Nutrition Corner with Dr D 

Understanding Dietary Protein Benefits for Health & Muscle

Dietary protein plays an indispensable role in preserving our health, stimulating growth, and powering our functions throughout our lifetime. Our protein requirements, chiefly guided by our lean body mass, energy balance, and physical activity, vary across age groups. Let's dive into dietary protein benefits, common misconceptions about pritein and look at how protein fits into your diet and why it is so important to your overall health and wellbeing.

In 2005, the Institute of Medicine (IOM) set the current Dietary Reference Intakes (DRIs) for protein, which include the Estimated Average Requirement (EAR), Recommended Dietary Allowance (RDA), and the Acceptable Macronutrient Distribution Range (AMDR). The EAR for protein sits at 0.66 grams per kilogram of body mass per day (g/kg/d) and is designated as the minimum protein amount that should meet the nutritional needs of half of the U.S. adult population. On the other hand, the RDA is at 0.8 g/kg/d, highlighting the minimal protein intake necessary to meet amino acid requirements, maintain nitrogen balance, and avoid muscle mass loss in almost all U.S. adults. These standards align with the international protein recommendations by the World Health Organization (0.83 g/kg/d). However, the RDA for protein is often misinterpreted as the recommended intake, leading to complications for health-conscious individuals and those dealing with health conditions requiring a higher protein intake.

The Reality Behind Protein MisconceptionsWhile dietary protein's popularity has risen over the years, especially due to its crucial role in muscle health, several misconceptions still prevail within the media, academia, and clinical practice. Common criticisms concerning protein-rich diets or specific sources of dietary protein often refer to potential harm to bone health, kidney function, inflammation levels, risk of cardiometabolic diseases, and cancer. However, these concerns are generally unsupported and contradict contemporary scientific data. The persistence of these unfounded fears and misconceptions might result in inadequate protein intake, potentially affecting optimal muscle health. Around a century ago, observations of higher levels of calcium in the urine (hypercalciuria) in individuals consuming more meat led to concerns about high-protein diets causing increased bone resorption and reduced bone mineral density. More recent evidence, however, suggests this theory is unfounded. Modern studies using advanced techniques indicate that the observed hypercalciuria with high-protein diets stems from increased calcium absorption potentiated by protein. In fact, a high-protein diet might actually protect against osteoporosis by increasing the release of insulin-like growth factor 1 (IGF-1) from the liver. There is also a common misbelief that high-protein diets might harm the kidneys. Although increased protein intake can increase renal workload, particularly in those with existing kidney disease, healthy kidneys are well-equipped to handle protein intakes above the RDA. Despite protein-rich diets increasing renal workload, they do not harm kidney health or increase the risk of developing chronic kidney disease in healthy adults.

Recent research has raised concerns about high-protein diets potentially increasing systemic inflammation. However, an analysis of the Framingham Heart Study Offspring Cohort found an inverse association between dietary protein intake and inflammation and oxidative stress scores. There has also been concern about potential links between dietary protein intake and the risk of cardiometabolic disease and cancer. However, the confusion often arises from misrepresentation of protein-rich foods, which might be high in total and saturated fats and processing additives. In fact, there are no concrete data showing a definitive link between dietary protein itself and cardiovascular disease or type 2 diabetes. Similarly, no direct link has been established between overall dietary protein intake and incidence of colorectal or breast cancers.

Embracing the Power of ProteinIn the past decade, we've witnessed the emergence of strong evidence showing the significant benefits of consuming higher-protein diets (> RDA but within the AMDR). A high protein intake can boost strength and muscle mass gains when combined with resistance exercise, aids muscle preservation during negative energy balance periods, curtails age-related muscle loss, and more. Furthermore, a National Health and Nutrition Examination Survey (NHANES) shows a negative correlation between protein intake (both animal and plant-based) and waist circumference, body weight, and body mass index (BMI). Yet, even with such compelling evidence, dietary patterns, especially those relating to protein, have seen little change among American adults. This gap between knowledge and action leads us to question whether this extensive understanding of dietary protein truly impacts nutrition guidance, and more importantly, our dietary choices. Decoding the Protein and Muscle Mass ConundrumSkeletal muscle protein is in constant flux, oscillating between states of negative and positive protein balance. This process largely depends on fasting and feeding. In a fasting state, muscle protein acts as the primary amino acid repository, which can be broken down to supply free amino acids for muscle protein regeneration or meet other physiological demands. Feeding, especially protein consumption, can stimulate muscle protein synthesis, suppress protein breakdown, and shift the balance towards positive. Factors influencing these include dietary protein content, quality, and format. When optimized, these can amplify the beneficial effects of resistance and aerobic exercise, fostering enhanced muscle maintenance and growth.

Revisiting Current Protein RecommendationsWhile the DRIs for protein set in 2005 have provided a guide, they have their limitations. The EAR and RDA were derived from nitrogen balance studies, a method with many drawbacks. Consequently, the method tends to give an inaccurate picture of nitrogen balance. Additionally, the AMDR for protein was established in such a way that has raised questions about its physiological relevance concerning a recommended upper limit for protein consumption. Moreover, the current RDA might suffice for healthy, sedentary young adults. Still, there's a compelling argument that this recommendation needs to be revisited, especially when it comes to certain populations.

For instance, some professional organizations recommend double the current RDA for physically active individuals. The RDA definition is also criticized for merely reflecting the minimal amount of protein required to prevent deficiency rather than promoting optimal health. Protein's Role in Physical ActivityThe advantages of consuming protein following resistance exercise are well-established, particularly regarding muscle hypertrophy and function. A recent meta-analysis revealed positive associations between combining resistance exercise with post-exercise protein ingestion and fat-free mass, strength, and muscle size. The type of exercise, age, and training experience of the individual play crucial roles in muscle protein synthetic responses to post-exercise protein ingestion. Additionally, the kind of protein consumed also impacts the net anabolic response. Sports nutrition recommendations reflect that incorporating post-resistance exercise protein ingestion with habitual protein intakes promotes favorable muscle adaptations to exercise training. ConclusionIn conclusion, embracing a higher-protein diet is essential for health preservation, muscle mass increase, and performance enhancement. As we advance in nutritional science, it's necessary to continually reevaluate and optimize our dietary guidelines and protein intake recommendations. Only then can we translate academic knowledge into real-life application and health benefits.

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