There are several beliefs in circulation regarding protein consumption, and utilization. Some say your body can not digest more than 30g of protein in one sitting, others claim up to 100g is necessary to maximize recovery and muscle growth. But as with most of these conversation the key element lacking is context.
Because admittedly there is a kernel of truth to both high and low/moderate protein intakes per meal, but it depends on the context and the magnitude of claims being made. In this short article we’ll explore the basics of protein digestion and utilization. Identifying some of the key elements that are required to anchor this discussion and make the information more applicable to various circumstances.
When you consume food, your body has various processes by which food is digested and nutrients are transported to their final destinations for utilization. Peristalsis is a wave-like series of muscular contractions. The purpose of which is to move the chyme (a pulpy mass of food) through the digestive tract.
A key component influencing protein digestion is the time it spends in the digestive tract. Cholecystokinin is a digestive hormone that serves many functions. In response to food consumption it regulates satiety signalling, and can also augment the speed of peristalsis to enhance protein digestibility and utilization (1)(2)(3)(4).
The majority of protein is digested in the small intestine, and although most people only view protein as required for muscle mass, it plays a critical role in many other metabolic functions (5)(6). For instance, a significant portion of protein consumed is directed toward supporting various functions of the gut (7).
The small intestines also have the ability to store amino acids for future use, although there are limitations to its storage ability and is dissimilar to how body fat is stored for future energy requirements (8).
Some research shows that consuming more than 30g of protein in one sitting results in a loss of the additional protein (9). This was also believed due to the higher urinary nitrogen concentration post feeding. However, we know that increased protein intake increases protein turnover (10). This means the increased nitrogen being excreted is more likely the byproduct of older proteins being replaced by new proteins (11).
Since hypertrophy is dependant on the relationship between muscle protein synthesis and muscle protein breakdown this is a relevant point. One paper by Kim et al. looked at the differing effects of consuming 40 vs 70g of protein. The researchers found “high protein resulted in greater plasma essential amino acid responses (P < 0.01) vs. MP, with no differences in insulin and glucose responses. In conclusion, whole body net protein balance improves with greater protein intake above that previously suggested to maximally stimulating muscle protein synthesis because of a simultaneous reduction in protein breakdown” (12).
Additionally the quality of protein consumed will impact the utilization and thus how much should be consumed to maximize the anabolic response. Practical considerations are also relevant here since a 120Lb female will have significantly different protein requirements than a 250Lb male. Assuming we adopt the standard 1g/Lb of bodyweight consumed daily, we have 120g vs 250g per day.
Research shows there is a refractory period by which MPS will not be maximally stimulated for roughly three hours post protein consumption assuming adequate protein was consumed initially (13). So if we assume the higher end of 30g per meal and a three hour window the 120Lb female will need to eat 4 meals per day spaced roughly three to four hours apart.
The 250Lb male on the other hand would require roughly 8.3 protein feedings spaced roughly three to four hours apart. That means this poor soul will be be waking up throughout the night to eat several times in order to meet his daily requirements.
In this case increasing the dosage will have a more beneficial effect on both adherence and likely muscle mass. I also want to share my personal opinion on the subject which is that I struggle to understand a valid rationale to support the idea that a 120Lb female and a 150Lb male will have the same protein ceilings that would limit the per meal consumption.
I understand at the moment there is no literature to directly support this but there are inferences which can be made based on the larger body of evidence that make me skeptical of the 30g limit applying equally to all types of athletes.
In summary, protein consumed beyond the 30-40g threshold will not be “lost” or “wasted”. It will simply be utilized in alternate ways. There is a benefit to increasing protein intake to up to 70g per serving if you are a larger athlete and consume a higher protein intake.
This is largely due to the attenuating effect it has on protein turnover. Protein feedings should be spaced roughly three to four hours apart due to the muscle full effect and in order to maximize the muscle protein synthetic response.