The Real Reason Endurance Fueling Got So Good (Hint: It's Your Gut)

By Nick Klastava a USATF and RRCA Certified Running Coach of over 9 years.

You have already upgraded your shoes. Somewhere in the last few years you (or the runner next to you at the start line) dropped a couple hundred bucks on carbon plates and springy foam, because the research was very clear. Super shoes are worth roughly 4% in running economy, and that is free, legal speed. Nobody argues about it that anymore, we just ended up buying the shoes.

That however is not where it stops. The next big chunk of free, legal time is not on your feet, it is in your fuel belt. The advances in endurance fueling over the last decade have stacked up into a bigger available gain than anything happening in footwear right now, and the wild part is that most runners have not claimed a cent of it. You banked the shoe gain years ago, but the fueling gain is still waiting for you.

And just like super shoes, the story is not about one magic product. It is about technology finally solving a problem your body has had all along.

Fueling for endurance sports has changed more in the last ten years than in the previous fifty. We went from "grab a gel and hope your stomach cooperates" to dual-source carb gels, hydrogel delivery systems, bicarbonate you can tolerate, and now lactate gels showing up at the Tour de France. It's a lot all at the same time. And most of the coverage treats each new product as if it unlocked some hidden metabolic superpower.

It helps to remember where we just came from. A few years ago, smart money(I didn't believe it personally) was betting the exact opposite direction. Keto and fat-adaptation were supposed to be the future, the idea being that if you trained your body to burn fat you could wean yourself off carbohydrate and never bonk again. Train low, race low, free yourself from the gel. Then the racing caught up with the theory. The fastest humans on earth did not get faster on less fuel. They got faster on absurd amounts of it. The pendulum swung all the way back, and "carbs are king" won decisively. Almost everything below is because of that swing. Once the goal became cramming in more carbohydrate instead of less, the whole industry pivoted to solving one problem: how.

The thing is, your body already knows how to do most of this. Your muscles have always been able to burn carbohydrates, buffer acid, and use lactate as fuel. That is not new. What changed is our ability to get enough of the good stuff past your stomach without wrecking your gut. Nearly every fueling advance of the last decade is a solved delivery problem dressed up as a metabolism breakthrough. Once you see fueling that way, the whole landscape gets a lot easier to navigate, and a lot easier to spend money on wisely.

So, let's walk through it, from the stuff that genuinely changed the game to the stuff that is mostly buzz. I am going to sort these by how strong the evidence is, because "new" and "proven" are not the same thing.

Tier 1: The actual revolution (dual-source carbohydrates)

If you only take one thing from this entire post, make it this section. For efforts over 90 minutes, you want 60 to 90 grams of carbohydrate per hour, and trained runners can push toward 120. Multiple transportable carbohydrates are the single biggest thing to happen to endurance fueling, and it is not close.

Here is the mechanism that you want to understand. Glucose gets absorbed through a specific intestinal transporter called sodium-glucose cotransporter 1 (SGLT1), and that transporter has a speed limit. It saturates at roughly 60 grams per hour. Push more glucose than that and it does not magically absorb faster. It backs up in your gut, pulls water in behind it, and hands you the sloshy, cramping, "why did I do this" feeling you already know too well. For decades, 60 grams per hour was considered the ceiling for a reason.

Then someone asked a smart question. What if we added a second type of sugar that uses a different door? Fructose is absorbed through a separate transporter, glucose transporter type 5 (GLUT5), so it does not compete with glucose for space. Open both doors at once and you can move a lot more fuel. Studies have shown up to 65% higher carbohydrate oxidation with a glucose-fructose blend compared to glucose alone, reaching about 1.75 grams per minute where 1 gram per minute was once assumed to be the hard limit.

This is the part that matters for anyone with a nervous stomach, which is most of us. The two-transporter approach does not just let you eat more, it tends to make it feel better. The extra fructose pathway improves fluid delivery and empties the gut faster, so the risk of GI distress goes down, not up. That is the whole magic trick. More fuel, less misery, at the same time.

Almost every fueling advance of the last decade is a solved delivery problem dressed up as a metabolism breakthrough.

On the ratio question, the old-school recommendation was 2:1 glucose to fructose, and you will still see that number everywhere. More recent work points to a ratio closer to 1:0.8 as the sweet spot when you weigh absorption, gut comfort, and performance together. Honestly, for most runners the exact ratio matters less than the fact that your gel or drink mix contains both sugars at all. Check the label and if it only lists one carbohydrate source, you are leaving fuel (and comfort) on the table.

It is also not just how much carbohydrate, it is what kind, and this one shows up on labels now. A lot of the newer high-carb mixes lean on highly branched cyclic dextrin (you will see it listed as cluster dextrin). It is a large-molecule carbohydrate that clears the stomach quickly while keeping the drink's osmolality low, which in plain English means you can pack a lot of fuel into a single bottle without it sitting heavy and sloshing around. Same theme as everything else here: it is a delivery upgrade, one more way to get more in without paying the gut tax.

Then there is dose, which is where things get spicy. The 2016 ACSM guidelines cap the recommendation at 90 grams per hour for efforts longer than about two and a half to three hours. Meanwhile, out in the real world, elite athletes are experimenting with 120 to 200 grams per hour. A 2025 Tour de France stage winner reportedly took in around 116 grams per hour, and some riders are training their guts toward 200 to 220. Just know that the science has not caught up to those top-end numbers yet. The efficacy of 150-plus grams per hour is not established. It is elite experimentation, not settled fact, and you should treat your own fueling that way too.

Which brings me to the most underrated concept in this whole conversation. You can train your gut. Carbohydrate tolerance is not fixed. It is trainable, the same way your aerobic system is. If your stomach rebels at 60 grams per hour today, that is a starting point, but not where you are stuck forever. Practice fueling in training at the rate you want to race at, build it gradually, and your gut adapts. This is the least sexy and most important fueling skill there is, and it costs nothing.

The delivery layer: hydrogels

Let's quickly pivot here, because you cannot understand the bicarb section without it. Maurten's hydrogel is a pH-sensitive coating (an alginate-pectin matrix) designed to encapsulate its contents, survive your stomach acid, and release the payload further down in the intestine.

That said, the evidence that hydrogel makes carbohydrate absorb meaningfully better than a normal gel is more marketing than proven. Head-to-head, the oxidation advantage is thin. Plenty of runners love Maurten anyway for the mild flavor and the smooth texture, and that is a completely legitimate reason to buy a gel. But the hydrogel's real importance is not what it did for carbs. It is what it made possible next.

Tier 2: Bicarbonate (a real tool, if you use it for the right thing)

The Maurten Bicarb System

First, let's kill a zombie myth, because it sets up everything else. Lactate is not your enemy. It never was. Lactate is a fuel. Your body makes it, shuttles it around, and burns it, especially when you are working hard. The thing that makes your muscles feel like they are filling with battery acid during a hard effort is the buildup of hydrogen ions and the drop in pH that comes with them. Acidity is the problem, Lactate just showed up at the crime scene and got blamed for it.

Sodium bicarbonate (yes, baking soda) works by buffering that acidity. It has been used in elite sport for decades for exactly this reason. The catch was always the same catch as everything else in this post: your gut. Choking down a big dose of baking soda reliably gave athletes the kind of explosive GI distress that cancels out any possible benefit. Great buffer, but a brutal delivery.

The innovation, once again, is a delivery fix. The Maurten Bicarb System packs bicarbonate into tiny mini tablets (about 3mm) that you take with a carbohydrate hydrogel, the idea being to shield the bicarb from your stomach acid and carry it into the intestine. The data on this specific system is consistent on one point. It raises blood bicarbonate while almost completely eliminating the GI mess. So they largely solved the delivery problem.

Now the part where I put my coach hat on, because this is where runners get it wrong. Bicarbonate is an event-specific tool, and the "event" it is best at is short and hard. The strongest evidence (from an umbrella review, which is about as high as evidence quality gets) says bicarb reliably helps with peak anaerobic power, anaerobic capacity, efforts lasting roughly 45 seconds to 8 minutes, and high-intensity intermittent work. In running terms, that is the mile through about the 3k, and your interval sessions. Those durations are where it performs best.

The steady-state distance side is a different story. A 2025 meta-analysis that looked specifically at continuous running found negligible benefits from a single dose of bicarbonate. So, if you were hoping bicarb was a marathon breakthrough, the evidence is not there. Two things worth flagging though, because they shape how much you should trust any of this. The running research is genuinely sparse compared to cycling, and it skews heavily male. In that continuous-running meta-analysis, about 84% of participants were men, median age 22. If you are a masters runner or a woman, a lot of this data was not built with you in mind, and that is just the truth of where the science sits right now.

Even the Maurten System's own running study lands on comfort over speed. In a small group of collegiate runners doing threshold intervals, it produced no measurable performance change (no difference in perceived exertion, heart rate, or blood lactate) but it did dodge the GI distress. Which is the recurring theme of this entire post. The delivery tech delivers. Whether the ingredient moves your race clock depends entirely on whether you are using it for the right kind of effort.

Bottom line on bicarb: it is a track-and-intervals tool, not a long-run tool. Use it for what it is good at.

Tier 3: The frontier (interesting, unproven, don't bet your race on it)

This is the "read about it, maybe experiment, but keep your wallet mostly closed" tier.

Lactate gels. The buzziest thing in the sport right now. Reports from the 2026 Tour de France describe at least one WorldTour team trialing a gel built around exogenous lactate, meaning lactate you eat rather than lactate your muscles make. The product (ExoLactate) came out of roughly seven years of development. The pitch is seductive. If lactate is fuel, why not just eat it? The evidence, though, is mixed and modest. Some trials show a small time-trial improvement or slightly lower perceived effort, others show nothing, and there is no published performance trial on the actual ExoLactate protocol yet. The most consistent finding is that exogenous lactate behaves like a mild acid-base buffer that can make an effort feel a touch easier, not a reliable speed booster. And here is the context that should keep you grounded. The riders using it are already fueling at 120 grams of carbohydrate per hour. They are chasing the last fraction of a percent at the absolute ceiling of human performance. For the rest of us, nailing carbs, hydration, and sodium will move the needle a hundred times more than a lactate gel will.

The barrier fell on the boring fundamentals done exceptionally well.

Ketone esters and salts. This one had its hype cycle and is deflating. Exogenous ketones come in two forms, and esters beat salts (they raise blood ketones higher and the salts tend to cause GI distress, sensing a pattern yet?). The famous result was a roughly 2% time-trial improvement in one cycling study when ketone ester was co-ingested with carbs. But the weight of the evidence since then has been underwhelming. Most studies have failed to show a performance or recovery benefit, and one trial found no benefit at all on 10k running performance in trained runners. When the sports science establishment titles a review "a new dawn fades," that tells you where the consensus landed.

(One you might expect in this section: broccoli shots, aka sulforaphane. I left them out on purpose. They are a recovery and antioxidant play, not a fuel, so they belong in a different conversation. If you want the full breakdown on those, I wrote about them separately here: Why Are Elite Athletes Taking Broccoli Shots?)

The other big shift in endurance fueling: your hydration got personal

Here is a change that gets a fraction of the hype of lactate gels and will do more for more runners. Hydration stopped being one-size-fits-all.

For years the advice was basically "drink a sports drink, maybe take a salt tab if it is hot." The problem is that how much sodium you lose in sweat is wildly individual. It runs from about 200mg to 2,000mg per liter of sweat, the spread is mostly genetic, and it has nothing to do with your fitness or how hard you are trying. So, a standard off-the-shelf electrolyte mix is roughly right for an average sweater and close to useless for anyone near the edges.

The shift is testing instead of guessing. Companies like Precision Fuel & Hydration built an at-rest sweat test (the same technology used to diagnose cystic fibrosis, no treadmill or needles required) that measures your actual sweat sodium concentration and builds a plan around your number. Two things fell out of that. First, personalization. Your sodium, your strategy, instead of whatever the bottle assumed. Second, the doses climbed. The strongest formulas now carry several times the sodium of the sports drink you grew up on, because those old products were underdosing the saltier half of us.

If you have ever cramped late in a race, faded when you should have been finishing strong, or wrapped a hot long run with a splitting headache, this is the rabbit hole to go down before you spend a cent on any frontier gel. Dialing in your own sodium is a bigger and far more reliable win than anything sitting in Tier 3.

(The personalization trend is creeping into hardware too. Some runners now fuel off continuous glucose monitors, watching blood sugar in real time instead of watching a clock. That one is a genuine rabbit hole, with a real evidence debate and some cautions worth handling carefully, so I am giving it its own post rather than a rushed paragraph here.)

So what do I actually use?

Let's talk about my fueling and how it has changed over the years. For the first seven or eight years of my distance running journey, from 2011 to 2018, I looked at fueling as something I wanted to do the bare minimum of, just to get by. I didn't want to risk upsetting my stomach, but I knew I needed fuel. I switched to Maurten gels in 2018, and their mild taste and hydrogel system changed how I looked at fueling. It went from "I should do this" to "how much can I take in," because I could feel it helping and my stomach was handling it. I started to see some positive results. Then from 2020 to 2022 I didn't race as often as before. But in 2023 I started to dive back into fueling and push what was possible for me. In addition to Maurten gels, I found Science in Sport Beta gels, and their dual-source carbs changed the game for me. 40g of carb in one gel, no GI distress, and something I generally looked forward to and could get down fast. I was soon pushing 60 to 80g of carb an hour. I started combining those gels with Skratch's High Carb mix before my runs and during specific long runs when I needed more carbs. Science in Sport also makes a Beta gel with 200mg of sodium that I now work into the rotation to help keep my sodium levels up.

As I got more serious about using fuel to improve my performance, that is when I started taking the biggest jumps in my results. Recently I have pushed 80 to 100g of carb on some of my longer efforts, including a 31-mile run around NYC, and felt incredible both during the run and in my post-run recovery, all because of how seriously I took the fueling. This fueling wave is going to define how people improve over the next 5 to 10 years. The runners who push themselves to see fueling as a challenge to take in more will reap the benefits in their results and in how they feel. The runners who keep trying to take in as little as possible will be left relying on genetics alone, and they will find themselves falling behind.

Here are my top fueling products.

Science in Sport Beta gels: I take a mix of the regular and the electrolyte, and for bigger long runs I take one of their Nootropics caffeine gels. I love the dual-source carbs, the taste is perfect, and the impact on my gut has been amazing. I have not had any issues with these and have consistently been able to take one gel every 30 minutes.

Maurten 100 & 160 gels: I have been a Maurten fan since 2018 and have kept taking their gels, albeit a little less now given my love for the Science in Sport Beta gels. The thing that always brings me back to Maurten is that the taste is minimal and I feel the gel working as soon as I take it. Gone are the days when I needed to take a gel 15 minutes before I needed it. With Maurten, the second I take them I start to feel the effects. That said, Maurten is a thicker consistency and is harder to get down quickly than the SiS gels.

Precision Fuel gels: This is a gel I love to mix in for a few reasons. The 30g of carb in one gel works perfectly alongside my other gels, and the taste is different enough that it fits in nicely. It matters to me to be able to push my carb intake and still enjoy each product, and these do not cause any GI distress for me.

Skratch High Carb mix: This product has changed so much of my fueling. It has become something I take race morning, or the morning of a long run, because I am usually not capable of taking in enough solid fuel that early in the day. And for longer efforts, being able to drink my carbs and sodium instead of chewing them has helped me really push. With almost 100g of carb in a full serving, this has become a go-to for when I need carbs and want them in something I can drink.

Frequently asked questions about endurance fueling

How many carbs per hour should you eat while running? For efforts over about 90 minutes, aim for 60 to 90 grams of carbohydrate per hour, and trained runners can push toward 120. The old 30 to 60 gram guideline is outdated. The ceiling is not your metabolism, it is what your gut can absorb, and that is trainable.

What are dual-source (glucose-fructose) carbs? Dual-source carbs combine glucose and fructose, which use two different intestinal transporters (SGLT1 and GLUT5). Glucose alone saturates around 60 grams per hour. Adding fructose opens a second pathway, so you can absorb more fuel, up to about 1.75 grams per minute, with less stomach distress, not more.

Can you train your gut to handle more carbs? Yes. Carbohydrate tolerance is trainable, the same way your aerobic system is. Practice fueling on your long runs at the rate you want to race at, then build gradually. If your stomach rebels at 60 grams per hour today, that is a starting point, not a limit.

What are lactate gels, and do they work? Lactate gels add exogenous lactate, meaning lactate you eat, on top of your carbs, and they appeared at the 2026 Tour de France. The evidence is mixed and modest. Lactate acts like a mild acid-base buffer that can make an effort feel slightly easier, not a proven speed booster.

Does sodium bicarbonate (bicarb) improve running performance? Bicarb buffers the acidity that builds during hard efforts. The evidence is strongest for short, high-intensity work of 45 seconds to 8 minutes and for interval sessions, so it suits mile-to-3k racing and track work. For steady-state marathon running, the benefit is negligible.

How much sodium do runners actually need? It depends on you. Sweat sodium loss ranges from about 200 to 2,000 milligrams per liter and is mostly genetic, so a standard electrolyte mix is close to useless at the extremes. An at-rest sweat test measures your concentration and builds a personalized plan around your number.

The takeaway (and the race that proves it)

Here is the story that ties all of this together, and it happened in real time in front of the whole running world.

At the 2026 London Marathon, two men ran under two hours. Sabastian Sawe crossed first in 1:59:30, the first athlete ever to break two hours under record-eligible conditions. Yomif Kejelcha came second in 1:59:41.

Now watch which fueling story is which. Kejelcha, the runner-up, is the one a company points to as a lactate-gel success. That is a marketing claim attached to a result, not proof the gel did anything. Meanwhile the guy who broke the barrier first did it on Tier 1 fundamentals, executed with almost obsessive discipline. Sawe's team spent a year training his gut. Maurten staff flew to Kenya six separate times, 32 days total, running carbohydrate-absorption testing, lactate testing, VO2 and running economy work, the whole lab. The payoff was a personalized carbohydrate protocol of about 115 grams per hour in London, 230 grams across the race. No exotic frontier supplement. Just carbohydrates, dialed into an extreme, delivered to a gut that had been trained for a year to handle it.

That is the entire point of this post in one race. The barrier fell on the boring fundamentals done exceptionally well. The shiny frontier product rode shotgun on the guy who came in second.

So here is my honest advice, as a coach and as someone who has been fueling runs for almost thirty years. Get your carbohydrate intake right first. Train your gut like it is a trainable system, because it is. Nail your hydration and your sodium. Do those three things and you have captured 95% of what modern fueling science has to offer. The bicarb, the lactate gels, the ketones, those are marginal gains you add on top of a solid foundation, not substitutes for one. And most of them are marginal gains you probably do not need yet.

Fuel the fundamentals, this is the most important thing here. The frontier will still be there when you are ready for it. And do not just fuel to your minimum, push what is possible, because the science keeps saying the same thing. Take in more fuel and be rewarded.

So, think of it exactly like your shoes. You did not hesitate to let carbon plates give you free speed. Fueling is the same deal, it is legal, external, proven technology that makes you faster without a single extra mile of training. The difference is that the shoe gain is already on your feet, and the fueling gain is still on the table. Go take it.

If you want more breakdowns like this, the science with none of the fluff, I send one every week in The Weekly Stride. Drop your email and I will see you in your inbox. [signup link]

Nick Klastava is the CEO and head coach of Running Explained, where he turns the science of running into training and fueling people can actually use. He has been coaching since 2017 and is USATF and RRCA certified, with a 2:30 marathon PR and a Boston Marathon finish. He has been running for nearly three decades and coaches as a masters runner and a dad of two, so he writes about fueling from both the lab and the start line. Find more of his work at runningexplained.com/blog.

Sources

Super shoes (running economy benchmark)

•     Hoogkamer et al. (2018), A Comparison of the Energetic Cost of Running in Marathon Racing Shoes, Sports Medicine: https://pmc.ncbi.nlm.nih.gov/articles/PMC9189692/

•     Whiting, Hoogkamer & Kram (2021), metabolic cost of level/uphill/downhill running in carbon-plated shoes: https://pmc.ncbi.nlm.nih.gov/articles/PMC9189710/

Dual-source carbohydrates

•     GSSI, Multiple Transportable Carbohydrates and Their Benefits (65% higher oxidation, 1.75 g/min): https://www.gssiweb.org/sports-science-exchange/article/sse-108-multiple-transportable-carbohydrates-and-their-benefits

•     GSSI, Dietary Carbohydrate and the Endurance Athlete: Contemporary Perspectives (2:1 vs 1:0.8 ratio, up to 120 g/h): https://www.gssiweb.org/sports-science-exchange/article/dietary-carbohydrate-and-the-endurance-athlete-contemporary-perspectives

•     From Metabolism to Medals, ScienceDirect (2016 ACSM 90 g/h guideline, Tour de France intakes of 116 and 200 to 220 g/h): https://www.sciencedirect.com/science/article/pii/S002231662600091X

Hydrogel delivery

•     The 5K Runner, Maurten Bicarb System review (pH-sensitive alginate-pectin barrier): https://the5krunner.com/2026/03/09/maurten-bicarb-system-review/

Sodium bicarbonate

•     Grgic et al. (2021), umbrella review of bicarbonate on exercise performance (45 s to 8 min window, high-intensity intermittent running): https://pmc.ncbi.nlm.nih.gov/articles/PMC8600864/

•     Negligible benefit of oral single-dose sodium bicarbonate on continuous running performance (2025 meta-analysis, 84% male participants): https://www.tandfonline.com/doi/full/10.1080/15502783.2025.2538606

•     A Runner's Edge systematic review, Journal of the Academy of Nutrition and Dietetics (velocity gains in distance runners): https://www.jandonline.org/article/S2212-2672(25)00664-1/fulltext

•     Keverkamp & Scanlon (2025), Maurten Bicarb System in endurance runners (no performance change, GI distress avoided): https://pmc.ncbi.nlm.nih.gov/articles/PMC12418788/

•     ISSN Position Stand on sodium bicarbonate and exercise performance: https://www.tandfonline.com/doi/full/10.1186/s12970-021-00458-w

Exogenous lactate

•     STYRKR, Lactate Gels at the Tour de France (ExoLactate, Viribay background): https://styrkr.com/en-us/blogs/training-and-nutrition-hub/lactate-gels-at-the-tour-de-france-what-the-research-actually-supports

•     BeetrootPro, ExoLactate & Exogenous Lactate Gels: Honest Evidence (no published RCT on the protocol): https://beetrootpro.com/blog/exolactate-exogenous-lactate-gel

Ketones

•     GSSI, Exogenous Ketone Supplements as Ergogenic Aids: A New Dawn Fades?: https://www.gssiweb.org/sports-science-exchange/article/exogenous-ketone-supplements-as-ergogenic-aids-in-athletic-performance-a-new-dawn-fades

•     Poffé et al., exogenous ketosis and prolonged endurance exercise (roughly 2% cycling time-trial result context): https://pmc.ncbi.nlm.nih.gov/articles/PMC7311686/

•     No Benefit of Ingestion of a Ketone Monoester Supplement on 10-km Running Performance, Med Sci Sports Exerc (2019): https://pubmed.ncbi.nlm.nih.gov/31730565/

Personalized hydration and sweat-sodium testing

•     Precision Fuel & Hydration, Our Sweat Tests (200 to 2,000 mg/L sweat sodium range, largely genetic, strongest formula up to roughly 3.5x the electrolytes of typical products): https://www.precisionhydration.com/sweat-testing/our-sweat-tests/

•     CTS / Precision Fuel & Hydration, Sweat Test (sodium loss variance is mostly genetic, why a standardized plan falls short): https://trainright.com/sweat-test/

Sub-2-hour marathon (London 2026)

•     Maurten, Sabastian Sawe 01:59:30 (115 g/h in London, 230 g race total): https://www.maurten.com/sabastian-sawe-sub-2

•     Marathon Handbook, How Sabastian Sawe Fueled His Sub-Two-Hour Marathon (six Kenya trips, 32 days, gut-training plan): https://marathonhandbook.com/how-sabastian-sawe-fueled-his-sub-two-hour-marathon-london/

•     Marathon Handbook, Lactate Gels: Marathon Fueling's Next Big Thing? (Kejelcha lactate-gel claim): https://marathonhandbook.com/what-are-lactate-gels/