Boost endurance with protein plus carbs
Carbs prolong endurance performance
The importance of carbohydrates for optimal performance has been deeply ingrained in the minds of athletes, particularly those involved in endurance training. During prolonged exercise, blood sugar levels usually begin to drop below resting levels late in exercise. This hypoglycemia effect is associated with glycogen depletion and fatigue.

A logical solution to mitigate low blood sugar is to ingest carbs during exercise. That’s exactly what top athletes running in the Boston Marathon did back in 1925 to improve their performance. Additional research in the late 1960s contributed to the knowledge that carbohydrate feeding during exercise improves prolonged endurance performance by preventing hypoglycemia and sparing glycogen (the storage form of carbs in muscles). But that’s old news!

Carbs with protein is better than carbs alone
An emerging trend with endurance athletes is taking protein with carbs. While it’s true that strength and power athletes are well versed on the importance of consuming protein to promote muscle growth, most endurance athletes don’t consider protein important because building muscle is not a priority. However, here are five reasons to take protein and carbs together.

1. Boost performance 13-51%
The most important factor for endurance athletes is reaching the finish line faster or lasting longer during training or a race. Will supplementing with protein help reach these goals? Seven studies all point to the same finding – protein fights off fatigue and enhances performance. These studies involved test subjects cycling to exhaustion at a submaximal intensity around 75% of their maximal oxygen consumption, a test that researchers call “time to exhaustion.” The goal was to last as long as possible. The time to fatigue was extended anywhere from 13-51% in each study.

2. Help build muscle proteins
Prolonged endurance exercise causes significant protein breakdown to provide fuel for exercise. This breakdown may be offset by adding protein to your diet. When protein is ingested, it’s broken down into amino acids that are absorbed into the blood. These amino acids, particularly leucine, are triggers that increase the rate of protein synthesis to rebuild muscle proteins broken down during exercise. Protein augments the repair and remodeling of tissue, speeds recovery and ultimately helps maintain muscle mass and optimal functioning of muscle. If no protein is ingested, the body actually breaks down its own protein stores, a process obviously not conducive to peak performance and optimal recovery.

It’s important to note that adding protein will not create huge muscles, which could be a negative for endurance athletes. Research shows that endurance exercise, as opposed to resistance exercise, stimulates synthesis of different proteins in muscle such as mitochondria that function in aerobic metabolism and contribute less to total muscle size. Simply put, the amino acids provided by protein serve as the building blocks for building muscle proteins that contribute to enhanced performance.

3. Decrease muscle damage by 27%
Prolonged exercise is associated with profound metabolic and mechanical stress, like with the continuous pounding that occurs when running. A significant disruption to the normal functioning of muscle occurs from the physical tearing of membranes combined with the biochemical stress associated with accelerated rates of metabolism. These processes contribute to delayed muscle soreness and eventually decreased functional capacity of muscle for several hours and days after exercise. Many studies indicate that protein helps dampen the overall stress response. In one study of runners, protein added to carbs reduced muscle damage by an average of 27% and muscle soreness by 30%. In another study of cyclists, researchers found that compared to a carb-only supplement, additional protein reduced markers of muscle damage and improved muscle performance the day following exercise.

4. Provide fuel to prevent muscle breakdown
During endurance exercise, protein is used by the body for energy. There are three branched-chain amino acids (BCAAs) that provide fuel for muscles: leucine, isoleucine and valine. These essential BCAAs make up about one-third of muscle proteins. They are used in proportion to energy expenditure, and the demand for them increases several-fold during prolonged endurance events. BCAA levels in blood and muscle drop significantly during exercise. Of all the amino acids, these three are the most important to consume. Protein ingestion during a marathon was shown to increase protein used for energy, thereby potentially sparing blood glucose and muscle glycogen, and contributing to an overall anti-catabolic effect by preventing muscle protein breakdown.

5. Beat fatigue with BCAAs
Another benefit of taking BCAAs, or protein containing BCAAs, is to prevent central fatigue. A decline in BCAAs results in an increase of the ratio of the plasma free tryptophan (f-TRP) to BCAA, which facilitates increased uptake of tryptophan in the brain that gets converted to serotonin. An increase in the concentration of serotonin can impair central nervous system function during prolonged exercise, a phenomena called central fatigue. Consuming BCAAs during exercise can influence the ratio of f-TRP to BCAAs to decrease serotonin levels and delay central fatigue.

Which protein and how much?
Nearly all the studies showing positive effects of supplemental protein for endurance athletes have used some form of whey or BCAAs. Whey is preferred because it contains a high amount of BCAAs that are burned during exercise. Plus, whey is absorbed very quickly, resulting in a rapid increase in blood levels of amino acids.

In the studies I reviewed, protein was added to a carbohydrate beverage and usually consumed before exercise and intermittently during exercise (e.g., every 15 minutes). The amount of protein consumed varied considerably in the studies that showed a positive impact on performance. Generally, for every 8 fluid ounces of a carbohydrate beverage containing 16 grams of carbs, you should consume 3-4 grams of whey protein or add 1-2 grams of pure BCAAs.

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