SPORTS NUTRITION

The science of nutrition is evolving all the time and it is now universally recognised that what you eat, when and how you eat it can enhance sports performance. The problem is that due to fantastic marketing by the big sports food brands, the tendency amongst athletes is to favour specialist sports foods or supplements to boost their diets rather than looking at readily available foods which maybe better and are certainly cheaper.

Milk is a nutrient dense food, containing many of the nutrients identified as being beneficial for sport and that are key components in the products specifically formulated to enhance exercise performance.

FUEL FOR SPORT

The biggest factor affecting sports performance is fatigue and the most common causes of fatigue are the lack of available energy and body dehydration.

Lots of research has shown that exercise performance is compromised by even minimal dehydration. As little as a 2% of body weight can affect speed and concentration and losses of 5% can decrease work capacity by up to 30% (1). Drinking water is sufficient to keep your body hydrated for light or moderate exercise sessions but research has found that where as individuals sip at water, they drink more if given a more palatable drink and when the drink is at the right temperature (2).

Energy is stored as the carbohydrate glycogen in the muscles and liver and as fat in adipose tissue. In adults, even in very lean  athletes, there is plenty of stored fat and fat shortage is not thought to impact performance, (though it may be more important in children). Poor glycogen stores, however can be performance limiting, causing athletes to ‘hit the wall’ or ‘bonk’ when stores run out. Because of the importance of glycogen stores eating carbohydrate rich foods in the 48hours before or during exercise can improve performance, both prolonging exercise time to exhaustion in endurance sports and boosting strength in high intensity short duration sports. This improvement in performance has lead to the huge boom in the manufacture and marketing of sports bars, gels, sweets and drinks for consumption before or during exercise.

Most commercially-available sports drinks are made using between 6% and 10% carbohydrate, typically in the form of glucose, sucrose and fructose or glucose polymers like maltodextrin. They also contain small quantities of electrolytes, to replace sweat losses and promote absorption of glucose, and water to enhance rehydration. Milk contains a similar concentration of carbohydrate to many sports drinks and recent studies comparing the benefit of consuming milk before and during exercise with plain water, have shown a similar improvements in performance (3). The table below shows the composition and energy content of plain water, a commercially available sports drink and skimmed milk and underlines their similarities. The osmolality of blood is ~285mOsm.

FUEL FOR RECOVERY 

Not long ago, the guidelines for what to eat or drink after rigorous exercise was basically to ‘drink lots of fluids’, or maybe ‘to eat a banana’. However, recent research has shown that recovery nutrition is one of the most important areas of performance nutrition. Eating or drinking the right foods immediately after training or competition, has not only been found to enhance later performance but is the key to training adaptation. Recovery nutrition is based on three Rs:-

REFUEL – Refueling involves carbohydrates. Carbohydrates provide our bodies and brains with the fuel needed to perform. As we exercise, we burn glycogen stores and the longer and the more intense the session, the more stores we use and the more important it is to recover properly. Research has found that the most effective way to do this is to eat a carbohydrate rich snack soon after exercising. Consuming between 0.8 and 1.2 grams of carbohydrates per kilogram of body weight as quickly as possible after your training session has been found to boost performance in subsequent training and competition.

REBUILD – Rebuilding involves protein. Bones and muscles are constantly being recycled and rebuilt. Protein taken after exercise helps you recover and aids the synthesis of muscle protein the key to building or repairing muscle. 0.3 to 0.4 grams of protein per kilogram of body weight is the recommended post-exercise intake. More protein post-workout does not mean you build more muscle and many young athletes eat too much protein. Post exercise protein intake also enhances glycogen storage.

REHYDRATE – which involves replacing lost fluid and electrolytes.

Studies show that drinking low-fat chocolate milk after a tough workout provides the optimal mix of carbohydrates and high-quality protein (4). The 4:1 ratio of carbohydrates to protein is ideal for replenishing tired muscles (5) and gives better muscle recovery when compared with carbohydrate-only drinks like sports drinks (6). Milk also has  enough water to aid rehydration and more electrolytes than the average sports drink. Milk also contains Calcium. Calcium is the most abundant, essential mineral in the human body and as well as being important in bone development, it has a major role in muscle contraction and nerve signalling and it is widely recognised that athletes need higher intakes than the general population.

FUEL FOR MUSCLE BUILDING

Protein in the diet is broken down into amino acids which may then form the building blocks for the formation of new muscle.  The major proteins in milk are casein and whey, both are excellent sources of all of the essential amino acids needed, but they differ in their speed of digestion and their effects on muscle synthesis. Whey protein is digested quickly, resulting in a spike in plasma amino acids, quickly boosting protein synthesis but leaving  protein breakdown unaffected. Whey proteins also have higher levels of the amino acid leucine which is known to stimulate protein synthesis, making whey superior at stimulating protein synthesis, but the effect is short-lived. Casein is more abundant in milk than whey and as it is relatively insoluble, it is digested slowly, resulting in a prolonged increase in blood amino acids. As well as boosting muscle synthesis casein reduces muscle breakdown.

Whey and whey powders are promoted widely as the answer for muscle building and whey does rapidly increases protein synthesis but as casein also blocks protein breakdown, a combination of both is of even greater benefit. Research on several markers of muscle anabolism during strength training have shown a mixture of casein and whey is better than either in isolation and better than other types of sport drinks (7,8). Milk is better for building muscle than whey protein in isolation.

FUEL FOR YOUR IMMUNE SYSTEM

Athletes who do regular strenuous training sessions have been found to suffer from impaired immune function possibly caused by the immunosuppressive actions of stress hormones such as adrenaline and cortisol (9). An adequate dietary intake of protein and specific micronutrients including vitamins A, C, E, B6 and B12 along with iron, zinc, copper and selenium are all critical factors for the maintenance of optimum immune function and carbohydrate supplementation has also been shown to boost immunity to infection (10). There are no studies on athletes showing that bottled milk improves immunity but milk is rich in protein, carbohydrate and many of the key mincronutrients involved in immunity, animal studies have shown that milk may be beneficial (11) and bovine colostrum, the ‘pre-milk’, produced cows in the first 48hours after calving has been shown to boost athlete immunity during intensive physical training (12).

BONE HEALTH

Lots of studies have found positive links between eating dairy products and bone mineral density. This has been attributed to the presence of good levels of calcium and phosphorus but there may also be significant benefits from eating whey proteins (13). Poor bone health has been found in athletes, particularly in weight limited sports. For further information on the links between milk and bone health see Dairy and Bone Health – Professor Kevin Cashman, University College Cork.

WEIGHT LOSS

There is growing evidence that calcium can also influence fat metabolism. Recently, a team of researchers from Northumbria University, lead by Dr. Emma Stevenson, conducted a meta-analysis on scientific literature published from 2005-2012, in order to evaluate the effects of a high intake of calcium on levels of fat oxidation. The researchers concluded that there is sufficient evidence that both acute (short term) and chronic (long term) high intake of calcium, provided through dietary sources (e.g. dairy foods) or supplementation, can accelerate body fat losses. Drinking chocolate milk during recovery also has been found to cause greater muscle gain and also increased loss of fat during training, compared to adults drinking other sports drinks (4).

ADVICE

I am in no doubt that eating traditional foods can be just as good, if not better at fuelling performance than eating highly processed specialist sports snacks, gels and drinks however convenient they may be. Drinking flavoured milk has been widely shown to be an effective way to fuel up before sport and boost recovery afterwards. I’m personally not convinced that it will take on as a halftime drink because of storage issues but would definitely recommend it. Most of the research has studies low-fat semi or skimmed milk. This is because fat is known to be a potent inhibitor of gastric emptying slowing down digestion. However it’s interesting to note that I have been at two conferences where the key speakers involved in performance physiology / elite sport have been asked what type of milk they would recommend and both times they replied “full fat” and there is a growing body of work that shows certain milk derived fatty acids may offer significant health benefits for diseases like cancer and CHD as well as affecting weight regulation (14).

REFERENCES

(1) Sawka and Pandolf (1990) The effects of body water loss on physiological function and exercise performance. In Perspectives in exercise science and sports medicine. Vol 3 Eds Gisolfi and Lamb. Benchmark Press

(2) Suzuki et al (2013). The effects of sports drink osmolality on fluid intake and immunoendocrine responses to cycling in hot conditions. J Nutr Sci Vitaminol (Tokyo) 59(3). 206-12.

(3) Lee et al (2008) The effects of milk ingestion on prolonged exercise capacity in man. Nutrition 24, 340-347

(4) Ferguson-Stegall, McCleave, Ding et al. (2011) Post-exercise carbohydrate-protein supplementation improves subsequent exercise performance and intracellular signaling for protein synthesis. Journal of Strength and Conditioning Research 25(5): 1210-24.

(5) Pritchett & Pritchett (2012) Chocolate milk: a post-exercise recovery beverage for endurance sports. Medicine and Sport Science. 2012;59:127-34.

(6) Pasiakos et al (2011) Chocolate Milk & Endurance Exercise Recovery: Protein Balance, Glycogen & Performance. Medicine and Science in Sports and Exercise, 2011 Sep 7. [Epub ahead of print].

(7) Willoughby DS, Stout JR, Wilborn CD. (2006) Effects of resistance training and protein plus amino acid supplementation on muscle anabolism, mass, and strength. Amino Acids. 2006 Sep 20.

(8)  Andersen LL, Tufekovic G, Zebis MK, Crameri RM, Verlaan G, Kjaer M, Suetta C, Magnusson P, Aagaard P. (2005) The effect of resistance training combined with timed ingestion of protein on muscle fiber size and muscle strength. Metabolism. 2005 Feb, 54(2):151-6.

(9) Gleeson, M, Nieman, D and Pedersen, BK  (2004), ‘Exercise, nutrition and immune function’. Journal of Sports Sciences,  22, pp. 115-25.

(10) Bishop et al (2002). Influence of carbohydrate supplementation on plasma cytokine and neutrophil degranulation responses to high intensity intermittent exercise. Int J Sports Nutr Exer Metab 12, 145-156

(11) Kobayashi et al (1998). Protective effects of administration of milk on exogenous and endogenous infection in mice. Microbiol immunol 42, 203-209

(12)  Shing, CM, et al. (2006)  The influence of bovine colostrum supplementation on exercise performance in highly trained cyclists. British Journal of Sports Medicine40(9):797-801.

(13) Kumegawa (2006). Prevention of osteoporosis by food and dietary supplements. Bone reinforcement factor in milk. Milk basic protein (MBP). Clin Calcium 16, 1624-1631.

(14) Nutritional Importance of Dairy Fats – Dr Adam Lock, University of Vermont . Publication from the Dairy Council.