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.
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:
- Is it possible to eat too frequently?
- 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.
Summary: Theoretical examination of meal frequency
It appears that eating too frequently could potentially be detrimental to the goal of gaining muscle mass in that muscle tissue becomes insensitive to further stimulation by amino acids, increasing protein oxidation in the liver. Eating more frequently than every three hours would seem to not only be unnecessary (based on the rate of digestion of whole proteins) but could possibly be detrimental.
Given a moderately sized whole food meal, the body will generally remain in an anabolic state for at least five to six hours (and possibly longer depending on the foods chosen). Conservatively, we might use five hours as the upper limit cutoff for time between meals.
This yields a duration between meals of anywhere from three to five hours. This should keep the body in an overall anabolic state without causing problems related to too frequent or too infrequent consumption of meals.
Full time athletes with time to eat very frequently are probably best served with the higher meal frequency simply to ensure adequate caloric intake. Again, smaller individuals with lower total energy intakes may want to use slightly larger meals eaten slightly less frequently for practical reasons. Similarly, individuals who work jobs and are unable to fit in a meal every three hours needn’t worry obsessively about becoming catabolic. A solid food meal containing a high quality protein, carbohydrates, fat and some fiber eaten every five hours will maintain an anabolic state readily.
Protein distribution throughout the day
Related to the topic of meal frequency is the question of whether the day’s protein should be spread evenly throughout the day, or if some other pattern of intake might be superior.
As discussed above, one early study examined whether providing 25% of protein at breakfast and lunch and 50% at dinner had any impact on nitrogen balance compared to spreading the protein evenly across the day’s three meals; no difference was found (9).
More recent work has examined a dietary strategy called “protein pulse” feeding. With that approach, 80% of the day’s protein was given at lunch with only 10% at the other two meals; this was compared to a “spread” pattern where the day’s protein intake was distributed evenly across four meals. In elderly women, the “pulse” pattern led to a greater protein gain compared to the “spread” pattern (25). However, in younger women, the “spread” pattern was superior and led to a greater nitrogen balance (26).
There is a substantial and increasing amount of data that putting some amount of the day’s protein around training is beneficial, a topic that is discussed in detail in the next chapter. Outside of ensuring adequate protein before, during and after training, there is no real indication that distributing the day’s protein in any pattern other than a basic spread pattern is beneficial (again, except possibly for older individuals).
So, for example, take an athlete who will be consuming 200 grams of protein per day with 40 grams of that placed around training. That leaves 160 grams of protein to be evenly distributed across the day’s other meals. With a four meal per day frequency, that yields 40 grams of protein per meal; at six meals per day, the athlete would consume roughly 27 grams of protein at each meal.
Is there an optimal intake pattern for different goals?
In the chapter on protein requirements, I mentioned Tipton and Wolfe’s contention that any discussion of protein requirements has to be context dependent: that is, the goals of the athlete determine what is optimal in terms of protein intake. While they were talking primarily about total daily protein intake, this idea can be extended to other aspects of nutrition including protein intake throughout the day and how it might interact with specific training goals.
Logically, gaining muscle mass versus maintaining muscle mass at maintenance calories versus trying to maintain muscle mass under conditions of caloric restriction (dieting) are different situations, potentially requiring different optimal intakes of protein, AAs, meal frequency or protein intake pattern. The possibility exists that different patterns of protein intake (in terms of both timing and type of protein) might exist for different goals (27).
For practical purposes, I’m going to consider the following discussion in terms of two different goals: muscle mass maintenance (either at maintenance calories or while dieting) and muscle mass gain. I want to note that most of this discussion will be somewhat hypothetical since little direct research exists to date.
The background for this discussion can be derived from a topic I’ve discussed previously in the book in terms of how different patterns of protein digestion (i.e. fast versus slow) can influence whole body metabolism differently.
Recapping briefly, large spikes in amino acid concentration appear to stimulate protein synthesis (recall also the infusion data I discussed above) with little to no impact on protein breakdown. In contrast, maintaining constant low levels of AAs appears to reduce protein breakdown with less of an impact on protein synthesis.
Consuming very large amounts of protein at once (as in the protein “pulse” studies discussed above) has an effect similar to a fast protein such as whey, spiking blood amino acids and promoting protein synthesis as well as oxidation (28).
In contrast, spreading protein out in smaller amounts throughout the day has an effect closer to that of casein, inhibiting protein breakdown with a smaller impact on protein synthesis (28).
I’d mention again that, in the original whey versus casein study, reducing protein breakdown via casein had a larger impact on net leucine balance compared to whey. Recall also that adding whey to other food, which had the effect of slowing down digestion, had a similar effect.
Given that data, it may very well be that simply maintaining relatively constant low levels of amino acids (with a spike around training, discussed next chapter) is optimal for all goals. This would be conceptually similar to the strategy of keeping insulin low but stable during the day with a spike around training. This is essentially the strategy that bodybuilders have empirically settled on under all situations: they eat small amounts of protein, carbohydrates and fat throughout the day with a relatively larger intake of nutrients around training.
With regards to muscle mass maintenance and dieting, there is little to discuss: based on the direct research available as well as the general difficulty in stimulating protein synthesis when calories are reduced, a slow/spread pattern of protein intake is clearly optimal. Maintaining continuous low levels of amino acids throughout the day (in addition to increasing total protein intake) to limit the body’s need to mobilize stored body protein from muscle and other tissues should be the goal. A combination of slow proteins combined with evenly spaced meals to keep blood AA levels stable throughout the day would seem to be optimal.
But is this also the optimal pattern for gaining muscle mass? On the one hand there is the suggestive study above where a group receiving three meals per day gained more LBM than a group receiving six per day; as well there is the research suggesting that maintaining constant levels of AAs might cause skeletal muscle to become “insensitive” to further stimulation; increasing extracellular levels of AAs and then allowing them to fall again appears to be superior. Both of these data points suggest that keeping blood AA levels stable throughout the day might not be optimal from the standpoint of muscle mass gains.
Another recent study throws a wrench in the typically held bodybuilder idea that simply maintaining continuous levels of amino acids with frequent meal feeding is optimal (29). In that study, two groups were compared. The first received three whole food meals while the second received the same three meals with an essential amino acid (EAA) supplement in-between. I should note that the study suffered from one huge design flaw: the groups got different amounts of total protein. It should have also tested a group that got 6 whole food meals and the same amount of protein as the EAA supplemented group.
Recognizing that limitation, the study made at least three major observations. The first was that the EAA supplement generated a greater protein synthetic response than the whole meals. The second was that the EAA supplement generated an anabolic response even when given in-between meals. That is to say, the previously consumed meal, which was still digesting when the supplement was given, didn’t blunt the effect of the EAA supplement. Finally, the EAA supplement didn’t blunt the anabolic response to the meal. Of course, the study didn’t examine what impact this would actually have in the long-term on muscle mass gains but is interesting nonetheless.
This study suggests that a potential pattern at least worth experimenting with for athletes seeking maximal muscle mass gains would be to alternate between slower digesting meals with faster acting sources (perhaps a whey protein drink or an EAA supplement) throughout the day (25).
It also plausible that a combination of slow and fast protein sources at a given meal could give the best of both worlds: a spike in AAs to stimulate protein synthesis followed by a slower increase to inhibit protein breakdown. Preliminary data that I discussed back in Chapter 2 supports that idea as well although it was being primarily applied to protein intake following resistance training. It’s interesting to note that old school bodybuilders often consumed copious amounts of milk to gain lean body mass as milk protein is a mixture of whey and casein.