Sport and exercise
Good nutrition is vital to performance for professional and amateur athletes alike. Making the right nutrition choices is also crucial in supporting those committed to an exercise plan with weight loss goals.
With carbohydrates and fats responsible for providing the majority of energy required during exercise, the primary role of protein lies in muscle repair and muscle growth.
Proteins are made of long chains of amino acid molecules linked together. When we digest food, proteins are broken down to individual amino acids that can then be relinked in different sequences to form proteins such as hormones, enzymes, haemoglobin and skeletal muscle.
We consume a variety of protein in our diet but not all proteins contain every amino acid required by the body. There are twenty different amino acids in total, nine of which are ‘essential’ and must be obtained from the diet. The other eleven amino acids are ‘non-essential’ and can be produced by the body. Foods containing all the essential amino acids are termed high-quality protein sources. Dairy, meat, eggs, and soy are examples of high-quality protein sources. Meat and dairy are considered high biological value (HBV) proteins because they contain all the essential amino acids and are more readily digestible than plant-based protein.
The benefits of dairy protein
Dairy foods contain two types of protein: casein (80%) and whey (20%). Casein is a slow-to-digest and slow-release protein which has been shown to reduce muscle breakdown. Whey is a fast-acting and quick-absorbing protein with a high concentration of leucine – a branched chain amino acid. Leucine specifically stimulates the building of new muscle tissue.
Timing and amount of protein
Resistance training is the major driver of muscle protein synthesis (MPS) and research indicates that there is an upregulation of MPS for up to 24 hours following a single bout of exercise. The primary benefit of including protein post-exercise is to not only limit exercise-induced muscle protein breakdown (MPB), but also maximise MPS. This means we end up with a net gain in muscle growth.
When determining an individual’s protein needs, a person’s weight as well as the volume and type of exercise must be taken into consideration. Daily requirements are expressed as grams of protein per kilogram of body weight per day (g/kg/d). Depending on energy intake and body composition goals, for most athletes this commonly ranges from 1.2 to 2.0 g/kg/d. For a 70kg person, this equates to 84-140g per day.1
The body can only store limited amounts of protein to draw upon for growth as well as ongoing building and repair of body tissues such as muscle. Eating protein regularly over the day, and following exercise, by including protein-rich foods at each meal and snack, helps to ensure a regular supply of amino acids for the body to use.
For a 70kg person, this can be achieved with 20-30g of protein at three main meals and an additional dose following exercise. Including dairy foods in the diet makes this easily achievable. Dairy protein has been found to be superior to other protein sources in optimising muscle protein synthesis following resistance training.2
While adequate amounts of protein can be acquired through a well-balanced and nutritious diet, protein supplements offer an effective method for increasing protein consumption without significantly increasing energy intake. Whey protein isolate (WPI) is made by separating the whey protein from milk and offers a convenient concentrated dose of protein. Twenty grams of WPI with 250ml milk, provides approximately 30g of protein and 3g of leucine, making it an ideal way to meet post-exercise targets. Numerous studies have highlighted the effectiveness of whey protein at increasing MPS following resistance exercise.
More recent research suggests including a moderate dose of casein protein before bed is able to prevent some of the MPB that occurs overnight. The slower digestion of casein helps to maintain plasma protein levels overnight when a majority of MPB occurs.3
Dairy as a source of carbohydrates
Milk and yoghurt contain good amounts of carbohydrate. The body prefers to use carbohydrate as its main energy source during moderate to high exercise as it’s able to break the carbohydrate down quickly and efficiently for readily available energy. Eating a carbohydrate-rich meal or snack before exercising ensures sufficient carbohydrate stores to fuel the entire exercise session to optimise performance and make the most training gains.
Carbohydrate-rich meals before exercise should be eaten 2-4 hours prior, to fuel the session. If a snack is preferred instead, this should be eaten 1-2 hours beforehand. For exercise before breakfast, a carbohydrate-rich snack eaten just prior to bed the night before, followed by a light carbohydrate snack on waking, will optimise energy stores. Sweetened dairy foods like flavoured milk, yoghurt and dairy desserts provide extra carbohydrate and are low in fibre, helping to maximise gut comfort.
Following a bout of exercise, eating high carbohydrate foods will replenish the stores depleted during exercise, thereby ensuring the body continues to have enough energy to fuel its ongoing physiological functions, fuel the brain, and prevent fatigue. The body is most efficient at replenishing fuel stores for faster recovery and to prepare for the next exercise session in the hours after finishing a training session.
A recovery meal or snack containing carbohydrate-rich food and eaten soon after completing exercise takes advantage of this. It is also thought eating carbohydrate-rich foods soon after exercise has a positive effect on the immune system as it may reduce exercise-induced immunosuppression.
Research has shown people who drink milk straight after training are able to exercise longer in their next session than those who drink sports drinks or plain water.4 Choosing dairy foods as a carbohydrate source also helps to tick off other aspects of recovery nutrition, like rehydration and muscle repair.
Milk for hydration
The body loses more fluid during exercise than at rest, mostly due to increased sweating. Dehydration can occur if fluids lost throughout the day and during exercise are not replaced regularly. Fluid and electrolytes after exercise help to rehydrate the body by replacing what has been lost through sweat. It is recommended replenishment of fluids not be delayed after exercise as rehydration will not commence until fluids are consumed. Rehydration following exercise is most effective when fluid intake is spread out rather than drinking large volumes early after the exercise. Drinking small amounts frequently over the 4-6 hours after exercise helps the body to be able to hold onto the fluid more effectively, promoting rehydration.
Milk assists with rehydration after exercise by replacing fluid and electrolytes (sodium and potassium) in the right balance. Other nutrients in milk, like protein, help the body to retain fluid more effectively.
While sports drinks are a popular choice for rehydration following exercise, milk in fact contains more sodium than a standard sports drink. By also containing protein and carbohydrate, milk has the additional benefit of providing all nutrients of importance for recovery following exercise.
A 2007 study found low-fat milk helped dehydrated cyclists replace sweat loss better than water or a sports drink.5 In four separate trials, volunteers undertook a series of cycling exercises until they had lost about 1.8% of their body mass. They were then given either low-fat milk, a sports drink or water to rehydrate. Four hours after exercise, the cyclists who drank milk were better hydrated by an average 600ml compared with those who drank water or a sports drink.
Gut discomfort and physical activity
Gastrointestinal (GI) discomfort including nausea, vomiting, abdominal cramps, diarrhoea and bloating have been reported by active people and can be a problem during training and competition. This can be caused by a number of factors including exercise intensity, eating too close to an event, stress and anxiety to name a few.
As such, active people commonly avoid eating before, during or after physical activity because of the belief that it can prevent or reduce possible GI distress.
There are several things athletes can do to avoid GI distress during physical activity without sacrificing their performance, body composition and health.
- Avoid eating a substantial meal within the 2-4 hours before exercise.
- If you use sports drink, use a standard concentration sports drink - these usually contain 4 – 8% carbohydrate and are less likely to lead to GI upset.
- Practice your competition diet during training to ensure that what you are eating and drinking before and during exercise do not cause any GI upset.
- Begin your physical activity well-hydrated and sip on fluid regularly during exercise to avoid becoming dehydrated.
- After exercise, milk-based beverages have been shown to be suitable in hydration as they lead to lower urinary losses in comparison to sports drinks.
Research has also shown, there is no need to avoid dairy foods before exercise unless there are diagnosed underlying medical conditions. Dairy can be included in meals consumed before strenuous physical activity without impacting either gut comfort or performance.6 In addition, excluding dairy food before exercise may unnecessarily reduce dietary sources of high-quality proteins and calcium with possible implications for performance, body composition and health.
Everyone is different so it is highly recommended individuals consult with a Accredited Sports Dietitian to develop a suitable nutrition and gut training plan.
Sport and exercise resources
Athlete David Crawshay, gold medal Olympian and national champion rower, discusses the role nutrition plays in his training.
Professor Luc Van Loon, Professor of Exercise, Physiology and Nutrition at Maastricht University, discusses how to maintain healthy muscle tissue.
1 Thomas T., Erdman KA, Burke LM. Nutrition and Athletic Performance - ACSM Joint Position Stand. Med. Sci. Sports Exerc. 2016:48(3):543-58.
2 Tang J, Moore D, Kujbida G, Tarnopolsky M, Phillips S. Ingestion of whey hydrolysate, casein, or soy protein isolate: effects on mixed muscle protein synthesis at rest and following resistance exercise in young men. J Appl Physiol. 2009;107(3):987-92.
3 Trommelen J, van Loon LJ. Pre-Sleep Protein Ingestion to Improve the Skeletal Muscle Adaptive Response to Exercise Training. Nutrients. 2016 Nov 28; 8(12): doi: 10.3390/nu8120763.
4 Thomas K, Morris P, Stevenson E. Improved endurance capacity following chocolate milk consumption compared with 2 commercially available sport drinks. Appl Physiol Nutr Metab. 2009;34(1):78-82.
5 Shirreffs SM, Watson P, Maughan RJ. Milk as an effective post-exercise rehydration drink. Br J Nutr. 2007;98:173–80.
6 Haakonssen E, Ross M, Cato L, et al. Dairy-based pre-exercise meal does not affect gut comfort of time-trial performance in female cyclists. International Journal of Sports Nutrition and Exercise Metabolism. 2014; doi: 10.1123