaboys, high-fives, etc., amongst ardent fans of carbohydrate restriction (I count myself a circumspect fan of LC) leading to metabolic advantage (eat as much as you want LC, no problem—I'm not a fan).
Let's begin with what I'd characterize as a strictly quantitative analysis from Anthony. In the first part of his post, Anthony takes time to review the fact that every single metabolic ward study going back to 1935—every single one—fails to find a statistically significant difference in weight loss amongst different sorts of diet compositions (including LC). In other words, weight loss always comes from caloric restriction. He goes into great detail on every single one of these studies in his book, The Fat Loss Bible. He then goes on to address this particular study; kinda doing so with one arm tied behind his back, because he doesn't make a lot of fuss about it not being a metabolic ward study, and thus tightly controlled (for my take, the team did appear to use an impressive array of state of art methods and incentives to motivate decent compliance and record data). An excerpt from the post.
Bodyweight was virtually identical during all three isocaloric diet phases which to me, as a rational indvidual whose head has never been embedded in his culo, quickly refutes the famous low-carb claim that greater weight loss will occur on a low-carb diet at a given caloric intake. At the caloric level calculated by the researchers to maintain weight, the low-carb diet did exactly what the other diets did – it maintained weight. It did not magically produce further weight loss while the other diets simply maintained the status quo.
I could by all rights end the discussion there, but the interesting thing about this study is that the lack of difference in weight status during the 3 diets is being roundly ignored by the very same low-carb advocates who are parading this study as proof of a metabolic weight loss advantage.
Instead, they are wanking on and on about an allegedly greater increase in resting energy expenditure and total energy expenditure experienced by the participants during the low-carb phase. This increase in REE and TEE, they are claiming, is proof that low-carb diets produce greater weight loss – even though the low-carb diet didn’t produce any weight loss at all.
Let me attempt a different way of conveying the essential point Anthony is making in hopes of getting just one or two more otherwise breathless LC metabolic advantage fans to take a breath.
Here goes, y'ready? ...
All 21 participants did lose a significant 13% average body weight over 12 weeks on a calorie restricted diet equal to 60% of daily energy requirements.
Did that escape everyone's attention, or only the fact that everybody didn't lose any weight regardless of dietary composition over a separate 12 weeks? And just as the first 12 weeks was designed to lose weight (via caloric/energy imbalance), the second 12 weeks was designed to maintain weight (via caloric/energy balance). Everything went according to plan, so is there really any meaningful news here beyond a curiosity that may merit further investigation?
Let me put it a different way, hopefully getting a few more breathless to take a breath:
Researchers gave 12 people free food, prepared it for them, and promised to pay them $500 if they could stand a 40% caloric deficit for 12 weeks. Additionally, they gave them another 12 weeks of free, prepared food, and promised to pay them another $2,000 if they would eat it and come to the hospital for 9 days of tests.
Again, everything went according to plan.
Another thing Anthony points out is important especially on the basis of what has already happened in the media and some blogs: '300 calorie per day metabolic advantage for low carb; step right up and get your metabolic advantage.'
On the TEE graph, 8 of 21 subjects experienced greater declines in TEE on the low-carb diet when compared to the low-GI diet, and four of these folks experienced similar or greater declines in TEE than they did on the low-fat diet.
So you can see that the true story is a little more complicated and somewhat different to the one low-carb shills are trying to portray. Rather than a clear-cut case of reduced drops in REE and TEE during a low-carb diet, the indvidual results are in fact much more haphazard, with some subjects in fact showing markedly greater drops in REE and TEE during the low-carb diet.
Meaning that if you adopt a low-carb diet expecting an increase in metabolism, based on the results of this study, there’s a very strong possibility you’ll be sorely disappointed.
Colpo goes on to address some of the hormonal markers and such, but I'll set that aside and focus just on the weight loss.
So let's move on to Stephan Guyenet who, while addressing some of these quantitative weight loss issues, also includes a qualitative angle, and it's just this sort of thing that makes for a good synthesis. Stephan summarizes the entire dispute in three points.
1. Calories don’t matter at all, only diet composition matters.
2. Calories are the only thing that matters, and diet composition is irrelevant.
3. Calories matter, but diet composition may also play a role.
The first one is an odd position that is not very well populated. The second one has a lot of adherents in the research world, and there’s enough evidence to make a good case for it. It’s represented by the phrase ‘a calorie is a calorie’, i.e. all calories are equally fattening. #1 and #2 are both extreme positions, and as such they get a lot of attention. But the third group, although less vocal, may be closest to the truth.
Sounds like he might be talking about real food, eh? He continues. You can check the post for his references.
Some people have suggested that the type of food we eat, not just the amount, influences energy expenditure, and in particular that this is related to the diet's carbohydrate content. In people who are not trying to lose weight (4, 5), or who are being overfed (6, 7), the carbohydrate:fat ratio in the diet has little or no detectable impact on energy expenditure, and if anything it favors carbohydrate, but could this be different during fat loss in people who start off overweight? This idea has been called the ‘metabolic advantage’, most notably attributed to the low-carbohydrate diet. The idea here is that you can lose fat eating the same number of calories if carbohydrate is kept low.
I’ve never really weighed in on this because it’s a topic of heated debate, and in any case it’s a fairly academic question. Why is it academic? Because previous weight loss studies have shown that if a metabolic advantage exists at all, it’s quite small, because the effect is undetectable in most studies (8, 9, 10). People who are not associated with the low-carbohydrate community tend to conclude that there's no metabolic advantage when they review the literature (11), although I haven't reviewed it closely myself. It’s clear that where fat loss is concerned, calorie intake is much more important than the amount of fat or carbohydrate in the diet. What previous studies have suggested is that low-carbohydrate diets suppress appetite — often resulting in lower calorie intake (12, 13). The reason for this remains a topic of speculation.
So we begin to come full circle with what Anthony said. To put my take on it, Anthony says it's dumb to believe in any metabolic advantage, while Stephan says it's pointless, because either it doesn't exist or is too small to matter.
At which point, I remind you:
All 21 participants did lose a significant 13% average body weight over 12 weeks on a calorie restricted diet equal to 60% of daily energy requirements.
Now enter the qualitative angle. Stephan again.
That being said, I’m actually quite open to the idea that food quality in addition to quantity can influence body fatness, and I would encourage people to think outside the macronutrient box: there are probably many different dietary factors that can have such an effect. Although this idea hasn’t received much support in the human literature so far, there’s quite a bit of evidence for it in the animal literature.
...Like, real food: meat, fish, fowl, vegetables and fruit, like we evolved to eat? Animals? You mean like all those animals in the wild that maintain body compositions exactly as they're supposed to, when able to eat what they're supposed to eat? And we're not even talking about health, yet. Is an animal going to generally fair healthier on a diet provided by nature, or industrial crap in a bag/box?
OK, so if there's anything that could be termed an antithesis from Guyenet contra Colpo's thesis in this regard, here it is—but it's certainly on no such level that all you have to do is eat zero carbs and you'll lose weight:
Does this support the idea that there is a ‘metabolic advantage’ to low-carbohydrate diets? Well, sort of. It doesn’t change the previous findings that the carbohydrate:fat ratio has little or no impact on energy expenditure during overfeeding, in weight stable people, or during weight loss, but it does suggest that a VLC dietary pattern has a metabolic advantage over a LF diet specifically in the context of weight maintenance after weight loss. It also suggests that a LGI diet has a smaller but still meaningful metabolic advantage in this setting, and that a LF diet are not very effective in this regard. It also opens a whole new can of worms for the research world, investigating the effects of diet quality on energy expenditure.
...It's that last phrase I'm most interested in: "investigating the effects of diet quality on energy expenditure." If that were actually to happen, what would that mean for fans of Paleo and WAPF, allied most specifically because of their advocacy of real, whole foods from all the available sources (sorry, veg*ns, no soup for you!)?
Here's an idea: eat real food first. If I can play loose with the term "metabolic advantage," I'd say that in the end, I think calories count, but that food quality matters. Low to moderate carbohydrate diets—when done right—tend to push out crap food for much better food. Much better food means improved satisfaction, satiation...a greater chance of being in control of appetite, cravings, and so on. Inasmuch as appetite, hunger and satiation are related to metabolism, loosely stated, there's your metabolic advantage, right there.
If this was recognized above all, perhaps we could get off macronutrient ratios and focus on real, quality food. In so doing—unless you're just going to eat tubers all day—you're likely going to be eating a pretty moderate carbohydrate load anyway, and even if that includes potatoes, a pretty low glycemic load (that's index, with over time thrown in because, y'know, time passes by).
The takeaway: Eat. Real. Food. Move. Around. If you need to lose weight: Eat. Less. Real. Food. Move. Around. More.
[As an endnote, I was already well into this post when I learned that Evelyn at Carb Sane also weighed in. We've had our differences, but fair is fair and she raises some of the same questions and issues: A Modest Proposal for Peer Review Research. Check it out.]