Gut Threshold Nutrition Principles

[Source: East Coast Cycos newsletter, in Tri-Rudy newsletter, January 13, 2010]

By Mitchell Anderson

My favourite ad on television has just started being re-run after at least 12 long months in absentia! It’s the HBA advert, where a small boy talks about a nasty experience with a crocodile. In a twisted little voice he says: “Crocodile came along. Bit me into parts. I mean pieces. Bit my guts out. Then my head went one way, my legs went the other way!” Minus the crocodile, kinda sounds like doing a triathlon. Your gut is twisted every which way whilst you’re exercising. This article will explain why!

So really, I want to talk about the concept of ‘gut threshold.’ I’m certainly not going to claim this description as my own…but I haven’t heard anyone else talk about it in this manner!! The term ‘gut’ globally describes your stomach and intestine. To start, the key is the word threshold. In VERY simplified terms, the way your gut works is almost digital. It’s either emptying, or it’s not. You either feel distended, or you don’t. It reaches a point (or threshold) and then shuts down. The very worst thing that can happen during an endurance event is for your gut to shut down. No gut equals no nutrition. Absorption of gut contents is affected by three main factors: thermoregulation (relying on heavily on environmental temp.), exercise intensity (relying on your aggro) and concentration of gut contents (relying on what you’re eating/drinking). Largely, it’s good to try and keep the first and last in check, so you can maintain exercise intensity…therby maximising performance.So ! if you can think of gut threshold in a way similar to lactate threshold- you reach a point of deflection on a graph where your lactate begins to rapidly accumulate in the blood. This means you have to slow down. Similarly, if you push your gut over threshold, if exercise continues…you’ll have to slow down. If you get too dehydrated or take in concentrated solutions, then intensity will suffer due to gut shut-down. Blood that was being sent to your gut is being diverted to muscle (for exercise) and skin (for thermoregulation).

So let’s think more about factors effecting gut emptying and why it’s important.It’s really not that difficult to understand why gut threshold is important. The three contributing energy systems during exercise are: fat, protein and sugar. Protein is not a vital piece of the exercising pie, but the others are. Fat is stored in limitless supply, some more limitless than others (!), but you have a finite level of access. Furthermore, it is a difficult substance to absorb across your gut membrane, as it requires processing prior to absorption. In addition, this absorption happens in the intestine, not the stomach. Carbohydrate, on the other hand, is readily absorbed across the stomach membrane utilising swanky co-transporters. These suck up carbohydrate and electrolyte and water, dumping these vital components straight into the blood stream for use. Your brain and exercising muscle demand glucose in mass quantities.

Quite differently from fat, carb’s are in limited supply in the human body (stored as glycogen in the liver and muscle), so any additions are greatly beneficial. If you run out, then you’ll hit the wall.The stomach is the first port of call for anything you pop into your mouth. Food and fluid shoots down your oesophagus and is processed by the stomach first. It mixes and mashes and adds acids to break the food into small parts. I mean pieces. So when you are racing, anything you pop into your mouth that isn’t glucose (or fluid and electrolytes), I think of as a distractor. Essentially I mean protein, fats and fibre, none of which are absorbed across the stomach membrane. There are a few reasons why they’ll behave as distractors. They’ll block the efficient absorption of the essentials, by not being absorbed until the intestine. They act to increase the concentration of the solution inside the gut, thereby dragging fluid from the blood to assist in equalising the concentratio! n. Furthermore, they aren’t needed by the body to perform exercise (there’s plenty of fats running around already, you don’t use much protein, and you sure as heck aren’t worried about your bowel health with the fibre )…so why eat them?The fact remains that palitibility is the main stimulus for eating and drinking during exercise. So whether or not you like the taste of something.

The real trainability of the mind lies in ensuring you stay positive and receptive to carb/electrolyte/fluid, rather than allowing your mind to force you into eating sub-optimal food and drink like bars or other solids. I’m not saying you shouldn’t eat what you like during training (especially on the bike), the intensity during training is much lower and shouldn’t be pushing your gut to the limit. I’m talking about racing and utlising largely liquids, allowing you to load your stomach optimally, rather than adding fibre. Furthermore, using sports drink in the correct concentration (6-8%), and gels (plus or minus salt tablets) will provide you with every nutrient you need in a race spanning 1h to 15h. They will also assist in adding nutrients in the correct concentrations.

So try and push your gut to it’s limit in the same way you push your muscle to it’s limit. Manage it at gut threshold, so you’re always pouring in as much water/carb/electrolyte as your membrane can absorb. Minimise the number of distractors. Maximise your performance. Race well. Stay away from crocodiles