Carbs on the move: when, how much and which kind

0:03 · An hour longer, the same muscle store

Seven cyclists rode until they could not go on. With a carbohydrate drink every twenty minutes, they lasted an hour longer than with flavoured water. Yet the sugar stored in their muscles ran down just as fast. And later in this video, the biggest dose study of its kind shows roughly where taking in more stopped helping.

0:20 · How many carbs per hour?

Somewhere in the second or third hour of a long ride or run, the question comes up. Should I eat, and how much? The numbers you hear range from a gel an hour to a hundred and twenty grams. This video looks at what the research measured. It is about carbohydrate taken in during the effort. What you eat the days before, and the hours after, is a subject of its own.

0:42 · Does it help at all?

First, does it help at all? A systematic review from two thousand and fourteen lined up time trials, races against the clock, that compared carbohydrate with a placebo drink. In trials under an hour, the average gain was two point six per cent. From one to two hours it was four point nine. Over two hours it was six point two. And of the twenty studies lasting over two hours, nineteen found a clear benefit. The spread around each average is wide, so one number tells you little about one race. But the direction holds: the longer you go, the more there is to gain. One position stand, the formal advice of a sports nutrition society, reports a more cautious reading. When riders have eaten beforehand, a consistent benefit shows up only from about ninety minutes. So why does duration matter so much?

1:32 · What you start with

It is because of what you start with. All your muscles together store about four hundred to five hundred grams of carbohydrate, as glycogen. Your liver stores about a hundred grams, and that is what keeps your blood sugar up. After a night without food, a scanner study measured about fifty grams in the liver of trained cyclists. A review puts a pace on it. Take an effort at about seventy per cent of the most oxygen the body can use. There, a seventy five kilogram athlete uses about thirty grams of liver glycogen an hour. Starting from a full liver, and without carbohydrate, low blood sugar sets in by about three hours. What you take in is the third source, and it arrives by the hour.

2:14 · What the drink keeps going

So what does eating on the move keep topped up? A classic study from nineteen eighty six had seven trained cyclists ride at about seventy one per cent of their maximum. Once with flavoured water, once with a carbohydrate drink every twenty minutes. With water they stopped after three hours. With carbohydrate they kept going to four. Their muscle glycogen fell at the same rate in both rides. The extra hour ran on the carbohydrate from the drink. One caveat: the water ride always came first. Five riders did it twice, and those two rides differed by seven minutes on average. To see which store the drink protects, you have to look inside.

2:52 · Liver or muscle?

One study looked inside with a scanner. Fourteen trained cyclists rode for three hours at a moderate effort, with a hundred and two grams of sugar an hour. Their liver glycogen held steady, while their muscle glycogen still fell. In four riders who also rode with only water, the liver fell as well. For the muscle, the pooled studies disagree a little. A two thousand and eighteen analysis of a hundred and eighty one studies found no sparing of muscle glycogen at all. A review from two thousand and twenty six describes a newer analysis of thirty one placebo controlled studies. That analysis found a small but real sparing effect. The same review says sparing shows up more often in running than in cycling. And in forty eight minutes of hard intervals, nine cyclists used about forty per cent less muscle glycogen with carbohydrate. So carbohydrate does spare your muscles, but on a long steady ride only a little, if at all. Mostly, the drink feeds the work directly, and it keeps the liver and your blood sugar going.

3:52 · Four sources, four ladders

Now the question in the title: how many grams an hour? It depends on how long you go, and on whom you ask. The position stand of the American College of Sports Medicine says it is not needed under forty five minutes. Small amounts for hard efforts of up to seventy five minutes. Thirty to sixty grams an hour from one to two and a half hours, and up to ninety beyond that. Another review from two thousand and fourteen splits the middle differently. Thirty grams for one to two hours, sixty for two to three, ninety beyond two and a half. The systematic review from the start of this video gives forty to a hundred and ten grams beyond two hours. And a review from two thousand and twenty six proposes raising the upper limit to a hundred and twenty grams, at least for trained athletes. The ladders also assume a certain athlete. That second review says its numbers are for well trained athletes. Its own example is a runner who takes five hours over a marathon. At that pace, ninety grams an hour comes close to, or above, all the carbohydrate the body burns. So the upper rungs were not written with a recreational pace in mind.

4:58 · Is more faster?

That is what the guidelines say. Now the question behind the trend toward a hundred and twenty grams. Does more actually make you faster? To answer that, we first need to know how much the gut lets through.

5:10 · Glucose, fructose and the gut

Glucose on its own runs into a limit in the gut, at about sixty grams an hour. In trained cyclists, more glucose hardly changed what was burned from it. By our conversion from grams a minute, seventy two grams an hour gave forty eight, and a hundred and eight gave fifty. Add fructose, which the gut takes up by another route, and more gets through. The highest rate, again by our conversion, reached a hundred and five grams an hour, from an intake of a hundred and forty four. For years the standard mix was two parts glucose to one part fructose. Newer reviews lean toward something closer to equal. In one study, twelve cyclists took ninety grams an hour in three different mixes. About one part glucose to point eight parts fructose gave the most burned from the drink. By our sum, sixty six grams an hour, against fifty five for the two to one mix. That shift rests on a handful of small studies like this one. So if the mix matters, does the form?

6:08 · Drink, gel or chew, and how often

Less than you might expect, it turns out. At a hundred and twenty grams an hour, four forms were compared. A drink, a gel, a chew and a mix of all three were burned within a few grams of each other. A bar came closest to an exception: it fell behind a drink late in a three hour ride, and left the stomach fuller. And what about how often it comes in? Guidelines say every ten to fifteen minutes. In one study, a gel every fifteen minutes or a double one every thirty made no difference. In runners, larger sips every twenty minutes even led to more carbohydrate burned than small sips every five. The one warning concerns very large portions. In skiers taking a hundred and forty four grams an hour, two big feeds caused more gut discomfort than six smaller ones.

6:55 · Where more stopped helping

So, back to where more stopped helping. The largest dose study had fifty one recreationally trained men. Each rider took a placebo and three of the doses, so each dose rests on about a dozen riders. They took between zero and a hundred and twenty grams an hour over two hours of riding, then did a time trial. The gain rose with the dose and then levelled off. The estimated gain peaked at seventy eight grams an hour, with the best dose somewhere between about sixty eight and eighty eight. At a hundred and eight and a hundred and twenty grams, the riders did no better. That curve fell just short of the authors' own test for significance, so read the peak as a region, not a number. Two recent reviews looked at the newer studies. Both find that the research does not show a faster time above about ninety grams an hour. The higher intake does get burned, but a smaller share of what goes in. In eleven men riding three hours, that share fell from eighty six per cent at ninety grams to seventy six at a hundred and twenty. The mix of sugars changed as well, so the dose was not the only difference. And where performance was timed, more did not help. In skiers, a hundred and forty four grams an hour gave the same thirty kilometre time as seventy two. There is one more thing to weigh here. The dose study's first author worked at a sports drink maker's research institute, and one of the ladders appeared in that institute's supplement. And five of the seven authors behind the hundred and twenty gram proposal report ties to a sports nutrition company. That does not make them wrong. It is a reason to read them next to the reviews without such ties. So what do athletes actually take in?

8:34 · What athletes take in, and the next day

Two hundred and twenty one athletes reported their intake in five kinds of race. The average ran from thirty five grams an hour in a marathon to seventy one in one Ironman. Individuals reported anything from six to a hundred and thirty six grams an hour. About thirty one per cent of the Ironman athletes reported serious stomach or gut symptoms. Those who took in more reported more nausea, though in the Ironman races they also finished faster, a link that does not show cause. And does it help you recover for the next day? It may, but only two small studies have tested it. In one lab study, seven cyclists rode to exhaustion on water, and a week later did the same work with carbohydrate. A time trial the next day took forty one minutes forty nine after carbohydrate, against forty two fifty after water. The water ride always came first, and their muscle glycogen was not measured. One field trial studied twenty six elite trail runners in a mountain marathon, all of whom had trained their gut. They took sixty, ninety or a hundred and twenty grams an hour. A day later, the hundred and twenty gram group showed fewer signs of muscle damage. But their race times did not differ, and only six or seven runners per group were analysed. And one thing holds for almost all of this research. It is on small groups of trained men, mostly on bikes. Across this field, fewer than three per cent of studies looked at women alone.

9:57 · What this leaves you with

So carbohydrate on the move does not keep your muscles full. It keeps you going when the small stores you started with no longer can. The more hours, the more it matters, and above about ninety grams an hour nobody has yet measured a faster time. The whole piece, with all its sources, is on enduranceproof dot com. Still to come is the other question from our video on fat and carbs: whether easy training has effects of its own.