Editor’s Note: Last month’s Physiology & Nutrition post, OSMO co-founder Stacy Sims’ regular column, discussed why she thinks gels are a poor choice for fueling endurance athletes. It’s a good read and generated a lot of comments and questions. It also piqued the interest of several brands known for their gels, one of which sent a rebuttal. As did one of the Peaks Coaching coaches, which serves as their column for this month. Both responses are posted below unedited, as was Sims’ post. 

As an introduction and a little background, we’ve interviewed Sims when OSMO launched. We’ve also interviewed Allen Lim when he launched Skratch and asked similar questions. Then, in preparation for last year’s TSEpic, I interviewed Sims again about food choices. That post has a primer about why solids work when gels may not, which was one of the common questions in the comments. And Sims has already prepared Part 2 of “Why No Gels” which expands on that. Look for it this Friday. In the meantime, here are a few counterpoints to the original.

Dear Bikerumor,

My name is Magda Boulet. I have been a pro athlete since 1997, training and competing with GU product for 17 years now. As the VP of Innovation and R&D at GU Energy Labs, I work closely with athletes of all walks of life who train and compete with gels every day at the highest competitive level. Understanding fueling strategies is essential to my long lasting success as an Olympic distance runner.

As an athlete, a scientist, and a consumer, I am passionate about formulating products and delivering research that are supported by experts in the scientific community and validated by athletes in the field. Having said this, I was disappointed to read the recently published article on “Why Not Gels?” in which the author misrepresented scientific facts and concluded that gels are “the most detrimental fuel sources for performance.”

There are many physiological and nutritional challenges faced by athletes that can have a profound effect on athletic performance. After decades of scientifically validated research and practical athletic experience, I know GU’s sports nutrition products provide a performance benefit to athletes. It is my responsibility as a sports scientist and coach to answer the daily questions of “When, how and what to fuel with?” To be honest, I don’t have one recipe that fits everyone, which is why a comprehensive endurance sports nutrition strategy will take into account an athlete’s current fitness level, environmental conditions, exercise intensity, type of activity, body size, gender, and portability and palatability of sports nutrition products.

GU Energy Gel was developed because endurance runners were facing GI distress from eating solid foods that were not easily ingested and digested during demanding efforts. Gels were designed to be concentrated for a reason, and when consumed with enough water, do not compromise the gut, as the author believes. The article referenced a study that claimed that maltodextrin in the small intestine promotes a hyperosmolar environment similar to that of fructose. However, the study referenced by Lambert, et al., did not use maltodextrin, but instead had athletes consume a 6% isotonic sucrose and glucose solution compared with water in the gut (1).

Maltodextrin is not broken down to any significant extent in the stomach and therefore does not increase osmolality, nor does it promote water influx into the stomach and cause dehydration as claimed by the athor (3). In fact, the beauty of maltodextrin is that the glucose molecules are linked together like cars on a train, and deliver a significant amount of carbohydrates to the body in a way that does not negatively increase osmolality the way free glucose does.

Also misrepresented in the article is the premise that gels cause high osmolality and draw in water. A packet of GU consumed with only 10oz of water contains 22 grams of carbohydrates and 100 calories, and has an osmolality of only 200 mOsmoles. If we chose to formulate our products with only simple sugars the osmolality would be much higher. Osmolality is also not the only factor to consider in intestinal absorption. Carbohydrate composition and the rate of flow of particles in a solution (solute flux) has been shown to be twice as important as osmolality in determining water absorption (2).

Gels have a significant place in the athlete’s nutrition plan. GI distress and dehydration are important issues facing many athletes, but gels are not to blame. Our bodies are not well equipped to consume calories during intense exercise (especially when dehydrated) due to limitations in blood flow to the gut. An athlete’s intensity level during exercise primarily dictates the source of fuel intake that can be tolerated.

Athletes all over the world perform with GU Energy Gels formulated with a blend of carbohydrates and branched-chain amino acids. These are ingredients that are scientifically validated and field tested by athletes of varying abilities. There is not one recipe that works perfectly for everyone, but gels are an option that works for many. I always recommend that athletes balance fuel intake and fluids by training with a combination of drinks, gels, chews, and solids.

Helping athletes find their own ideal nutrition plan so they can pursue and enjoy their endurance lifestyle is my passion. Thanks for reading and keeping an open mind while thinking critically about your performance nutrition options.



VP of Innovation, Research & Development – GU Energy Labs


  1. Lambert GP, Chang RT, Xia T, Summers RW, and Gisolfi CV. Absorption from different intestinal segments during exercise. J Appl Physiol (1985) 83:204-212, 1997.
  2. Shi, X, Summers RW, Schedl HP, Flanagan SW, Chang R, and Gisolfi CV. Effects of carbohydrate type and concentration and solution osmolality on water absorption. Medicine and science in sports and exercise 27:1607-1615, 1995.
  3. Vist GE, and Maughan RJ. The effect of osmolality and carbohydrate content on the rate of gastic emptying of liquids in man. J Physiol 486 (pt 2):523-531, 1995.


By Chris Myers, PCG Elite Coach

As a triathlon/cycling coach, exercise physiologist, and researcher, I firmly believe my athletes should have all the information possible in order to make educated decisions to optimize their training. In the field of exercise nutrition, science can prove one thing with one body of research while disproving the same point with another, so when my athletes look for nutrition supplements, I try to give them as much data as I can.

Any nutritional supplement needs to be used within its boundaries. For example, you shouldn’t drink a carbohydrate (CHO) mix as a substitute for eating to get calories during a long workout. There is a saying that “one should drink to drink and eat to eat.” What this means is that during exercise we should drink liquids to stay hydrated and eat food for calories to make energy. The use of gels is a staple for many endurance athletes as a quick source of energy, because gels offer the dual avenues of energy transport via maltodextrin and fructose absorption combined with proper hydration for moderate to high moderate exercise.

Gels are sometimes given a bad rap as a common source of dehydration. This is not the case, however. Both dehydration and hypovolemia (decreased blood flow) are mainly caused by thermoregulation of body temperature during prolonged exercise and environmental factors, not gels, and I’d like to explain why I advise my athletes to use gels.

As part of any endurance exercise at or below threshold (usually <75% of VO2Max) for an extended period of time, dehydration becomes an issue. Loss of water, whether from environmental or biological factors, reduces blood volume, more particularly blood plasma (hypovolemia), thus increasing the viscosity (thickness) of your blood. Hypovolemia causes a decrease in venous blood return (end diastolic volume, or EDV) to the heart, which causes a decrease in the amount of blood ejected from the heart to the arteries in a single heartbeat (stroke volume, or SV) (Oöpik, Timpmann, Burk, & Hannus, 2013). Overall, this decreases the most important factor, cardiac output (Q) (Powers & Howley, 2011; Smith & Fernhall, 2011).

Cardiac output (Q) is defined as the amount of blood ejected from the left ventricle of the heart in a minute’s time. Mathematically, Q looks like this:

Q = heart rate (BPM) x SV
(Powers & Howley, 2011)

During exercise this becomes very important. Q needs to be kept at a high rate during prolonged endurance exercise to meet your body’s respiratory demands. When your stroke volume drops, your heart rate increases to compensate to keep Q at the required levels to meet your exercise intensity (Myers, 2001). If a decrease in blood volume causes a significant decrease in stroke volume, your heart won’t be able to compensate and performance will decrease (Bassett & Howley, 2000; Myers, 2001).

The maltodextrin and fructose in a gel do require water for digestion, but not in excessive amounts. This is why it’s important to read the instructions for each product and understand the implications. For example, the printed instructions for GU gels state:

1. Wash down GU down with a few gulps of GU Brew© or water.
2. As a guideline, drink 20-24 unces of fluid per hour throughout training and racing.

Hammer Nutrition gives similar instructions for their gel product:

“Consume 0.5-2.5 servings per hour, along with 16-28 ounces (approximately 475-830 ml) of plain water per hour from a separate source.” (

Other products include similar language. Essentially you need to drink 2-4 ounces of water with a gel for initial digestion of the gel. However, each product’s instructions also specifically state that you should continuously consume water, not just when you initial take the gel.

It is well established within the realm of academia and athletic performance that rate of hydration is dependent on both the intensity of our exercise and environmental factors such as heat, humidity, wind, etc. The constant loss of water via sweat is part of thermoregulation, and dehydration-induced hypovolemia is not caused by the ingestion of gels. It’s typically recommended that we drink a minimum of 16 ounces of water or an 8-10% CHO mix every 30-60 minutes during exercise. This is where the saying “drink to drink” comes into play. You must be aware of your rate of water loss. When you lose water in an amount greater than 3% of your body weight, your endurance performance starts to decrease (Goulet, 2012). For cyclists this means a decrease in wattage, and for triathletes this means an increase in swim and run pace times.

It is ultimately up to each individual athlete to answer the question, “Do the benefits of gel products outweigh the risks?” Gels do use water as part of the digestion process, but it isn’t enough to cause dehydration and hypovolemia. The dual delivery of fast and sustained energy is an attractive benefit of using gels, though as with anything else, they should be used in moderation.

As with any product containing fructose, gels can potentially cause GI issues. When too many gels are ingested in a short period of time, there isn’t enough time for the fructose to digest, which is the main cause for GI issues with gels. So where do we draw the line? Each of us has to answer that for ourselves, but as a coach, I advise my athletes to eat solid food in combination with gels. As an athlete and consumer, I strongly recommend reading each supplement’s instructions prior to using it. As a junior researcher, I advise all my athletes to stay informed and to investigate the research aims (and possible conflicts of interest) of all supplements and over-the-counter nutritional products.

Bottom line? Gels are a good source of energy as long as they’re taken as intended.

Peaks Coaching Group Chris MyersChris Myers, M.S., is a certified TSAC-F (Tactical Strength and Conditioning Facilitator), a USA Cycling Level 2 coach, a USA Swimming Level 2 coach, a USA Triathlon Level 1 coach, and a Peaks Coaching Group Elite Coach. Additionally, he is a second year doctoral student studying exercise physiology in the Department Nutrition, Exercise, and Health Sciences at Florida State University and is the head coach for the FSU Triathlon Team, Trinoles. He and the other PCG coaches create custom training plans for all levels of athletes. Chris can be contacted directly through



Bassett, D. R., & Howley, E. T. (2000). Limiting factors for maximum oxygen uptake and determinants of endurance performance. Medicine and Science in Sports and Exercise, 32, 70–84. doi:10.1097/00005768-200001000-00012

Goulet, E. D. B. (2012). Dehydration and endurance performance in competitive athletes. Nutrition Reviews, 70 Suppl 2, S132–6. doi:10.1111/j.1753-4887.2012.00530.x
GU Gels. (2014).

Hammer Gel – Carbohydrate Energy Gel | Hammer Nutrition. Hammer Nutrition. Retrieved May 15, 2014, from

Myers, J. N. (2001). The physiology behind exercise testing. Primary Care – Clinics in Office Practice. doi:10.1016/S0095-4543(05)70005-1
Oöpik, V., Timpmann, S., Burk, A., & Hannus, I. (2013). Hydration status of Greco-Roman wrestlers in an authentic precompetition situation. Applied Physiology, Nutrition, and Metabolism = Physiologie Appliquée, Nutrition et Métabolisme, 38, 621–5. doi:10.1139/apnm-2012-0334

Powers, S. K., & Howley, E. T. (2011). Exercise Physiology: Theory and Application to Fitness and Performance. Ed Human KineticsPub Champign (8th ed., Vol. 4th, p. 640). New York City.
Smith, D., & Fernhall, B. (2011). Advanced Cardiovascular Exercise Physiology – Denise L. Smith, Bo Fernhall. Champaign, IL: Human Kinetics. Retrieved from


  1. I’m glad that someone that works for GU thinks I should buy their product. Toyota wants me to buy their trucks and Levis wants me to buy their jeans.

    See the problem with peppering a report with your own trademark’d product name?

  2. I think Magda has some solid advice, and she does admit, ” To be honest, I don’t have one recipe that fits everyone, which is why a comprehensive endurance sports nutrition strategy will take into account an athlete’s current fitness level, environmental conditions, exercise intensity, type of activity, body size, gender, and portability and palatability of sports nutrition products.”

    The additional information from Chris Myers backs up what she’s saying without mentioning any specific products.

  3. And the author of last month’s post denouncing gels co owns a company that makes powders. There’s your bias as well.

    I can be the most cynical of New Yorkers which means I don’t believe anything at first. But I do know 10 minutes after consuming a gel I feel much better. But to each his own.

  4. Never found hammer nutrition, GU, or others ever letting me down on a ride. Ever.

    The Osmo stuff tastes terrible. If I ever need to drink calories it’s going to be perpetum by hammer (which actually has flavor). Or I’ll just man up and drink beer. Works for those crazy natives from Mexico. Works for me.

    Ride ride ride. That’s all you need to know. Ignore the BS, find what works for you, and rock on.

  5. @Justin!, and if that inhibits you from sussing out the evidence she offers, than maybe you should work on your critical reading skills.

    I don’t particularly like the marketing mixed with Mada’s rebuttal, but that doesn’t inhibit me from understanding the scientific basis of her argument.

  6. Both actually reference scientific studies, and state that nutrition and hydration are not mutually exclusive and require balance…balance that is tweaked according to the individual athlete combined with environmental factors.

    I do know that eating sandwiches and sodas available during most gran fondus works for those people who don’t look like they ride, and for whom the century takes 9-10 hours.

    I’m looking forward to the article that states solid food is better than gels…although I do know a few guys that race on cheeseburgers.

  7. Nerd fight! This is an interesting series of articles. I am a big fan of Osmo because that hydration/nutrition strategy works for me, but I want to hear all sides of the debate and let people make up their own minds and try different approaches. A great result of this debate is the renewed focus on hydration as being critical to performance, not just fueling.

    Note that the amount of water recommended with the gels is a lot….more than the standard 16oz bottle an hour most athletes drink on the bike. Most of the folks I ride with don’t drink enough regardless of what is in their pockets/bottles.

  8. GU Salted Caramel is my new favorite flavor. I only use GU or any other gels when riding and space the intervals recommended by each vendor. I have yet to experience GI distress due to consuming gels.

  9. I go back and forth when it comes to what I eat on the bike…. alternating between Skratch labs drink, rice cakes and other portables one time, then maybe just Skratch Labs and gels the next ride. I’ve never had any GI issues going either route, as long as I’m drinking enough fluid.

    I think it’s great that BikeRumor is doing a series of ‘competing’ views on this subject, seeing as how it can only benefit us in the long run. The more you know about the ways you can fuel yourself, the better you can tailor your own nutrition. We all win in the end.

  10. Ultimately it comes down to absorption. Some can tolerate more than others. That is why it is important to test and figure out what is tolerable per individual.

  11. I am no scientist but I have had a few rides where I had an amazing “second wind” after downing a gel.

    I read the first post complaining about dehydration, which I think is funny because if I am exercising, I am already dehydrating. And I am going to drink something whether it is bar or a gel.

  12. Excellent articles. It is obvious there is no one perfect answer that works for everyone. For me, the nut I have yet to crack is to figure out my nutrition for endurance racing (5+ hour races) – biking or running. I can train for hours and eat and drink pretty much anything without any problems. But put me in an endurance race and it is completely different story. Almost always end up with some GI distress that make the last few hours miserable and with me unable to consume pretty much anything. One obvious answer is to train at race like pace and figure out what works, but it is hard to replicate actual race conditions in training, from the stress, to the inadvertent pace change to match the competition, etc. Of course I could take it easier on race day, but where is the fun in that.

  13. Great work BikeRumor, I think this fits the everything in moderation rule and more specifically what works best for each individual. I have had good luck with gels for years and just make sure to consider hydration before, during and after. Pedialite the night before a big ride or race is one of my favorite ways to avoid dehydration while riding.
    I’m also a special case study and hypersensitive rider/racer when it comes to nutrition, due to having my large intestine removed to acheive a cure for Ulcertive Colitis a few years ago. I have not experienced any ill affects from using gels and honestly would find it hard to supplement there noticeable benefit. Science is great, but everyone should thoughtfully see what works best for them when it comes to energy food supplements. That said, without an inovative company like GU, we would all be choking down those awful original PowerBars!

  14. I’ve never bonked worse than 30 minutes after eating a GU gel. My professional, licensed nutritionist with over 30 years of experience recommended brown rice syrup, as it gives you a more even energy surge. You can buy big jars of the stuff at the grocery store. Blend it up with fruit, cocoa powder, finely ground coffee … whatever your taste buds desire. Put it in a water bottle or flask. I did a century ride on Saturday eating nothing but my blend for five hours and had plenty of energy.

  15. ok Magda, here’s a tip: when claiming to be a scientist, you need to tell us at a minimum where you earned your phd and in what exactly. As far as I know, you aren’t really a scientist. Also, claiming to be a “professional athlete” doesn’t mean anything. You could be a pro ping pong player for all we know – not someone we’re likely to take nutrition advice from. You say later “olymipic distance runner”, again, is that a marathon or a 100m?
    when you state your qualifications that vaguely, they sound exaggerated and it makes it difficult to believe what you have to say

    Overall, your title sounds like “director of bullsh… I mean marketing [that’s what marketing is]”, your qualifications are not stated, and you clearly have a conflict of interest since your employer does nothing but make gels.

    and I’m not 100% against summary executions for people that toss/drop gu wrappers on the side of the trail.

  16. Well this athlete SHOULD NOT use gel’s according to my wife’s edict. The result of ingesting even one gel per ride will result in the most foul smelling odors for up to 8 hours after. Dubbed the lethal “GU Gas.” In my opinion if you train with gels, ride and eat with gels. Should you be a 5 hour a week rider such as myself, the gastric discomfort CAN be ruinous for your ride.

  17. This is a response to “i” — please note that I do publicity for GU and have for years, and have enjoyed this healthy debate on Bikerumor and in the comments in particular.

    I’m responding to this ad hominem attack for two reasons: first, because it is so tone-deaf and so contrary to the discourse on this board and on this subject. I don’t know what ax you’re trying to bury, “i” — but you come across like a pure troll.

    Secondly, I’m responding because Magda shouldn’t have to. She doesn’t need to trot her accomplishments in front of her like a banner because: Google. Magda represented the United States, in the marathon, in Beijing in 2008. “i” — I assume that’s meaningful enough for you? Feel free to share your highest level of athletic accomplishment. This year, she won the Way Too Cool and theCayuga Trails 50k last week, and was the #1-ranked American marathoner as recently as 2010.

    Magda earned her undergraduate degree from UC Berkeley in human biodynamics, and her Master’s from Cal State Hayward in exercise physiology; she’s worked in applied science for GU for years.

    Lastly, Magda clearly stated her subjectivity: she works for GU. So do I, though not as an employee. Her reply is no more a conflict of interest than Stacy Sims’ original post. Who do you work for “i’? Why would you post anonymously?

    Finally, as a refresher, you should read the Commentary Policies of this website

    To everyone else: sorry to feed the trolls, but this really pissed me off — not the least because as anyone in the running world can tell you, Magda is a dear, dear woman and a true professional.

  18. I use GU (and don’t work for them)… works great and i continue to use it because
    it provides what i need when i need calories with zero stomach issue. I have had other gel brands bother my stomach. I use SKRATCH labs drink. I found drinks that have lots of calories bother me. So i hydrate/sodium from liquid and calories are from GU or Rice cakes and solids. On the bike i like rice cakes and some solids. I ran the Leadville 100 and i completely believe that GU kept me on point the while way…I ate one every 45min. for 20hrs. (yes it got nasty, but effective, and no stomach issues)

  19. I believe the GU guy. The other ones sound like they do not now what they are talking about – pseudo science gibberish.

  20. @Sevo: Indeed, Osmo tastes terrible. I prefer clean water in my water bottle – and electrolyte tablets and gels and bars for nutrition. Goes smooth and good variety.

  21. @Gordon Wright: Here you go. But those credentials should have been noted in the introduction to this article.

  22. I don’t use GU gels cos the amino acids in them is derived from CHICKEN FEATHERS!

    I use Torq, Cliff, High 5 & Hammer gels instead. I want to eat carbs, not ground up chicken feathers!

    100g of Dates per hour or 100g of organic sugar in water also works.

  23. This is a lively discussion regarding fueling choices. I have no issues with gels and have been a GU fan since inception. But along with the discussion on energy sources, there’s quite a bit of dated dogma regarding hydration requirements during exercise being bandied about. Anyone taking the time to read and comment here should read Waterlogged by Tim Noakes. The information there is equally as compelling as our discussion here.

  24. To the person who was questioning Magda’s credentials as an athlete, she did give you her name. Why don’t you do a little research before posting such silly questions? When someone says they are an olympic distance runner that kind of throws out the 100m don’t you think? Not only is she a USA olympic marathoner, a few weeks ago Magda won the USATF 50 Mile Trail National Championships! Yes 50 miles and not 50K! Do some research and you’ll probably become one of her fans. She is pretty amazing! 🙂

What do you think?