Determining Protein Intake Protein is a funny old macronutrient. The majority of the media will have you believe that more than 1 shake a day will snap your kidneys in 12 different places, yet some will tell you that anything up to 4g/kg/day and above will have no negative impacts on your health, provided no pre-existing medical issues. As usual, in the over complex world of nutrition, the answer is fairly simple and lies between the two. First off, The RDA for protein in the UK is 0.8g/kg/day, however, in terms of the RDA, people often forget that this recommendation is based on preventing deficiencies, and ensuring a safe quantity for almost all individuals (even those with pre-existing medical problems). Therefore, clearly this is not an adequate amount for maximising muscle protein synthesis (MPS), and there is even research to suggest that this is not even adequate to prevent net Muscle Protein Breakdown (MPB). That is to say, consuming 0.8g/kg/day may result in a net loss of muscle protein. Ok then, the RDA is not enough, so why is it so low? The main reason is for safety. This amount is suitable to all populations, even those with pre-existing medical issues. The fear is that high protein intake may promote renal damage by chronically increasing glomerular pressure and hyper-filtration. This is basically fancy jargon for overuse of the kidneys. However, the literature does not support this claim and suggests that protein-induced changes in renal function are likely a normal adaptive mechanism well within the functional limits of a healthy kidney (1). i.e our kidney simply adapt to higher intakes, almost like a muscle adapts to a heavier weight. So then, what is optimal. Now this is where it gets interesting (or confusing as the case may be). Inter individual variation is huge with this topic, and science can only give us averages! This means that even though a study may state that 2.5g/kg/day is optimal, this may not actually have been optimal for even 1 person in that study! its just the mean. That said, science is the only way in which we can make justifiable recommendations. So, start with 2g/kg/day then adjust according from there. If in a caloric deficit go higher, anything up to 3g/kg/day. Note however this amount is unlikely to yield extra benefit in terms of MPS, but may be beneficial for adherence to the diet due to protein’s satiating qualities. A recent study in endurance trained women found that with 95% confidence a protein intake of 1.1-3.8g/kg.day was necessary to maintain positive nitrogen balance (2) (nitrogen balance is often used as an estimate of MPS v MPB due to the nitrogen found in protein). Thats a huge inter-individual variation and shows just how hard it is to suggest a certain amount based simply on bodyweight. Tracking results is a must, and adjusting intakes accordingly is simply the only way to obtain a specific optimal intake for a given individual. Remember, science gives us the ball park figure, it is down to the individual/coach to pinpoint the optimal intake based on results. ncbi.nlm.nih.gov/pmc/articles/PMC1262767/ ncbi.nlm.nih.gov/pubmed/24476478
Posted on: Fri, 26 Dec 2014 09:15:58 +0000
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