Sufficient dietary protein is essential for human health, metabolic function, tissue repair and growth. Protein is set apart from the other four as it is the only nitrogen-containing macronutrient and thus the only source of dietary nitrogen. As proteins serve functional and structural purposes in cells and organisms, they are present in all life and therefore all whole foods. Protein is majorly obtained in the diet through meats, eggs, dairy, high-protein plants such as soy/tofu, and protein powder supplements. Unless hydrolyzed, dietary protein is in the form of long polypeptide chains, i.e. thousands of single amino acids linked together with peptide bonds.
Amino acids are the smallest structural unit of proteins and are the result of the digestion of dietary protein. There are 20ᵃ amino acids: 12 of which humans are able to synthesize from other nutrients. The remaining 8 are termed "essential amino acids" and must be obtained through the diet: phenylalanine, threonine, tryptophan, methionine, leucine, isoleucine, and valine. The latter three are the branched chain amino acids (BCAAs; see Supplementation). Protein sources are rated on their amino acid profile (content). Sources containing all 20 amino acids are complete proteins; conversely, incomplete proteins lack one or more of the amino acids. Proteins higher in essential, and specifically branched chain amino acids are considered higher quality with respect to muscle protein synthesis.¹
Recommended Daily Protein Intake for Building Lean Body Mass
In terms of physique and strength building, muscle protein synthesis (MPS) is the main interest of bodybuilders, resistance-trained athletes and fitness enthusiasts. Being the building blocks of muscles, dietary proteins (amino acids) are anabolic as they promote and fuel MPS. There is a certain amount of protein an individual can consume that optimizes MPS, where any extra dietary protein is catabolized (not used). For (omnivore) individuals on maintenance or surplus caloric intakes, the daily recommended protein intake is 0.8 grams per pound of body mass.² For individuals on a caloric deficit, a slightly higher value of 0.9-1.3 g/lb (approximate due to dependence on body composition) is supported in the literature.³ Due to the average lower quality of plant protein sources, I recommend that vegans consume 25% more protein than omnivores.⁴
Although consuming more than these recommendations will not be directly harmful, it can inadvertently impact training. Consuming a higher macronutrient proportion in the form of protein takes away from the available calories for carbohydrates. An increased daily amount of the latter has been shown to augment performance (SOURCES). Better performance in the gym allows for more efficient muscle stimulation and increased muscle growth.
Fibre is a type of carbohydrate that originates from plant material. Because it is predominantly indigestible, bulky, and water absorbing, fibre slows down the digestion process and inhibits some nutrient absorption. Humans lack enzymes required to break down fibre’s chemical structure. Due to the presence of natural flora (bacteria) in the large intestine, some energy from fibre is extracted and absorbed.
Although the aforementioned properties give fibre a greater thermic effect of food (TEF; more energy is expended in processing and thus less net energy is absorbed than from other carbohydrates), its net caloric value is not zero and therefore cannot be ignored.
Fibre is essential in the proper functioning of the digestive tract. It is possible, however, to over-consume fibre, leading to symptoms of bloating and malabsorption of nutrients. I generally recommend a daily fibre intake of around 10% of total carbohydrates consumed or, alternately, 20-30 grams for a daily consumption of 2000-3000 calories⁵, but not to exceed 15-20% of total carbohydrates if gastric distress is experienced⁶.
a. Referring to coded amino acids, namely before post-translational modification.
Phillips, S., & Van Loon, L. (2011). Dietary protein for athletes: from requirements to optimum adaptation. J Sports Sci., 29(1), S29-38. Retrieved from http://www.ncbi.nlm.nih.gov/pubmed/22150425
Pikosky, M., Smith, T., Grediagin, A., Castaneda-Sceppa, C., Byerley, L., Glickman, E., & Young, A. (2008). Increased protein maintains nitrogen balance during exercise-induced energy deficit. Med Sci Sports Exerc., 40(3), 505-12. Retrieved from http://www.ncbi.nlm.nih.gov/pubmed/18379214
Helms, E., Zinn, C., Rowlands, D., & Brown, S. (2013). A Systematic Review of Dietary Protein During Caloric Restriction in Resistance Trained Lean Athletes: A Case for Higher Intakes. Int J Sport Nutr Exerc Metab. Retrieved from http://www.ncbi.nlm.nih.gov/pubmed/24092765
Barr, S., & Rideout, C. (2011). Nutritional considerations for vegetarian athletes. J Nutrition., 20(7), 696-703. Retrieved from http://www.sciencedirect.com/science/article/pii/S0899900704001066
MacDonald, Lyle. "Fiber - It's Nature's Broom." Body Recomposition. N.p., 2009. Web. 8 Jan. 2014. Retrieved from http://www.bodyrecomposition.com/nutrition/fiber-its-natures-broom.html
Helms, E. (2010, January). Bodybuilding Science Blog with Eric Helms: Q & A. Retrieved from http://www.3dmusclejourney.com/2010-01qa.php