Physiology and Nutrition: Why Not Gels?

energy-gelsWhen we look at some of the biggest issues endurance athletes face, the balance between nutrition and fluid intake to successfully fuel his or her activity without suffering GI distress and delay fatigue rate right up there with proper training and staying injury-free. Different types of upper and lower GI symptoms occur in ~45-50% of endurance athletes. The symptoms may be related to more than one causal factor. The physiology is complex, so the fuel (carbohydrate choices primarily) and fluid you put into your system may compound the problem(s).

The Physiology: When exercise is intense or when dehydration causes hypovolemia (decreased blood volume), exercise induces changes in blood flow by the virtue of shunting blood from the gut to the working muscles. This blood shunt effectively causes a bit of hypoxia to the GI tract and increases neural activity of the submucosa of the gut (the connective tissue). This change to the GI tract increases the secretion of certain hormones and decreases absorption through the intestinal cells. This combination induces diarrhea, intestinal cramping, delayed gastric emptying (extra pressure in the stomach-“slosh” factor), and some bleeding of the stomach and colon may result (which is why some individuals experience blood in the urine and stool).  The common use of anti-inflammatory drugs (NSAIDs, aspirin) aggravate the bleeding and interferes with fluid balance at the level of the kidneys (perpetuating the dehydration issue). Anxiety tends to induce lower GI symptoms and of additional interest, there tends to be a sex difference in symptoms as well.  Women have a 5 time increased risk of diarrhea, intestinal cramping, and side aches as compared to men; men tend to have greater risks of vomiting and nausea. Most of this increased lower GI symptom risk is attributed to the fluctuation of estrogen and progesterone, with a greater incidence of lower GI issues during the 5-7 days preceding menstruation (aka the high hormone phase of the menstrual cycle). But the ingestion of fructose also contributes to women’s GI distress and dehydration.

With energy gels being one of the preferred sources of calorie-dense-easy-to-put-in-the-pocket- fuel-sources, I thought I’d spend some time explaining why these are one of the most detrimental fuel sources for performance…

First, let’s look at the overall nutritional scope. Of a standard gel, the calorie content ranges from 100-120 kcal per serving (typically 33-40g), comprised of maltodextrin and fructose, with a bit of sodium, potassium, flavorings and preservatives. Most usage directions state that a gel must be consumed with 2-4oz water.  Here’s where it starts to get tricky.

In basic terms, a gel is a concentrated carbohydrate: minimum 73% solution (73g CHO per 100ml). By recommending water, the companies are trying to reduce the concentration of this solution. Why? Osmolality and carbohydrate concentration affect gastric emptying: the higher the osmolality, the slower the gastric emptying; the higher the carbohydrate concentration (even mixed sugars), the slower the gastric emptying1.  By the nature of the concentration, a gel will sit in the stomach and increase the osmotic pressure, drawing water into the stomach to effectively dilute this pressure and allow the solution to exit into the small intestines. This is the first place of “effective dehydration”.

The second factor is the carbohydrate matrix of the gel. Research does show that the combination of two sugars is much faster than one for promoting carbohydrate absorption. When fructose and glucose are ingested in combination (either as fructose plus glucose, or as sucrose) the mean oxidized amount of the mixed sugars is ~66%, as opposed to fructose at 29% (women) to 45% (men) and glucose at 58%2.  But the actual absorption rate of the sugars is the contention here: glucose is absorbed from the intestine into the plasma via more than one active glucose co-transporter protein; reducing the contact time with the gut lumen. Fructose, however, is less efficient and slower to be absorbed due to less active transport mechanisms; leading to increased contact time with the gut lumen. Why is contact time significant?  With incomplete and slow absorption, fructose produces a hyperosmolar environment in the intestines. What this means is that there is more solute than water, causing an increased pressure, signaling fluid to be drawn into the intestines, producing the known feelings of bloating, gas, diarrhea, and general GI discomfort.

Maltodextrin, a polysaccharide with the building blocks of glucose, is used in gels instead of straight glucose for several reasons. The primary rationale that maltodextrin does not affect osmolality as significantly as glucose, fructose or dextrose. Because maltodextrin is a long chain of glucose molecules, it doesn’t add as much to the number of solutes in a solution, thus a solution (gel or sports drink) can contain quite a bit of maltodextrin and still have a faster gastric emptying rate. From a carbohydrate availability standpoint, this is appealing as resultant glucose molecules are absorbed through the several glucose co-transporter proteins.  Here is the caveat: because maltodextrin is a long chain of several glucose molecules, it is not completely broken down in the stomach; but continues in the small intestines. In the small intestines3, these multi-chain glucose molecules create the same hyperosmolar environment in the intestines as fructose.

Final words. Why not gels? First, they are a concentrated carbohydrate ingested into a compromised gut (blood flow is diverted to the muscles and skin), increasing the osmotic pressure within the digestive system (read: slow gastric emptying, water drawn into the stomach to aid in the emptying). Second, they are usually comprised of maltodextrin and fructose; the two carbohydrates which create a significant hyperosmotic environment in the small intestines, causing additional water to be pulled into the GI tract to reduce the pressure exerted by the sugar molecules. Why is this significant in the world of training and performance? Fluid loss during exercise is difficult to mitigate and maintain blood volume. Blood volume is critical for sweating and muscle metabolism. Why would you ingest a product that accelerates dehydration and GI distress?


Dr Stacy Sims cofounder of OSMO and Bikerumor contributorStacy Sims, MSc, PhD, served as an exercise physiologist and nutrition scientist at Stanford University specializing in recovery and nutritional adaptations for health, body composition, and maximizing performance. During the past decade she has worked as an environmental physiologist and nutrition specialist for top professional cyclists and triathletes, ultra-endurance athletes, the Garmin/Slipstream Pro Cycling Team, USA Cycling Olympic Team (BMX and women’s track cycling), Team Tibco, Flying Lizard Motorsports, and Team Leopard-Trek, among others. She competes as a Cat 1 road cyclist and elite XTerra triathlete and is co-founder of OSMO Nutrition.

Recommended reading

1. Murray R. The effects of consuming carbohydrate-electrolyte beverages on gastric emptying and fluid absorption during and following exercise. Sports Med, 4(5):322-51, 1987.

2. Sun SZ & Empie MW. Fructose metabolism in humans-what isotopic tracer studies tell us. Nutr&Metab, 9:89, 2012.

3.Lambert G.P., Change R.T., Xia T, Summers, RW, and Gisolfi CV. Absorption from different intestinal segments during exercise.  JAP 83:204-212, 1997.

 

 

 

Subscribe
Notify of
guest

This site uses Akismet to reduce spam. Learn how your comment data is processed.

58 Comments
Oldest
Newest Most Voted
Inline Feedbacks
View all comments
iperov
iperov
8 years ago

lol bcuz too expensive. its 100-200kcal for 2$ every 30 mins.
500$ month for just nutrition, car became cheaper xD

Randall
Randall
8 years ago

I’d like to answer your question with a question: What’s the alternative?

What you’re saying about gels makes perfect sense(to me), except that people need to eat while riding. As a fan of Clif bars, I can’t help but think that the duration of small-intestine gastric osmotic pressure increase would be shorter for a gel than, for example, an almond or a cranberry.

I’m really curious about this too, I have no idea… it seems like risk of GI distress is hard to avoid. All I try and do now is avoid things that are hard to digest, like meat.

skinewmexico
skinewmexico
8 years ago

So if gels are bad, what is good?

Daren
Daren
8 years ago

I have gotten in the habit of taking bananas and raisins on long training rides with very good results. I still use gels in races though because they are just so darn easy to eat.

dicky
8 years ago

Baby potatoes.

BikeAndBrew
BikeAndBrew
8 years ago

So, she basically says that gels are crap but then offers no alternative. I would be very interested in hearing what type of nutrition she recommends that is better for you than a gel. I run marathons, so currently a gel is the only real choice for in-race nutrition. You simply can’t carry around a banana or several clif bars during a race, so you’re kind of stuck with gels. I personally, and runner friends of mine, have ran very fast marathon times using only gels, water, & gatorade as nutrition, so they can’t be all that bad for you…

satisFACTORYrider
satisFACTORYrider
8 years ago

stacy looks annoyed in that pic. props on the raisins. works for me.

Dan E
Dan E
8 years ago

So…..the concept of taking gels with water as recommended is not addressed. I do significant amounts of endurance events, so water every hour is required, as is nutrition. Osmo’s products are designed around hydration, not nutrition.

Also not addressed is that through training, each individual’s ability to absorb nutrition (whatever it may be, gels, powders, bananas, coconut water, pbj sandwiches, etc.) can also be trained.

Fact is, you can’t ride more than a few hours without fluid and calorie absorption.

I agree with other posts, instead of stating what doesn’t work (again), what does work? (absent of product bias)

uglyyeti
uglyyeti
8 years ago

My best ride ever was fueled by gumdrops and rootbeer. Don’t mess with perfection.

j bone
j bone
8 years ago

I always ride with a few pieces of pizza in my jersey pocket. They even heat up and soften a bit when I start sweating really bad.

Agent Phil Coulsen
Agent Phil Coulsen
8 years ago

This is a great analysis, and I’m happy I read it. I agree with other posts though: This article is deficient without the authors recommendations about an alternative.
Furthermore, it doesn’t address the success people have with gels (I’ve personally had success with Clif Shot gels) during long rides or events.
I would be interested in a ‘Part II’ of this article. Thank you!

MB
MB
8 years ago

Homebrew maltodextrin/electrolyte mixed in water bottles works great for me. And many other guys much faster than me. I also know guys that do zero nutrition for anything less than 4hr races and still kick my ass.

Quickie
Quickie
8 years ago

Next your going to try to tell me 1lb of aluminum weighs exactly the same as a 1lb of carbon. I’m onto your lies science.

Matt
Matt
8 years ago

Do isotonic gels improve the situation from a scientific perspective? They’re certainly a lot easier to eat. With most gels, I feel like the water is being leeched from my body while the gel is still in my mouth. I get a similar effect with regular Coke, worse with Pepsi, and with almost any sugary sweets not designed for exercise. But isotonic gels (High5, specifically) cause me no problems.

Wiz without
Wiz without
8 years ago

Gels don’t settle well with me either. What I have been using that works better than ANYTHING I’ve ever tried is my own drink mixture using organic brown rice syrup (about one tblspoon per bottle of watter. BRS is about 45% maltose (releases glucose into the blood faster than plain glucose), and about 50% maltotriose (smallest maltodextrin), and some glucose; no fructose. It isn’t really sweet tasting, so I use a little honey to flavor. BRS is cheap too!

And about the whole osmotic pressure being to high: glucose is small enough to pass through a semi-permeable membrane without a transporter (you can absorb it through the skin in your mouth). Concentrated amounts of glucose may cause some osmosis (water flowing across a semi-permiable membrane from areas of low concentration to areas of high concentration), but glucose will also be pulled into lower concentration gradients by diffusion.

Rick
Rick
8 years ago

My question is then on long rides when you are into fat burn as a fuel you need a certain amt of simple sugar along with O2 to burn fat. Therefore one needs to replenish this sugar store for this efficiency. Also some of the unsettling could be that time where you are turning from carb burn to fat burn which is about the 2 hr mark. If your body is not accustomed to that then you bonk!

dj_pal
dj_pal
8 years ago

Come on ! The girl owns OSMO NUTRITION !

They don’t sell gel. They sell powder to mix with water.

She is obviously has a bias. I don’t mean that she’s wrong, but it’s like a pharmaceutical company pushing a product (or, in this case, bashing another). The pill may be right, but how it is done is wrong.

The Conductor
The Conductor
8 years ago

>>and is co-founder of OSMO Nutrition.<<

Really should have been big and bold under the headline, not the last line…

Sci
Sci
8 years ago

@BikeandBrew & others desiring an alternative

I would recommend reading Alan Lim’s book Feed Zone Portables. It has a really nice, through but easily understandable introduction going over a lot of alternatives to gels for fuel. Essentially he recommends small snacks for long rides that contain easily adsorbed sources of carbs like homemade rice cakes. I’d recommend it to anyone who is interested in learning more about nutrition’s connection to exercise physiology OR anyone who wants to make their own bars/nutrition.

Plug to the publisher:
http://www.velopress.com/books/feed-zone-portables/

Wiz without
Wiz without
8 years ago

@Rick. I think it’s 2 reasons. Carbs are used in the body to transport fat and fatty acids.

The other reason is probably related to the body’s starvation response. Your brain must use glucose for energy (300 to 400 calories/day). Your brain is selfish, if glucose becomes low, other less important systems in your body will start shutting down to conserve resources for the brain (that sudden feeling known as bonk).

stacy sims
stacy sims
8 years ago

(hmmm. I do kind of look annoyed in this picture..reality is that I was freezing cold..)
Ok all- first I ‘m trying to highlight what different
sugars do in your body- not all sugars/carb work the same way. Second- great alternatives are things like blocs, energy chews, glucose tablets , jelly beans for the quick hits of sugar- These are smaller amounts of carbohydrate ingested in more frequent intervals eliminating the slower gastric emptying issue. As for the intestines and pressure issue, these alternatives do
not usually contain maltodextrin or fructose. For longer slower stuff, real food is always the best option(tailor your nutrition to training intensity, duration, environmental conditions..)
And finally, an alternative to those who want gels and water is pretty simple: in every 8 oz water add 1/8th tsp salt (sodium is essential to fluid absorption) and use blocs or chews.

I am happy to write a part 2 if you all would like.

Reynard
Reynard
8 years ago

I know it’s anecdotal evidence, but I’ve never had a single issue with gels and use them regularly in training ad racing. I have had issues with bonking (again anecdotal) when I’ve run out of gels. The 3 studies cited aren’t really damning for the use of gels. I’d say that a relevant, quality study has yet to be performed.

adam
adam
8 years ago

Replace liquid carbs with liquid crabs. Energy of the future circa 2014.

Colin
Colin
8 years ago

Stacy,

Since it looks like you are keeping tabs on this discussion, what are your thoughts about the Pro Bar Fuel and Bolt products?

I have recently switched to using these as a pre/ and during ride energy and have noticed a really difference in sustained energy levels.

dK
dK
8 years ago

This article does indeed raise more questions than it answers. The call for an explanation why other foods are better alternatives is a very valid one,
I thing both Sims and Lim are in the camp of “drink to hydrate and eat for calorie intake”. And all the reading I have done does not explain why it would be better. A piece of pizza or rice cakes would still requite a lot of fluid to be moved into the stomach or intestines to be able to be absorbed, ultimately causing similar problems as gels. And why is a high glycemic index food a problem during exercise? I doubt it causes hyperglycemia and a massice insulin release while you are racing your bike.
I really don’t get it. Is it just marketing or another failed attempt to explain the science to a lay public?

Osteo
Osteo
8 years ago

Good article, and does go alongside what Allen Lim says in his booked as mentioned above, a worthwhile read (FeedZone portables over the FeedZone). Alternates that Allen believes in also mentioned are the rice cakes, small bites of real food. Over the past 2 yrs we’ve been slowly incorporating and experimenting with real food and variations in his recipes, some with success and some with not and have found that what we can take in also depends on the activity we are doing.

As much as there limits to the what can and cannot be absorbed, our tolerance to those effects can differ between people, hence some people are saying that gels work fine and some not so much and then you add in activity, heat, training state, etc…

We do a lot of adventure races (not obstacle course) and real food tends to work well as the pace is slower (24-30hr), as well as when doing long bike rides/training/racing, but it is a fine balance as to what real food works while running and Allen mentions this I believe somewhere and notes that the occasional gel although not ideal may still be useful.

Myself for ultra running I mix between the occasional gel, stinger chew and lots of home made macaroons, it seems to work well for me.

Lanny
Lanny
8 years ago

Gels are crap, pack a pocket full of dates!

jon
jon
8 years ago

Has anyone ever experimented with a water/honey solution? Honey seems like a good carb source to me and is easily diluted in water.

Ron
Ron
8 years ago

Stacy is correct about about that diversion of blood and fluid from the gut to the muscles during activity. This is because evolutionarily speaking during activity we are supposed to be trying to survive from some type of threat, which is never a good time to be sitting around digesting food. The fact that we electively choose to be physically active at high intensities is not conducive to our biology. To be successful at competitive activities we “have to” replenish our glucose requirements. Gels and other sugar replacement products are necessary. And.., its always fun to show off all our biology norminclature to the general public. In other words, So what?

NUNDER1
8 years ago

Gels are crapola and you can eat normal food it works fine and all I eat is some hot cheetos and some whip cream and go………SOUMYEAHXD Pizza is cool c:

Mike Mathewson
8 years ago

Full disclosure:
I am the President of Crank Sports, an energy gel manufacturer (we make e-Gel). I obviously have a biased opinion as I have been in this industry for 12 years and have seen first hand how well energy gels work for endurance athletes, and not just our product … GU, Hammer Gel, Powerbar Gel, etc., they are all very similar and work the same way as far as this article is concerned. The key is that they DO work when used properly. Unfortunately many people don’t know how to use energy gels, and this article certainly didn’t help any! To fully explain I have taken the time to post a complete explanation here:

http://www.cranksports.com/ePower/docs/article.asp?docid=45757

It’s pretty straight forward and I’ll be happy to respond to any questions.

Mike Mathewson
8 years ago

Stacy –
I’m not sure how you concluded that I am not aware or have forgotten that dehydration can impact performance, nothing could be further from the truth. That’s why we recommend PROPER water intake when using gels (not just 2-4 ounces). You may want to go back and re-read my post where I discuss this in detail:

http://www.cranksports.com/ePower/docs/article.asp?docid=45757

I always tell athletes that endurance athletes need three things: water, energy and electrolytes. Of those, water is by far the most important because not only does it keep you hydrated, it is also the transport vehicle for the energy and electrolytes. If you are not prepared to drink your fluids you might as well go home, you’re not going to have a good race.

The problem is that lots of people do not use enough water with their gels, or they try to use a sports dink instead of water with their gels. This is a problem and the athlete usually knows it because they typically will experience sloshing, GI discomfort, etc.

You have recommended using Bloks and Chews, but these are even more concentrated forms of carbohydrate. What ever you eat and drink can’t be looked at in a vacuum, it all ends up as a “soup” in your stomach. If you eat bloks and chews without remaining hydrated (like you are some reason assuming gels users do), then this will cause the same problem only worse. Since chew type products tend to be much higher in simple sugars they require even more water per gram of carb to “move things along”. The chews and bloks also have the additional benefit of containing carnauba wax (yes, the same stuff you wax your car with)!

You also recommended chew type products over gels because they are smaller servings. However, most chew type products contain 200 calories per pack (twice that of a typical gel pack) and it’s not uncommon to eat the entire pack. Likewise, many gel users put their gel in a flask and take more frequent small doses. The portion size is completely in control of the athlete, but yet you have concluded that energy gels are “one of the most detrimental fuel sources for performance”.

generalee2010
generalee2010
8 years ago

Nutrition company owner showdown!!!
(this is when all the other little kids on the playground start yelling “fight, fight, fight!!”, or maybe in our case, “Race, Race Race!!!”)

spokejunky
spokejunky
8 years ago

Good read and I would definitely like to see a part 2 maybe covering glycemic index of foods or how pH affects transport.

devun
devun
8 years ago

when it comes to recreational mountain biking but still riding a good pace…

I throw a 32oz Gatorade mixed with water into my 100 oz camel pack and carry a cliff bar on most of my rides which last from 2-4 hrs…for longer rides I try to pre hydrate and eat a bit more.

If I take a gel its usually well into a ride after I’ve already consumed much water and still have plenty left in the camel pack

Not sure who the target audience is for this article…road racing? mountain biking? weekend warriors?

Basically whatever your using as fuel make sure you drink enough water along with it

Joe
Joe
8 years ago

Part 2? Yes, please.

stream
stream
8 years ago

Interesting discussion. Stacy, can you address the challenge of consuming a chew product or actual food during shorter, high intensity races? It is one thing to consume them during long z2 rides, rest intervals on higher intensity rides, or perhaps even during longer road races when the pace slows. But in a two or three hour xc race, I find it next to impossible to eat chews, let alone real food. It is physically hard to do at high intensity levels and I have no appetite for it. But I can consume gels, and I have never had any significant gastric issues. Without gels, I would have to drink close to 48 oz per hour of your product to get the carbs and calories needed, which would undoubtedly cause gastric problems. Thanks.

Randall
Randall
8 years ago

Stacy, if you’re going to do a part two, one more thing I’d be interested in seeing is the effect over shorter duration efforts.

A CAT5 race will often be only 70-90 minutes long, as can be evening group rides. While I normally mix gatorade powder to about 50% strength (as do others above), on shorter days I mix full strength to get the calorie component, because the dehydration and GI distress are short-lived anyway.

Thanks!

stacy sims
stacy sims
8 years ago

Hey all- Sweet. Part two coming up.

Mike Mathewson
8 years ago

stream –
you’ve nailed the primary benefit of using drinks (or gels) with complex carbs over simple sugars, your body can uptake as much as twice as many calories (twice the energy energy). This has been indisputably proven in independent studies over the past 20 years. Relying just on simple sugars doesn’t allow you to get the energy that you need in longer events as you have pointed out.

stacy –
I admire your persistence that “gels are one of the most detrimental fuel sources for performance” despite the real world data in the form of customers that have been very successfully using GU and other gels for more than 20 years. I too will look forward to your part 2. What would be even better would be if bikeforum.com (or any other forum) would host a higher level debate of this topic, it would be much more beneficial to the athletes.

generalee2010 –
I love to race and when I do I use gel:)

Bridget
Bridget
8 years ago

V8 juice is where it’s at for me on road rides, and on an endurance mtb ride, it’s a can of tomato soup — Soup In Hand (has the ez open top) — has 10 oz of liquid, a ton of sodium, and a ton of carbs. Nothing works better for me!

Psi Squared
Psi Squared
8 years ago

@Mike Mathewson: note that those customers are providing anecdotal data, not real world data. Real data would require measurement of the relevant parameters while holding other parameters constant. It’s certainly not clear what factors influenced those customers’ experiences.

Mike Mathewson
8 years ago

Psi Squared –
Agreed, kind of. My point is simply that there is no shortage of people using energy gels and enjoying success, many of them using just gel and water and setting personal records. To these athletes this is the real world. I’m sure you can try to argue that if they had done something different they would have performed even better, but to these people energy gels certainly don’t seem to be “detrimental”.

Psi Squared
Psi Squared
8 years ago

To be fair, Mike, without data, we can’t say what was a detrimental and what was beneficial in those athletes performances. After all, correlation is not causation, and the history of sport is full of winning athletes who believed in things that weren’t necessarily true. The value in data that Stacey Sims has is that it makes clear what at least some of the physiological responses are to to certain components of gels.

Mike Mathewson
8 years ago

Psi Squared –
There are no shortage of independent scientific data, not anecdotal, to support the benefits of complex carbohydrates for endurance athletes. That said, every person is different and every workout is different, what works for you very well may not work for me. I’m happy to allow the athletes determine what works best for them:)

Will
Will
8 years ago

This was a really interesting article, and I especially enjoyed reading the comments.

I like it when someone backs their products with science, so huge Kudos to Stacy. Allen may be better at instagram, but I will always prefer something that is better thought out vs better photographed. Or, in other words, Annotations FTW.

Unintended take away: gels can be ok if you dont consume it too fast, because even though it may be sub-optimal, it is the consumption of the whole thing at once (over consumption) that really does you in. Which is easy to do, because they are messy and it sucks putting them back into a jersey pocket… but if you find yourself in a situation with a gel packet, and need it, just take it in two or three servings over an hour, never slammed all at once.

Caffery
Caffery
8 years ago

hold up – this article seemingly goes on about the consequences of consuming gels ASSUMING NO ADDITIONAL WATER INTAKE. the logic of her arguments are sound but they seem negated if you just supplement gels with appropriate amounts of water, as the manufacturers recommend – which is true of almost ANY on-the-bike nutrition products, yes? it’s like she’s saying clincher tires aren’t as good as tubular tires because they don’t perform well if you don’t put air in them. no sh*t.