Is a high-carb meal before an endurance event a good idea?

Eating a high-carb meal before an endurance event has been considered the norm for years. But is it the right thing to do, asks Rachel Jacqueline

PUBLISHED : Tuesday, 05 August, 2014, 9:44am
UPDATED : Tuesday, 05 August, 2014, 9:44am

If you're running a marathon, traditional wisdom suggests you should eat a bowl of pasta the night before. Carbo-loading, so the logic goes, will help you store energy reserves in your muscles.

But now sports scientists are reconsidering the need for endurance athletes to consume foods that are high in carbohydrates before they partake in endurance sports.

Carbo-loading is based on science, which says our bodies need carbohydrates to carry out high-intensity exercise. Stored as glycogen in muscles and liver, carbs offer a fast and readily available source of fuel, so before a big run, swim or bike you need to "load up".

Starches like rice and potatoes - are bad when consumed in excess, but used in moderation can help control one's weight
Brian Frank, founder and CEO of Hammer, nutrition 

However, our carb tank is finite. "Our untrained bodies are only designed to carry enough energy to sustain around 90 minutes of moderately intensive exercise," says Dr Duncan Macfarlane, a sports physiologist and associate professor at University of Hong Kong's Institute of Human Performance.

"While you can train your body to store more glycogen … you need to eat during the race to boost your carbohydrate metabolism. That's the type of exercise when you are working so hard that you cannot hold a conversation at the same time."

Yet if you've depleted your glycogen levels, you will become tired and slow down. You can't perform at a high intensity for an extended period without muscle glycogen; you can supplement your stores, but can't do it quickly enough to keep up a fast pace.

In a marathon, reaching this stage of fatigue can mean "hitting the wall". But it doesn't have to mean your race is over and you have to stop.

Luckily, your body has more than one source of fuel, as it also has a conveniently large fat tank. Fat is surprisingly good as a source of energy as it has more calories per gram - nine - than the four in carbohydrate. What's more, you have enough fat stores in your body to run from here to the Great Wall of China - and back.

The catch? Fat takes more time for your body to process. That means you are not able to run like Usain Bolt all day. "Your fat stores will only let you dawdle along," Macfarlane says.

Some of us are better than others at using fat stores. Evidence shows that women, for example, are slightly better at fat oxidisation than men.

Here's where the concept of carbo-loading gets curious for endurance athletes - those who exercise for 90 minutes or more at a moderate intensity.

If you have plenty of stored slow-burning fat, and if you could become more efficient at using it, would you need to ingest carbohydrates at all?

"Surely, our abundant body fat stores could provide most if not all the energy necessary to fuel activities of a submaximal intensity," sports scientists Professor Tim Noakes, Jeff Volek and Stephen Phinney are quoted as saying in the British Journal of Sports Medicine.

What's more, they argue, habitually consuming a high-carbohydrate diet is linked to health risks such as insulin resistance and diabetes, no matter how much you exercise. Paradoxically, they point out, research has found potential links between high carbohydrate diets and heart disease.

From a performance perspective, too many carbs before and during exercise are known to cause stomach upsets.

Despite a steadfast belief in carbo-loading, research has long proven that athletes can perform endurance exercise without carbs, in a state called ketosis. That refers to a state when the body is starved of carbohydrates, and converts fat into fatty acids and ketone bodies, which replace glucose in the brain as an energy source. A study by Phinney and others published in Metabolism in 1983 found that when five elite cyclists spent four weeks on an ultra-low carbohydrate diet (reaching ketosis), not only did they adjust, they became better at processing fat for fuel and reduced their reliance on muscle glycogen four-fold compared to a high-carbohydrate diet.

Later studies have supported the research, and even showed a potential performance benefit.

In a study published in the International Journal of Sports Nutrition and Exercise Metabolism in 2001, Lambert and others found that a 14-day diet high in fat was associated with better fat processing, a decreased reliance on muscle glycogen, and improved time-trial performance after prolonged exercise.

The randomised cross-over trial compared the performance of five endurance-trained cyclists during a 150-minute cycle at 70 per cent of peak effort, followed by a 20-kilometre time trial, after either a high fat diet for 14 days, or their habitual diet for 10 days followed by a three-day carbo load.

So do endurance athletes really need carbs? While perhaps not as much as first thought, carbohydrates still play an important role for athletes.

"Ingesting carbohydrates is not a must … all organisms can convert fat and protein to carbohydrate after all," says Roy Chun Laam Ng, a postdoctoral fellow in the department of medicine at the University of Hong Kong.

"But carbohydrates have the advantage of rapid energy supply … [they] can satisfy the instant needs of a large amount of energy in a very short period of time, which is especially good for athletes. Moreover, your brain is wired to love glucose [and not ketos] for energy."

For performance, carbs prevent the breakdown of muscle that occurs during endurance efforts and are also important for "refuelling" the body after exercise.

They also play an important role in several bodily functions, including the immune system, says Ng. Besides, ketosis for extended periods may lead to ketoacidosis, whereby the blood becomes more acidic, which may be fatal, particularly for diabetics. A high-fat diet also carries risk of stroke, heart attack or other heart disease.

Even the so-called paleo diet has been adjusted for endurance athletes by creator, Dr Loren Cordain, and athlete Joe Friel; the diet includes increased carbohydrates in The Paleo Diet for Athletes.

A word of caution: not all carbs are equal. "Leafy greens, cruciferous vegetables, and high water content vegetables are the 'good' carbs," says Brian Frank, CEO and founder of leading sports nutrition company Hammer Nutrition.

"On the other hand, wheat and sugar are 'bad' carbs that should not only be moderated, but preferably eliminated from one's diet, for optimal health and peak athletic performance."

"The third group of carbs - starches like rice and potatoes - are bad when consumed in excess, but used in moderation can help control one's weight by moderating or increasing them after all other dietary requirements have been met with and abundance of 'good carbs', lean protein and high quality fats," says Frank.

While "dietary periodisation" - periods of low carbs and high fat interchanged with higher carbs - may make you better at burning fat, it takes time. In Phinney's study, subjects had four weeks to adjust; in Lambert's, they had 14 days.

There are still many unknowns ,because research has only so far followed athletes over a period of few weeks and during efforts of around two hours in length.

For some, a low-carb approach may not work at all.

"I've never been a fan of high carb, but I do know that when I was performing at my best, I included whole grains in my diet. Not a lot, but some grain with breakfast and dinner," says Kami Semick, a top ultra runner.

"Everyone processes fuel differently. There are different fuelling needs for different types of training - faster or harder efforts require more carbs versus long slow runs, where I tend to eat more protein and fats."

Even self-proclaimed "low carb" endurance athlete, Tim Olsen fuels his long runs with carbohydrates, including sugary drinks, sports gels and fruits. On his blog, he admits to eating carbs "in the form of sweet potatoes and fruits" and using them "strategically".

"I'll eat sweet potatoes with coconut oil the night before a long or intense run. I'll have a green smoothie after a hard run with fruit and whey protein to replenish my glycogen and rebuild muscles," he says.

So what about your pre-race pasta party? Forget it, says Frank, himself an endurance cyclist. "Maintaining a steady caloric intake - carbohydrates, protein and healthy fats - leading up to an event when training will provide all the 'loading' an athlete needs.

"We caution eating a large meal the night before an event and recommend only taking in 400 to 500 calories in the morning, and only then if they can be comfortably consumed three hours before exercising."

So, depending on your goals and training regime, maybe it's time to ditch the pasta buffet for a fat fiesta instead.

Protein vital for endurance runners

Regardless of whether carbs are friend or foe, endurance athletes have greater protein demands than ordinary athletes. Protein plays an important role in repairing and strengthening muscle tissue.

It's also a key fuel for athletes during endurance efforts, says nutritionist Dilal Ranasinghe, co-founder of Nutrition Nation Hong Kong

"As a general rule, endurance exercise burns up to 15 per cent of the total calories from protein by extracting particular amino acids from muscle tissues," he says.

"If an endurance athlete does not provide this protein as part of their fuel mixture, more lean muscle tissue will be sacrificed through gluconeogenesis [converting carbs to energy] to provide fuel and preserve balance.

"When you exercise more than two to three hours, you need protein from a dietary source or your body will 'borrow' amino acids from your muscle tissue."

Generally, endurance athletes need 1.2 grams to 1.4 grams of protein per kg of body weight a day, compared with a recommended daily allowance for normal adults of 0.8 grams per kg of body weight.