pintoca, one of the "experts" I most respect in the field of bodybuilding nutrition is Lyle McDonald (creator of the UD2 and PSMF diets that I personally would argue are "the best" out there). He has his own board, bodyrecomposition.com, and to save time (as I'm at work) I'm going to use a bunch of quotes from him to get my point across.
Here are the reasons why people claim 6 meals is better, followed by why this is not true (and no I'm not saying, nor would I ever say, that 3 meals is better...merely that it makes no difference). So, in no particular order:
1) You can only utilize a certain amount of nutrients in a certain duration of time.
I'm not sure where this myth began, but I don't believe it's ever been proved or disproved. The only "evidence" out there is that which I cited in the other thread about our ancestors possibly not eating for days, then having a massive feast (when they found something to eat), and repeating the process indefinitely. There's also another group of people worth looking at, and this is mentioned in something I will quote shortly: prisoners.
As for a greater chance of fat storage if you can't properly utilize all of the calories, here's something to think about. Let's say you DO store more fat after consuming a larger meal. Well, what do you burn in between meals? Answer: stored calories. So, while the person eating less meals/day may store less calories/meal as fat, he is also spending less time per day using stored fuel. So, the net effect is zero difference.
2) Eating more meals keeps your metabolism humming all day.
"First and foremost, human metabolism doesn't slow on a meal to meal basis. In rats/mice, probably. In humans, no way.
Second, the usual argument has to do with the thermic effect of food, every time you eat, metabolic rate goes up a bit. And this is true. But if you look at the net TEF over a given day, whether you bump it a little 6X/day or a lot 3X/day, the end result is the same." -Lyle McDonald
3) You must eat every 2-4 hours to maintain a positive nitrogen balance.
Again, I'll let Lyle handle this one:
"Nitrogen balance is an attempt to measure changes in the body's nitrogen content (proteins contain some proportion of nitrogen). So they measure nitrogen going into the body, which is food. Then they attempt to measure nitrogen going out. This includes fecal losses, urinary losses, losses in sweat, skin loss, breath loss and I even saw one study that collected women's tampons to measure nitrogen in the blood (I highlighted that quote). In most cases, some estimations are made for a lot of these because they are a hassle to measure directly (serious studies will sew people into suits to collect sweat and skin so it can be measured). Unfortunately, these estimates are probably wrong when you put exercise into the mix.
The difference is presumed to indicate how much the body's nitrogen status is changing. So, in premise, if you're in positive nitrogen balance, you're storing protein; negative nitrogen balance, losing it.
The problem is that, as a method, it's basically not very accurate. This is one of the primary criticisms of the work of Lemon and Tarnopolsky (i.e. by Phillips and Millward): if you take the nitrogen balance estimations at face value, the lifters in those studies should have gained kilos and kilos of muscle mass. But they didn't. Conclusion: nitrogen balance vastly overestimates things and isn't a good measure. As well, there's no way to know where the nitrogen is going anyhow.
Protein synthesis is an attempt to be a bit more accurate/specific. Usually a radioactive tracer is used like leucine (presents problems due to metabolism w/in the muscle) or phenylalanine (much less difficult) and you measure uptake. This can be done at the whole body level or for a specific tissue. The problem with measurements of whole body protein synthesis is that, once again, you don't know what tissue the protein is being synthesized in. Could be muscle (we hope), frequently it's changes in liver proteins and such. It's more accurate to measure direct muscular uptake but more expensive and invasive.
So, back to the original question: does eating more frequently impact on nitrogen balance or protein synthesis. There's one study that chronically gets trotted out on meal frequency and ntirogen balance: it's a Russian study done in rats. The problem: rat metabolism is way faster than ours; extrapolation is problematic. Other than the afforementioned boxer study (where 2 vs.6 meals led to a more negative nitrogen balance, and note my other problems with that study above: liquid protein, 2 vs. 6 is an extreme difference and I suspect far different than 3 vs. 6 would have been), I don't recall seeing anything comparing meal frequencies given an identical amount of protein. I assume if it was out there and it was positive, the protein powder ads would cite it constantly (note: if anybody has seen such a paper, send the reference my way).
Now, eating stimulates protein synthesis, both whole body and muscular. In muscle specifically, the key plaers are the BCAA's, especailly leucine. Note that the quantitative effect on muscle protein synthesis is quite tiny in the big scheme of things. One researcher (Tipton? Aaronf will correct me here) has done some back of the hand calculations suggesting that anything over 40 grams of amino acids may max out muscular protein synthesis. As I recall, he was going from an infusion study. I think this is an important point to make because infusing aminos all at once is way different than eating.
The issue as I see it is that the digestion of protein in humans is fairly slow. A large meal of a solid protein may still be releasing amino acids into the bloodstream at the 5-8 hour mark. It's hard for me to see how the assertino that you MUST eat protein every 3 hours or you will fall into the pit of catabolism can possibly hold true. Basically, larger meals release the nutrients into the system over a much longer time frame than smaller meals. I have trouble seeing how 3 meals of 80 grams of protein is going to be massively different than 6 of 40 grams of protein.
So even if Tipton's 40 gram thing turns out to be correct, it's not as if eating 80 grams of protein in a meal means that 80 grams of protein all hit your bloodstream all at once. You'd expect a spike of nutrients, at which point this would feedback on gastric emptying and keep the rest of the meal in the gut, followed by a more steady release.
Do I think it hurts? Of course not. Do I think it makes all of the difference in the world? Not so much. To steal an arguably bad example from that website someone trotted out a few weeks back: look at prisoners in jail, lifting their brains out and getting fed what the jail feeds them. They get HUGE. Somehow I doubt they are eating 30-40 grams of protein 6X/day to do so."
4) Studies have been done showing more meals equates to less LBM lost during a diet.
Again:
"Ok, one goofy ass study on boxers found more LBM loss on an extreme diet comparing 2 vs. 6 meals/day. Study had many problems IMO. Not the least of which was too little protein in general, and using liquid protein (faster digestion). Not to mention that 2 vs. 6 is a different situation, IMO than 3 vs. 6.
Usually when studies find a difference between meal frequency, it's because meal frequency ends up affecting caloric intake.
So early studies suggested that adding snacks to 3 meals/day made you fatter. But people were adding calories to their daily total and probably snacking on junk food.
Later studies found that splitting your calories into more meals made people eat less, so they lost weight.
The counfound in both sets of studies: meal frequency ended up impacting total caloric intake and it was the change in caloric intake that caused the results. When you control calories, within a realistic range of meals (3+), differences would appear to be insignificant (there's a good British Journal of Nutrition review out there on the topic)."
As for studies that would appear more practical:
"The studies done to date, using identical caloric intake and varying meal frequencies generally find little to no difference in anything."
He does note that one might make an argument for increased partitioning effects around training time, which might lead to slight differences in body composition if a greater % of one's daily calories were consumed at this time.
You see, what people fail to realize (and is the point I keep stressing) is that when broken down to it's most basic level, dieting comes down to calories. Food choices and meal frequency are generally quite moot, given a few basic requirements are met (adequate protein, mostly coming from whole food sources, EFA's, and equal calories across all conditions).
And finally, pintoca mentioned taking this to the extreme and consuming only a single meal/day. If it all comes down to calories why wouldn't this approach be just as good? Well, it's explained above. Protein synthesis and nitrogen balance aren't as important as most people (typically supplement companies looking to push their powders) would have you believe. That being said, aminos are only released into the bloodstream for so long. Going 24 hours between meals would surely not be adequate in this respect.