Ok, since I'm such a nice guy, I thought I'd give Anssi a free lesson on the thermogenics of diet. Maybe he'll learn something.
Now, in their papers, Feinman et. al. made two primary arguments for a metabolic advantage of low-carbohydrate diets.
1. The first, as I mentioned, was the thermic effect of protein. And, of course, a diet higher in protein will show a greater caloric expenditure (via thermic effect) than one lower in protein.
It really shouldn't require stating that this has nothing to do with the carbohdyrate content of the diet per se. So rather than referring to low-carb diets, they should be referring to high-protein diets. Again, a point so obvious to anyone with basic intelligence but one apparently missed by Anssi and his pals.
In any event, having never seen a bodybuilder eating the kinds of protein that normal people eat, I see this as a non-issue and a non-argument. As well, for the reasons above, it's stilly to compare diets differing in protein and make conclusions about diets differing in carbohydrates. Yes, if you want to look at hte typical american diet or the stupidity given out by RD's and compare that to the generally increased protein intake seen on ad-lib low-carb diets, that's fine. But be honest,you can eat a high protein intake within the context of a carb-based diet just as easily as on a low-carb diet. If the advantage is due to higher protein, say it's due to higher protein. Don't wank about low-carbohdyrates having an advantage.
Anyhow, let's assume two different diets:
High carb: 30% protein, 50% carbs, 20% fat (a rather typical bodybuilding diet)
Low carb: 30% protein, 10% carbs, 60% fat (a typical ketogenic/low-carb diet).
Ok, protein is identical, there can be NO advantage of one diet over the other from the standpoint of the thermic effect of food, can there Anssi? Of course there can't.
So first let's look at the overall TEF of carbs vs. fat.
The typical values given are 6% for carbs and 3% for fat. So of 100 calories of carbs eaten, you burn about 6 calories. For 100 calories of fat, you burn about 3. Clearly, the carb based diet has the advantage in terms of resting energy expenditure here. It's pretty damn small, mind you, but it exists. And so many studies show this, examining the effect of higher carbs to higher fat on TEF, that it's just stupid that Ansii and Feinman can only seem to reference diet studies based on self-reported food intakes and uncontrolled diets.
Even the mechanisms of this are clear. Carbs raise insulin which jacks up nervous system activity which increases caloric expenditure. Fats do not. Carbs stimulate their own storage and oxidation, fat does not stimulate its own oxidation; it simply gets stored as fat. This is all basic nutritional biochemistry.
Ok, so let's calculate out the projected difference in TEF between the diets. Again, since protein is identical, we can ignore that and look only at the carbs/fat. I'm interested here in the difference in TEF between the diets.
Let's say that both diets above contain 3000 calories. The
high carb diet will contain 1500 cal of carbs and 600 calories from fat.
The total estimated TEF of the carbs+fat would be 108 calories.
The low-carb diet will contain 1800 calories from fat and 300 calories from carbs.
The total estimated TEF of the carbs+ fat will be 72 calories.
For a whopping difference of about 36 calories/day wth the (tiny-ass) advantage going to the carb-based diet. Hooray. Basically, with a fixed protein content, switching out carbs and fat has basically no major effect on anything. Which is probably a big part of why controlled studies (such as the one by Hirsch I posted as well as the one by Brehm) with identical protein which vary carbs and fat find no effect on metabolic rate.
Oh, by the way, Anssi claims that metabolic chambers can't pick up the differences in metabolic rate because they are not sensitive enough. Yet hundreds of studies over a couple of decades of work have reliably picked up differences between different dietary and feeding conditions. Yet, somehow, they cannot seem to measure a 'metabolic advantage' for low-carb diets. He can dismiss the method out of hand but he's just blowing smoke out of his ass on that one.
2. Ok, but now we turn to the second argument by Feinman et. al. which rests on the caloric value of gluconeogenesis. they go through a lot of biochemical and thermodynamic wanking in their first paper without really quantifying exactly how much of an energy expenditure this should add up to over the course of a day. Maybe Anssi can clear this up for me because Feinman et al's writing is, frankly, incomprehensible.
Ok, so let's assume that gluconeogensis is significant enough during a low-carb diet to contribute meaningfully to total caloric expenditure. First off any gain from gluconeogenesis has to be gained against the loss of TEF from eating less carbs. Of course, that TEF is small in the first place.
In any case, here's the major problem, something that apparently Feinman and Anssi are both unaware of: one of the primary adaptations to ketosis, that occurs over the first 2-3 weeks, is an increase in utilization of ketones by the brain (other tissues such as muscle use a combination of fatty acids and ketones in varying concentrations). This occurs to spare glucose, which occurs so that the gluconeogenesis from protein can decrease significantly. Because, if it didn't, during something like fasting, you would lose so much body protein that you'd die.
I want everyone to read that again. Gluconeogenesis, which is initially high to produce glucose for the brain which isn't coming from the diet, drops significantly by the 2nd or 3rd week of adaptation to ketones.
What does this mean? That any metabolic advantage predicated on that biochemical process is basically rendered moot. Well, except for the first couple of weeks of the diet I suppose.
Now this at least gives some type of plausible mechanism for why the entire difference in weight loss shows up as an early event only (as I mentioned previously) although apparently I have to make Anssi's arguments for him since he's incapable of bringing anything useful to the table. Although the huge amount of water loss (Still denying that it occurs, Anssi) still colors that. When the total difference in weight loss between diets is 2.5 kg and people are dropping 2-3 kg of water in the first few days, well.....
But predicating a metabolic advantage on a process that is made basically irrelevant after 2-3 weeks seems hopeful at best, and ridiculous at worst.
Any advantage of low-carb/high-protein diets is going to be predicated primarily on the fact that protein blunts hunger (Skov et. al found that the individuals eating 25 vs 12% protein ate approximatly 400 cal/day less and lost weight because of it) and people eat less. As one of the reviews I posted clearly showed.
Studies have typically indicated an ad lib intake of 1600-1800 calories on ketogenic diets which creates a huge deficit for fat people. Contrast this to the fact that people routinely underreport their intakes on a carb-based diet by up to 50%, they may say they are eating 1600calories, but they are really eating 3200. Now consider that within the context of all of the food diary studies that Anssi continuously relies on for his data.
One recent study in diabetics showed that a shift to a low-carb diet caused them to decrease caloric intake by 1000 calories/day. Now you can wank all day long about metabolic advantages but, at the end of the day it comes down to this: people who are losing weight/fat on a low-carb/high-protein diet are doing it because they are eating less, not because of some mystical metabolic advantage that no study has ever been able to directly measure (i.e. metabolic chamber).
The end.
Lyle
