by Joe Giandonato, MBA, MS, CSCS
Recommendations concerning protein intake have ignited a spate of controversy among fitness professionals, dieticians, and the medical community. Seemingly everyone has refused to arrive at a consensus as to what intake levels are appropriate. However, a number of variables, which include one’s activity level, hormonal status, and existing metabolic functioning impact daily intake levels.
Protein is vitally important to health and performance. Proteins are polymeric structures composed of amino acid chains and comprised of carbon, hydrogen, oxygen, and nitrogen molecules. Proteins are involved in host of physiological functions and are classified as structural, transport, enzymes, or messengers.
Structural proteins are fibrous proteins which protect the body and enable movement. These proteins can be found in hair (keratin) in muscle fibers (actin, myosin, titin), and within tendons and the extracellular matrix (collagen and elastin).
Transport proteins are water soluble proteins which carry biological constituents throughout the body. These proteins consist of hemoglobin, which carries oxygen to working tissue in bronchial circulation; myoglobin, which sequesters oxygen from the hemoglobin and stores it until needed by the working tissue; and cytochromes, which are instrumental in the conversion of ADP to ATP, as they carry electrons from hydrogen atoms in the citric acid cycle and bind them to oxygen molecules.
Enzymes are proteins which catalyze reactions within the body. They are integral in digestion (breaking down foodstuffs) and substrate utilization, clotting blood (prothrombin), convert ATP to storable ADP via hydrolysis.
Messengers are proteins which elicit physiological effects by way of communicating with cells throughout the body. Messenger proteins include: insulin, which regulates glucose metabolism; vasopressin, which is an antidiuretic, growth hormone; which drives cellular growth, proliferation, and regeneration.
So we gather that protein is pretty important, right? So important, that it necessitates mammoth daily intakes, especially if one is seeking gains in muscle mass. Wrong.
Metabolic Mishap of Mega Protein Intakes
An investigational report authored by Metges and Barth in 2000, revealed that mega dosing protein may render a refractory effect as it results in metabolic acidosis which hampers protein synthesis, increases protein breakdown, and shift the body into a negative nitrogen balance (3). For reference, a positive nitrogen balance is conducive to growth and repair and often termed as an anabolic environment, by bodybuilders, strength athletes, and strength coaches.
The report also indicated that high protein intakes may reduce plasma levels of the amino acids glutamine, alanine, and glycine and suggested that the reduced circulating glutamine may decrease lympocytic functioning, in turn reducing the secretion of interleukin 2 (3). Interleukin 2 is a cytokine involved in growth, proliferation, and differentiation of T cells which confer reparatory and immunologic effects within the body.
The results of high protein diets are rather confounding. Among overweight and obese men and women, short term high protein diets which averaged 1.92g per kilogram of bodyweight rendered improvements in total cholesterol and triglycerides, and reduced bodyweight (2). A recently published study by Antonio and colleagues revealed that resistance trained subjects who consumed up to 5.5 times the national recommendation showed no significant improvements in body weight and fat free mass (1).
And though dietary protein boasts a greater thermic effect than dietaty fat and carbohydrates, consuming too much of it may lead to greater fat storage. When excessive protein is consumed, amino acids are redirected from gluconeogenesis (which is the breakdown of amino acids into glucose) and ATP pathways and converted into lipids in the liver. Bottom line? Consuming inordinate quantities of any macronutrient will lead to fat storage if energy intake exceeds expenditure.
Protein Intakes Revisited
Dietary Reference Intakes, or DRIs, suggest that individuals consume at a minimum, 0.8g of protein per kilogram of bodyweight. Individuals engaging in regular physical activity should consume between 1.2 – 1.4g of protein per kilogram of bodyweight and those engaging in vigorous physical activity on a regular basis should consume between 1.6 – 1.7g of protein per kilogram of bodyweight. Contrarily, those with nephritic conditions may require lower protein intake amounts with concordant medical care.
The DRIs are limited as they only provide numeric guidelines and do not account for the quality of the protein source and one’s hormonal status.
Plant proteins are not as digestible as animal proteins and do not have a full amino acid profile. Those who consume only plant proteins in conjunction with the DRIs may not be meeting their protein needs.
Adolescent athletes and those who participate in vigorous strength training may benefit from greater protein intakes, as cell turnover, protein breakdown and synthesis is elevated in growing and highly active individuals. Further, those supplementing with anabolic androgenic steroids have a heightened capacity for protein synthesis. Higher protein diets may also result in enhanced insulin sensitivity and satiety.
In conclusion, daily protein intakes do not have a linear correlation with gains in lean body mass. A multitude of variables need to be accounted for to determine efficacy among individuals. Blanket recommendations and trends entrenched in pseudoscientific dogma best be avoided. In addition to compromising metabolic functioning and consequent undesirable weight or fat mass gain, excessive protein intakes may lead to nutrient deficiencies, especially if fat and/or carbohydrates are not consumed and will likely impede athletic performance, recovery, and health.
- Antonio, J., Peacock, C.A., Ellerbroek, A., Fromhoff, B., & Silver, T. (2014). The effects of consuming a high protein diet (4.4 g/kg/d) on body composition in resistance-trained individuals. Journal of the International Society of Sports Nutrition, 11-19.
- Clifton, P.M., Bastiaans, K., & Keogh, J.B. (2009). High protein diets decrease total and abdominal fat and improve CVD risk profile in overweight and obese men and women with elevated triacylglycerol. Nutrition, Metabolism, and Cardiovascular Diseases, 19, 548-554.
- Metges, C.C. & Barth, C.A. (2000). Metabolic consequences of a high dietary-protein intake in adulthood: assessment of the available evidence. Journal of Nutrition, 130, 886-889.
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