High Food: Climbing and the Glycemic Index

Article by planetFear
Monday 14th September 2009

- All photography copyright David Pickford / www.davidpickford.com -

It must be hard work being a nutritionist these days, with a new wacky diet  popping up almost every month and attempting to rewrite the established rules of good nutrition. It no longer seems okay to just stick with your five fruit portions and a balanced diet of carbohydrate, protein and fat. No, it looks like we should, in fact, be eating just fruit... No, wait a minute, just eating protein... no, fat, oh sorry no, we shouldn't eat anything at all and just get our nutrition from the sun (the person who thought up this last one obviously lived in Boulder, not Barnsley).

A recent fad in the diet-world came from that troublemaker Dr. Atkins, with his philosophy of 'eat meat - stay thin'. After considerable research it was finally demonstrated that this simply doesn't work well for most people.

Freshly barbecued Tandoori chicken piled up for sale in a street stall in Old Delhi, India. Dr. Atkins controversially argued that a diet consisting almost entirely of protein and fat was the best way to stay slim and healthy.

Climbers, although notoriously obsessed with body fat, require more out of their diet than a way of getting from meal to meal. Food fuels all physical activity, and so applying the right food for whatever type of activity you do is crucial for success. Luckily for us the latest dietary trend could offer us some valuable ideas on how to get the most out of the food we have, important if weight/energy ratio is crucial for success.

One of the major modern developments in nutritional science has been the creation of the Glycemic Index (or G.I.). Its central principle is that you no longer look at carbohydrates in the narrow terms of simple calorie content in order to work out how much energy they release. Instead, carbohydrates are broken down further so you can look at the numerous components that make up the carbohydrate, and the different ways in which they release energy. This newer approach and understanding holds much promise to anyone willing to apply it to climbing, especially if that climbing involves endurance-based routes. 

Cooking a carbohydrate-rich meal in the evening after a hard day's climbing: understanding the Glycemic Index and eating accordingly is extremely important in terms of optimising your energy levels.


Imagine the human body as a car, with its digestive system being the engine. This engine runs on a fancy twin fuel system, carbohydrate and fat, with protein only normally being used to repair the dented bodywork unless things are pretty desperate (a bit like running your car on Turtle Wax). The engine converts both off these nutrients into sugar (technically this is glucose), which produces the spark that turns your engine (your cells). You can view carbohydrate as a high-octane rocket fuel while fat is the diesel, a slow burn fuel, designed to keep us ticking over day after day. This twin fuel system gave us the ability to sprint off when chased by a sabre tooth tiger and survive the famine when the tiger ate all the sheep you were supposed to be looking after.

This difference in expected fuel usage can be seen in the amounts stored by the body. The average person has 160,000 calories stored in their body (Chilean rugby players may have more), which makes it obvious why we made good sabre tooth tiger food. Of this only 2,500 calories comes from sugar, while 23,000 comes from protein (muscles, skin etc) and the rest, all 134,500 calories of it, from fat. As you can see the amount of sugar available is severely limited, giving you about two hours worth if working hard (anaerobically) and is why you can easily bonk or hit the wall if you don't top up the tank. It makes sense that using fat as fuel would be best, but unfortunately fat takes longer to break down into the sugar your engine needs to burn and most people won't go into an affective fat burning state for over two hours when exercising, meaning by then it might be too late.


Sugar is designed to supply energy to the nervous system, brain and to provide that emergency power boost. Sugar also provides that power-up energy used to get us started and hopefully allow us to slip into a more long term and efficient fat burning state.

Fresh fruit juice is a fantastic source of sugar in the form of fructose (fruit sugar) which the body can transform very quickly into glucose. 

When this limited store of sugars begins to slip into a deficit of 20%, the brain sends you a signal to warn you of this fact (a bit like your petrol warning light coming on after only half an hour after filling up). The body is programmed not to run out of juice if something big and nasty takes an interest, and it will try to avoid reducing its stores by more than 25%.

This low blood sugar warning signal takes the form of loss of concentration, dizziness, irritability, lack of co-ordination and, in extreme cases, blurry vision. These warning signals have been experienced by anyone who's climbed, walked or run hard in the mountains; a kind of narrowing of vision where all you can think about is the pain and all the joy and colour drains out of the experience. We interpret these signs that we need more food to revive us and turn the situation around and what food do we know will give us fast energy? That's right, sugar, in the form of carbohydrates (chocolate, banana, sandwich).

So what's the problem? Just keep on downing that sugar and keep the tank topped up and everything will be fine? Well, unfortunately, like anything that works so well, sugar has a number of side effects if taken to excess.

Once in your small intestine, that chocolate bar or sandwich is broken down into simple sugars so it can be transferred into the blood and absorbed by the body. Now this sugar is new in town and doesn't know where it is supposed to be heading, plus the cells of the body where it's heading are pretty cautious and won't be letting them in unless they are sure the sugar is kosher. This is where the pancreas comes in. It gets a call from the brain telling it that there's a long cue of sugar molecules waiting at the small intestine that need dealing with straight away (remember the brain might be a bit irritable at this point). So the brain sends out its insulin hormone to pick them up and take them to the right destination. Once picked up they are whisked off through the blood to the nearest cell, where the sugar is then transformed into energy.

To begin with the pancreas taxi HQ sends out just the right amount of taxis to get all the sugars to their cells, but as the shift goes on and the work load stays high, with sugars coming and going constantly, the old pancreas loses control sending out more and more taxis until the bloodstream picks up every stray sugar molecule they find and whisks them off to the nearest cells. This causes the normal blood sugar level to drop (hypoglycaemia), triggers the brain to send more signals that you need sugar, even though your cells are chocker with the stuff. With all this sugar going around all the organs get on the case and ignoring fatty molecules, start asking for more sugar, putting you even further into the red.

This is the classic sugar rush and sugar crash experience. It goes without saying that this kind of boom and bust state isn't conducive to a healthy state of body or mind and doesn't just limit your performance but can also lead to mistakes, low morale (leading to failure) and worse of all, ratty partners. In the long term this kind of sugar-burning state is very destructive on the body, leading to a whole host of serious problems including diabetes and carbohydrate intolerance. Furthermore a lot of this excess sugar is stored away as fat, meaning even if you're exercising hard, eating lots of bananas will make you as fat as eating chocolate.



Now the importance of the Glycemic Index is that it breaks down the carbohydrates into those that enter the blood stream quickly (gushers) and those that enter slowly (tricklers). Now many people will immediately link this with the principle of complex and simple carbohydrates, which it was thought had the same effect on blood sugar levels. The problem is that it's been found that it's not that simple, as some complex carbohydrates are gushers and some simple carbohydrates are tricklers. The problem with the gushers (processed carbohydrates most usually) is that they enter the blood stream in a huge dose, increasing insulin levels and causing a huge spike. Such a huge amount of sugar cannot be used and so is changed into fat, which is one of the reasons why obesity levels are so high. The tricklers on the other hand are much harder to break down, meaning they drip into the bloodstream, reducing the stress on the pancreas and stopping the side effects of variable blood sugar levels.



A typical cross-section of optimal climbing foods: fruit, biscuits, chocolate, and energy bars. Such foods provide an excellent balance of carbohydrates and fats, and also (apart from fresh fruit) offer a very good weight to calories ratio, which is important if you have to carry your food up a climb.  

Most foods contain a mixture of tricklers and gushers, but the important thing is to know which is which foods have low and high GI ratings, and attempt to maintain an overall low to medium GI. If, say, you're running a mountain marathon and it's day two then it's fine to swallow a mouthful of jelly babies, but if you're scrambling up the Matterhorn and come over all tired, then doing so isn't going to do you much good long term. If you look at your food - which is often limited - as to what type of calorie you'll be getting, then you will hugely improve your energy levels.

There isn't room here to go into the ratings of all food, but I guarantee there are some major surprises. For example, couscous and potato powder are  'gushers', whereas most types of pasta and rice have a low to intermediate GI, and - amazingly - a sugar cube has a lower GI than a slice of white bread. Once understood, you'll be eating whole wheat bread with Nutella for lunch rather than baguette with cheese when in the Alps, more apples and less bananas when cragging and feel less guilty eating Snicker bars rather than the power variety. Understanding the GI levels of different foods, and turning what looks like another daft dietary fad into something that lets you keep the weight on, will definitely help you to maintain your energy levels and also guarantee that as many calories as possible will be used to power your body. In the process, this will help you stay alert, positive, and make that 'let's go down' feeling far less common.

Rehydrating on a hot summer's day on Lundy Island. As a final thought, remember that no intake of nutrition can be fully optimised by the body unless it is sufficiently hydrated. A dehydrated body  simply cannot digest or metabolise food properly. Conversely, good hydration is a major factor in optimising an athlete's nutrition, since this allows the body to make full use of all the energy available from food consumed. 


Further reading

  • The New Glucose Revolution Complete Guide to Glycemic Index Values (Miller)
  • Good Carbs, Bad Carbs (Burtani et al)


This is a recipe for a muesli hill mix, which follows the principles of a low trickle diet. It can be made in half an hour and is very adaptable to your tastes. This recipe can also be used as the foundation of a flapjack recipe for snacks or bad bivvy breakfasts (where you just want to gobble the food down in your sleeping bag).

The recipe makes around 10 servings.

  • 1/2 cup honey
  • 6 cups oats
  • 1/4 cup ground flaxseed
  • 1 tbs cinnamon
  • 3/4 cup almonds (or any nuts)
  • 1/4 cup soy nuts
  • 1 cup dried berries or currants
  1. Grease a large baking pan (9 x 10 x 21/2) with vegetable oil and then add in the honey.
  2. Place the pan in a cold oven and turn on to 350°.
  3. In another bowl mix all the other ingredients apart from the dried fruit.
  4. Once the honey has melted remove it from the oven and mix in the oat mixture, mixing it all together so the oats are all coated in honey, then spread the mixture out.
  5. Bake for 25 minutes or until oats are toasted, turning the mixture every five minutes.
  6. Remove from oven and allow to cool.
  7. Add the dried fruit, plenty of milk powder and anything else you want (sugar, chocolate drops) and bag it for your trip.

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confused - 17/09/2009
The GI concept is not exactly new since it has been around for more than 20 years now. I assume this article is not "attempting to rewrite the established rules of good nutrition" by advising that high GI carbs should be avoided after exercise - conventional wisdom substantiated with a non-negligeable body of research seems to suggest that high GI carbs help to replenish the depleted glycogen reserves post-exercise.

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