IS THE CARB STILL KING?
Tour de France champ Chris Froome kicked the hornets’ nest last year when he posted images of his carb-light meals on social media. Decades of orthodoxy on fuelling were thrown into question, so we decided to ask science whether carb-loading was now a dea
Chris Froome has kicked carbs in to touch. Should you too? We examine whether carb loading is a dead duck?
St Mary’s University, Twickenham, is a beautiful place – a mixture of leafy spaces, lush grassy sports fields, imposing Gothic buildings and ultra-modern laboratories. It’s in this idyllic setting, beneath a wall adorned with the messages of gratitude from clients including Olympic and world champion Mo Farah, that Stuart Forrest is being sick over a very expensive Wattbike.
Stuart, along with Ewan Burns and Matthew Ketchell, is a volunteer in a study of one of the more contentious areas of sports nutrition – the Low Carb, High Fat (LCHF) diet. Proponents believe it’s a diet that leads to performance gains, boundless energy, sharper thinking, weight loss and better long-term health prospects. Detractors believe it’s a fad that comes into fashion periodically before fading away as people realise its benefits are overstated.
The study is detailed but straightforward – the current crop of volunteers is given a series of baseline tests covering their height, weight, VO max, body 2 composition, grams-per-minute fuel consumption, plus sub-max and Functional Threshold Power (FTP) scores by St Mary’s lead physiologist, Paul Hough. These tests are repeated three more times, at weekly intervals, while the subjects use a smartphone app to track their macronutrient intake. With the help of nutritionist Sarah Danaher, the subjects will cut their carbohydrate intake from its current level of around 60 per cent of their diet down to around 20 per cent while repeating the same set of tests for a further three weeks and following an exercise plan set by the St Mary’s team.
If the LCHF theory is correct this should see them becoming ‘fat adapted’, increasing their e ciency and ability to burn fat for fuel. As the body can only convert and store a limited supply of carbohydrate in the liver and muscles, but can store vast quantities of fat, the upshot should be a huge supply of energy with no need to rely on expensive gels, powders and bars. As a side benefit, burning fat as fuel rather than accumulating unspent sugar around the waist has an advantage when it comes to weight loss or, more accurately, body composition.
BURNING FAT AS FUEL HAS AN ADVANTAGE WHEN IT COMES TO WEIGHT LOSS OR, MORE ACCURATELY, BODY COMPOSITION
The downside, at least as far as the participants in the study are concerned, is that sub-max and FTP tests are two of the most uncomfortable things you can put yourself through on a bike, and they’ll have to do them both every week for the next seven weeks.
“The nice thing about this case study is that because we’re tracking everything, we see the real-world practicalities of this type of diet,” says Paul, “It’s difficult, these guys are living off meat and unprocessed foods, and still there’s an accumulation of carbs. At one point Matthew said ‘I had a sandwich, and that was it, I’d had all my carbs for that day’. And carbs are in stuff that you don’t expect – you see beef jerky and think it’s just protein, but there’s a coating on it that’s full of carbs.”
Lab Rats
So great are the difficulties of cutting out carbs that Paul believes many proponents of low-carb diets aren’t actually on them at all. He tells numerous tales of clients recounting their meticulous efforts to cut the pasta, rice, bread and sweets from their diet while putting sugary pre-packaged sauces on their spiralised courgettes, or substituting sugary energy drinks for sugary electrolyte drinks. While it’s perfectly possible to achieve a low carb, or even the more extreme ketogenic, diet, it can’t be done simply by cutting the obvious starchy carbohydrates. You need meticulous monitoring of everything you eat and drink, and advice on satiating substitutes for carbs. Even then it takes very little to catch you out.
“I bought things like BBQ sauce to flavour up the copious amounts of chicken I was eating, without checking the label,” says Matthewhew. “It had lots of sugar and sent the carb count skyward! My speciality dish is homemade scotch eggs and I thought they’d be great for the low-carb period – all that egg, sausage and black pudding – but you have to flour and breadcrumb them before they’re deep fried and that means carbs.”
Ewan had similar experiences, ordering chilli without rice only to discover that the sauce itself was going to push him over his daily limit. Even things that sound like they came straight from the whole food shop can trip you up, as Stuart discovered: “Supposedly healthy stuff like a green tea and peach drink had an alarming amount of carbs in it. I got caught out by edamame beans too, and legumes, who knew?”
As the trio got into the study it became apparent that simply moderating their carb intake wasn’t enough - they had to cut so much out of their diet that a plan was needed to replace what was missing. High fat, high protein meals were prepared, and an unusual array of foods were pressed into service as satiating snacks.
“I had my first omelette during this phase,” says Stuart, “and now I’m slightly obsessed with them. A large breakfast sees me through to 1pm without feeling hungry,
THESE GUYS ARE LIVING OFF MEAT AND UNPROCESSED FOODS, AND STILL THERE’S AN ACCUMULATION OF CARBS
that and a bag of peanuts by my desk in the afternoon. For snacks Kabanos (Polish sausages) and Leerdammer cheese slices have been great.”
Ewan also found that nuts and cheese were a great help in feeling full. “I would snack on nuts and seeds mostly, and chunks of cheese, which I don’t usually have much of. You can buy snack packs of seeds with a soya dressing, which were handy. For breakfast I usually had a coconut milk-based yogurt or double cream with low-carb fruit like raspberry and some seeds. Lunch would be a salad with cheese, meat and a dressing with more seeds, and an omelette with cheese plus courgette and onions for dinner.”
The tests
Having mastered the difficult task of staying sated, the participants returned to the lab for further testing. The main tests for the study are the sub-max and FTP. In the sub-max the Wattbike’s resistance is increased by 25 watts every four minutes while the riders’ blood and exhalations are repeatedly checked to observe the increase in blood lactate and the change in ratio of oxygen and carbon dioxide in the breath. The FTP is more familiar to cyclists as it can be done, albeit less efficiently, outside of the lab – it’s essentially a 20-minute time trial effort that’s used to establish the maximum power you can hold for an hour.
Our volunteers approach both tests very differently. Stuart, a publisher with generally the highest fitness of the participants is relaxed, staring straight ahead with the occasional glance around the room. Matthewhew, a journalist, is stoic, staring straight ahead and disappearing into his own head during the test. Ewan, a physiotherapist who competes in Iron Man triathlons, has the leanest body composition and most relaxed attitude, occasionally engaging lab assistant Glenda Anderson in conversation during the early stages of his efforts.
Despite their differences in demeanour, power output and body composition, it becomes clear that they’re responding to the diet in similar ways. Their oxygen consumption is increasing, and they’re struggling to hit the markers from their baseline tests. In fact, it’s two weeks into the diet when Stuart has his gastric incident all over the biohazard warning tape that’s been placed over the display to prevent him from riding to known data.
“It felt terrible,” says Stuart, reflecting on the process. “I feel as if I’ve lost some top-end power, and it felt as if my heart rate was spiking higher during the first couple of weeks. In general, the low-carb period has been a lot harder. I had one great session where I felt a lot stronger, but the first week was tough and the final one was really hard. I struggled and it felt as if I’d lost maybe 10 per cent. I’d been spinning happily at 91-93rpm in most sessions but in the last I was struggling to keep it above 83-84rpm.”
Interestingly, Stuart’s “one great session” is the one in which he was ill, and the only one in which he came close to replicating his carb-fuelled efforts. He wasn’t the only one to suffer during the low-carb phase.
“It wouldn’t be the end of the world if I never have to do an FTP again, they’re horrible,” laughs Matthewhew. “I think I had a lab test on day one of the low-carb period, which wasn’t great timing. I remember feeling irritable at work, I had a headache and by the time I arrived at the lab I felt ready for bed. I battled through but would be staggered if that wasn’t my lowest score of all the tests. By the following week I felt back to normal.”
Ewan is perhaps the most composed when discussing the tests, remaining understated. “During the sub-maximal test the wattage is increased every four minutes, which felt fine while on the carbs. On low carbs the higher wattages felt very difficult, like my legs were empty. That said, the FTP test didn’t feel much different… Maybe I wasn’t pushing hard enough!”
Some Pain, No Gains
The big question after all this effort is did it work? And the answer is, it depends.
I’D BEEN SPINNING HAPPILY AT 91-93RPM IN MOST SESSIONS BUT IN THE LAST I WAS STRUGGLING TO KEEP IT ABOVE 83-84RPM
“Pretty much all of them showed similar responses,” says Paul. “To varying degrees each saw a change in their body fat percentage, their grams-per-minute of fuel consumed and a change in respiratory exchange ratio – that’s the big one, it takes more oxygen to burn fat, so it shows that the ratio of fat to carbohydrate oxidation is changing.
“No one’s performance improved on the low-carb diet,” he emphasises. “With Ewan and Matthew, I don’t think it massively diminished performance, whereas with Stuart, I think it did. If you’re a more highly trained athlete with a higher max or average power output, then you’ve got more to lose.”
After three weeks on the low-carb diet, Stuart’s FTP performance had declined by 3.9 per cent, while his oxygen consumption had shot up by 17.4 per cent – meaning he’d become both less powerful and less efficient. Ewan had suffered a similar decline in power, albeit with an almost inconsequential drop in efficiency, and Matthewhew had suffered almost no drop off in power, but had increased his oxygen consumption by 10 per cent.
“The trend was that with both of the stronger cyclists, their FTP performance did suffer. If we compare the third week of Stuart’s normal diet with his third week of LCHF, there’s a real drop in performance. The energy yield per gram from fat is less than from carbohydrate, and although you can increase fat oxidation, you also increase your oxygen consumption, which affects your economy. If you’ve got poor exercise economy and you periodically do low-carb training to improve your fat oxidisation, that’s probably a good idea, but when carried out chronically that improvement in fat oxidisation doesn’t seem to improve performance.”
fuel your engine
It’s not uncommon for cyclists to use motoring analogies: he’s a diesel, she’s got a big engine. When it comes to low-carb, high-fat diets, these analogies seem pretty accurate. The ability to run off multiple fuel sources has benefits, but performance isn’t one. There are a hundred reasons to buy a hybrid car, but you won’t win a Grand Prix with one.
There are other advantages to a low-carb diet. Using a skinfold test, each of our participants had their body mass and body fat percentages measured, and for both Matthewhew and Stuart, the diet saw big improvements, with Matthew’s numbers dropping by nearly 10 per cent in three weeks, and Stuart’s dropping by almost as much. Ewan, who was by far the leanest of the participants in the test, held steady.
Losing weight by shedding fat is usually the holy grail for cyclists, but according to Paul even this result is only a starting point rather than a net gain: “The two effects will have cancelled each other out: they might have lost body mass, but they’ve lost power as well, so their watts per kilo won’t have shifted around too much.”
It seems that a low-carb diet might be incredibly useful to help you drop weight during the off-season, but using it during competition or in the build-up to an event will likely hamper your power output.
Building the ability to use multiple substrates will benefit anyone who does a lot of regular low-intensity riding, such as challenge cyclists, but even then there’s a possible caveat as Supernova, a recent study into elite walkers by the Australian Institute of Sport, suggested that low-carb diets might not just be preserving your glycogen stores, but might also be hampering your ability to use them – that becoming ‘fat adapted’ might mean you become less efficient at burning carbs.
THE TREND WAS THAT WITH BOTH OF THE STRONGER CYCLISTS, THEIR FUNCTIONAL THRESHOLD POWER PERFORMANCE DID SUFFER