Tag: low carb diets

Can a low carb diet help or hinder your performance?

With so many diet trends out there, it’s hard to know which ones help or hinder your performance. One trend that’s recently become popular among endurance athletes is the low-carbohydrate high-fat (LCHF) diet. The idea behind it is that training with low glycogen (carbohydrate) stores trains your body to burn fat more efficiently and increases muscle adaptations to endurance exercise. Theoretically, this should allow you to keep going longer before reaching fatigue and may even help you avoid ‘bonking’ or ‘hitting the wall’ in a marathon (running out of stored carbohydrate).

Indeed, studies have found that ‘training low’ (i.e. with low glycogen stores) increases the number of mitochondria – the fat-burning powerhouses – in the muscle cells. Others have also shown that ‘training low’ enhances cell signalling proteins, gene expression and fat burning enzyme activity.

However, despite these cellular changes, there’s a lack of evidence that chronically training on a LCHF diet improves performance. What’s more, it has been shown to hamper the muscles’ ability to break down glycogen during high intensity exercise and hinder power output during sprinting. You literally lose your top gear.

The most definitive evidence comes from the ‘Supernova’ study of 21 elite race walkers who followed either a high carbohydrate, a periodised carbohydrate or a LCHF diet for 3 weeks. The researchers found that

  • Although the LCHF diet increased the body’s ability to burn greater amounts of fat during exercise, it also reduced exercise efficiency i.e. the athletes required MORE oxygen to exercise at the same speed
  • the LCHF diet impaired race performance
  • High carb and periodised carb diets improved exercise economy and race performance

 

In practice, many athletes find that training low feels harder, especially when they want to pick up the pace. Think hills, intervals, tempo runs, breakaways or sprinting for the finish line in a race. The truth is high intensity exercise (such as running fast) feels easier when you eat carbohydrate (such as potatoes, rice, pasta and bananas).

Another downside of ‘training low’ is that it can deplete your immune function and increase the risk of infection. The key to preventing this is to avoid high intensity sessions when your glycogen stores are low.

Body fat may be available in abundance (compared with carbohydrate) but it is a ‘slow’ fuel, which means it converts to energy comparatively very slowly. You can produce up to 25–30 kcal per minute from carbohydrate but only 6 kcal per minute from fat. Train above 85% VO2max, and you’ll be burning almost exclusively carbs.

A LCHF diet may suit those doing mostly low intensity workouts, like long slow runs or ultras. It means you won’t need to carry as many high carb snacks with you! But if you want to train hard and fast, then you’re better off with carbs.

If you want to get the best of both worlds – maximum fat-burning plus maximum performance – then ‘flexible fuelling’ could be the way to go. It’s backed by cutting edge science and is used by some top endurance athletes to give them a competitive edge. It involves matching your fuel (carbs) to your workout. The advantage of this approach is that you get the dual benefits of ‘training low’ – namely an increased ability to burn fat – as well as the performance benefits of high intensity training.

Here’s how it works:

  1. Before your easy or low intensity workouts (e.g. long, easy runs), minimise carbohydrate beforehand. This will encourage the muscles to become more efficient at using fat as fuel. Suitable pre-workout meals or snacks include an omelette or poached eggs, an avocado salad, or hummus with vegetables.
  2. Before harder or high intensity workouts, eat carbohydrate-based meals or snacks. This will help you train at a higher intensity for longer. Good options include porridge, rice and beans, or potatoes with cheese.
  3. The simplest way to ‘train low’ is to run before breakfast but other protocols may be used.
  4. If you struggle with ‘training low’, try taking caffeine approximately 45 – 60 min before your session. The optimal ergogenic dose is around 3mg/ kg body weight. This can reduce perceived effort and fatigue.

What’s the evidence? The best evidence for this flexible fuelling comes from two recent studies. One study with 21 triathletes , found that those who cut carbs around selected training sessions (a ‘sleeping low’ protocol) for three weeks improved their cycling economy (power output per calorie) by 11 per cent, 10km running performance by 2.9 per cent, time to exhaustion during high intensity exercise by 12.5 per cent, compared with those who did all their training with high glycogen stores.

The second study with 11 cyclists found that the same ‘sleeping low’ protocol followed for just 6 days resulted in a similar (3.2%) performance improvement.

In summary, there may be small advantages to gained from ‘training low’ before specific workouts. The research is fairly limited and there’s no definitive proof that it leads to big performance improvements. If you do decide to try it, pick just one or two low-intensity sessions a week alongside your normal training when you are fully fuelled. Keep a training log and see whether it helps your performance or not. If you suffer gut problems when consuming food during running, then ‘training low’ may suit you. Also, not having to carry bars and gels during long runs may be helpful from a practical point of view.

If you enjoyed this post and want to find out more about sports nutrition, then check out my brand new book, The Runner’s Cookbook. It features more than 100 delicious recipes to fuel your running. With a foreword from five-time Olympian Jo Pavey, the book also provides practical nutrition advice on fuelling before, during and after running, guidance on hydration and supplements, weight loss tips, how to recover from injury, and how to prepare for 5k, 10k, half marathons, marathons and ultra races.

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How Periodised Carbohydrate Training Can Help Your Performance

 

Periodised carbohydrate training has become the latest buzzword among endurance athletes. Essentially it means matching your diet to your workload and new research suggests it may improve endurance performance and make you a more efficient fat burner.

The idea behind training with low glycogen stores (‘training low’) is that it forces the muscles to burn more fat for fuel and rely less on carbohydrate. By teaching your body to tap into its fat stores, you should in theory be able to keep exercising for longer before reaching fatigue.

Indeed, studies (here and here) have shown that when you ‘train low’ you increase the muscle’s adaptive response  to training. It increases mitochondrial biogenesis, so you get an increase in the number and volume of mitochondria – the fat-burning powerhouses – in the muscle cells. The more mitochondria you possess, the greater your muscles’ ability to use fat as fuel, sparing your glycogen stores.

But – and it’s a big but – chronically training on a LCHF diet hasn’t been shown to translate into any performance benefit. It can hamper your muscles’ ability to break down glucose and glycogen during high-intensity exercise. You literally lose your top gear.

High-intensity exercise feels much harder. Your performance, rather than improving, may drop. Your immune system may become depressed, increasing the risk of infection. And you could lose muscle.

But with periodised carbohydrate training you get the dual benefits of ‘training low’ – namely fat adaptation – as well as the performance benefits of high intensity training. Also, it’s a more sustainable approach. Essentially, it means doing some of your low-intensity sessions in a carb-depleted state, and your higher intensity sessions with high glycogen stores.

The simplest way to ‘train low’ is to train in the morning before breakfast. However, this should be done before an easy session, nothing too long or too intense. Alternatively, if you want to train low in the evening, cut carbohydrate at breakfast and lunchtime (keeping to mainly high-protein foods and vegetables). Another method is ‘sleeping low’. This means doing a tough session before sleep, eating a low carb dinner then doing a low-intensity session the next morning.

This method looks more promising in terms of performance improvement. A multi-centre 2016 study with triathletes found that those who followed a ‘sleeping low’ protocol for three weeks improved their cycling efficiency (power output per calorie) by 11%, 10km running performance by 2.9%, time to exhaustion during high intensity exercise by 12.5%, and also reduced their body fat compared with those who did all their training with high glycogen stores.

A follow-up study with cyclists by the same team found that using a ‘sleeping low’ strategy for just six days resulted in a 3.2 percent improvement in a 20K time trial.

Most recently, a study at the Australian Institute of Sport  compared the performance effects of a high-carb diet (60 – 65% carb), a periodised carb diet (same macro’s but periodised within or between days) and a LCHF diet (<50g carbs) in a group of 21 elite race-walkers. After 3-weeks on each diet, all athletes improved their aerobic fitness (VO2 max) but only those on the high carb or periodised carb diet improved their 10k race performance. The athletes on the LCHF diet did not make any improvement. Although they were burning a higher proportion of fat during exercise, their muscles became less efficient at producing energy, requiring more oxygen at any given speed. All of which suggests that fat adaptation incurs an efficiency penalty.

To date, this is the highest quality study on low carb vs high carb that we have. Although It makes a pretty damning case against chronic low carb diets, it also provides good evidence for a periodised carbohydrate approach.

In summary, eating low carb all the time is unlikely to benefit your performance unless you’re exercising at a relatively low intensity for long periods, such as ultra-distance events. For other endurance activities, it may be worth trying a periodised low carb approach.

Pick just one or two short low-intensity sessions a week alongside your normal training when you are fully fuelled. Keep a training log and see whether it helps your training or not. If you suffer gut problems when consuming carbs during running, then ‘training low’ may suit you. Also, not having to carry bars and gels during long runs may be helpful from a practical point of view. Remember, whatever the research says, a good nutrition strategy boils down to doing whatever works for you as an individual.

If you enjoyed this post and want to find out more about vegetarian diets, then read my new book, The Vegetarian Athlete’s Cookbook – More than 100 recipes for active living (Bloomsbury, 2016)

It features:

anita-bookMore than 100 delicious, easy-to-prepare vegetarian and vegan recipes for healthy breakfasts, main meals, desserts, sweet and savoury snacks and shakes. 

  • Expert advice on how to get the right nutrients to maximise your performance without meat
  • Stunning food photography 
  • Full nutrition information for each recipe, including calories, carbohydrate, fat, protein and fibre

 

 

 

 

 

 

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