International Society of Sports Nutrition position stand: Nutrient timing.
Abstract
Position Statement: The position of the Society regarding nutrient timing and the intake of
carbohydrates, proteins, and fats in reference to healthy, exercising individuals is summarized by
the
following eight points:
1.) Maximal endogenous glycogen stores are best promoted by following
a high-glycemic, high-carbohydrate (CHO) diet (600 1000 grams CHO or ~8 10 g CHO/kg/d), and ingestion of free amino acids and protein (PRO) alone or in combination with CHO before resistance exercise can maximally stimulate protein synthesis.
2.) During exercise, CHO should be consumed at a rate of 30 60 grams of CHO/hour in a 6 8% CHO solution (8 16 fluid ounces) every 10 15 minutes. Adding PRO to create a CHO:PRO ratio of 3 4:1 may increase endurance performance and maximally promotes glycogen re-synthesis during acute and subsequent bouts of endurance exercise.
3.) Ingesting CHO alone or in combination with PRO during resistance
exercise increases muscle glycogen, offsets muscle damage, and facilitates greater training adaptations after either acute or prolonged periods of supplementation with resistance training.
4.) Post-exercise (within 30 minutes) consumption of CHO at high dosages (8 10 g CHO/kg/day) have been shown to stimulate muscle glycogen re-synthesis, while adding PRO (0.2 g 0.5 g PRO/kg/day) to CHO at a ratio of 3 4:1 (CHO: PRO) may further enhance glycogen re-synthesis.
5.) Post-exercise ingestion (immediately to 3 h post) of amino acids, primarily essential amino acids, has been shown to stimulate robust increases in muscle protein synthesis, while the addition of CHO may stimulate even greater levels of protein synthesis. Additionally, pre-exercise consumption of a CHO + PRO supplement may result in peak levels of protein synthesis.
6.) Durin consistent, prolonged resistance training, post-exercise consumption of varying doses of CHO + PRO supplements in varying dosages have been shown to stimulate improvements in strength and body composition when compared to control or placebo conditions.
7.) The addition of creatine (Cr) (0.1 g Cr/kg/day) to a CHO + PRO supplement may facilitate even greater adaptations to resistance training.
8.) Nutrient timing incorporates the use of methodical planning and eating of
whole foods, nutrients extracted from food, and other sources. The timing of the energy intake and the ratio of certain ingested macronutrients are likely the attributes which allow for enhanced recovery and tissue repair following high-volume exercise, augmented muscle protein synthesis, and improved mood states when compared with unplanned or traditional strategies of nutrient
intake.
Summary of pre-exercise nutrient ingestion findings
Glycogen stores are limited and depend largely on the nutritional status and the intensity and training level of the athlete [7,14]. Endogenous glycogen stores during moderate to high intensity levels (65 85% VO2max) of
exercise may only last from 90 min to 3 h [15].
Exercise intensity, pace and work output decrease as glycogen levels diminish [14]. Depletion of glycogen is associated with increased levels of muscle tissue breakdown and suppression of the immune system [16,17].
Maximal endogenous glycogen stores are best promoted by following a high-glycemic, high-CHO diet (600 1000 grams or ~8 10 g/kg/d) [2,3,15].
The optimal CHO and PRO content of a pre-exercise meal is dependent upon a number of factors including exercise duration and fitness level, but general guidelines recommend ingestion of 1 2 grams CHO/kg and 0.15 0.25 grams PRO/kg 3 4 hours before competition [15].
Pre-exercise ingestion of essential amino acids or PRO alone increases muscle protein synthesis. In addition, ingesting PRO + CHO pre-exercise has been shown to produce significantly greater levels of muscle protein synthesis [9,31].
Regular ingestion of various PRO sources in conjunction with CHO stimulates greater increases in strength and favorably impacts body composition when compared to CHO alone [8,10,11].
Summary of during exercise nutrient findings
CHO availability during exercise and muscle glycogen levels are major determinants of endurance performance. CHO administration becomes even more important when muscle glycogen levels are low at the onset of exercise [35,42].
As exercise duration increases beyond 60 min, exogenous sources of CHO become important to maintain blood glucose and muscle glycogen stores. This CHO source should supply 30 60 grams of CHO per hour and can typically be delivered by drinking 1 2 cups of a 6 8% CHO solution (8 16 fluid ounces) every 10 15 minutes [49].
Mixing different forms of CHO has been shown to increase muscle CHO oxidation from 1.0 g CHO/min to levels ranging from 1.2 g 1.75 g CHO/min [50,52-54]; an effect which is associated with an improvement in
time
trial performance [56].
Glucose, fructose, sucrose and maltodextrin can be used in combination, but large amounts of fructose are not recommended due to the greater likelihood of gastrointestinal problems.
The addition of PRO to CHO at a ratio of 3 4:1 (CHO: PRO) has been shown to increase endurance performance during both acute exercise and subsequent bouts of endurance exercise [57,58].
Ingesting CHO alone, or in combination with PRO, during resistance exercise increases muscle glycogen stores [40], offsets muscle damage [37], and facilitates greater training adaptations after acute [38,39] and prolonged
periods of resistance training [41].
Summary of post-exercise nutrient ingestion findings
Post-exercise (within 30 minutes) consumption of CHO at high dosages (8 10 g CHO/kg/day) has been shown to stimulate muscle glycogen re-synthesis [15,65].
Adding PRO (0.2 g 0.5 g PRO/kg/day) to CHO at a ratio of approximately 3: 1 (CHO: PRO) has been shown to stimulate glycogen re-synthesis to a greater extent [69].
Post-exercise ingestion (immediately after through 3 hours post) of amino acids, primarily EAAs, have been shown to stimulate robust increases in muscle PRO synthesis [73,74,83]. The addition of CHO may increase PRO synthesis even more, while pre-exercise consumption may result in the best response of all [9].
During prolonged resistance training, post-exercise consumption of CHO + PRO supplements in varying amounts have been shown to stimulate improvements in strength and body composition when compared to control, placebo, or CHO-only conditions [10,87,90].
The addition of Cr (0.1 g Cr/kg/day) to a CHO + PRO supplement may facilitate even greater adaptations to resistance training [84,88].
Conclusion
The scientific literature associated with nutrient timing is an extremely popular, and thus ever-changing, area of research. Upon reviewing the available literature, the following conclusions can be drawn at this point in time:
Prolonged exercise (> 60 90 min) of moderate to high intensity exercise will deplete the internal stores of energy, and prudent timing of nutrient delivery can help offset these changes.
During intense exercise, regular consumption (10 15 fl.) of CHO/electrolyte solution delivering 6 8% CHO (6 8 g CHO/100 ml fluid) should be consumed every 15 20 min to sustain blood glucose levels.
Glucose, fructose, sucrose and other high-glycemic CHO sources are easily digested, but fructose consumption should be minimized as it is absorbed at a slower rate and increases the likelihood of gastrointestinal problems.
The addition of PRO (0.15 0.25 g PRO/kg/day) to CHO at all time points, especially post-exercise, is well tolerated and may promote greater restoration of muscle glycogen.
Ingestion of 6 20 grams of EAAs and 30 40 grams of high-glycemic CHO within three hours after an exercise bout and immediately before exercise have been shown to significantly stimulate muscle PRO synthesis.
Daily post-exercise ingestion of a CHO + PRO supplement promotes greater increases in strength and improvements in lean tissue and body fat % during regular resistance training.
Milk PRO sources (e.g. whey and casein) exhibit different kinetic digestion patterns and may subsequently differ in their support of training adaptations
