The Core Diet Blog

The following content was provided by Registered Dietitian, Rachel Gargano.

As a triathlete, you work your tail off throughout the season to perform your best in that A race.  The first part of your season consists of building a solid base; gaining strength in the gym that will transition to power on the bike and in the run.  The second half of your season is devoted to speed and continued aerobic improvement.

For some athletes, performing their best means losing fat mass to get to a lean, healthy race weight. Yet without proper nutrition, not only will fat be lost, but muscle mass as well. This could lead to substandard performance via decreased strength and aerobic capacity.  Not ideal. 

No matter what your plan entails, the one piece that should never be left out is nutrition.  We having a saying at QT2 Systems & The Core Diet: Never be nutritionally limited in any training session. You have full control!  Depending on what phase of training you’re in, your fueling may change to help promote muscle gain and muscle maintenance.

Skeletal muscle responds to exercise in a variety of ways.  Endurance training alters muscle cells to be more fatigue resistant, be able use fats for fuel, and have the capacity for a more efficient use of carbohydrate fuels.  Resistance trained muscles use primarily chemical reactions for power rather than carbohydrates or fat, and these exercises increase muscle fibers to generate greater force. 

In fact, resistance exercise is a potent stimulator of Muscle Protein Synthesis (MPS – the building of muscle), and this process if further enhanced by eating specific nutrients.

This is whereLeucinecomes in.

Leucine is an essential amino acid that has been found to be the limiting factor of MPS.  While all amino acids are necessary to build protein, if there isn’t enough leucine, muscle accretion is not nearly as great. 

Leucine content of different protein sources different dramatically:

  • Whey: 108 mg/g
  • Milk solids: 77 mg/g
  • Casein: 82 mg/g
  • Soy: 62 mg/g

As you can see, whey (the liquid that is left behind when milk is curdled and the solids removed) protein provide the highest concentration ofLeucineof all other sources. 

Leucine and Muscle Gain



*Phillips, Stuart. The Role of Milk- and Soy- based Protein in Supports of Muscle Protein Synthesis and Muscle Accretion in Young and Elderly Persons.  JACN, Vol 28, No. 4, 343-354, 2009.


The above graph, created as a review of nine studies, shows resistance training-induced changes in lean muscle mass using different protein sources, with Whey supplementation post-exercise creating the highest gains.

Along with the type of protein, the amount consumed also plays a key role.  Studies have found that MPS plateaus with anything above a single dose of 20 grams of protein (about 8.5g of essential amino acids), consumed after resistance training.  Any extra protein ingested at that one time is burned as fuel and not used to build more muscle.

Finally, the timing of protein supplementation is important for MPS.  Taking in 20g of high quality protein within 1-2 hours after a workout is optimal, and/or 30-45 minutes before the workout.

Milk (Leucine) and Muscle Maintenance

In addition to increasing muscle mass, consuming enough milk may help shed fat while maintaining, and even building, muscle mass.  A difficult task, indeed! 

A study released in the Journal of Nutrition, December 2011 followed three groups of women over 4 months.  They were each either eating high, medium, or low dairy; but all were on a reduced calorie diet and were exercising seven days per week.

By the end of the four months, all groups had lost the same amount of weight.  However, the higher protein/ higher dairy group lost twice as much abdominal fat, more total whole-body fat, as well as had the greatest gains in strength and muscle mass.

The researchers hypothesized these changes were primarily due to the Leucine content of the high dairy group’s diet.

So what does this mean for YOU?

Training: Strength Phase

During the strength blocks of your training plan, when muscle accretion is an important factor, focus on having 20 grams of high quality protein (whey isolate, preferably) within an hour of your resistance training session.  This will help you make the most of your time in the gym.

If you’re on a weight loss track, fitting dairy into your diet could mean the difference between losing muscle mass as a result of your calorie deficit, or maintaining it.  Aim for 3 servings of low fat or fat-free dairy per day. 

Diary Options: Greek yogurt is a great option as it has twice as much protein as regular yogurt; low fat cottage cheese is also very high in protein; and of course there’s always skim or 1% milk.  Choose lactose free if you’re intolerant, or take Lactaid.   However, most lactose intolerant individuals can tolerate Greek yogurt due to its low lactose content. 

Training: Speed/Aerobic capacity

During the second half of your season as time in the gym diminishes, and spending time out on the road becomes more valuable, it’s imperative to focus on some nutritional aspects.  During this time, it’s imperative to fuel your workouts well with a carbohydrate pre-workout snacks as well as refueling with a 4:1 ratio of carbs to protein recovery drink.

To help maintain muscle mass during this time, keep in the whey protein or dairy to ensure adequate Leucine intake.

Athletes need to side down to the plate before they can step up to the win. 

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