Frank’s back with some more great nutritional advice. Following on from part 1’s focus on protein, it’s time to talk carbs. We all know they are important to endurance athletes, but what should we be eating for best performance?

Remember ‘a calorie is NOT a calorie? Well, ‘not all carbs are carbs’

Okay, I made that one up. And it also depends how you take them; let me explain – and try to stick with the science as it underpins why you might choose to change your diet.

Carbohydrates are sugar molecules (saccharides) arranged in chains of varying lengths. The simple or single sugars (monosaccharides) are glucose (from starch), fructose (fruit) and galactose (milk); the sugars sucrose (table sugar or just ‘sugar’; glucose-fructose), lactose (milk; glucose-galactose) and maltose (malt; glucose-glucose) are paired (disaccharides); the maltodextrin in your powders and gels is glucose in chains of 5-15 derived from starch which consists of very long and branching chains of glucose.

Your temple doesn’t run on ‘carbs’ or ‘sugar’; it burns glucose (stored as glycogen) and fortunately there’s plenty of this in starchy foods. Importantly, galactose can be converted easily to glucose but your temple’s ability to turn fructose to glucose is very limited and so this particular sugar must be taken carefully in small amounts. Another problem with fructose is that your gut can’t absorb it as quickly as glucose, which is one reason why some gels and powders can cause intestinal problems. On this theme, remember that lactose is glucose-galactose? Well, babies have an enzyme lactase which splits the lactose in breast milk so that it can be absorbed but about 5% of Europeans and up to 90% of some Africans and East Asians stop making this later in childhood; this is what’s meant by lactose intolerance meaning that the carbs in milk are not available to you and instead cause problems when the bacteria lower down in your large bowel get to party on all that undigested sugar (cue fart jokes). This is also the reason why fructose from some gels and powders can cause problems if you take too much too quickly and overwhelm the absorption process. You can get around lactose intolerance by substituting yoghurt (or kefir!) as fermentation breaks down most of the lactose for you.

The next issue with carbs is how you take them…

In nature, carbs are not floating free but built in to the structure of plants and have to be extracted. This is done physically by chewing followed by chemical breakdown (acid then enzymes) in your upper guts (stomach and small intestine). Finally, some important stuff goes on in your lower bowels (large intestine) where friendly bacteria contribute to further digestion. The problem is that most of us have switched from ‘brown’ food (I’m using this as a general term for unprocessed) to ‘white’ yuk (ditto for processed) that has been ground and cooked or liquefied so we don’t have to bother. In terms of nutrition, this is a bit like driving a car instead of going by bike; you don’t have the effort of pedalling and you get there much more quickly. Also, you don’t get the extra goodies like fibre, protein, and minerals and vitamins; just like you don’t get the sounds and smells of nature when you switch from bike to car.

Enough of the science and cruelly tortured metaphors; let’s talk specific foods. Wholemeal grains come with all the outside fibre (bran) not to mention the protein (wheat germ) that gets milled off making white flour; making brown food white in this way also loses healthy fats as well as vitamins and minerals stored in the fibre and germ. Wholemeal foods take time to chew and digest so your temple slowly releases insulin to deal with the gradual increase in glucose in your bloodstream; technically, this is termed low GI (glycaemic index; low GI = nutritional bike ride). Fibre in your large bowel delays hunger (chemicals released by gut bacteria which like fibre) not to mention being protective against cancer and other conditions. White food is absorbed quickly so your temple releases a lot more insulin to take care of the sugar rush (high GI = nutritional car drive).

I’m going to talk ‘sugar’ in more detail next time, but what does all this mean for carbs in general terms? During exercise and immediately after (the 20min ‘insulin window’), rapidly available (high GI) glucose fuel is required which is what powders and gels provide packaged as maltodextrin (short chains of glucose). But don’t bother unless you’re doing more than 60min sustained aerobic as your temple has lots of glycogen all ready and waiting. When not exercising, get your carbs from low GI brown food with all the added goodies; this means wholegrain bread, pasta and rice. Cooking releases starch from inside plant cells and also changes it into a digestible form; a neat trick is to chill and reheat your rice/pasta/potato as this changes some of the starch back to an indigestible form meaning reduced calories from the same portion. Eat your fruit don’t drink it as liquefying gives you tons of sugar (and particularly fructose) with the fibre and micronutrients removed; eat one piece between meals when hungry and your liver’s not busy so can cope with the fructose. Sadly, the same is true for all that dried fruit in anything and everything. Remember, the name for a meal with lots of fruit in is… dessert.