The trend for rising carbohydrate intake in professional cycling has pushed up speeds in racing and shattered climbing records, and we’re seeing evidence lower down the ladder, too.
Gut training and science-backed formulations have raised the ceiling of what riders can consume on the bike, from a historic 90g to 120g and more.
In this context, it makes these recent comments by sports nutrition expert Tim Lawson concerning. “An increasing amount of amateur riders are calling me for nutritional advice because they’re pre-diabetic,” the founder of Science in Sport and currently of Secret Training, told me.
“These aren’t overweight people. One rider was racking up 15-hour training weeks. I spoke to Garry Palmer about this the other day and he said the same.”
Fuelling the workload
We got in touch with Dr Palmer, at the Cannock HQ of his performance centre Sportstest, to hear more on what he had to say about the subject.
“I first recall this phenomenon around 25 years ago,” he says. “I was working with a female rider who was funded by The Rayner Foundation [a charity to support up-and-coming youngsters].
"She was dead against carbohydrates because she was convinced they were making her prediabetic. At that point I thought what a load of nonsense. But my thinking has shifted a little."
“Part of that shift is down to a growing awareness of genetics,” Palmer continues. “We offer DNA testing and can see that some people naturally respond well to a relatively high carbohydrate, low fat, calorie-restricted diet. Others don’t. Like all of my advice, fuelling is about individualisation.”
There’s evidence that DNA testing for sport is still too simplistic, that we’re not yet at a stage of seeing how genes directly and indirectly impact sporting performance.
But there’s little doubt that Palmer’s individualised assessment rings true for training and nutrition, and is a lesson in not copying elite cyclists.
“It’s clear that professional riders can optimise performance by consuming 120g, 140g… of carbohydrates an hour. They’re putting out significant wattages and burning through huge amounts of glucose.
"Amateurs, even when they’re at threshold [the power you can achieve for an hour], are looking at around 4g of glucose a minute. That doesn’t demand such a high intake.”
Especially, says Palmer, when you ease off the throttle. “Suddenly you’ve all this available glucose, meaning a sharp insulin response when you stop. I’m sure that’s one of the main reasons why fit riders are showing up as prediabetic.”
- Read more: How many carbs can your body use per hour when cycling? I tried the new at-home test that tells you
Managing your insulin
Insulin is the key hormone here, because it regulates blood sugar levels. It’s produced by the pancreas and enables sugar to enter your cells, shifting up a gear when food is digested. When your blood sugar levels start to drop, your pancreas puts the brakes on insulin secretion.
When you have prediabetes [a condition where you have elevated blood glucose and are at risk of developing type 2 diabetes] this process simply doesn’t work as efficiently.
That could be down to your pancreas making insufficient insulin or your cells becoming resistant to insulin and accepting less sugar. Or both.
The causes are many, including obesity, waist size and smoking – not applicable to the majority of cyclists.
But it’s also impacted by diet, so even if you’re a fit cyclist, a constant feeding of sugar can damage this system. This, says Palmer, is something he’s seen among older riders in particular.
“As a youngster, you can get away with a lot more than your older self. Yes, you may have a good VO2 max for your age – which is a big indicator of life expectancy – but that’s less impactful if you’ve been consuming too high a level of carbohydrate for years.”
It’s a double-edged sword. On the positive side, a 2018 study tracked more than 122,000 adults for 13 years and discovered that those with the lowest VO2 max scores had a mortality rate nearly four times higher than those with the highest.
Further research showed that for every 1 MET (metabolic equivalent of task) increase in cardiorespiratory fitness (equivalent to approximately 3.5ml/kg/min of VO2 max), mortality risk drops by 11 to 17%.
But as the good doctor says, that’s not a total compensator if you continue to mainline sugar as you age. That’s due to various reasons, including your mitochondrial function naturally declining, so your cells become less efficient at using fuel; low-grade inflammation rises, which interferes with insulin signalling; and beta cells in your pancreas may not release insulin as effectively under stress.
“That’s not everyone as the years roll by, of course,” says Palmer. “Like everything in life, it’s about individualisation, moderation and balance, especially when you’re not training.”
Off-the-bike fuelling advice
This last point is key. Textbook training means consistent rides, following your plan to the letter. But life often gets in the way, meaning unscheduled breaks in training. The longer these are, the greater the warning signs.
“I’ve just been through a period of around four months where I trained little,” says Palmer. “My wife, a nurse, kept saying to me, ‘Gary, stop eating so much bloody carbohydrate. You’re going to give yourself diabetes’.
"I took a resting blood glucose test the other morning and I’m borderline pre-diabetic. The problem is, I’ve been an ‘athlete’ my entire life. I’m habituated to a high-carbohydrate diet.”
In other words, when the 50-plus Palmer doesn’t train, he still eats as if he is. It’s left his blood glucose readings close to the 5.6mmol/L figure (glucose per litre) that is prediabetic. If that figure rises to over 7mmol/L, you’re in diabetic territory.
This off-the-bike impact on your glucose levels is stark. A 2023 study in the UAE found that moderate-intensity aerobic training improved glucose metabolism, insulin regulation and fat profiles of the subjects during an initial four-week training period.
But after a subsequent eight-week block of detraining, many of these metabolic benefits diminished or reversed, including how the body handled glucose.
Earlier research echoed those findings. Twelve weeks of consistent endurance training cranked up insulin efficiency and raised GLUT-4 levels. This is a key glucose transporter in muscle. The body had become a furnace, burning through energy and maintaining a happy equilibrium. Until, that is, 14 days of no training that returned both insulin and GLUT-4 to pre-exercise levels.
In short, continuing to feed as you were when you were cycling during periods off the bike is no good for your blood-glucose markers or your weight.
“It’s why I recommend regular blood tests,” says Palmer. “You can monitor your levels over time. A key thing to keep an eye on is HbA1c.”
HbA1c is a measure of your blood sugar over time, not just in the moment. When glucose circulates in your blood, some of it naturally sticks to haemoglobin, the protein inside red blood cells that carries oxygen. Because red blood cells live for about two to three months, the amount of glucose attached to them reflects your average blood sugar over that period.
If your blood glucose has been higher more often, more sugar sticks to haemoglobin and your HbA1c goes up; if your glucose has generally been lower, your HbA1c will be lower.
In essence, it provides a more rounded picture of your blood-sugar levels, rather than giving just a single snapshot like a finger-prick test.
Muscle-mass concerns
Palmer reveals another growing trend: amateur riders using weight-loss drugs such as Ozempic and Mounjaro, which work by stimulating the release of insulin, reducing appetite, slowing digestion and increasing feelings of fullness (WADA has placed these GLP-1 agonists into its Monitoring List due to concerns about their use by athletes already vulnerable to disordered eating).
“I’m seeing riders losing massive amounts of muscle mass on those drugs,” he says. “One female rider, she lost 8kg in the first three or four months of treatment. I think 1kg of that was muscle mass, which was okay. But the following three months she shed another 6kg, of which 4kg was muscle.
"It’s the same with these prediabetic issues: what might look good on the outside might not be good on the inside.”
Education is key, adds Lawson. He’s concerned that the high carbohydrate craze is overflowing with misinformation. That’s not just the quantity of gels riders are taking but the composition.
“There are plenty of studies showing that fructose is malabsorbed,” he says, “but some of the studies highlighting high carbohydrate intake don’t factor that in.”
The science of this is deep and for another time but, in short, the signals emanating from carbohydrate metabolism can be distorted when measuring how much fructose is burnt.
The repercussions are that numbers banging the drum for high amounts of glucose and fructose could be erroneous, says Lawson, since those fructose figures could be incorrect.
The knock-on effect is not only gastro distress and nausea but, down the line, too much sugar intake for the workload, raising the chances of prediabetes. “I’m studying this at the moment,” says Lawson, “and hope to have more results soon.”
Both Palmer and Lawson agree that carbohydrates are critical to peak performance. But context is king. Match fuelling to workload, age and genetics, not the professional peloton.
It’s simple: eat like an amateur athlete when you train like one, ease back when you don’t. Performance gains mean little if your long-term metabolic health is paying the price.
