article by Stacy Sims
When it comes to protein type, timing and quantity, we see conflicting information regarding intake everywhere.
Weight loss? Protein!
Reduce blood sugar swings? Protein!
Body composition change? Protein! Protein! Protein!
But there’s much more to it than just eat more (or less) protein. In this month’s post, I’d like to focus on the athletic population (a way to state a disclaimer that the general population is different and has different nutritional needs).
Flipping through various peer review publications, several themes have come to the forefront: Daily protein intake vs training protein intake; Timing and distribution of protein for strength vs endurance athletes; and protein intake prior to sleep (to maximize recovery from a muscle and immunity standpoint). The actual accrual of skeletal muscle protein requires a sustained positive muscle protein balance (eg. rates of muscle synthesis exceed muscle breakdown). It is well known that a bout of exercise, followed by the ingestion of protein helps stimulate muscle synthesis and maintain a positive nitrogen balance; but the “gray” area is how much protein is necessary? Moreover, what are the critical windows for anabolic stimulus; post exercise or spread across the day via meals?
The long standing hypothesis behind protein intake post exercise is that ~20g provides a maximal anabolic stimulus in the early recovery process (~5 hours post exercise). This theory originated in the resistance training literature, and has been generalized to the endurance athlete. Upon examining the endurance literature, there are several other factors which come into play, including: if the athlete is male or female, if the athlete is energy deficit, the composition of the overall diet (high or low protein), and the composition of the protein ingested.
Amino Acids and Endurance Exercise
It is well known that carbohydrate is the predominant energy used for continuous endurance events (with fat oxidation playing an increasingly important role over 2h); however amino acids (from dietary intake and muscle protein breakdown) can provide up to 10% of total energy during endurance exercise. The use of amino acids can be increased during higher intensity, longer duration exercise, but also if there is low glycogen availability and/or a habitually high-protein dietary strategy. Although endurance exercise does lower the activity of the enzyme responsible for amino acid use, endurance athletes run the risk of being in a negative leucine balance. This can prevent the longer term goal of muscle mass adaptation/accumulation with body fat mass loss. Thus, the amino acids must be replaced through dietary sources.
Amount of Protein
In men, mixed muscle and myofibrillar protein synthesis rates are enhanced post-exercise with a small (~10g) ingestion of protein, but further enhanced after the ingestion of ~20g protein. Greater quantities (up to 40g), do not increase synthesis rates, but increase amino acid oxidation and urea production.
In women, estrogen inhibits muscle protein synthesis, progesterone enhances muscle breakdown and a sex difference (of hepatic origin) exists in amino acid oxidation. With these additional factors, research findings indicate muscle protein synthesis is enhanced post-exercise with the ingestion of ~30g protein (the leucine content is the contender here; muscle protein synthesis is reliance on tissue-leucine concentration; and the effects of estrogen on protein synthesis inhibits the oxidation of leucine within the muscle).
Weight loss and lowered calorie intake
During high intensity training and racing blocks, and/or motivated times of weight loss (New Year’s Resolutions??), the negative energy balance can directly affect recovery, lean mass gain, and subsequent fuel use during training; e.g. greater use of amino acids during exercise. It is during periods such as these where higher protein intake can greatly benefit lean mass, body fat loss, adaptations, and performance. Haakonssen et al (2013) and Areta et al (2013) have demonstrated the benefit of daily protein intake of 1.8-2.3g/kg (0.8-1.0g/lb) of body weight. The novelty of this research is not on the acute post-exercise protein ingestion, but the ingestion of 4x~20g protein over the course of 12 hours to elevate muscle protein synthesis. In practical terms, timing protein intake across the day with meals (0.25g/kg protein per meal) and training can enhance lean mass preservation in times of lowered calorie intake. If dietary changes are made to induce negative energy balance, protein should not be the main macronutrient excluded.
Types of protein and timing of their consumption
Dietary proteins differ in their amino acid composition as well as rates of digestion and absorption; all which have measureable effects on post-exercise muscle protein synthesis and whole body protein synthesis. The Essential Amino Acid (EAA) content of the protein, in particular the leucine content, can dramatically affect muscle protein synthesis. For example, compared with casein and soy sources of protein, whey protein has distinct anabolic characteristics (and anti-inflammatory properties) which result in a greater synthesis of muscle protein; holding true both at rest and after exercise. When the overnight fast is taken into consideration, casein provided before sleep is absorbed more rapidly than casein provided during the day; increasing rates of muscle protein synthesis by ~22% as compared to a placebo, and 10% as compared to whey.
Where does this leave me as an endurance athlete? Lean mass and its subsequent function (strength, power, endurance) in performance is critical; and the support of preservation (during low energy intake) and adaptation (training stress) is a complex balance. Ideally, post exercise ingestion should comprise ~20-30g high-quality protein within 30 minutes (any delay compromises tissue leucine concentration, and enhances muscle tissue breakdown); with subsequent doses of ~20 g protein across the day. Meal content should be ~0.25g/kg; with one last dose of protein before bed. This strategy will support muscle adaptation, body fat loss (with negative energy balance), and lean mass preservation. In this holiday season, taking protein ingestion seriously will help you in the bigger picture for early season training and body composition adaptations. (That said, remember the 80/20 rule- be spot on 80% of the time, and live life 20%….).
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