Optimal DX Hot Topics: Protein Intake Recs

Dietary protein is a macronutrient made up of an array of amino acids that contain nitrogen, the element that makes protein unique; carbohydrates and fats do not contain nitrogen.

When protein intake is insufficient, the body breaks down muscle tissue to supply amino acids for essential protein synthesis in critical organs. Inadequate intake disrupts muscle and whole-body protein balance, negatively affecting muscle mass, physiological function, exercise adaptations, bone and calcium homeostasis, immune response, fluid and electrolyte balance, enzyme activity, and hormone synthesis.

Certain pathological conditions—such as burns, COPD, HIV/AIDS, cancer, and sepsis—also challenge protein homeostasis and often lead to muscle wasting, suggesting that higher dietary protein intake may be necessary, tailored to the individual's clinical scenario.

Energy and/or dietary protein restriction induce net muscle catabolism, releasing amino acids for energy production, gluconeogenesis, and synthesis of peptide hormones, plasma proteins, immune system components, and enzymes (representative examples, not an exhaustive list; not drawn to scale). AA, amino acids; ADH, antidiuretic hormone; hGH, human growth hormone; T3, triiodothyronine; T4, thyroxine.

Protein Guidelines

Institute of Medicine (IOM):

• Dietary Reference Intakes (DRIs): Established to guide protein consumption.
  • Estimated Average Requirement (EAR):
    • 0.66 grams per kilogram of body weight per day (g/kg/day).
    • Meets the minimum indispensable amino acid requirements for 50% of U.S. adults.
  • Recommended Dietary Allowance (RDA):
    • 0.8 g/kg/day.
    • Satisfies amino acid needs, maintains nitrogen balance, and prevents muscle mass loss for the majority of U.S. adults but does not address optimal health.
    • The RDA is often incorrectly used as the recommended intake rather than the minimum requirement. This misinterpretation can be problematic, especially for:
      • Healthy individuals who need more protein for optimal health.
      • Aging adults who may require higher protein to prevent muscle loss.
      • People with medical conditions that increase protein needs.
  • Acceptable Macronutrient Distribution Range (AMDR): Provides a percentage range of total daily calories from protein.

• Protein AMDR is 10–35% of total daily energy intake
  • The lower end is based on the RDA of 0.8 g/kg/d,
  • The upper end is the difference achieved if carbohydrates (45–65% of energy) and fat (20–35% of energy) are consumed at the lower ends of their respective AMDR (i.e., 100% − 45% − 20% = 35% as the upper end of protein AMDR).
  • Most American adults consume protein on the lower end of this range, e.g., 14–16% of total energy intake

International:

• World Health Organization (WHO) Recommendation:
  • 0.83 g/kg/day.

• Joint recommendation of the American College of Sports Medicine, Dietitians of Canada, and the American Academy of Nutrition and Dietetics
  • 2 – 2.0 g/kg/day

• The International Society for Sports Nutrition
  • 1.4 – 2.0 g/kg/day for physically active individuals

Sports nutrition recommendations

• Combine post-resistance exercise protein ingestion of ~20–30 grams or 0.25–0.30 g/kg with habitual protein intakes of ~1.6 g/kg/day to promote favorable muscle adaptations to exercise training.
• Consuming protein after resistance exercise significantly promotes muscle hypertrophy and strength gains.
• The anabolic response is affected by the type and volume of exercise, age, training experience, and the type of protein consumed.

Energy deficit or weight loss

• At least 1.2 g/kg/day can help prevent unintentional weight loss.
• 5 g/kg/day can help mitigate the loss of muscle and function seen with sarcopenia.
• 6 g/kg/day helps preserve muscle mass during intentional weight loss.
• At least 0.4 g/kg body weight or 1.6 g/kg of lean body mass at each meal can help preserve muscle mass and strength and reduce frailty in the elderly.
• Increasing protein while decreasing total energy intake preserves muscle mass despite a catabolic setting.
• However, the protective effect of protein on lean body mass and protein homeostasis is reduced as an energy deficit extends beyond 40% of daily energy needs.

Beyond the RDA is OK

Despite the popularity of dietary protein for muscle health, some argue that higher protein intake may harm bone health and kidney function, cause inflammation, or increase the risk of cardiometabolic diseases and cancer. However, contemporary research generally refutes these concerns.

Studies have shown that higher-protein diets do not adversely affect bone density and may enhance bone health by increasing calcium absorption and protecting against osteoporosis.

Regarding inflammation, evidence indicates that higher protein intake is not associated with increased systemic inflammation and may even correlate with reduced levels of inflammatory markers.

Concerns about kidney damage from higher protein consumption in healthy adults are also unfounded. While increased protein intake can elevate renal workload due to the processing of additional nitrogenous waste, studies demonstrate that this does not negatively impact kidney health or raise the risk of developing chronic kidney disease in individuals without pre-existing renal conditions.

Overall, higher protein diets are considered safe for healthy adults and may benefit muscle integrity and overall health.

An evaluation of NHANES data found those in the highest decile for protein intake (~1.4 g/kg/day) exhibited a normal BUN of 14.8 mg/dL (5.28 mmol/L) within the standard reference range of 7 – 20 mg/dL (2.5 – 7.14 mmol/L). This observation was true for animal, non-dairy animal, and plant protein sources. Neither glomerular filtration rate (GFR) nor blood creatinine concentrations were associated with dietary protein content.

A recent meta-analysis of randomized controlled protein intervention trials demonstrated a small but positive relationship between higher protein intakes (i.e., ≥ 1.5 g/kg/d or ≥ 20% energy intake) and GFR, confirming the benefits of higher protein intake in healthy individuals.

Optimal Takeaways

• Dietary protein provides nitrogen and the building blocks for muscle, bone, hormones, immune cells, enzymes, and all body tissues.
• Adequate protein can help prevent unintentional weight loss, preserve muscle mass during an intentional calorie deficit, promote muscle strength and exercise resilience,
• Although the Estimated Average Requirement (EAR) for protein is 0.66 g/kg/day and the minimum RDA is 0.8 g/kg/day, higher intakes are recommended for physically active individuals and older individuals at risk for sarcopenia.
• Intake of 0.25–0.30 g of protein/kg after exercise with habitual protein intakes of ~1.6 g/kg/day can help promote muscle mass and strength and exercise adaptation.

Reference

Carbone, John W, and Stefan M Pasiakos. “Dietary Protein and Muscle Mass: Translating Science to Application and Health Benefit.” Nutrients vol. 11,5 1136. 22 May. 2019, doi:10.3390/nu11051136 This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).