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30 June 2009

Have dairy after exercise

Research that might be a blow to the sports-drink industry shows that milk and yoghurt are great options for post-exercise recovery.

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Research that might be a blow to the sports-drink industry shows that milk and yoghurt are great options for post-exercise recovery.

Like most people, I've always thought in terms of sports drinks when recommending beverages to sportsmen and women to assist them in sustaining their performance and recovering after exercise.

However, the other day I came across a fascinating article published by the Consumer Education Project (CEP) of Milk SA. For the first time, it alerted me to the idea that, instead of sports drinks, athletes can also use dairy products before, during and after exercise.

Why dairy?
The following are all excellent reasons why you can turn to dairy products such as low-fat milk and yoghurt to assist recovery after strenuous exercise:

  • Liquid dairy foods contain carbohydrates to aid muscle glycogen recovery, and protein for muscle repair and growth.
  • Athletes have to maintain normal blood-glucose levels and replenish their glycogen stores during and after exercise to maintain energy for performance.
  • Athletes require additional protein post-exercise to replace protein that's broken down during exercise, and to promote muscle repair and growth (CEP, 2009).

Energy and muscle glycogen stores
Carbohydrates, stored in the skeletal muscles in the form of glycogen, are the most important readily available source of energy fuel for muscles during strenuous exercise.

During moderate and high-intensity aerobic exercise lasting longer than an hour, for example long-distance running, cycling or rowing, fatigue occurs when muscle glycogen stores are depleted. Fatigue can be defined as "an inability to sustain a given power output or speed during physical activity" (Bean, 2006).

Research shows that intense endurance exercise decreases muscle glycogen stores, leading to reduced performance and eventual exhaustion upon depletion (Costill & Hargreaves, 1992). It's therefore critical for athletes to replenish their glycogen stores during and after exercise.

Protein breakdown during exercise
Sports activities involving eccentric muscle actions (the lengthening of a muscle while under tension) trigger the utilisation of amino acids (the building blocks of protein) as a fuel source during and immediately after exercise, causing exercise-induced muscle damage (EIMD).

EIMD can cause delayed onset of muscle soreness, the increased release of intramuscular enzymes into blood plasma and thus decreased muscle performance. The inclusion of protein in a post-exercise meal may provide critical amino acids for improved muscle protein repair and muscle growth, speeding up recovery and decreasing the risk of injury (Bean, 2006).

Post-exercise food intake
The timing and composition of post-exercise food intake depends on a number of factors. This includes the type, length and intensity of the exercise session, which influences the extent of glycogen depletion and when the next intense workout will occur.

For people participating in less intense exercise with longer rest periods between exercise sessions (for instance, a one-hour gym workout every day or every second day), the timing and composition of post-exercise meals are less critical. It's usually sufficient to consume adequate amounts of carbohydrates over the next 24 hours.

However, a meal or snack containing both carbohydrates and protein shortly after the completion of an exercise session may be important for athletes to meet daily carbohydrate and energy needs.

The timing and composition of post-exercise meals are particularly important for athletes participating in intense multiple exercise sessions (for instance, multi-event endurance athletes) in order to optimise their recovery between exercise sessions (in other words, replacing muscle glycogen and muscle protein) and subsequent performance (ADA, 2000).

Recommendations: carbohydrates
How much carbohydrate is enough?

Athletes should consume 1 to 1.2g of carbohydrate for every kilogram body weight within 30 to 60 minutes after exercise, and at least 50g of carbohydrate every two hours until the next main meal to ensure efficient glycogen recovery (Bean, 2006).

Examples of such meals and snacks include a 300ml fruit shake, a drinking yoghurt, a sandwich with low-fat cheese or cottage cheese and one fruit, as well as a bowl of cereal with low-fat or fat-free milk.

If you experience reduced appetite after exercise, the consumption of a carbohydrate-rich beverage is recommended (with an ideal carbohydrate concentration of 6 to 8%), followed by a high carbohydrate meal or snack (Havemann, & Bosch, 2008).

Which carbohydrate-rich foods should you have?
The type of carbohydrate to be consumed post-exercise depends largely on your training frequency and intensity. A combination of low-glycaemic index (GI) and medium- or high-GI foods is often required.

Medium- to high-GI foods or snacks are recommended if you train intensely once or twice a day. This is particularly important during the first 20 to 30 minutes after intense exercise, when the enzyme promoting glycogen recovery is at high levels, but also for the six hours following exercise (Havemann, & Bosch, 2008).

On the other hand, the consumption of low-GI foods (GI below 55) will increase your endurance performance during subsequent workouts (Bean, 2006). Milk (full-cream, low-fat and skimmed), yoghurt (plain or flavoured, low fat or fat free, sweetened or sugar free) and flavoured milk (low fat, sweetened and sugar free) are all examples of low-GI foods.

Recommendations: protein
How much protein is enough?

Simultaneous ingestion of protein (0.2 to 0.4g per kg body weight) with carbohydrates (0.8 to 1 g per kg bodyweight) immediately following resistance exercise may improve net protein balance in the early post-exercise period and enhance the rate of glycogen storage.

Which protein foods should you have?
Low-fat dairy products are good choices and are often recommended as post-exercise snacks (Bean 2006). Dietary sources of low-fat, high-quality protein are skim milk casein, skimmed milk whey, skinless chicken (white meat), fish and egg white.

Milk as a post-exercise recovery aid
Scientific evidence
Recent scientific research has focused on the positive impact of dairy foods on muscle recovery and muscle gain:

  • Chocolate milk consumed after glycogen-depleting exercise may be considered an effective alternative to commercial sports drinks, sustaining performance in subsequent exercise sessions. The high carbohydrate, protein and mineral content of chocolate milk is believed to be critical in this regard (Karp et al, 2006).
  • Milk (low fat) consumed 20 to 30 minutes after resistance-based eccentric muscle damaging exercise reduced EIMD after 48 hours. Consequently, athletes could perform closer to optimal levels in subsequent training and could potentially experience faster recovery.
  • Fermented skimmed milk decreased delayed-onset muscle damage (after prolonged exercise) by reducing muscle damage, decreasing inflammation and increasing antioxidant capacity through increased expression of antioxidant enzymes in skeletal muscles (CEP, 2009).

Good food choices
Dairy products are often recommended as part of post-exercise snacks, providing a combination of carbohydrates, protein and minerals. Good choices include:

  • A drinking yoghurt
  • A sandwich with cheese or potato with cottage cheese
  • A fruit milkshake or smoothie
  • Flavoured milk

Visit www.dairy.co.za to read more about the use of dairy products in the diets of sportsmen and -women.

(Dr Ingrid van Heerden, DietDoc, June 2009)

Any questions? Ask DietDoc

References:
(American Dietetic Association (ADA). 2000. Position of the ADA Dietitians of Canada, and the American College of Sports Medicine: Nutrition and athletic performance. J. Am. Diet. Assoc., 100(12):1543-1556; Bean, A. 2006. The complete guide to sports nutrition. 5th Ed.. A & C Black Publishers: London; Costill DL & Hargreaves M, 1992. Carbohydrate nutrition and fatigue. Sports Med.., 13:86-9;.Havemann L & Bosch A, 2008. Evidence-based sport nutrition. Master class - 22nd Biennial Congress of the Nutrition Society of South Africa, Pretoria, 2 October 2008; Karp JR et al, 2006. Chocolate milk as a post-exercise recovery aid. In. J. Sports Nutr. Exerc. Metab., 16:78-91; CEP, 2009 Dairy & muscle recovery after sport. Consumer Education Project of Milk SA.)

 
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