New Guidelines For Fueling

I was sharing with some my patients this past week how I found it amazing that Sebastian Sawe was able to consume 115 grams of carbs an hour in his sub-2 hour marathon. Previous recommended guidelines were between 60-90 grams an hour.

Lo and behold, a patient shared that in the Nice Ironman last year, Casper Stornes (1st place) and Kristian Blummenfelt (3rd) took 120 grams of carbs while running and up to 180 grams on the bike.

Intrigued by what he sent me, I found a recently published review article by Morton et al (2026) which revisits carbohydrate guidelines for endurance athletes. So are the previous fueling recommendations enough?

When training and/ or racing for prolonged periods, carbohydrate intake will spare liver glycogen while maintaining your blood glucose levels. Most importantly, it helps one to sustain higher intensities nearer the end of your race. When everyone else is going faster, you do not want to run out of fuel and slow down.

Fueling is not to just avoid bonking (or hitting the dreaded wall). It is also to delay the shift from using carbohydrates to fat. That shift is not bad, but when you are trying to go fast without carbohydrates it is going to be very difficult. Note that if you are doing Zone 1 or 2 for many hours (like in an ultra marathon) at low intensities, then this shift may not occur.

When one consumes enough carbohydrates during endurance exercise, long ultra race, Ironman event etc, it delays the "crossover point".  This is when carbs stop being the predominant fuel due to glycogen depletion or low carb availability.

You can see from the diagrams above that if no carbs are consumed (0 grams each hour), this happens around 2 hours. With 45-90 grams/ hour, it delays the crossover point by 30-60 minutes. If 120+ grams/ hour of carbs are consumed, there is no crossover point since carbohydrates remain the predominant fuel source while exercising. At least not in cycling studies as the subjects exercised at 90 percent lactate threshold for 3 hours. It may still occur in longer races.

For runners, the review looked at elite male marathoners with personal bests under 2:30 hrs. They completed a 2 hour treadmill protocol close to marathon race intensity while consuming 60, 90 or 120 grams of carbs each hour. 

Those who ingested 120 grams used more of the ingested carbs leading to higher carbohydrate oxidation. They had a roughly 3 percent improvement in running economy compared to 60 grams per hour. There was also greater carbohydrate contribution to total energy expenditure late in the run. Now you know why Sabastion Sawe never slowed down in his sub-2 hour London marathon. 

There's a catch. Gastrointestional (GI) symptoms were also higher at 120 grams/ hour. Nausea, stomach fullness, and cramping were worse in the highest carb intake. More carbs may offer an advantage, but only if your gut can absorb and tolerate them.

The researchers say that runners should use 90 grams of carbs or more per hour as a realistic target for long, hard events. For trained athletes, the range may extend closer to 120 grams per hour. Fueling should be treated like a trainable skill, provided the gut has been trained to handle it.

Runners will find it more challenging compared to cycling since it's much easier to eat on the bike. All the moving, reduced blood flow to the gut, heat stress may lead to higher rates of GI distress.

This is an exciting review for fueling, but do note that most of the research comes from cyling, male athletes and in controlled lab settings. Female athletes are under-represented as well as real world running/ racing conditions.

My takeaway message? For some of you runners, 90-120 grams/ hour will most certainly help your times. Others may benefit from 60-75 grams/ hour. For other runners, it may be just progressing from under-fueling to consistently fueling and getting a personal best no matter how many grams of carbs that may be.

Reference

Morton JP, Fell JM, Gonzalez JT et al (2026). From Metabolism To Medals: Contemporary Perspectives And Revisiting Carbohydrate Guidelines For Fueling Endurance Athletes During Exercise. J Nutrition. 156(5). DOI: 10.1016/j.tjnut.2026.101442

Need To Poop Mid Race?

Our Singapore cycling champion Donaben Goh came to see me yesterday for one last tune up before he leaves for the Vietnam SEA Games tomorrow morning. We were discussing his fuelling needs in the cycling road race event (167 km long) and talking about stomach upsets while racing.

Familiar sight at races

If you're an endurance athlete, you would definitely have experienced gastrointestinal (or stomach) issues (GI). That includes nausea, bloating, abdominal pain, reflux, flatulence and diarrhoea during your longer traning sessions or races.

How and why does this happen? 

It all starts at the lining of our gut (or alimentary canal from the stomach to the anus, consisting of the small and large intestine), which has 2 jobs. First, it allows food to pass from the gut to our bloodstream and it also prevents nasty bacteria and toxins from entering the same route.

When we exercise, blood from our digestive organs (up to a quarter of our blood) are diverted to our muscles to supply more oxygen to them. Moderate exercise can reduce the blood supply to the gut by up to 70 percent. 

During prolonged endurance exercise (usually longer than 2 hours at 60 percent VO2 max or more), the gut lining starts to malfunction since it is now lacking oxygen and energy. Food that the gut is trying to absorb gets blocked while toxins start to leak into our bloodstream.

In addition, the bouncing and jostling from exercise can cause direct mechanical damage to the lining of the gut. This is why GI issues happen more with running compared to cycling.

Heat and dehydration will divert more blood away from the gut, allowing more gases and/ or toxins to pass through. 

What's worse with GI distress is, it often gets worse when you're anxious or stressed, for example before your big race. Anxiety and psychological stress trigger adrenaline which further diverts blood away from the digestive system while increasing leakage in the gut lining.

How do we prevent it? In a perfect world the obvious approach would be to find out the food that triggers our GI distress and avoid them prior to our races and long training sessions.

Studies show that a class of poorly digested carbohydrates known as FODMAPs (fermentable oliosaccharide, disaccharide, monosaccharides and polyols) may cause GI distress for many of us as they are not well absorbed in the small intestine. This causes fermentation and produce gas in the colon.

This include food containing wheat, milk, onions, garlic, legumes (beans, peas and lentils) and stone fruit (apricots, peaches, plums, mangoes, lychees etc).

Timing matters too, as eating too much fat, protein or fiber 90 minutes before exercise may increase the risk of GI problems. 

Please note that people who keep to low FODMAP diets tend to have less healthy and diverse gut microbiomes.

Personally I've found that 'training your gut' works well. Many other athletes I've spoken to and treated say that eating and drinking energy gels/ bars and sports drinks that are palatable over time makes them less susceptible to GI issues. 

You have to try them out during your long training sessions or less important races. A gel or bar may taste fine at room temperature, but may taste terrible and be difficult to swollow in hot, humid conditions. Research suggests that 2 weks of training the gut can make a difference (Miall et al, 2018).

All the best to Donaben and the rest of Team Singapore at the Hanoi SEA Games.

References

Miall A, Khoo A, Rauch C et al (2018). Two Weeks Of Repetitive Gut Challenge Reduce Exercise-associated Gastrointestinal Symptoms And Malabsorption. Scand J Med Sci Sports. 28: 630-640. DOI: 10.1111/sms.12912 

Smith KA, Pugh JN, Duca FA et al (2021). Gastrointestinal Pathophysiology During Endurance Exercise: Endocrine, Microbiome And Nutritional Influences. Eur J Appl Physiol. 122(10): 2657-2674. DOI: 10.1007/s00421-021-04737-x

*I did not write about probiotics (supplements) as they are capable of producing a good environment in the gut but do not eliminate symptoms entirely. That's my personal experience as well. Plus 3 out 5 of this review's authors receive research funding from companies that make supplements.

Oops, Just Pooped During My Run

*Wouldn't wish this on anyone

Do you often need to go to the toilet just before your race? For lots of runners, the urge to go to the toilet happens during the race as well. I've occasionally needed to when I was racing, especially before a big race. But thankfully, never during an important race.

Well, you'll be surprised to know that the cause of you going to the toilet may be coming from your head.

A recently published study done only on 150 runners suggest that runners' gastrointestinal (stomach) problems during training runs and races were significantly related to their stress and anxiety levels. The runners were followed up for 30 days in this particular study.

This is after accounting for other known causes of stomach issues such as caffeine, medication, carbohydrates consumed during the run and workout intensity.

There is previous ample evidence that running intensity is closely linked to gastrointestinal issues. The faster (or eventually further) you run, the more blood is diverted temporarily from elsewhere (such as from digestion areas) to running muscles.

In this study, the runners who reported more anxiety and stress in their daily life were more likely to have flatulence, stomach distress and mid-run pit stops while running.

Other than running intensity and other contributing factors tracked, the major reason from this study showed that the runners' reported level of stress and anxiety was the other major factor linked to "on the run" gastrointestinal problems.

Bear in mind that the runners' in the study were not stressed about their running. From the questionnaires, the reported stress were based on people recalling their daily lives, not a specific activity such as work, or in this case, exercise.

So if you're having stomach issues before, during or after a stressful or anxiety provoking event, it makes it more likely that your stomach symptoms (and the need to use the toilet) are stress and anxiety related. Make sure you try to use the toilet before you run.


Reference

Wilson PB (2017). Perceived Life Stress And Anxiety Correlate With Chronic Gastrointestinal Symptoms In Runners. J Sports Sci. Dec 1:1-7. DOI: 10.1080/02640414.2017.1411175.

*Took the picture off the computer from rantlifestyle.com