Is 120 grams per hour worth it?
Learn to train smart, run fast, and be strong with this endurance performance nerd alert from Thomas Solomon, PhD.
13-C labelled glucose-fructose show greater exogenous and whole-body carbohydrate oxidation and lower oxygen cost of running at 120 vs 60 or 90 g/hour in elite male marathoners
Ravikanti et al. (2025) J Appl Physiol (click here to open the original paper)
What type of study is this?
◦ This study is a randomised controlled trialThe “gold standard” approach for determining whether a treatment has a causal effect on an outcome of interest. In such a study, a sample of people representing the population of interest is randomised to receive the treatment or a no-treatment placebo (control), and the outcome of interest is measured before and after the exposure to treatment/control. with crossoverCrossover means that all subjects completed all interventions (control and treatment) usually with a wash-out period in between..
What was the authors’ hypothesis or research question?
◦ The authors hypothesised that ingesting more carbohydrate during prolonged hard running would produce a dose-dependent rise in exogenousExogenous means “from the outside.” It describes something that comes from outside a system, organ, or body, rather than being made inside it. For example, exogenous carbohydrate oxidation means the rate at which your body produces energy from breaking down carbs that have been eaten/drunk. and whole-body carbohydrate oxidationCarbohydrate oxidation is the process where your body breaks down carbs and uses them for energy, usually with oxygen. It’s what happens when you burn glucose or stored glycogen to fuel activity. and improve running economyThe rate of energy expenditure (measured in kiloJoules [KJ], kilocalories [kcal] or oxygen consumption [V̇O2]) per kilogram body mass (kg) per unit of distance, i.e. per 1 kilometre travelled. A runner with a lower energy cost per kilometre has a higher economy than a runner with a higher energy cost., but might increase gastrointestinal symptoms.
What did the authors do to test the hypothesis or answer the research question?
◦ The researchers recruited 8 elite male marathoners with an average best marathon time of about 2 hours 23 minutes. On separate days, each runner completed three 2-hour treadmill sessions: 15 minutes at roughly lactate threshold (a.k.a. LT1)Lactate threshold is the exercise intensity where blood lactate starts to gradually rise faster than your body can clear it, but you can still keep going for a while. It marks the shift from “this is hard but manageable” to “this is going to catch up with me soon” if you hold it., 90 minutes at about 94 percent of lactate turnpoint (a.k.a. LT2)Lactate turnpoint (LT2) is a higher intensity than lactate threshold (LT1) where blood lactate shoots up rapidly, effort begins to feel hard, and fatigue comes on quickly. It’s the “red zone” where you can only last a short time before you have to slow down, and signals a shift toward more glycolytic (glucose-using) and anaerobic energy use., then 15 minutes again at roughly lactate threshold. On the separate days they drank either 60, 90, or 120 grams per hour of carbohydrate delivered every 15 minutes in 125 millilitre drinks. The maltodextrin dose in the drinks was held constant while fructose was increased to change the total carb intake and the maltodextrin to fructose ratio (1:0, 2:1, 1:1). Drinks were enriched with ¹³C stable isotope tracersA stable isotope tracer is a harmless “tag” scientists put on a molecule so they can track where it goes in the body. For example, 13C (carbon-13) is a natural, non-radioactive form of carbon. If you attach 13C to a nutrient (e.g. glucose) and then measure where that 13C shows up (e.g., in the breath, blood, or tissue), you can see how the body absorbs, uses, or burns that nutrient (without using radiation). to quantify exogenousExogenous means “from the outside.” It describes something that comes from outside a system, organ, or body, rather than being made inside it. For example, exogenous carbohydrate oxidation means the rate at which your body produces energy from breaking down carbs that have been eaten/drunk. carbohydrate oxidationCarbohydrate oxidation is the process where your body breaks down carbs and uses them for energy, usually with oxygen. It’s what happens when you burn glucose or stored glycogen to fuel activity..
What did the authors find?
◦ ExogenousExogenous means “from the outside.” It describes something that comes from outside a system, organ, or body, rather than being made inside it. For example, exogenous carbohydrate oxidation means the rate at which your body produces energy from breaking down carbs that have been eaten/drunk. carbohydrate oxidationCarbohydrate oxidation is the process where your body breaks down carbs and uses them for energy, usually with oxygen. It’s what happens when you burn glucose or stored glycogen to fuel activity. during hour 2 increased stepwise at 60, 90, and 120 grams per hour, with large effect sizesA standardised measure of the magnitude of an effect of an intervention. Unlike p-values, effect sizes show the size of the effect and how meaningful it might be. Common effect size measures include standardised mean difference (SMD), Cohen’s d, Hedges’ g, eta-squared, and correlation coefficients. Peak exogenous oxidation reached roughly 1.00 ± 0.10, 1.41 ± 0.12, and 1.77 ± 0.13 grams per minute. Whole-bodyWhole-body oxidation means the total oxidation rate (the rate at which your body produces energy from breaking down nutrients) of carbohydrate, fat, or protin from both endogenous (“from the inside”; produced in the body) and exogenous (“from the outside”; consumed in food/drink) sources. carbohydrate oxidation showed the same pattern across the full 2 hours: roughly 2.08 ± 0.03, 2.46 ± 0.12, and 3.06 ± 0.19 grams per minute for 60, 90, and 120 grams per hour. During hour 2, the contribution of exogenous carbohydrate to total energy expenditure was about 21, 30, and 39 percent for 60, 90, and 120 grams per hour, and fat’s contribution was lowest with 120 grams per hour.
◦ Running economyThe rate of energy expenditure (measured in kiloJoules [KJ], kilocalories [kcal] or oxygen consumption [V̇O2]) per kilogram body mass (kg) per unit of distance, i.e. per 1 kilometre travelled. A runner with a lower energy cost per kilometre has a higher economy than a runner with a higher energy cost. improved: the oxygen cost of running was about 2.6 percent lower with 120 grams per hour than with 60 grams per hour.
◦ Gastrointestinal symptoms were common in every condition; cumulative scores were not different, but peak nausea, stomach fullness, and cramps were highest with 120 grams per hour. Seventy-five percent of runners reported nausea with 120 grams per hour versus 25 percent with the lower intakes.
◦ The authors concluded that 120 grams per hour of a 1 to 1 maltodextrin–fructose drink improves carbohydrate availability and lowers the oxygen cost of running (improves running economy) in elite male marathoners, but the high prevalence of gut symptoms means athletes may need targeted practice before using such a strategy in competition.
What were the strengths?
◦ The design is tight for a sports-nutrition lab study: double-blindBlinding is when people in a study don’t know which treatment they’re getting. It stops expectations or beliefs (from patients or researchers) from skewing the results. “Single-blind” means participants don’t know; “double-blind” means participants and researchers don’t know; “triple-blind” means that the participants, researchers, and data analysts are kept in the dark. The goal is simple: fair tests and trustworthy findings. randomised crossover with standardised high-carb diet the day before each trial and a fixed fluid schedule during exercise. Methods are detailed and appropriate, including stable isotopeA stable isotope tracer is a harmless “tag” scientists put on a molecule so they can track where it goes in the body. For example, 13C (carbon-13) is a natural, non-radioactive form of carbon. If you attach 13C to a nutrient (e.g. glucose) and then measure where that 13C shows up (e.g., in the breath, blood, or tissue), you can see how the body absorbs, uses, or burns that nutrient (without using radiation). tracing for exogenous oxidation and repeated indirect calorimetryIndirect calorimetry is a way to measure how much energy your body is using by analyzing your breathing. It tracks how much oxygen you breathe in and how much carbon dioxide you breathe out. From that, it estimates how many calories you burn and how much of that energy comes from fat or carbohydrate. with clearly reported statistics. A sample-size power calculationA power calculation is a way to figure out how many people or data points you need in a study so you can reliably spot a real effect if it exists. It balances four things: the size of the effect you care about, how much random variation there is, how strict you are about false alarms, and how likely you want to be to detect the effect. In plain terms: it helps you avoid running a study that’s too small to be useful or so big that it wastes time and money. was presented, and the exercise model — 2 hours near marathon intensity — hits the right physiological notes for this population (elite male marathoners).
What were the limitations?
◦ The trial is small (N = 8), which can increase the risk of missing real effects for some outcomes, and it included only elite male athletes, preventing generalisabilityGeneralisability is about how far you can confidently stretch a study’s findings beyond the specific people, place, and conditions that were tested. In simple terms, it asks: “If this result is true here, how likely is it to also be true in other groups or real-world settings?” It’s closely linked to external validity, which is the overall strength of those broader conclusions. to female and recreational runners. There was no water-only placebo day, so we cannot quantify the absolute benefit of any carbohydrate versus none. Drinks differed not only in dose but also in concentration, maltodextrin:fructose ratio, and perceived sweetness, so true blindingBlinding is when people in a study don’t know which treatment they’re getting. It stops expectations or beliefs (from patients or researchers) from skewing the results. “Single-blind” means participants don’t know; “double-blind” means participants and researchers don’t know; “triple-blind” means that the participants, researchers, and data analysts are kept in the dark. The goal is simple: fair tests and trustworthy findings. may also have been compromised. There was also no performance test, so we cannot say whether the metabolic changes translate to faster marathon running performance.
How was the study funded, and are there any conflicts of interest that may influence the findings?
◦ The study was funded by a research grant from Science in Sport PLC. One author consults for Science in Sport, has received prior funding from multiple sports-nutrition companies, and another author received an honorarium and co-founded a related analytics company. These relationships are disclosed in the paper.
How can you apply these findings to your training or coaching practice?
◦ For coaches and pros eyeing big city marathons, this is actionable physiology. If you can train your gut and your logistics, pushing toward 120 grams per hour of a maltrodextrin–fructose mix can keep carbohydrate use high and oxygen cost a touch lower—which is exactly what you want late in the race. But if nausea knocks you sideways, the extra carb won’t save your day. The force is strong with this one, but it needs skill to wield and we don’t know whether 120 grams per hour will actually increase performance in a real race. Future research needs to hone in on that.
What is my Rating of Perceived scientific Enjoyment (RPsE)?
7 out of 10 → I experienced moderate scientific enjoyment because the design and measurements were solid and marathon-relevant, but a key practical question remains unanswered: can you actually race faster when guzzing 120 grams of sugar per hour, without puking or shatting one’s pants?
Important: Don’t make any major changes to your daily habits based on the findings of one study, especially if the study is small (e.g., less than 30 participants in a randomised controlled trial or less than 5 studies in a meta-analysis) or poor quality (e.g., high risk of biasRisk of bias in meta-analysis refers to the potential for systematic errors in the studies included in the analysis, which can lead to misleading or invalid results. Assessing this risk is crucial to ensure the conclusions drawn from the combined data are reliable. or low quality of evidenceA low quality of evidence means that, in general, studies in this field have several limitations. This could be due to inconsistency in effects between studies, a large range of effect sizes between studies, and/or a high risk of bias (caused by inappropriate controls, a small number of studies, small numbers of participants, poor/absent randomization processes, missing data, inappropriate methods/statistics). When the quality of evidence is low, there is more doubt and less confidence in the overall effect of an intervention, and future studies could easily change overall conclusions. The best way to improve the quality of evidence is for scientists to conduct large, well-controlled, high-quality randomized controlled trials.). What do other trials in this field show? (opens in new tab) Do they confirm the findings of this study or have mixed outcomes? Is there a high-quality systematic review and meta-analysis evaluating the entirety of the evidence in this field? (opens in new tab) If so, what does the analysis show? What is the risk of bias or certainty of evidenceCertainty of evidence tells us how confident we are that the results reflect the true effect. It’s based on factors like study design, risk of bias, consistency, directness, and precision. Low certainty means more doubt and less confidence, and that future studies could easily change the conclusions. High certainty means that the current evidence is so strong and consistent that future studies are unlikely to change conclusions. across the included studies? I’ve written a deep-dive series article on this topic; check it out at veohtu.com/performancenutrition.
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