1. ABSTRACT
Obesity is a significant health concern. Our research investigates various studies
involving participants engaging in intentional weight loss through exercise
coupled with a hypocaloric diet. As a result, individuals may be losing fat mass along
with lean muscle mass. Branched-chain amino acids (BCAAs) are essential amino acids
that may stimulate protein synthesis through the Mammalian Target of Rapamycin
pathway (mTOR). Based on current research we recommend consuming BCAAs post-
exercise, which may increase protein synthesis and help retain lean muscle mass.
INTRODUCTION/BACKGROUND
Currently, the CDC and other researchers estimate 2/3 of Americans are overweight
(BMI = 25.0–29.9) or obese (BMI≥30.0).1,2
With a BMI in one of these categories,
Americans are at increased risk for various diseases, e.g. hypertension and Type 2
diabetes.1
Americans spend $20 billion annually on weight loss aids like diet books,
supplements and weight loss surgeries.
To lose weight, adults often perform cardio and resistance training and may follow a
hypocaloric diet. When done in conjunction they run the risk of not only losing fat
mass, but lean muscle mass as well.3,4
As lean muscle mass deteriorates through age,
performing simple activities of daily living can become difficult, ultimately leading to a
decrease in quality of life.
Branched-chain amino acids consist of three essential amino acids that your body needs
to have a complete protein profile: leucine, isoleucine and valine.3­
(Figure 1)These
amino acids have a positive effect on muscle protein synthesis and overall production
of a positive protein
balance.3
Thus, BCAA
intake higher than the
current RDA while
on a hypocaloric diet
in conjunction with
resistance training may help prevent loss of lean muscle mass.5
OBJECTIVES
• To describe the effects of BCAAs on protein synthesis
• To describe the Mammalian Target of Rapamycin (mTOR) pathway
• To provide nutrition recommendations
PHYSIOLOGICAL ASPECTS
Maintaining Protein Balance
Maintaining lean muscle mass while reducing fat mass is essential in healthy weight loss.
Individuals often adopt a hypocaloric diet coupled with resistance training to promote
loss of fat mass. A restriction in calories or specifically carbohydrates may promote an
increase use of fat as a fuel while sparing protein degradation.4
RELATED NUTRIENTS6
Sources of BCAAs
• Meat & Dairy: cheese, eggs, chicken, turkey, beef
• Legumes: lima beans, soy beans, peanuts
• Seafood: salmon, trout, crab, lobster, shrimp
Figure 3: Dietary sources of BCAAs
Branched-chain amino acids can be found through exogenous sources or supplementation.
RDA Daily Protein Recommendations7
(gram of protein per kilogram of body
weight)
• Healthy individuals: 0.8g/kg
• Elderly: 1.0 - 1.1g/kg
• BMI<30: 1.2 - 2.0g/kg
• BMI 30-40: 2.0g/kg of ideal body weight
• BMI>40: 2.5g/kg of ideal body weight
• Estimated amount to maximize protein synthesis: 1.3 - 1.8g/kg4
CONCLUSION
Obese individuals face the risk of a decreased quality of life when there is insufficient
lean muscle mass. Preserving muscle mass while targeting fat mass is a priority for those
partaking in exercise coupled with a hypocaloric diet. BCAA consumption is becoming
increasingly popular among those participating in weight loss and diet activities. Several
studies have shown promise that greater protein intake above the RDA can improve lean
muscle mass retention. Additional studies are warranted to determine an ideal protein
amount to achieve optimum protein balance. Although evidence focuses on the benefits
of BCAAs, there is no general consensus on the roles of each individual BCAA.
ACKNOWLEDGMENTS
Thank you Colleen Burke, Dr. Leslie Cunningham-Sabo, and James Peth for your guidance throughout this semester.
REFERENCES
1. Adult Obesity Facts. Centers for Disease Control and Prevention. Available at: http://www.cdc.gov/
obesity/data/adult.html. Published 2015. Accessed: April 11, 2016.
2. Yanovski S, Yanovski J. Obesity Prevalence in the United States – Up, Down, or Sideways? The New En-
gland Journal of Medicine. March 17, 2011; 364: 987-989. DOI:10.1056/NEJMp1009229
3. Dudgeon W, Kelley E, Schett T. In a single-blind, matched group design: branched-chain amino acid
supplementation and resistance training maintains lean body mass during a caloric restricted diet. Journal of
the International Society of Sports Nutrition. 5 January 2016; 13. DOI:10.1186/s12970-015-0112-9
4. Koopman R, Loon L. Aging, Exercise and Muscle Protein Metabolism. Journal of Applied Physiology. 1
June 2009; 106: 2040-2048. DOI:10.1152/japplphysiol.91551.2008
5. Phillips S, Loon L. Dietary Protein for Athletes: From Requirements to Optimum Adaptation. The Jour-
nal of Sports Sciences. 09 December 2011; 29: 529-538. DOI:10.1080/02640414.2011.619204
6. Foods List. Foods List. https://ndb.nal.usda.gov/ndb/search. Accessed: April 11, 2016.
7. Mahan LK, Escott-Stump S, Raymond JL. Krause’s Food Nutrition And Diet Therapy. 13th ed. Philadelphia:
WB Saunders; 2011.
8. Rowlands DS, Nelson AR, Phillips SM, et al. Protein–Leucine Fed Dose Effects on Muscle Protein Syn-
thesis after Endurance Exercise. Medicine & Science in Sports & Exercise 2015;47(3):547–555. DOI: 10.1249/
mss.0000000000000447
9. Reidy PT, Walker DK, Dickinson JM, et al. Protein Blend Ingestion Following Resistance Exercise
Promotes Human Muscle Protein Synthesis. Journal of Nutrition 2013;143(4):410–416. DOI: 10.3945/
jn.112.168021
10. Norton LE, Layman DK. Leucine regulates translation initiation of protein synthesis in skeletal muscle
after exercise. The Journal of Nutrition. 136: 533S-S537.http://jn.nutrition.org/content/136/2/533S. Pub-
lished 2006. Accessed: April 11, 2016.
11. Rajendram DR. Branched Chain Amino Acids in Clinical Nutrition. Humana Press. Humana 2014; 2.
33-60 DOI: 10.1007/978-1-4939-1914-7_25.
12. Dickinson JM, Gundermann DM, Walker DK, et al. Leucine-Enriched Amino Acid Ingestion after Re-
sistance Exercise Prolongs Myofibrillar Protein Synthesis and Amino Acid Transporter Expression in Old-
er Men. Journal of Nutrition 2014;144(11):1694–1702. DOI:10.3945/jn.114.198671.
13. Morita M, Gravel SP, Hulea L, et al. mTOR coordinates protein synthesis, mitochondrial activity and
proliferation. Cell Cycle, 14:4, 473-480. DOI:10.4161/15384101.2014.991572
14. Stipanuk MH, Caudill MA. Biochemical, physiological, and molecular aspects of human nutrition. 3rd edition. St.
Louis, Missouri:Elsevier Inc;2013 14:291-292.
Evidence
Study - 2016, Journalofthe
InternationalSocietyofSportsNutrition
• 17 resistance trained men were split into two different groups
• Both groups followed a hypocaloric diet
• One group received BCAAs supplementation and the other received carbohydrate supplementation post-resistance
training
• Results: BCAAs supplementation group lost fat mass and maintained lean muscle mass, while the carbohydrate sup-
plementation group lost lean muscle mass and body mass.3
Study - 2013, Medicine&
ScienceinSports&Exercise
• 12 endurance trained male cyclists
• Leucine drinks were given to athletes following intense 100 minute cycling workout
• Muscle biopsies were performed on cyclists post-exercise
• Results: Cyclists had a 25% increase in myofibrilar fractional synthesis rate (FSR)
• Protein supplementation with leucine post-exercise can increase the muscle protein synthesis rate.8
Study - 2013, JournalofNutrition
• 19 Adults - 17 males and 2 females
• Participants engaged in resistance training regime
• One hour post resistance training, participants were given leucine containing drinks
• Results: Stimulated muscle growth following exercise with BCAA supplementation
• Showed an increase in muscle protein synthesis and skeletal muscle mTOR signaling.9
Table 1. Summary of three scientific studies which show the relationship between BCAA supplementation and protein synthesis.
Autophagy
(Protein Degradation)
mTORC1
Protein Synthesis
PLASMA MEMBRANE
Intracellular Space
Extracellular Space
Figure 2: Activation of the Mammalian Target of Rapamycin (mTOR) Signaling Pathway
When active, mTOR pathway promotes increased protein synthesis and decreased protein degradation. Activators of the pathway include insulin,
oxygen, amino acids, particularly branched-chain amino acids, and other growth factors; inhibitors include glucagon, rapamycin, and stress.
Amino Acids Insulin Oxygen Glucagon Rapamycin Stress
Individuals who participate in a hypocaloric diet coupled with resistance training may encounter a sudden state
of negative protein turnover, which is defined as the rate of protein degradation exceeding protein synthesis.7
Current literature has shown that individuals who consume BCAAs after resistance exercise can help restore
protein turnover by creating a positive net balance of protein synthesis and a decrease of protein breakdown.3
This can lead to maintenance of lean muscle mass while promoting loss of fat mass.
Mammalian Target of Rapamycin Pathway
Branched-chain amino acids stimulate protein synthesis via the Mammalian Target of Rapamycin pathway.10,11
mTOR consists of two distinct complexes, mTORC1 and mTORC2. mTOR Complex 1 (mTORC1) pathway
regulates cell growth, reproduction, and survival.12,13
mTORC1 (Figure 2) is a highly controlled pathway that
consists of receptors that respond to numerous intracellular and extracellular stimuli. Stimuli include oxygen,
energy status of the body, insulin, amino acids, and growth factors.13
When an individual consumes a protein-rich meal after exercise, the proteins are digested to amino acids and
taken up into circulation then transported throughout the body.14
Branched-chain amino acids, such as leucine,
bind to the receptor resulting in activation of mTORC1 leading to upregulation of protein synthesis, while
simutaneously repressing protein degradation.11
Kevin Leung, Jackie Nelson, Andrea Rapp
FSHN 492 | Spring‘16
Keep Your Muscles!Branched-Chain Amino Acids and Lean Muscle Retention
Voet et al. Fundamentals of Biochemistry: Life at the Molecular Level, 4th Edition.