Role of Leucine in the Regulation of Human Myofibrillar Protein Synthesis at Rest and Following Resistance Exercise

Summary

Muscle mass is normally maintained through the regulated balance between the processes of protein synthesis (i.e. making new muscle proteins) and protein breakdown (breaking down old muscle proteins). Proteins are composed of amino acids and we know that amino acids increase muscle protein synthesis. However, not all amino acids are the same. Essential amino acids are ones that must be consumed through food, while non-essential amino acids can be made by our body. Interestingly, the essential amino acids are all that are required to increase the rate of muscle protein synthesis. In addition, the essential amino acid leucine appears to be particularly important in regulating protein synthesis. However, how leucine is able to increase protein synthesis is not entirely understood. Previously, it has been shown that 20-25 g of high-quality protein, such as that found in milk, appears to be the amount of protein that maximizes the rate of muscle protein synthesis after performing a bout of resistance exercise. Thus, the aim is to measure the synthesis of new muscle proteins after ingesting the following:

1. 25g whey protein
2. 6.25g whey protein supplemented with leucine
3. 6.25g whey protein supplemented with essential amino acids but no leucine

The investigators will measure muscle protein synthesis after consumption of the above beverages in a leg that has done no exercise ( ie. a rested leg) and in the other leg that has done resistance exercise. The hypothesis is that 6.25g whey supplemented with leucine will stimulate muscle protein synthesis as effectively as 25g whey, but that 6.25g whey supplemented will all the essential amino acids except whey will be less effective at increasing muscle protein synthesis. Whey protein is a dairy-based protein found in cow's milk, thus when you drink a glass of milk you are consuming some whey protein. However, the investigators will be using an isolated form of whey protein, meaning it has been removed from milk. As mentioned previously, amino acids are 'strung-together' to make protein. The 'essential' amino acids must be consumed through food because our body cannot make them, thus they are consumed when you eat protein-rich foods like milk or chicken.

Conditions

• Regulation of Muscle Protein Synthesis

Interventions

DIETARY_SUPPLEMENT

whey protein

25 g whey protein

DIETARY_SUPPLEMENT

whey protein supplemented with leucine

6.25 g whey protein supplemented with free form leucine

DIETARY_SUPPLEMENT

whey protein supplemented with essential amino acids

6.25 g whey protein supplemented with essential amino acids devoid of leucine

Sponsors & Collaborators

• University of California, Davis

  collaborator OTHER

• Canadian Institutes of Health Research (CIHR)

  collaborator OTHER_GOV

• Natural Sciences and Engineering Research Council, Canada

  collaborator OTHER

• McMaster University

  lead OTHER

Principal Investigators

• Stuart M Phillips, PhD · McMaster University

Study Design

Allocation

RANDOMIZED

Purpose

TREATMENT

Masking

SINGLE

Model

PARALLEL

Eligibility

Min Age

18 Years

Max Age

35 Years

Sex

MALE

Healthy Volunteers

Yes

Timeline & Regulatory

Start

2010-06-30

Primary Completion

2010-08-31

Completion

2010-09-30

Countries

• Canada

Study Locations