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Back to Milk and Sports Nutrition

The Role of Milk in Physical Activity

The evidence to date indicates that both white milk and chocolate milk may play an important role in the context of sports nutrition.

Highlights

Research to date suggests that milk (white and chocolate) has many properties that could make it an effective recovery beverage after endurance and resistance exercise. Actually, milk:

  1. contains carbohydrates (i.e. lactose) in amounts similar to those of many commercially available sports drinks;
  2. contains casein and whey proteins in a ratio of 3:1, which provides for slower digestion and absorption resulting in sustained elevations of blood amino acid concentrations;
  3. Whey proteins also contain a large proportion of branched-chain amino acids, which have an integral role in muscle metabolism and protein synthesis;
  4. also has a high concentration of electrolytes, which can replace those naturally lost through sweating during exercise.

Introduction

A growing body of scientific evidence suggests that milk (white and chocolate) may have an important and beneficial role in the context of sports nutrition. Research to date suggests that milk may be as effective as or even more effective than commercially available sports drinks as a rehydration beverage post endurance exercise. As well, drinking milk appears to result in favourable acute alterations in body composition following resistance-related exercise. The mechanisms associated with these benefits remain to be clarified, but are likely related to milk’s overall “nutrient package,” which includes:

  • Water,
  • Electrolytes (especially sodium and potassium),
  • Protein,
  • Carbohydrate,
  • Lipids.

The Evidence

A narrative review published in 2008 indicated the following:1

  • There is growing scientific evidence to support the use of low-fat milk following exercise by both individuals and athletes who habitually undertake strength or endurance training;
  • There is data which suggests that fat-free milk is at least as effective as, and possibly even more effective than, commercially available sports drinks at promoting recovery from strength and endurance exercise;
  • In the case of chocolate milk, some performance data suggest that it is as effective as commercially available sports drinks in facilitating recovery post endurance exercise;
  • To date, there have been no well-controlled studies that have directly measured the efficacy of milk to promote muscle glycogen recovery following prolonged endurance exercise;
  • In addition to being an excellent source of water, electrolytes, and carbohydrates, milk also has the added benefit of providing additional nutrients that are not present in commercial sports drinks.
  • There is both acute and long-term evidence to support the use of low-fat milk as a post-resistance exercise beverage;
  • Consumption of low-fat milk appears to create an anabolic environment following resistance exercise, leading to greater gains in lean mass and muscle hypertrophy;
  • Milk may also lead to greater losses of body fat when it is consumed following resistance training.

Resistance Exercise

In a randomized controlled trial of 24 healthy young volunteers who had not participated in regular resistance training for at least 5 years prior to the study, Elliot et al. looked at the protein metabolic response to 3 different types of milk beverages:2

  • whole milk,
  • fat-free milk, isocaloric to whole milk,
  • fat-free milk.

The results showed the following:

  • All three milk groups resulted in an increase of net muscle protein synthesis after resistance exercise;
  • All three milk groups showed an improvement in protein metabolism with a single dose of milk after resistance exercise.

Wilkinson et al. examined the effects of consuming soy or milk beverages on protein kinetics and net muscle protein balance following resistance exercise in 8 healthy young men (mean age 21.6 years).3 In a randomized, crossover design, subjects consumed milk or soy beverages after a single bout of resistance exercise.

  • Ingestion of both soy beverages or milk resulted in a positive net protein balance;
  • Analysis of area under the net balance curve indicated an overall greater net balance after milk ingestion compared to soy beverages (p < 0.05);
  • The fractional synthesis rate in muscle was also greater after milk consumption than after soy beverage consumption (p = 0.05).

Similarly, in a randomized controlled crossover study, Hartman et al. aimed to determine the long-term consequences of milk or soy protein or equivalent energy consumption on training-induced lean mass accretion.4 Fifty-six healthy young men (18 to 30 years) who trained 5 days/week for 12 weeks were randomly assigned to consume drinks immediately and again 1 h after resistance exercise. These drinks included:

  • fat-free milk (Milk group, n = 18),
  • fat-free soy beverage (Soy group, n = 19),
  • maltodextrin containing drink (Control group, n = 19).

The findings were as follows:

  • Type II muscle fibre area increased in all groups with training, but with greater increases in the Milk group than in both the Soy and Control groups (p < 0.05);
  • Type I muscle fibre area increased after training only in the Milk and Soy groups, with the increase in the Milk group being greater than that in the Control group (p < 0.05);
  • DXA-measured fat-free and bone-free mass increased in all groups, with a greater increase in the Milk group than in both the Soy and Control groups (p < 0.05).

In a single-blind, randomized controlled trial, 24 healthy males (mean age 21) were randomly assigned to 1 of 4 independent groups:5

  1. milk-based carbohydrate-protein (CHO-P);
  2. milk;
  3. carbohydrate sports drink (CHO);
  4. water (Control).

The study examined the effect of acute milk and CHO-P supplementation on the attenuation of exercise-induced muscle damage (EIMD). The beverages were consumed post EIMD. Participants were asked to complete 6 sets of 10 repetitions of exercises that caused muscle damage. Delayed-onset muscle soreness, isokinetic muscle performance, creatine kinase, and myoglobin were assessed immediately before and 24 h and 48 h after EIMD.

  • Delayed-onset muscle soreness was not significantly different between the groups at any time point;
  • Peak torque was significantly higher 48 h after CHO-P compared with CHO and Control (p < 0.05);
  • Peak torque was significantly higher 48 h after milk consumption compared with CHO (p < 0.05);
  • Total work of the set was significantly higher 48 h after CHO-P and milk consumption compared with CHO (p < 0.05);
  • At 48 h post EIMD, milk and CHO-P supplementation resulted in the attenuation of decreases in isokinetic muscle performance and increases in creatine kinase and myoglobin.

In a randomized controlled trial of 20 healthy young women (mean age of 23 years), fat-free milk was compared to an isoenergetic carbohydrate drink with respect to gains in lean mass and reductions in fat mass following resistance exercise.6

  • There was a greater net gain increase in lean mass with milk compared to carbohydrate (1.9 ± 0.2kg vs. 1.1 ± 0.2kg, respectively, p < 0.01);
  • Fat mass decreased with training in the milk group only (-1.6 ±0.4 kg, p < 0.01);
  • Isotonic strength increased more in the milk than the carbohydrate group for some exercises;
  • Serum 25-hydroxyvitamin D increased in both group but to a greater extent in the milk group and parathyroid hormone decreased only in the milk group;
  • The authors concluded that: “heavy, whole-body resistance exercise with the consumption of milk versus carbohydrate in the early post-exercise period resulted in greater muscle mass accretion, strength gains, fat mass loss, and a possible reduction in bone turnover in women after 12 weeks.”

Endurance Exercise

In a randomized controlled study, the effects of 3 beverages consumed during recovery from prolonged exercise on subsequent endurance capacity in cycling was examined.7 Nine trained male cyclists (mean age 25.4 years) completed 3 experimental trials, separated by at least 1 week, in which they consumed chocolate milk, a fluid replacement drink, or a carbohydrate replacement drink.

  • Participants cycled 51% and 43% longer after ingesting chocolate milk (32 ± 11 minutes) than after ingesting the carbohydrate replacement drink (21 ± 8 min, p = 0.01) or after ingesting the fluid replacement drink (23 ± 8 minutes, p = 0.01);
  • There was a trend for feelings of fullness to be higher and feelings of hunger to be lower following chocolate milk ingestion immediately post-drink and at 30 minutes compared to the other 2 drinks (p = 0.08).

Karp et al. conducted a randomized controlled study of similar design in nine trained male cyclists (mean age 22 years) who consumed chocolate milk, a fluid replacement drink, or a carbohydrate replacement drink.8

  • Time to exhaustion and total work were significantly greater (p < 0.05) for the chocolate milk and fluid replacement compared to the carbohydrate replacement;
  • There were no significant differences among the 3 groups in any of the other variables examined, including heart rate.

In another randomized controlled crossover trial involving 10 trained cyclists and triathletes, chocolate milk was compared to a whey protein-based isocaloric, carbohydrate replacement beverage in terms of achieving optimal recovery between bouts of high-intensity exercise.9

  • There was no significant difference in cycling time to exhaustion between the 2 groups;
  • There was no significant difference in pre-creatine kinase levels between the 2 groups;
  • There was no significant difference in pre- or post-muscle soreness between the 2 groups;
  • All 10 participants preferred the taste and consistency of chocolate milk compared to that of the carbohydrate replacement beverage.

Shirreffs et al. also conducted a randomized controlled study that was designed to assess the effectiveness of low-fat milk, alone and with an additional 20 mmol/L of NaCl, at restoring fluid balance after exercise-induced hypohydration compared to a sports drink and water. Eleven healthy volunteers (5 male, 6 female: mean age 24 years) agreed to participate.10

  • Cumulative urine output was less after the milk drinks were consumed compared to the sports drinks and water (p < 0.001);
  • Subjects remained in net positive fluid balance throughout the recovery period after drinking the milk drinks but returned to net negative fluid balance 1 h after drinking the sports drinks and water (p < 0.001).

Potential Mechanisms

The exact mechanisms by which milk may confer benefits remain to be clarified, but the unique “nutrient package” provided by milk is likely involved.

Bovine-based milk and milk products represent a very good source of protein, amino acids, vitamins and minerals.1 Low-fat milk has a number of characteristics that theoretically make it a potentially good recovery beverage:1

  1. It contains carbohydrates (i.e. lactose) in amounts similar to those of many commercially available sports drinks;
  2. It contains casein and whey proteins in a ratio of 3:1, which provides for slower digestion and absorption resulting in sustained elevations of blood amino acid concentrations;
  3. Whey proteins also contain a large proportion of branched-chain amino acids, which have an integral role in muscle metabolism and protein synthesis;
  4. Milk also has a high concentration of electrolytes, which can replace those naturally lost through sweating during exercise.

Conclusions

A growing body of scientific evidence supports the use of milk, including lower-fat milk and chocolate milk, as an appropriate, and maybe ideal, recovery beverage post endurance and resistance-related exercise.

Research is needed to elucidate the role of other milk products such as yogurt and cheese in this context.

More studies are needed to provide definitive answers for other groups, such as women, children and adolescents, and older adults.

Studies to assess glycogen recovery following endurance exercise are also needed.

References

  1. Roy BD. Milk: the new sports drink? A Review. Journal of the international society of sports nutrition 2008;5:15 doi: 10.1186/1550-2783-5-15.
  2. Elliot TA et al. Milk ingestion stimulates net muscle protein synthesis following resistance exercise. Med Sci Sports Exerc
  3. Wilkinson SB et al. Consumption of fluid skim milk promotes greater muscle protein accretion after resistance exercise than does consumption of an isonitrogenous and isoenergetic soy-protein beverage. Am J Clin Nutr 2007;85:1031-1040.
  4. Hartman JW et al. Consumption of fat-free fluid milk after resistance exercise promotes greater lean mass accretion than does consumption of soy or carbohydrate in young, novice, male weightlifters. Am J Clin Nutr 2007;86:373-381.
  5. Cockburn E et al. Acute milk-based protein-CHO supplementation attenuates exercise-induced muscle damage. Appl Physiol Nutr Metab 2008;33:775-783.
  6. Josse AR et al. Body composition and strength changes in women with milk and resistance exercise. Medicine and Science in Sports and Exercise 2010; DOI:10.1249/MSS.0b013e3181c854f6.
  7. Thomas K et al. Improved endurance capacity following chocolate milk consumption compared with 2 commercially available sports drinks. Appl Physiol Nutr Metab 2009;34:78-82.
  8. Karp JR et al. Chocolate milk as a post-exercise recovery aid. International Journal of Sport Nutrition and Exercise Metabolism
  9. Pritchett K et al. Acute effects of chocolate milk and a commercial recovery beverage on postexercise recovery indices and endurance cycling performance. Appl Physiol Nutr Metab 2009;34:1017-1022.
  10. Shirreffs SM et al. Milk as an effective post-exercise rehydration drink. Brit J Nutr 2007;98:173-180.2006;38:667-674. 2008;16:78-91.

Keywords: milk , electrolytes , carbohydrates , endurance exercise , resistance exercice , sport , body fat , muscle , post-exercise recovery , chocolate milk , protein , physical activity

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