{"id":225894,"date":"2026-01-07T19:48:15","date_gmt":"2026-01-07T19:48:15","guid":{"rendered":"https:\/\/www.newsbeep.com\/il\/225894\/"},"modified":"2026-01-07T19:48:15","modified_gmt":"2026-01-07T19:48:15","slug":"oxidative-efficiency-and-5-other-crucial-things-all-runners-should-know-about-carbs-and-marathon-fuelling","status":"publish","type":"post","link":"https:\/\/www.newsbeep.com\/il\/225894\/","title":{"rendered":"\u2018Oxidative efficiency\u2019 and 5 other crucial things all runners should know about carbs and marathon fuelling"},"content":{"rendered":"

If you want to have a terrible marathon experience, don\u2019t fuel for it \u2013 and hit the wall<\/a> the hard way. If you want to have a fantastic marathon experience, do consume plenty of carbohydrate<\/a> before and during it \u2013 because that way, your body will have enough energy to power you through those 26.2 miles, wall-free.<\/p>\n

But what is \u2018plenty of carbohydrate\u2019? Precisely how many gels do you need to chow down mid-marathon? Regrettably, there is no one-size-fits-all solution and the amount of carbohydrate that your body uses \u2013 known as oxidation efficiency \u2013 doesn\u2019t necessarily match the amount that you take in. So, to deduce my exact marathon fuelling needs, quite literally to the gram, I turned to science, hopped on the treadmill<\/a> and, under the expertise of ExoAnalytics<\/a> and Puresport<\/a>, undertook a 90-minute carbohydrate oxidation test.<\/p>\n

The results were startling \u2013 as were the six surprising things that I learnt about marathon fuelling along the way.<\/p>\n

What is a carbohydrate oxidation test?<\/p>\n

Good question. A carbohydrate oxidation test determines exactly how much of the carbohydrate that you consume during exercise can be processed through your digestive tract, absorbed into your bloodstream, transported to your working muscles and used for energy \u2013 or \u2018oxidised\u2019. So just because you take a gel containing, say, 25g of carbohydrate, it doesn\u2019t mean that your body can actually use the full 25g for energy.<\/p>\n

What did my carbohydrate oxidation test involve?<\/p>\n

While the thought doing a driving test might make you want to break out into a cold sweat, doing a carbohydrate oxidation test will make you break out into a hot sweat \u2013 because, yes, it involves running.<\/p>\n

My test involved 90 minutes of continuous running on a treadmill<\/a> and was directed by leading sports scientist Dr Sam Impey<\/a>, co-founder of Hexis<\/a> and performance nutritionist to some of the world\u2019s top athletes. I initially assumed that I\u2019d need to run at my marathon PB pace \u2013 that\u2019s about 4:00 min\/km (6:26 min\/mile) \u2013 and put in a real shift. But thankfully and surprisingly, Dr Impey advised me to run at a constant easy pace<\/a> which I could comfortably hold for the full 90 minutes. So, I set my treadmill to a pace of 4:55 min\/km (7:55 min\/mile).<\/p>\n

Before I got moving, I gave breath samples \u2013 which involved blowing through a straw into two test tubes \u2013 so that they could later be analysed in the lab. Then, after 10 minutes of treadmill running, I took my first piece of mid-run fuel: a Puresport Energy Gel<\/a>, containing 30g of carbohydrate. Although I wanted to try both flavours, orange and berry, I had to stick with one for testing consistency \u2013 so I went for berry. For me, the flavour was sweet but impressively palatable and, consistency-wise, it was smooth enough to drink easily in a few mouthfuls, but not so watery that it spilled out everywhere and turned my hand into a sticky spider web. So far, so good.<\/p>\n

I took the next gel \u2013 again, a berry Puresport Energy Gel \u2013 after 40 minutes of running, then the third and final one after 70 minutes. So, over the 90-minute running period, I consumed 90g of carbohydrate in total. <\/p>\n

For the final 10 minutes, I also ran with a mask over my mouth to capture my \u2018metabolic measurements\u2019 \u2013 that is, in this case, the amount of carbon dioxide that I was exhaling.<\/p>\n

\"bundle<\/p>\n

Puresport<\/p>\n

What is the general recommended fuelling requirement?<\/p>\n

Let\u2019s first ask another question: which types of carbohydrate do you find in an energy gel? Well, you can forget Fibonacci, because the golden ratio for energy gels is a carbohydrate blend that\u2019s one part glucose and 0.8 parts fructose. Ever since researchers first proposed this ratio in 2013<\/a>, sports scientists have continued to agree that this is the best carbohydrate balance for supporting athletic performance while minimising gut issues<\/a>.<\/p>\n

Understandably, Puresport has stuck to this ratio for its own gel, which it developed with Dr Impey. What\u2019s different, though, is the amount of carbohydrate in each gel. While most other standard energy gels contain between 20g and 25g of the good stuff, Puresport energy gels contain 30g \u2013 and there\u2019s scientific reason for this. Following a series of carbohydrate oxidation tests on amateur and elite runners alike, the research team of Puresport, ExoAnalytics and Dr Impey deduced the optimal marathon fuelling rate to be about 60g of carbohydrate per hour. So that\u2019s one 30g gel every 30 minutes \u2013 two gels per hour. No mid-run mental maths required. Easy. <\/p>\n

Of course, this is an accurate but not bulletproof suggestion \u2013 and just because one marathoner\u2019s sweet spot might be 60g of carbohydrate per hour, it doesn\u2019t mean that mine is the same… <\/p>\n

How does my test result compare with the recommendation?<\/p>\n

I genuinely thought that there was a mistake when I received the results of my carbohydrate oxidation test \u2013 or that it was possibly even a marketing ploy. My recommended carbohydrate intake is, to the gram, 60g per hour. That\u2019s exactly what Puresport and its scientific advisors are recommending for the general running population. (I can confirm that this was not a marketing ploy \u2013 all runners who tested alongside me on the day received different results.)<\/p>\n

This is noticeably different to what I\u2019ve taken on before. Having clocked 17 marathons over the past few years, I\u2019ve had plenty of opportunity to improve my fuelling technique and arrive at a strategy that gets me across the finish line without a squiffy stomach. Even though I\u2019ve come a long way since my first marathon, where I woefully took on less than 70g of carbohydrate in the space of three hours and 27 minutes, I\u2019m still falling about 10g short of 60g of carbohydrate per hour. Yikes.<\/p>\n

But here\u2019s the thing: I don\u2019t use all 60g in any given hour of running. The results revealed that my exogenous oxidation rate \u2013 which refers to the amount of carbohydrate that I actually use \u2013 is 48g per hour. This means that my oxidative efficiency is 80%.<\/p>\n

What does it mean if I don\u2019t use all the carbohydrate this I ingest? Does my oxidative efficiency change over time? And is timing still important when it comes to fuelling? I chatted with Dr Impey to discuss my result \u2013 and here are my key learnings.<\/p>\n

\"group<\/p>\n

Kate Allan<\/p>\n

6 things that I\u2019ve learnt about marathon fuelling1. My oxidative efficiency hits the marks<\/p>\n

I don\u2019t mean to brag, but\u2026 \u2018Research shows that 80-90% oxidative efficiency is ideal,\u2019 Dr Impey told me. \u2018This range means that you\u2019re absorbing and using carbohydrate effectively, without leaving excess unprocessed fuel sitting in your gut.<\/p>\n

\u2018Some runners in our testing oxidised nearly all 60g, giving them almost 100% oxidative efficiency \u2013 and this suggests that they could potentially tolerate slightly more carbohydrate per hour,\u2019 he continued. Meanwhile, anyone below 80% would probably benefit from reducing their carbohydrate intake slightly to dodge the risk of gut problems. In other words, it\u2019s not about cramming in as much as possible, but matching your intake to your body\u2019s ability to absorb and use it.<\/p>\n

2. Your fuelling requirement changes after two hours<\/p>\n

According to Dr Impey, after about two hours of continuous running, your body\u2019s metabolism subtly changes. As glycogen stores deplete, the system becomes more willing to take on and use external carbohydrate. \u2018It\u2019s only about a 10% increase, but it can make a difference during those longer efforts,\u2019 he said.<\/p>\n

This explains my test results, which suggest 60g of carbohydrate per hour for the first two hours of running, then 68g per hour after that. <\/p>\n

Interestingly, though, this adaptation is modality-specific \u2013 it doesn\u2019t behave the same way when you\u2019re cycling<\/a> as it does when you\u2019re running, for example. So if you\u2019re a triathlete, each discipline will change how you process fuel.<\/p>\n

3. Your running pace doesn\u2019t affect your oxidative efficiency<\/p>\n

I was a little confused as to why I was asked to run at an easy pace for the carbohydrate oxidation test, when I run marathons faster. Does this lead to inaccurate recommendations?<\/p>\n

\u2018Most people assume that as pace increases, so does carbohydrate oxidation \u2013 but the opposite can actually happen,\u2019 said Dr Impey. \u2018At higher intensities, blood is redirected from the gut to working muscles, which reduces the amount of carbohydrate that is absorbed. Many people reach their peak oxidation rate at moderate intensities, rather than during all-out efforts.\u2019<\/p>\n

4. You can still have a gel on the start line<\/p>\n

I always eat a light but carbohydrate-rich breakfast<\/a> a few hours before a morning race \u2013 it\u2019s quite bland. For my past few marathons, I\u2019ve also made a habit of taking an energy gel<\/a> about 10 minutes before the start gun sounds to offer me another boost off the line. Does this pre-race fuel impact mid-race carbohydrate oxidation?<\/p>\n

\u2018Your breakfast before a race or long run mainly serves the purpose of topping up liver glycogen stores that drop overnight,\u2019 noted Dr Impey. \u2018It doesn\u2019t have much impact on how efficiently you\u2019ll use gels later. And taking a gel on the start line is absolutely fine \u2013 think of it as your first 30 or 45 minutes of fuelling covered.\u2019<\/p>\n

5. There\u2019s a reason we avoided corn<\/p>\n

I was told to avoid eating corn and certain plant-based foods in the 24 to 48 hours preceding the carbohydrate oxidation test \u2013 and that\u2019s because of isotope science. <\/p>\n

As explained by Dr Impey, carbon-12, which contains six protons and six neutrons, makes up 99.9% of carbon, while carbon-13 has an extra neutron, which makes it slightly heavier. \u2018Plants that use \u2018C4 photosynthesis\u2019, such as corn, naturally contain more carbon-13,\u2019 he continued. \u2018We wanted your body\u2019s baseline carbon-13 to be low when you went into the test so that we could measure the rise in carbon-13 from the Puresport gels, which are enriched in it.\u2019 That allowed Dr Impey to detect changes in exhaled carbon dioxide \u2013 via the mask that I wore during the final 10 minutes of the test \u2013 and calculate how much of the ingested carbohydrate was actually burned as energy.<\/p>\n

6. Women had been underrepresented in the data<\/p>\n

I was one of several women involved in the carbohydrate oxidation testing with Puresport, ExoAnalytics and Dr Impey. At the time, I didn\u2019t realise that this was such a novel thing. <\/p>\n

\u2018When we began testing, there was almost no published data on recreationally active female runners\u2019 exogenous oxidation,\u2019 said Dr Impey. \u2018Most existing studies were on elite male marathoners or cyclists. We wanted to change that \u2013 and it\u2019s partly why we deliberately included more women than men in our testing. So, by gathering this data, we\u2019re helping to define realistic recommendations for most runners.<\/p>\n

\u2018Your 80-90% oxidative efficiency supports our recommendations for everyday athletes,\u2019 he added. \u2018It shows that taking around 60g of carbohydrate per hour, using two types of sugar \u2013 glucose and fructose \u2013 strikes an effective balance between energy use and gut comfort.\u2019<\/p>\n

\"breathing<\/p>\n

Kate Allan<\/p>\n

Fuel for thought<\/p>\n

With these test results and some more Puresport energy gels to hand, I\u2019m entering my new marathon training cycle<\/a> with an even finer understanding of \u2013 and respect for \u2013 carbohydrates and the way that they operate within the body of an endurance runner. The next step is for me to habitualise consuming my individualised target of 60g of carbohydrate per hour on my long runs<\/a>. Then, with this strategy hopefully locked down, who knows what it might do for me on race day. <\/p>\n

Carbohydrate oxidation testing takes time, comes at a cost and, as such, isn\u2019t for everyone \u2013 it\u2019s for runners who really want to pick apart and finesse their fuelling. So if taking a test isn\u2019t for you, remember to experiment with your fuelling in training and know that 60g of carbohydrate per hour is a convenient, science-based ballpark that many runners can aim for. (It\u2019s a perfect recommendation for me, at least.) <\/p>\n

\u2018Personalisation is the future,\u2019 concludes Dr Impey. \u2018But even before we get there, understanding how your body burns what you give it is the most powerful insight of all.\u2019<\/p>\n

Related Story<\/p>\n","protected":false},"excerpt":{"rendered":"If you want to have a terrible marathon experience, don\u2019t fuel for it \u2013 and hit the wall…\n","protected":false},"author":2,"featured_media":225895,"comment_status":"","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[7],"tags":[7157,123667,637,85,46,636,141,123666],"class_list":{"0":"post-225894","1":"post","2":"type-post","3":"status-publish","4":"format-standard","5":"has-post-thumbnail","7":"category-science","8":"tag-content-type-default","9":"tag-contentid-9e5646cc-2a57-4fdd-a251-130ec3f4b0e4","10":"tag-displaytype-standard-article","11":"tag-il","12":"tag-israel","13":"tag-locale-gb","14":"tag-science","15":"tag-shorttitle-oxidative-efficiency-and-5-other-crucial-things-all-runners-should-know-about-carbs-and-marathon-fuelling"},"_links":{"self":[{"href":"https:\/\/www.newsbeep.com\/il\/wp-json\/wp\/v2\/posts\/225894","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.newsbeep.com\/il\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.newsbeep.com\/il\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/il\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/il\/wp-json\/wp\/v2\/comments?post=225894"}],"version-history":[{"count":0,"href":"https:\/\/www.newsbeep.com\/il\/wp-json\/wp\/v2\/posts\/225894\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/il\/wp-json\/wp\/v2\/media\/225895"}],"wp:attachment":[{"href":"https:\/\/www.newsbeep.com\/il\/wp-json\/wp\/v2\/media?parent=225894"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.newsbeep.com\/il\/wp-json\/wp\/v2\/categories?post=225894"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.newsbeep.com\/il\/wp-json\/wp\/v2\/tags?post=225894"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}