Amino Acid Absorption

• Most amino acids (AAs) are absorbed in the proximal third of the small intestine, specifically the duodenum and upper jejunum.
• Enterocytes contain AA transporters that carry AAs across the brush border membrane via active transport, utilizing sodium-dependent transporters.
• Amino acids compete for the same transporters, and ingesting large amounts of one AA can affect the absorption rate of others.
• Intact small peptides can sometimes be absorbed into enterocytes or pass between them, and some di- and tripeptides can also be absorbed.
• Small peptides can be broken down into free AAs in the cytosol or secreted into the bloodstream, potentially having bioactive effects or causing adverse reactions like irritable bowel syndrome, celiac disease, or allergic reactions.

Absorption of AAs

• Absorbed AAs and small peptides enter capillaries within the villi, which converge into venules and then the hepatic portal vein, providing a direct link to the liver.
• Enterocytes are where AA absorption occurs.

Fate of AAs

• The free AA pool is replenished through the degradation of body proteins, dietary protein intake, and transamination which creates non-essential AAs from other AAs.
• In the liver, AAs are used for energy production (oxidation), glucose synthesis (gluconeogenesis), synthesis of non-protein nitrogen-containing molecules, or new proteins (protein synthesis).
• Branched-chain amino acids (BCAAs) are spared by the liver for use in other tissues like skeletal muscle, where they are important for muscle protein synthesis.

Protein Synthesis

• Protein synthesis is the process by which the body creates proteins from amino acids.
• The genetic code is transcribed from DNA to mRNA, which then moves from the nucleus to ribosomes in the cytosol.
• Transfer RNA (tRNA) translates the genetic code and brings the necessary free amino acids to the ribosome to form a polypeptide chain.
• Protein synthesis rates vary across different tissues, with enzymes being synthesized quickly and structural proteins, like those in bone and muscle, being synthesized more slowly.

Fate of Proteins: Muscle Mass

• Muscle growth depends on factors other than just AAs.
• The rate of protein turnover, indicated by the ratio of muscle protein synthesis (MPS) to muscle protein breakdown (MPB), determines whether there is net protein accretion or loss.

Are we getting enough protein???

• Nitrogen balance measures the relationship between nitrogen intake (primarily from food) and nitrogen excretion (in urine, feces, skin, etc.).
• Only proteins contain nitrogen.
• Intake = excretion indicates balance.
• Intake < excretion indicates a negative balance, leading to atrophy.
• Intake > excretion indicates a positive balance, leading to hypertrophy (common in pregnant women).

Assessing Nitrogen Balance

• Nitrogen balance is used to determine protein requirements.
• Subjects are fed a controlled protein diet, and their urine, feces, and sweat are collected over several days to measure nitrogen excretion as urea, creatinine, ammonia, and uric acid.
• A problem with this technique is it is difficult to collect all excreted nitrogen, costly, time-consuming, has compliance issues and tends to underestimate output, leading to underestimation of protein requirements.

‘Newer’ technique…… IAAO Method

• The Indicator Amino Acid Oxidation (IAAO) method is used to determine protein requirements.
• It involves using a stable isotope of an essential amino acid (EAA), such as phenylalanine or leucine.
• When protein intake is low, the labeled AA will be oxidized (detected in breath CO2) instead of being used to make new body proteins, because not enough AA's in body for protein synthesis so body uses them for oxidation instead.
• As protein intake increases, the labeled EAA will be incorporated into new proteins, and less will be oxidized.
• The "break point" indicates the protein requirement for the person.
• For healthy young males in the experiment, their breakpoint was 1.4g/kg.

Protein Quality

• Protein quality measures how efficiently dietary protein can be used to make body proteins.
• It depends on AA content, AA digestibility and AA composition.
• Animal proteins are 90-99% absorbed, while plant proteins are 70-90% absorbed due to antinutrients.
• EAAs are important because the liver produces nonessential AAs.
• Limiting amino acids are EAAs supplied in less than the amount needed to support protein synthesis.
• Complete proteins contain all the EAAs and incomplete proteins are missing one or more EAA, making them harder to digest.
• Plant proteins are generally lower quality due to lower available AAs, the impact of limiting AAs, and poorer digestibility due to antinutrients.

Considerations for Protein Quality

• Protein Quality: The ability for the body to use the protein source to synthesize new proteins (i.e. anabolic potential).

• Indicates if protein source is able to sustain anabolism.

• Protein digestibility corrected AA score and Digestible indispensable AA score (PDCAAS or DIAAS). PDCAAS go until 1, DIAAS past 1.

• Legumes grow in a pod, peas, beans, garbanzo beans/chickpeas, black eyed peas, peanuts, soybeans*

• Limiting AAs: cysteine, methionine, tryptophan

• Soy is considered complete, one of the most complete plant proteins

• Nuts and Seeds

• Limiting AAs: isoleucine & lysine

• Grains and Cereals

• Limiting AAs: isoleucine and lysine

• Protein Complementation

• Combining plant foods to improve protein quality of diet

• Used by vegetarians and vegans

• Rice (↓Lys) and Beans (↓Met+Cys)

Improving Plant Protein Quality

• Protein Supplement Terminology

• Concentrates :

• Concentrated protein source in food taken out

• Has some nutrients from whole food, higher fat and CHO

• Slower to digest, cause digestive issues

• Suitable for people who wish to enrich their food with protein and when fast abortion not required

• Not suitable for people with problem digesting protein or allergic to milk

• Isolates

• Higher percentage of protein and lower fat and carbs

• Lower amount of biologically active ingredients compared to concentrate

• Faster absorption, easy digest

• Hydrolysate

• Broken down into shorter peptide , fast digestion and absorption

• Lower amount of biologically active ingredients

• Reduce allergenicity

Sports and Exercise Nutrition - Protein

• Individuals engaged in regular exercise training require more dietary protein than sedentary individuals, and protein intakes of 1.4 - 2.0 g/kg/day for physically active individuals is not only safe but may improve the training adaptations to exercise training.
• protein supplements are OK
• Different types and quality of protein can affect amino acid bioavailability, but the superiority of one protein type over another in terms of optimizing recovery and/or training adaptations remains to be convincingly demonstrated.
• Appropriately timed protein intake is an important component of an overall exercise training program and essential for proper recovery, immune function, and the growth and maintenance of lean body mass.
• Under certain circumstances, specific amino acid supplements, such as branched-chain amino acids (BCAAs), may improve exercise performance and recovery from exercise.

ISSN Position Stand

• Endurance exercise: 1.0-1.6 g/kg/d
• Strength/power exercise: 1.6-2.0 g/kg/d
• It is the position of the ISSN that exercising individuals ingest protein ranging from 1.4 to 2.0 g/kgBW/day. Individuals engaging in endurance exercise should ingest levels at the lower end of this range, individuals engaging in intermittent activities should ingest levels in the middle of this range, and those engaging in strength/power exercise should ingest levels at the upper end of this range.

Meta-analysis RE + Protein and FFM

• Dietary protein supplementation augments changes in fat-free mass (DXA) and strength during prolonged RET.

• Protein supplementation beyond a total daily protein intake of ~1.6 g/kg/day during RET provided no further benefit on gains in lean mass (or strength).

• 1.6 g/kg/day = no further benefit for gain in lean mass= PLATEAU

• Athletes require VERY large quantities of protein for optimal athletic performance and consuming 15% E from protein (low end of AMDR)

• 150/80kg = 1.9g/kg/d protein

Protein Requirements for Exercise

• Aerobic exercise requires more AAs for oxidation and muscle repair.
• Strength exercise requires more AAs to build and repair muscle.

Questions to answer…

• How to maximize recovery, repair and growth:
• Amount of protein post-exercise?
• Optimal timing of protein ingestion?
• Type of protein to ingest?

Daily Pattern – MPS/MPB

• Eat balanced meals (with enough protein) = protein (N) balance which means that Fed gains are greater than fasted losses, therefore attaining lean muscle mass over time with resistance exercise and protein

• Exercise + balanced meals = MPS > MPB

• Resistance exercise induces a sustained increase in MPS (muscle protein synthesis) for up to 48 h (i.e., fasted).

• Greater increase in MPS if AA’s are also consumed (i.e., fed) because of the Additive effect!!

How much protein post-exercise?

• 20-30g at 1 time is what maximally stimulates MPS for Young, healthy males after 1 bout of resistance exercise in response to increasing amounts of dietary protein (e.g., egg protein).
• 40g did not show a greater increase than 20g.
• Or 0.3-0.4 g/kg/meal
• More protein does not (necessarily) = more MPS.

So, what is that per meal?

• Calculations……. (0.3 or 0.4 g/kg/meal)
• 0.4 x 3 meals/day = 1.2 g/kg/d
• 0.3 x 3 meals/day = 0.9 g/kg/d
• 0.3 x 4 meals/day = 1.2 g/kg/d
• Adults need more than the RDA when exercising to promote health

How much protein post-exercise?

• 20g of whey protein ingested every 3h (4x) was the optimal feeding pattern for promoting enhanced rates of MPS in healthy trained males

Timing of Protein Intake

• Protein ‘immediately’ post-exercise likely beneficial – but is it necessary?
• Supply AA’s when system is “most ready” (anabolic window). Right after, within 2 hours.
• AA+CHO also a strategy (increase insulin secretion?)
• Anabolic state up to 48h after single exercise bout.
• Chocolate milk good post exercise

ISSN position stand – Nutrient Timing

• Meeting the total daily intake of protein, with evenly spaced protein feedings (e.g., every 3 h), should be viewed as a primary area of emphasis for exercising individuals.
• Post-exercise ingestion (immediately to 2-h post) of high-quality protein sources stimulates increases in MPS.
• Ingesting a 20–40 g protein dose (0.25–0.40 g/kg/dose) every 3 to 4 h appears to most favorably affect MPS rates compared to other dietary patterns and is associated with improved body composition and performance outcomes.
• Consuming casein protein (~ 30–40 g) prior to sleep can acutely increase MPS and metabolic rate throughout the night

Timing of Protein Intake

• Protein intake before bed increases quad muscle size when combined with 3 months of resistance exercise training + 27.5g of casein protein consumed before bed
• Benefit because providing AA to body overnight. Increases positive protein balance throughout the night.

Types of Protein for Building Muscle

• Whey casein and soy are different with initial 3 hours. Casein MPS not as high, soy a bit lower than whey.
• Both whey and soy are fast absorbing protein, casein slow.

What about whole-foods?

• Dairy such as Milk increased CSA more than Soy and CHO

• Greek Yogurt increased FFM more than CHO

• 3x/wk Resistance Training, healthy young females + potato Protein Isolate (25 g of potato protein isolate twice daily = 1.6 g/kg/d total protein [2x RDA])

• Vegan athletes

• healthy older males + whey, pea or collagen protein Isolate (25 g twice daily = ~1.32 g/kg/d total protein) showed With supplementation, only whey and pea significantly increased MPS, not collagen

• Healthy older adults with an Omnivorous Meal vs. Isocaloric and Isonitrogenous Vegan Meal containing ~0.45g/kg/meal Protein

• meat meal showed greater increase in FSR compared to the plant meal even though same amount of protein

• Healthy young adults Ground beef patty vs. soy-based meat alternative.

• SBMA can stimulate MPS when enough is consumed, but the corresponding caloric content exceeds that contained in a 4 oz serving of beef.

Protein sources for building muscle

• ~3g leucine threshold
• Can build muscle with many different proteins!
• Just need more plant protein to reach “threshold”

RECAP…..

• Protein to optimize resistance exercise benefits in on FFM in healthy active people= 1.6 g/kg/d (2x RDA)
• Amount of protein post-exercise (consumed at 1 time) = 20-40g or ~0.3-0.4g/kg/meal, 3-5x/d.

Optimal timing of protein ingestion?

• intakes should be steady…. ~4 ‘meals’/day of adequate protein
• Before bed bolus?
• Considerations for wholefood protein sources vs. protein isolates