Abstract 

Peri-workout carbohydrate and protein supplementation has become an increasingly popular strategy amongst athletes looking to increase athletic performance. Mounting evidence over the recent decades has demonstrated the performance-enhancing effects of carbohydrate intervention, especially in cases of prolonged exercise.

Recent advancements in food science have led to the creation of designer carbohydrates, including highly branched cyclic dextrin (HBCD). Due to the physical properties of HBCD, these molecules undergo a unique metabolism that may elicit performance advantages over simple carbohydrate sources during exercise. When combined with amino acids, this protein-carbohydrate mixture may be the most current and up-to-date peri-workout supplement protocol to fuel performance and maximize recovery.

 

Field Rations is a peri-workout supplement that utilizes HBCD as the primary carbohydrate source combined with 10g of EAAs per serving. This article will explore the relatively new carbohydrate source, HBCD, and its utility in peri-workout nutrition protocols when combined with amino acids and their synergistic relationship. Lastly, this article will provide a rationale for its use as the optimal peri-workout protocol based on the current literature. 

Introduction

Peri-workout carbohydrate and protein supplementation has become increasingly popular for athletes across various disciplines. Ingestion of these nutrients can increase athletic performance, glycogen synthesis, and recovery by providing energy substrate and stimulating multiple pathways associated with recovery. 

Exercise is catabolic- the degree to which it depends on the type of exercise 1. Muscle contractions are fueled by both carbohydrate and fat oxidation. As heart rate increases, carbohydrate oxidation is relied upon for ATP production. The increased ATP demand stimulates catabolic pathways that promote cell glycogenolysis and nutrient uptake. Muscle contractions stimulate catabolic pathways that preserve ATP. 

To fuel exercise, stored energy must be relied on. Humans can store seemingly unlimited amounts of fat; however, glycogen stores are more limited and the preferred energy source during exercise. The primary organs that store glycogen are the liver and skeletal muscle. Unique to the liver, stored glycogen can be broken down into glucose and released into the bloodstream due to the expression of glucose 6-phosphatase. Muscle tissue lacks the expression of glucose 6-phosphate, and once glucose enters a muscle cell, it is the cells to keep. Therefore, the liver is solely responsible for rescuing falling blood glucose levels.

The pancreas monitors blood glucose levels and uses the hormones insulin and glucagon to adjust blood glucose levels. When blood glucose begins to fall, pancreatic α-cells respond by secreting glucagon. Glucagon primarily acts on the liver and promotes glycogenolysis. As a result, the liver breaks down stored glycogen and releases glucose into the bloodstream to provide energy. Adult livers can store ~50g-100g of glycogen.

Glycogen depletion is the primary cause of fatigue during endurance exercise 2. Peri-workout carbohydrate consumption restores blood glucose and glycogen levels during and after exercise by providing energy substrate and stimulating anabolic pathways. The International Society of Sports Nutrition (ISSN) recommends 0.7-1.0g CHO/kg/hr during prolonged exercise 3. For a 200lb man, this is ~64 - ~91g CHO/ hr. 

Blood glucose levels rise following ingestion of a carbohydrate solution and stimulate pancreatic β-cells to secrete the storage hormone insulin. Opposite to glucagon, insulin stimulates anabolic pathways, which increases MPS, nutrient uptake, glycogen storage, and blood flow in muscle tissue.

After consuming a sports-drink solution, ingested fluids sit in the stomach until emptied into the small intestine and absorbed. Delays in gastric emptying time (GET) could affect exercise performance depending on the situation and metabolic demands 4, as well as increase the likelihood of GI disorders during exercise 5. The primary factors influencing GET include the volume, energy density, osmolality of the ingested fluid, and exercise 4. 

HBCD has recently become a popular carbohydrate source. Its unique properties, including high molecular weight and low osmolality, influence gastric emptying time and subsequent effects on insulin secretion. Research has shown HBCD to have benefits over other carbohydrate sources, such as increased athletic performance, lower GI-related issues during exercise, and increased glycogen synthesis rates.

During exercise, muscle protein breakdown (MPB) increases and exceeds MPS, resulting in a negative protein balance1. Therefore, for the recovery process to occur, leucine must be ingested to increase MPS over MPB, resulting in a positive protein turnover. 

When branched-chain amino acids (e.g., leucine) are added to peri-workout drinks, there is an increase in MPS. The increase in MPS will lead to quicker recovery in the post-exercise period. Reducing the recovery window significantly improves player performance across day-to-day practice and competition. 

Together, amino acids and insulin synergistically amplify MPS 1. Leucine is shown to increase insulin sensitivity and maximize insulin secretion, while insulin drives amino acids into muscle cells and prevents catabolism. Amino acids and carbohydrates work together to maximize each other's effects and amplify anabolic signaling to achieve maximal rates of MPS. 

Physical Characteristics

HBCD

HBCD comprises glucose monomers linked together through α-1,4-glycosidic bonds and branching α-1,6-glycosidic bonds. HBCD is produced from a series of enzymatic reactions to waxy corn starch with a high molecular weight average of 400,000 g/mol 6 and an empirical formula (C6H10O5)n. In a 10% HBCD solution, HBCD has an osmolality of 9 mOsmol (comparatively, a 10% glucose solution has an osmolality of 646 mOsmol 7). HBCD is efficiently digested into maltose and maltotriose by α-amylase and further digested into individual glucose monomers by brush border enzymes, sucrase, and iso-maltase 8. Glucose is absorbed through the enterocyte primarily by SGLT1 at low concentrations and GLUT2 at high concentrations. 

 

Gatorade 

Sucrose is the primary carbohydrate in Gatorade. Sucrose is a disaccharide comprised of a glucose and fructose molecule bound together. It has a molecular weight of 342.3 g/mol 9, and the empirical formula is C12H22O11. In a 10% solution, sucrose has an osmotic pressure of 313 mOsm 7. Brush-boarder enzyme sucrase efficiently digests sucrose into its monosaccharide constituents, glucose and fructose. Glucose and fructose are absorbed into enterocytes via SGLT1 and GLUT5 proteins. High concentration will recruit GLUT2 proteins to help facilitate absorption.

 

Gastric Emptying & Intestinal Absorption

Several factors affect the rate of gastric emptying post-beverage consumption. The fluid initially sits in the stomach upon ingestion, which acts as a reservoir. Next, the stomach empties its contents into the small intestine, where most absorption occurs. The most significant factors that affect gastric emptying are the total volume, energy density, and osmolality of the beverage and exercise 4. 

Exercise delays gastric emptying and intestinal absorption depending on the intensity of the exercise 10. A study 10 recruited six healthy adult males and had each participant exercise at 40, 60, or 80% of their VO2 max for 40 minutes the morning after an overnight fast. After 10 minutes of exercise, blood was taken, and a 200ml glucose-electrolyte solution containing deuterium tracers was ingested. Blood samples were taken at 2, 4, 6, 8, 10, 15, 20, 25, and 30 min post-ingestion 10.

A solution's osmolality will influence the gastric emptying rate and intestinal absorption. A solution with a low osmolality creates a pressure gradient favorable for rapid emptying from the stomach and optimal intestinal absorption 4.

The luminal contents have an osmolality of ~270-290mOsmol/kg in the fasted state. Ingested contents will influence osmolality. Water and other nutrients will flux across membranes until the osmolality is isotonic. At this point, absorption can occur. The time to make hypotonic solutions isotonic is rapid, whereas hypertonic drinks take much longer and must travel further down the small intestine before isotonicity is achieved and absorption occurs 4. 

For example, it has been shown that hypotonic solutions empty faster than hypertonic solutions 4,7. One study observed water absorption after ingestion of a hypotonic (229mOsmol/kg), isotonic (277mOsmol/kg), and hypertonic carbohydrate-electrolyte solution. All solutions contained the same amount of carbohydrates and sodium yet differed in osmolality. The hypotonic solution was absorbed ~2x as fast as the isotonic solution, which was absorbed ~2x as fast as the hypertonic solution.

One study 7 observed the gastric emptying rates in HBCD and other various carbohydrate solutions at 5 and 10% concentrations. At a 10% HBCD solution, GET was 26.7 minutes. At a 10% glucose solution, GET was 39.9 7.

 

Besides carbohydrate-only solutions, the researchers mimicked a sports drink and added minerals, vitamins, and organic acids, increasing osmolality to 150mosmol/kg. As a result, GET decreased to 21.9 min 7. 

 

In this study 5, gastrointestinal disorders were observed after ingesting sports drinks differing in carbohydrate sources during bicycle exercise in seven untrained men 5. The test fluids included water and three proto-type sports drinks based on HBCD, DE16, or glucose with an osmolality of 150, 269, and 787 mOsm, respectively. The exercise included a warmup of cycling for 3 minutes at three loads, 71, 85, and 99 W, respectively. Participants then consumed the given solution to be consumed within a minute. Next, exercise resumed for 30 minutes, consisting of (3) 10-minute blocks at workloads 71, 85, and 99 w. After the test beverage was consumed, the participants were asked to rate RPE, flatulence, and belching every 5 minutes until the end of the exercise bout. The HBCD-based sports drink resulted in the lowest GET and was significantly faster compared to the glucose-based sports drink 5. The HBCD-based sports drink was associated with the lowest flatulence value and induced the fewest number of belches 5.

 

Muscle Glycogen and Recovery

Muscle glycogen resynthesis rates were measured in drinks containing carbohydrates from high molecular weight (C-drink) and low molecular weight monomers and oligomers (G-drink). The osmolalities of the drinks were 84 and 350 mOsmol, respectively. Thirteen healthy trained men 11 completed 120 minutes of submaximal aerobic exercise followed by short sprints to deplete glycogen stores. Participants then consumed 300g of carbohydrates diluted in 2L water over the next 90 minutes, ingesting 75g diluted in 500ml water immediately post-workout and again at 30, 60, and 90 minutes post-exercise. Plasma insulin and glucose concentrations were monitored every 30 minutes over 4 hours post-workout. The high molecular weight carbohydrate solution restored muscle glycogen at an increased rate compared to the low molecular weight carbohydrate beverage during the first two hours 11. 

 

Exercise Performance and Endurance

In this double-blind, randomized, cross-over study, 24 healthy adult males were recruited to compare the effects of a 15g HBCD solution to a 15g maltodextrin solution during exercise 12. Participants were split into two groups, one consuming each beverage. All participants ate the same meal the night before each lab visit and consumed only water until they reported to the lab at 0900 the following morning. The participants were then instructed to consume bread (2kcal/kg) to prevent hypoglycemia during exercise and rested for 60 minutes. Participants then began exercise on an aero bike bicycle ergometer for 30 minutes at 40% VO2 max and 90 minutes at 60% VO2 max, 120 minutes of total exercise. Each group’s respective beverage was consumed at the 60-minute mark. The rate of perceived effort (RPE) increases during exercise; however, RPE in the HBCD group was significantly less at 30 and 60 minutes post-ingestion.

 

Shiraki

A study investigated the effects of HBCD administration on endurance performance in 7 elite swimmers who participated in the Japanese National Championships in the year prior 6. Each subject took part in 3 total trials, conducted in random order. In each trial, the subjects received either HBCD, glucose at 1.5g/kg BW, or water as a control. After ingestion, they immediately swam ten cycles of 5 minutes swimming at 75% VO2 max, followed by 3 minutes of rest (1 cycle), and subsequent swimming at 90% VO2 max until failure. All subjects ate the same meal the night prior, consisting of 1,010 kcals; 23% protein, 60% carbohydrate, and 17% fat between 2000 and 2100 the night before the lab visit. At this point, no more food and only water are allowed. The participants arrived at the swimming pool at 0630 the following morning. The participants swam at 90% VO2 max with the following results:

• 309.4 + 73.9, 283.7 + 48.2 seconds in the water, glucose group
• 504.4 + 113.3 seconds in the water, HBCD group

The time to exhaustion was ~70% longer in the HBCD trial compared to the water and glucose trials 6.

Blood glucose and lactate levels were also measured. Blood glucose was significantly higher in the HBCD trial compared to water and glucose trials 6.

After swimming at 90% VO2 max until failure, blood lactate was significantly higher in the HBCD trial compared to other trials 6. Increased levels of blood lactate suggest increased rates of carbohydrate oxidation. In anaerobic conditions, pyruvate is converted to lactate. Lactate leaves the cell and travels to the liver, where it is then converted to glucose and returns to the muscle to complete the Cori cycle 13.

Amino Acids and mTOR

Amino acids are the building blocks of protein. Of the 20 amino acids, only 9 are considered essential. They are essential, meaning the body cannot make these and must be consumed through diet. From these 9 EAAs, the body can make the rest of the non-essential amino acids. The branched-chain amino acids (BCAAs), leucine, isoleucine, and valine are 3 of the 9 EAAs. Aside from building blocks, amino acids are involved in various metabolic pathways. For example, the amino acid leucine acts as a signaling molecule and stimulates mTOR, which increases MPS 14. 

Upon ingestion, the gut and liver initially metabolize many amino acids before entering the blood stream 15. However, the branched-chain amino acids are unique because they can bypass metabolism in the small intestine and liver and directly enter circulation at the concentration of ingested 16. From there, leucine can passively diffuse into muscle cells, not requiring a transporter. The body monitors explicitly leucine through the protein sestrin2, which functions as the leucine sensor of the cell. Once a minimum leucine threshold is met, leucine binds to sestrin2, activating mTORC1 and increasing MPS 17. 

mTORC1 is a protein complex that integrates different anabolic stimuli and regulates the rate of growth in cells. There are two mTOR subunits: mTORC1 and mTORC2 18. We will focus on mTORC1 as this complex is more responsive to nutrients such as insulin and leucine. mTORC2 is more sensitive to mechanical stress, like resistance exercise. 

Once activated, downstream targets of mTOR, including ribosomal protein s6 kinase (P70s6k), eukaryotic initiation factor (eIF), and 4E binding protein-1 (4E-BP1), become phosphorylated and initiate mRNA translation at the ribosome 14.

In order for leucine to stimulate mTOR, a minimum plasma leucine threshold is met 19,14. This response requires a 2-3-fold increase in plasma leucine levels 19.  As additional leucine is added, mTOR becomes more stimulated until eventually becoming maximally saturated. Adding additional leucine at this point will not further increase the rates of MPS. Research has shown that 2-3g of leucine can maximally stimulate MPS in young, healthy individuals 20, 21. Older adults have a lower anabolic response to protein and may require 3-4g of leucine to achieve the same anabolic response as younger adults 22.

mTOR is activated by anabolic stimuli such as leucine, insulin, and IGF-1; however, mTOR can be inhibited by catabolic stimuli such as exercise. During exercise, ATP is consumed to fuel muscle contractions. During prolonged exercise, ATP levels decrease, which consequently increases intracellular AMP concentrations. AMP-activated protein kinase (AMPK) is a protein that acts as an energy sensor in the cell, regulated by the AMP to ATP ratio. When intracellular energy levels are low, AMPK is activated. Upon activation, phosphorylation of downstream proteins inhibits mTOR and increases MPB to preserve ATP 1. Other expensive ATP-consuming reactions are inhibited by AMPK, including glycogen synthesis.

Post-exercise, MPB will exceed rates of MPS, resulting in a catabolic state. The type of exercise determines the magnitude; however, both endurance and resistance training result in a net catabolic state. For the recovery process to begin, leucine is required to stimulate mTOR and relieve inhibition of downstream proteins involved in MPS and glycogen synthesis. Therefore, ingesting leucine during exercise will prevent this catabolic state. 

A study 23 compared two groups consuming 10g EAAs enriched with varying amounts of leucine while cycling at 60% VO2 max. The first group’s drink was enriched with 3.5g of leucine; the second’s contained 1.87g of leucine. Results showed a 33% increase in MPS and a ~20% decrease in MPB in the first group compared to the second.

Further, MPS is elevated for about 60-120 minutes after consuming a BCAA supplement, whereas a meal or EAA supplement containing leucine increases MPS for nearly twice as long (about 180 minutes). Peak activation of MPS is proportional to the amount of leucine ingested 14.  

Synergy: Insulin and Protein

Leucine and insulin work in concert to maximally increase MPS by activating mTOR through separate pathways. Together, they feed each other; leucine directly stimulates insulin secretion 24, while insulin drives amino acids into muscle cells and increases blood flow to the muscle tissue 25. 

A study 26 looked at the effects of p70S6K activation after a leucine infusion, an insulin infusion, and a leucine + insulin infusion. Their data shows that p70S6K was most activated when leucine + insulin was infused simultaneously.

Leucine alone stimulated insulin secretion by 1.7-fold (Fig. 2). Similarly, glucose-stimulated the release of insulin 2.4-fold. However, leucine and glucose together elicited a much more significant increase in insulin release by ∼4.5-fold, suggesting an additive effect on insulin release by leucine and glucose 27.

Discussion

Gatorade was the 1st-generation peri-workout protocol invented in the late 1960s containing simple carbohydrates and electrolytes. To this day, it remains the staple sports drink for many disciplines. However, recent advancements in food science have led to the development of the superior peri-workout protocol of HBCD, specifically in combination with EAAs. While research is limited due to the novelty of this innovation, studies conducted so far have concluded an increase in athletic performance and recovery due to HBCD + EAA consumption peri-workout.

Studies have shown that up to 50% of the US population is unable to absorb a 25g fructose load 28, and 80% is unable to absorb a 50g fructose load 29. If following the ISSN recommendations for carbohydrate consumption peri-workout (64-91g CHO/hr for a 200lb man), an athlete choosing Gatorade would consume roughly 32-45g of fructose. This scenario has a higher likelihood of GI disruption and slower GET. This could lead to decreased athletic performance during training or competition and less optimal recovery. 

Field Rations was developed utilizing HBCD as the primary carbohydrate source. Recall the studies referenced earlier; the low osmolality (especially when compared to the primary carb sources in Gatorade) leads to a shorter GET, as well as fewer GI disruptions. An athlete choosing HBCD as their peri-workout supplement may experience an increase in performance and duration due to quicker gastric emptying 10. 

To further aid recovery, each serving of Field Rations contains 3.7g leucine (enough to stimulate mTOR and initiate MPS) and 10g EAA total (sufficient to extend the duration of MPS to ~3 hours 30). Again, recall various studies discussed in this article; leucine is required post-exercise to start the recovery process 1. When leucine and EAAs are consumed peri-workout, in combination with HBCD, athletes can ensure they stimulate the recovery process instead of relying on post-workout nutrition. This eliminates the risk of athletes needing a better understanding of post-workout nutrition or needing access to quality food. 

Based on current literature, Field Rations should be considered the “gold-standard” peri-workout supplement. The powder dissolves in water, making it as easy as Gatorade. In a time of rapid sports science and nutrition innovations, peri-workout supplementation has not yet evolved. Athletes of all ages and disciplines can reap the benefits from a scientifically proven protocol of HBCD + EAAs.

Field Rations Intra-Workout Formula and Education by Justin Harris and Thomas Lackie (Troponin Nutrition)

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