We need to reassess our relationship with carbs,’ says Laurent Bannock, a performance nutritionist and lecturer who works with both elite and amateur athletes (guruperformance.com). Eating lots of carbohydrates makes you good at metabolising them, explains Bannock – which sounds great until he adds ‘instead of fat’. ‘As an endurance runner you should be using body fat as your primary fuel source, so why do runners get obsessed with consuming carbs?’
Bannock is not alone in questioning the accepted carb doctrine. ‘Skilful marketing has made carbohydrate consumption a religion among athletes,’ says Professor Tim Noakes. ‘They believe that you cannot get energy from anywhere but carbs.’ Noakes – who as author of The Lore of Running (£13.43, Human Kinetics) can safely be classed as a running and sports science heavyweight – recently turned his thinking around on carbs and caused some controversy by advocating a Paleo-style diet (high-protein and low-carb, based on the meat-, nut-, berry- and veg-eating habits of our hunter-gatherer ancestors).
For Noakes, it’s not just about performance, but health too. He argues that some people simply can’t metabolise carbs as efficiently as others. And for the carb-intolerant, eating large quantities won’t just limit fat-burning capacity, it will fail to properly fuel performance, and lead to weight and health problems. For him, the switch was driven by the fact that, despite clocking 200K a week as an ultra runner, his weight was always an issue. He ate the traditional high-carbohydrate, low-fat diet that he had advocated for 33 years, but still ‘expressed his familial predisposition and developed type 2 diabetes’, he says.
‘There’s never reason to eat more than 200g of carbs a day,’ argues Noakes. ‘Some athletes eat 700g a day, and the probable outcome of such high-carb intakes in those with the genetic predisposition is the development of type 2 diabetes – as happened to me.’
Retraining your metabolism
Even if you’re not carrying the carb-intolerant genetic hand, over-consumption of carbs, some argue, can negatively affect your running performance. ‘The body adapts and if you eat lots of carbohydrates, it will become good at metabolising carbohydrates,’ Bannock reiterates. ‘Your body will use the fuel it’s been given and initiate the carb management system. But to see improvements to your endurance-running performance, you
need to retrain your metabolism to get your body used to becoming efficient at using fat as a fuel source – becoming fat-adapted,’ he continues. ‘Improving your ability to burn fat will preserve limited carbohydrate stores for when they’re needed (for instance, at the end of the race), and improving your metabolic efficiency will also boost your health.’
Noakes is reading from the same menu here: ‘Humans are designed to burn fat as the primary fuel during endurance workouts,’ he says. ‘That’s why we store so much of it in our bodies and relatively little carbohydrate. While one might argue that high-intensity exercise of short duration might be improved by a high-carbohydrate diet, the majority of people eating high-carbohydrate diets are involved in prolonged, low-intensity exercise for which fat is the optimum fuel.’
So how do committed ‘carbivores’ retrain their metabolisms to burn fat for fuel? ‘By eating less carbohydrate and more healthy fat, and timing it right,’ says Bannock. ‘It’s what you do on average that affects how your metabolism utilises carbohydrates. So make your daily plate contain 50 per cent starchy vegetables/fruit, and 25 per cent each of lean protein and healthy omega-3-rich fat.’
‘Save the starchy carbs until after your workouts; eat 50 per cent carb/50 per cent protein up to an hour after your run. Then, after two hours, opt for protein, veg, fat and carbs in equal measures,’ explains Bannock. ‘Your body is like a fire, and just after you’ve trained the fire is burning, and this is the time to throw your carbohydrate logs on.’
Other experts agree on the potential performance benefits of limiting your carb intake. ‘New studies suggest it is possible to ‘train’ your muscles to use fat preferentially for fuel by consuming a low-carb diet,’ says Anita Bean, author of The Complete Guide to Sports Nutrition (£10.87, A&C Black). ‘Over time, the muscles will make more fat-burning enzymes and mitochondria,’ she explains. ‘Though low-carb diets will best suit those training for shorter races or those who are pre-diabetic [insulin-resistant].’
To take your carb-limiting strategy a stage further, consider the maxim of ‘train low, race high’. ‘Eating a low-carb diet in training and a high-carb diet 24 hours before a race gives you an advantage of having more fat-burning enzymes, plus more carbs as fuel for your muscles in the latter stages,’ says Bean.
Also pay attention to your intake of energy drinks, which are very high in carbs with 30g or more per 500ml, ‘which you simply don’t need if you’re running at a moderate speed for less than 60 minutes’, says Bean. ‘Then, water is all you need to hydrate.’
Training your metabolism to be ‘fat-adapted’ means you ‘won’t need to ingest sugary sports drinks, because you have all the energy you need in your body’, says Noakes. ‘If you are carbohydrate-adapted, you will probably need to take in sugary drinks during exercise,’ he says. ‘But whether or not drinking sugary drinks during exercise is healthy is another question entirely: there is growing evidence that sugary drinks increase the risk of developing diabetes. Even one can of sugary drink a day is associated with an increased diabetes risk.’