Multiple Carb Transporters - rethink your sport nutrition

 

The ideal fueling strategy during training/racing is the consumption of carbohydrates in a way that can be quickly emptied from the stomach, be rapidly digested and quickly absorbed so it can be used by the working muscles.  Just because you are consuming a gel, bar, solid food or drink with carbohydrates, this doesn't mean that your muscles are receiving those carbohydrates. The takeaway from this is not all carbs are the same.

Exercise shifts blood flow away from the GI (Gastrointestional tract) towards the active muscles and lungs. Digestion is compromised during exercise. This is why it's important that your carb choices during exercise do not require a lot of digestion. The quicker and easier those carbs are emptied from the stomach, the quicker those carbs can be used by the active muscles. Also, the more digestion that is required, the greater risk for GI issues. 

After digestion comes absorption. For the muscles to continue to perform during long distance activity, absorption moves nutrients, water and electrolytes from the small intestines into the cell and then into the blood. Because cell membranes are careful not to let dangerous substances into the body, they make it difficult for nutrients to enter the body. Therefore, nutrients need the help of a transporter (protein) to move across the cell membrane barrier. For carbohydrates to be absorbed, a transporter takes the digested and broken down carbohydrate from the intestional lumen inside the intestine, through the intestinal wall and into the body circulation. 

There are two specific protein transporters (SGLT1 and GLUT5) that allow for carbohydrate absorption. When your sport drink contains glucose, sucrose, galactose, maltodextrin or starch, exogenous carbohydrate oxidation peaks ~60g/hr (~240 calories). This is because the SGLT1 transporter becomes saturated ataround 1 gram of carbohydrate per minute. This is very important because if your sport drink, bar, or gel contains only the carbohydrates listed above, consuming more than 60 grams per hour will not result in more carbohydrate oxidation. The excess carbohydrate will not be absorbed and will accumulate in the intestines. This means the muscles will fatigue despite continuing to consume a large amount of carbohydrates and the risk for GI issues increases dramatically.

Because fructose uses a different transporter (GLUT5), the additional of fructose to a sport drink will allow for higher oxidation rates (up to 90g/hr) so long as you saturate the SGLT1 transporter with 60 grams of glucose or maltodextrin. Because these carbs use different transporters, you can deliver more carbohydrate to the muscle per hour.

If you are simply consuming carbohydrates without the awareness of how much you are consuming, what types of carbs you are consuming and how often you are consuming them, there's a good chance that you are not optimizing absorption - which means a greater risk for bonking, early fatigue, dehydration and GI issues. 

According to research, the ideal combination of carbs include: 

• maltodextrin : fructose 
• glucose : fructose 
• glucose : sucrose : fructose

If you are trying to consume more than 60 grams of carbs per hour (which is around 240 calories), you need to consume a product with multiple transportable carbohydrates so that you don't clog the SGLT1 transporter. 

Because most endurance athletes will benefit from consuming between 60-90g of carbohydrates on the bike per hour, I put together the helpful chart above to help take away the guessing when trying to plan how to fuel based on the duration of your workout/race.

To increase the capacity to absorb carbohydrates, it's critical that your sport drink has the right formulation. Simply eating/drinking whatever you want, whenever you want, does not guarantee that what you are consuming is being digested and absorbed.

Sport nutrition for endurance athletes - recent research and tips (part 1)

Ironman Lake Placid 7.28.13

There's no better feeling that putting all your hard training to good use on race day and having a strong race day performance.

Ironman World Championship 10.12.13

But if there was one factor that would make or break an endurance athlete's "perfect" race, most athletes would blame their performance on nutrition (or, perhaps how often they saw the inside of a port-a-potty). 

I work with a lot of athletes on nutrition, specifically sport nutrition. I find that most athletes are not in need of nutrition help to enhance performance but instead, performance is limiting because of nutrition. 

You see, there's a big difference between the two. For most age-group athletes, sport nutrition is another confusing topic that is thrown into the mix of understanding how to eat "healthy" on a daily basis. Among the athletes that reach out to me for nutrition help, the majority have some issue with nutrition/fueling/sport nutrition that is negatively affecting performance. Or in other words, the athlete feels limited in performance because of some area of nutrition. Because it's easy to jump into endurance racing by simply following a training plan, many athletes struggle to understand what they need before, during and after workouts in order to meet hydration and energy needs, to reduce GI distress, to postpone fatigue and to enhance recovery. I find that many athletes struggle with fueling in different phases of a periodized training plan, particularly because of the change of intensity and duration of workouts and even more so, a change of weather or training environment. 

The athlete who has worked hard on his/her fueling regime and has nailed down how to properly fuel before, during and after workouts may reach out to me in hopes to enhance performance. This athlete may not have any red flags but through some experimentation and looking beyond the obvious, I can help an athlete take an already strong and fast body, to that next level. 

In the Spring 2014 issue of SCAN's PULSE (Vol 33, no.2) there was a great section on Sport Nutrition Conference Highlights from a Sport Nutrition Conference on Nutrition Support for the Marathon Runner (sponsored by PowerBar/Nestle Nutrition Institute) with speakers sharing their latest research. 

If you feel you are in need of some nutrition help to help your training routine, it's recommended to reach out to a RD who specializes in sport nutrition so that you can find yourself enhancing performance and putting all your training to good use on race day. 

Here are a few highlights from the conference:

Preparing for the Olympic Games Marathon - tips from Louise Burke, PhD, from the Australian Institute of Sport

In elite runners, about 85% of energy used during a marathon comes from carbohydrates; during surges, closer to 100% of the energy comes from carbohydrates. Because marathoners typically have enough stored carbohydrate (glycogen) to lat about 20 miles, they need to both carbo-load as well as consume carbohydrates during the marathon. 

Consuming a low-residue diet for 2-3 days prior to a marathon helps to minimize intestinal contents (and hence, the need for bowel movements) and body weight. This is a good time to eat white bread and white pasta. On the day before the marathon, some elite marathoners carbo-load primarily with hard candies and liquid carbohydrates. The loss of body weight might counter the gain in water weight associated with the storage of extra glycogen. 

A runner who is well carbo-loaded can gain water weight equating to about 2% of body weigh (ie 3lb for a 150-lb runner). While this additional water weight can offer hydration benefits during a full marathon, the added weight could be detrimental during a faster-paced half-marathon. 

Caffeine is a popular ergogenic aid for runners and can be consumed both before and during endurance exercise. If runners are nervous before the event, they might want to consume the caffeine only during the event before the onset of fatigue. 

During the marathon, the suggested intake of 30-60g of carbohydrate per hour has been updated to 60-90g carbohydrate per hour. Because elite marathoners find it difficult to drink and run (some may consume only 0.3L per hour) they consume concentrated carbohydrates in the form of gels or concentrated drinks. 

"Drink early, drink often" helps to keep marathoners from becoming dehydrated so they will be stronger at the end of the event. Runners should try to drink enough to minimize the fluid deficit to to less than 2 percent of body mass. A study of athletes with a defined food and fluid strategy indicated that they performed 6 percent better in a 40-K time trial compared with those who raced ad libitum. The message: Plan ahead! 

When a runner with intestinal distress cannot tolerate any more carbohydrates or fluids, swishing and spitting can be a positive tactic to help maintain performance. 

Stressed runners often experience diarrhea and urgency to defecate. Nestle's research on subjects with gastrointestinal (GI) issues indicates that people who are less stressed have fewer GI issues. 

After a marathon, the majority of elite runners experience diarrhea. That's because during the marathon, blood shunts away from the intestines and to the muscles - but once exercise stops, the blood flow returns to the intestines, along with a lot of water. This contributes to urgency to defecate. 

Alcohol suppresses post-exercise protein synthesis and can hinder recovery. The wise path is to have a healthful, alcohol-free diet for the first 8 hours of recovery.

Caffeine as an ergogenic aid in endurance sports, John Hawley , PhD from Australian Catholic University

Caffeine is an exceptional ergogenic aid. It is effective for a wide range of athletes, from rowers (who work for 5 min) to Ironman triathletes (who exercise for hours) to Tour de France cyclists (who perform multiday events). 

Historically, caffeine was thought to aid performance by enhancing fat burning, which in turn would spare limited glycogen stores. We now know caffeine's bigger effect is on the central nervous system; caffeine makes the effort seem easier. 

Historically, 6 mg - 9 mg of caffeine per kg body weight was thought to be the effective dose. We now know less is fine and the current recommended dose is 2 mg/kg body weight to 3 mg/kg body weight taken 1 hour before exercise. Due to genetic differences, some athletes metabolize caffeine quickly and others are slow metabolizers. As with all ergogenic aids, some people respond more than others. 

Athletes do not seem to habituate to caffeine. That is, regular users and abstainers get the same benefits. 

During an event, athletes wold benefit from ingesting caffeine before they feel fatigued. 

If caffeine interferes with sleep, athletes should be warned that sleep is more important and they should use lower doses of caffeine. 

Hawley reminded us that food is the key message. No amount of caffeine or any other ergogenic aid or supplement will ever substitute for a scientifically-based and aggressive training and nutrition program, nor will caffeine overpower depleted glycogen stores. Hawley also emphasized the list of effective ergogenic aids is quite short (despite popular belief); caffeine, carbohydrates, protein, and sodium bicarbonate.

Nitrate as an ergogenic aid, Andrew Jones, PhD from the Universty of Exeter UK

Dietary nitrate breaks down during several steps into nitric oxide (NO). NO regulates blood flow and vascular tone, making exercise easier due to enhanced oxygen availability and uptake. Nitrate can reduce the oxygen cost of exercise by 5 percent and improve performance by about 3 percent. An athlete would have to train very hard to achieve that same beenft. As with all ergogenic aids, some athletes will improve more than others. The rapid growth in sales of beetroot juice supplements (18 times more in 2013 than 2012) suggests the supplement "works."

Non-elite athletes are likely to enjoy more benefits from dietary nitrate than highly trained, elite athletes, perhaps because elite athletes have already "maxed out" their ability to improve. 

Nitrates are found in beets, as well as spinach, bok choy, arrugula, celery and lettuce. For homemade beetroot juice,  blenderize (or juice) a pound of beets and add some pineapple (to mask the taste of the beets and enhance flavor). 

The ergogenic effects of beetroot juice peaks in 2-3 hours. It is used primarily for endurance psorts but has been shown to improve the performance of soccer player by 4 percent, with 13 of the 15 players in the research study performing better. 

Beetroot juice might be helpful for athletes who train and compete at altitude. Stay tuned for more research. 

The conversion of nitrate into NO starts with bacteria in the mouth. Warning: Do not use mouthwash if you are using beetroot juice. 

Nitrates are good for overall cardiovascular health as well as for performance. People with cardiovascular disease who take beetroot juice can more easily walk up stairs: this improves their quality of life. 

Stay tuned....more research tips will be posted!

Energy and nutrient deficiencies in female endurance athletes

Marathon training strategy periodization and diet
Clinical issues in endurance athletes

Protein and weight management in long distance runners