July 17th, 2009, Thoughts for the Day (1)
Meal Frequency and Mass Gains
Written and posted by Lyle McDonald, July 07, 2009
Meal Frequency and Mass Gains
The issue of meal frequency for muscle mass gains would seem to be pretty well decided, right? Bodybuilders have been pushing for 6 (or more) meals per day spread out every 2.5-3 hours for decades and this is taken as an almost de-facto requirement for success in terms of optimal mass gains.
Then again, the people who have used Intermittent Fasting (for examples, check out Martin Berkhan’s LeanGains.com) appear to be making exceedingly good progress in terms of muscle gain despite not eating for 14-16 hours during the day suggesting that perhaps the above dogma regarding meal frequency isn’t quite as well established as folks might think.
Now, I’ve discussed meal frequency previously, in terms of its effects on weight, body fat and body composition in the research review on Meal Frequency and Energy Balance and won’t rehash those points here. Rather, what I want to discuss here is the potential impact of meal frequency on mass gains for athletes trying to increase muscle mass.
And since I covered the topic in exceeding detail in The Protein Book, I’m simply going to excerpt that section of that chapter. I’d note that I cover a tremendous number of other topics related to meal frequency in that chapter including many practical issues along with the impact of meal frequency on muscle mass maintenance during fat loss.
I’d also note that apparently Layne Norton (a professional natural bodybuilder and all around smart guy who is doing scientific research on the issue of protein and muscle gain) has been experimenting with the ideas I’m going to discuss below (he calls it protein bolusing) but I have no idea how or if it actually panned out.
Finally I’d note that I’m not going to include the reference list for this excerpt. It’s in the book.
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Optimal meal frequency: A theoretical approach
In Chapter 3, I discussed how eating impacted on both protein synthesis and breakdown following a meal. To briefly recap, an increase in blood AAs primarily stimulates protein synthesis with a much lesser impact on protein breakdown; in contrast, increasing insulin levels appears to primarily decrease protein breakdown with only a small impact on protein synthesis. With that information as background, I now want to examine the topic of meal frequency from a slightly more theoretical standpoint by examining two separate questions:
1.
Is it possible to eat too frequently?
2.
How long will a typical meal maintain the body in an anabolic state?
By determining a potential maximum and minimum amount of time that should pass between meals, an optimal meal frequency can be developed. As well, I want to examine the idea that different meal frequencies might be optimal under different conditions (i.e. maintenance versus mass gains versus dieting).
Is it possible to eat too frequently?
It’s not uncommon to read about bodybuilders or other athletes taking the eat-more-frequently dictum to extreme levels, eating every one to two hours. The idea behind this is the idea that optimal results should occur by maintaining a near continuous influx of nutrients into the body. I imagine if they could find a way to do it, some enterprising athletes would set up a continuous intravenous drip with carbohydrates, amino acids and essential fatty acids.
This may not be a good idea in the first place. Some research, primarily using amino acid infusion, suggests that skeletal muscle can become insensitive to further stimulation of protein synthesis. In one study, amino acids were infused for several hours to 70% over normal levels (17). Protein synthesis increased after roughly 30 minutes and was maintained for the next two hours at which point protein synthesis decreased back to baseline.
Importantly, this decrease occurred despite the maintenance of high levels of blood amino acids. Additionally, there was an increase in urea production (a waste product of protein metabolism), indicating that the excess AAs were simply being catabolized in the liver to be excreted in the urine; that is, those AAs were wasted and never utilized by the muscle.
The researchers took this as a suggestion that there might be a maximum amount of protein synthesis that can occur at any one given time before a “muscle full” situation is reached (18). Perhaps more interestingly, based on the amounts of AAs infused, the researchers estimated that only 3.5 grams of AAs would be required to result in this “muscle full” situation (18). I want to make it very clear that this doesn’t mean that 3.5 grams of orally ingested AAs would cause the same effect. Rather, this represented the delivery of 3.5 grams of AAs to the muscle itself.
However, the total amount of dietary protein to achieve this amount wouldn’t be huge. Most dietary proteins are roughly 40-50% EAAs, and due to processing in the liver, slightly less than half of the ingested AAs actually make it into the bloodstream. To provide 3.5 g EAAs to skeletal muscle would require roughly 15-20 grams of whole protein over a two hour time span.
Interestingly, other more direct research supports this value. In a study I described in an earlier chapter, subjects received doses of EAAs ranging from zero to 20 g EAAs and protein synthesis was studied (19). In young subjects, muscle protein synthesis was maximized with an intake of 10 g EAAs and there was no further increase with 20 g EAAs. This represents roughly 20-25 grams of whole protein.
Consumed every three waking hours (roughly six meals per day), this would allow for a maximum protein intake of 120 grams per day before skeletal muscle protein synthesis is maxed out. For a 100kg (220 pound) athlete, this is only 1.2 g/kg, lower than even the most conservative estimates discussed in Chapter 4. As discussed previously, this research is a difficult to reconcile with other, much higher recommendations or empirical results.
However, recall from Chapter 4 that dietary protein has more functions for athletes than simply the stimulation of protein synthesis. Although the amount described above might very well maximize skeletal muscle protein synthesis, optimizing the function of other important pathways of AA metabolism would very likely raise requirements even further (20). As well, while excess amino acids may simple be oxidized off, there is evidence that increased AA oxidation is involved in the overall “anabolic drive” of the body.
Finishing up this discussion, in their most recent study, the same group examined the effect on protein synthesis of a variety of doses of infused AAs (21). Infusing AAs at four different ranges, the group saw a similar pattern to their earlier work, an initial increase in protein synthesis followed by a return to baseline despite maintenance of high AA levels. Additionally, while the lower infusion rates caused a significant increase in protein synthesis, further increases at the higher concentration levels showed smaller additional benefits. Essentially, providing low to moderate amounts of AAs gave the greatest result.
Finally, and perhaps most interestingly, the paper demonstrated conclusively that it was extracellular AA concentrations (rather than the concentration of AAs inside the muscle cell) that were involved in stimulating protein synthesis. The researchers suggested the existence of some type of amino acid “sensor” in the muscle cell membrane that sensed AA levels. The study also suggested that it was the changes in extracellular AA concentration, rather than the absolute amounts that were driving the changes in protein synthesis. That is, it was the change from lower to higher that had the effect more than the absolute amount of AAs present.
Along with the indication of a “resistance” to further stimulation of protein synthesis, it appears that raising AA concentrations (after a meal) followed by a decrease in concentrations yield the best results. Basically, spacing meals apart and allowing blood AA levels to drop, rather than maintaining AA concentrations at continuously stable levels, appears to have the greatest impact on protein synthesis. Unfortunately, this still gives no indication of how far apart those meals need to be spaced to allow a “resensitization” of the muscle to a subsequent increase in AA concentrations.
Additionally, since it was based on an amino acid infusion, it’s unclear how this would relate exactly to the consumption of meals. Between digestion and the hormonal response that occurs with eating, it may very well be that eating protein would yield a different result than what the above research found using AA infusion.
In this vein, it’s interesting to look back at the original casein versus whey research that I discussed in Chapter 2. In that study, whey protein showed an initial spike in protein synthesis followed by an increase in amino acid oxidation in the liver, a pattern not dissimilar to the work examined above (22). It seems plausible that once whey had maximally stimulated protein synthesis, the remaining AAs were simply metabolized in the liver.
In contrast, when very small amounts of whey (a few grams at a time) were sipped over a six hour span to mimic the effects of casein, there was no increase in amino acid oxidation (23); however the impact on protein synthesis was also smaller. It may very well be that flooding the body with large amounts of AAs simply overloads the muscle’s ability to utilize amino acids, causing the excess to be burned off. This would also be consistent with the fact that the slower protein, casein, actually generated a higher overall gain in leucine in the body compared to whey; by never overloading the body’s protein synthetic machinery, overall better results were obtained.
Related to the above research, another group compared the body’s use of leucine with subjects either given small hourly meals or three separate meals (24). They found that protein oxidation was decreased (by 16%) in the group given three meals. Essentially, providing amino acids too frequently appears to decrease the body’s utilization of those aminos. Rather, having discrete meals where blood amino acid levels first increase (stimulating protein synthesis without overloading the body’s ability to utilize AA’s) and then decrease for some time (so that muscle can become “sensitive” to the effect of aminos again) would seem to be ideal.
At this point it would appear that eating too frequently (less than every three hours) has no real benefit, and could possibly be detrimental due to the muscle becoming insensitive to the impact of amino acids. It’s interesting to note the preliminary report above which found increased LBM gains with three versus six meals per day. Perhaps by spacing the meals further apart, greater stimulation of protein synthesis occurred when protein was eaten.
For the remainder of this chapter, I’ll take three hours to represent the minimum amount of time that should pass between meals. Eating more frequently is unlikely to be beneficial and may very well have a negative effect.
How long does a meal maintain the body in an anabolic state?
Having looked at the possibility that eating too frequently might actually be detrimental (or at least not particularly beneficial) given how long a typical meal takes to digest, I want to look at how long a given meal might possibly maintain an anabolic state.
Mentioned above, considering the relatively slow rate of protein and other nutrient digestion, it appears that even a moderate sized meal maintains an anabolic state for at least five to six hours (8). Individual whole food meals are still releasing nutrients into the bloodstream at the 5-hour mark (7). Very slowly digesting proteins such as casein may still be releasing AAs into the bloodstream seven to eight hours after ingestion (22). Considering this research, we might set a conservative limit of five hours as the absolute longest time that should pass between eating some source of dietary protein during waking hours.
Part two next