It's training day and you've planned a 10K after work; that means you need a decent lunch to keep you going. Scanning the various options at your local café you opt for a large plate of carbohydrate-packed pasta, no added cheese. The perfect meal, you might think, but not so, according to the many nutritionists who have turned the concept of healthy eating on its head.
In recent years carbohydrates have taken a battering because they have been linked to the increasing incidence of obesity. A jacket potato or bowl of pasta, once seen as a healthy choice, became foods likely to increase your weight.
A number of low-carbohydrate diets have emerged and become very popular, though the total avoidance of carbohydrate is still largely seen as potentially damaging to our health. This is especially so for those in training, as carbohydrates provide a vital source of energy, fibre, vitamins and minerals. Nonetheless, a few health experts maintain that some carbohydrates should be avoided - or at least eaten in moderation.
Digestible carbohydrates fall into two broad camps - simple and complex, both of which contain sugars. There are also indigestible carbohydrates - fibre - which are also integral to a healthy diet.
Simple carbs are made up of one or two molecules, which means they are rapidly absorbed into the bloodstream. Fresh or dried fruit, milk and honey are ideal when you need a quick burst of energy - after a hard training session, or during transition.
In contrast, complex - or starchy - carbs are made up of many molecules, which are usually harder for your system to break down, so the sugars are released more slowly into your bloodstream, helping to keep energy levels on an even keel.
Avoid the sugar rush
That brings us back to the bowl of pasta you were planning for lunch. You don't need a nutritionist to tell you that refined, processed foods such as cakes, biscuits and pastries have little nutritional value, but many complex carbohydrates are also refined, which complicates the picture.
White bread, white pasta and white rice have been stripped of their outer bran coating and inner germ, and therefore also much of their nutritional content. Eat a bowl of spaghetti and you'll enjoy energy and calories, which are vital when you're in training, but you'll miss out on essential proteins, vitamins and minerals.
What's more, without the presence of whole grains, the sugars in carbs are more quickly absorbed, which causes blood sugar levels to peak quickly and then crash, which can leave you feeling weak, hungry and craving more carbs. This is not an ideal situation when you're halfway through a 40K cycle.
"The primary source of energy for an athlete is carbohydrate, because it's the easiest fuel for the human body," explains nutritionist Patrick Holford (www.patrickholford.com). "But if you load too much too quickly the body dumps the excess into the liver, to convert it into fat for storage. So you are better off having a steady supply of unrefined carbs that release their energy more slowly."
According to nutritionist Dr John Briffa, a simple way to discern the facts about food is to go back to basics and look at what our ancestors ate. It makes sense to suppose that the foods that have been in the human diet for the longest period of our evolutionary process are the ones to which we are best adapted genetically, physiologically and biochemically.
Therefore, the reasoning goes, these are the ones most likely to maintain our health and well-being. "It is perhaps easy to visualise our hunter-gatherer ancestors filling up with fruit, veg, nuts and seeds, as well as, occasionally, meat, fish and eggs," says Briffa. "But there's something not quite right about an image of early men and women sitting around campfires tucking into plates of pasta, bowls of processed breakfast cereals and stacks of bread."
The good food guide
Another indicator that can help when deciding how to efficiently fuel your body is the Glycaemic Index, or GI. Developed in 1981 by Dr David Jenkins, a professor of nutrition, it ranks foods based on their effect on blood sugar levels.
The rise in sugar levels is graded from 0 to 100; the higher the number, the faster the absorption of carbs. Foods such as oatcakes, strawberries and cashew nuts have a low GI (under 55), while bananas and baked beans are listed as moderate, as they fall between 55 and 70 on the scale.
The problem with this system, however, is that the index is based on a standard amount of carbs - 50g. To get that amount of carbs from some foods would mean eating more than most of us would normally eat in one week - let alone one meal. For example, you would need to consume a whopping 700g of carrots to hit the 50g target.
"GI gives us the first part of the story," explains dietician Nigel Denby. "It tells us that not all carbohydrates are created equal; some are absorbed more quickly than others, but it doesn't take into account how much carbohydrate a food contains. This means some very healthy foods are excluded."
Loading up the smart way
Enter the Glycaemic Load (GL). This takes the GI scale one step further, using its rating system but also taking into account the amount of carbohydrate in an average food portion. So food with a high GI but small amounts of carbohydrate will generally have a low GL.
"If we eat low-GL foods we store less excess energy and blood glucose levels are kept stable, giving a slow-release, prolonged energy supply," says Denby.
It's not just refined carbs that have come under scrutiny - the humble, versatile potato also has a surprisingly high GL. "I don't classify potatoes as a vegetable as they're not nutritious enough, but this doesn't mean you have to take them out of your diet," says Denby. "If you eat them with protein such as meat, and vegetables, this will balance out the sugar effect."
Cutting down, not out
The same goes for all other carbohydrates, so rather than shunning cheese on your pasta because of its calorie content, you should sprinkle it on as protein and fat, slowing down the rate at which the carbs are digested and absorbed. How you cook your food also
affects the way your body breaks it down.
According to Denby, over-boiling and baking breaks down the starch in carbs, making it more digestible and enabling sugar to be released far more rapidly into the bloodstream. Similarly, mashing increases the GL because it breaks the food down into smaller, more easily digested particles.
While sports nutritionist Claire Loades agrees that some carbs are digested and absorbed more quickly than others she is loath to label any food type as 'good' or 'bad' because she feels to do so only perpetuates fad diets.
"There are different carbs that suit different occasions - especially if you're an athlete. For everyday eating, low GL is preferable because it keeps blood-sugar levels stable and hunger at bay, but when you need refuelling after training, slow-release carbs just aren't going to cut it. A milkshake is one of the best post-training snacks, or just a glass of milk, as it provides protein, fluid and lactose."
Deciding how much of your diet should come from carbs is another contentious issue. According to the British Nutrition Foundation we should get half our energy needs from carbohydrates, which is around 200g for women and 270g for men. However, Dr John Briffa disagrees.
"I believe that what represents an ideal diet varies from person to person, but one thing I'm clear about is that many health professionals and even our governments advise intakes of carbohydrate that are greater than is good for us."
Eat for your needs
Patrick Holford agrees that the amount of carbohydrate needed depends on the individual and a key factor is how much exercise you do.
"A practical guide for those in endurance sports is that a third of what's on your plate should be protein, a third fresh, raw or steamed vegetables and a third starchy carbs," he explains. "But try to go for brown rice and whole-wheat pasta because they are going to give you more nutrients, which means you use the food fuel more efficiently."
When you're training hard your body will use up the glucose that carbohydrates create, whether you're a white-sliced addict or a wholemeal fan. But if you take sport seriously, opting for wholegrain and unrefined carbohydrates will undoubtedly improve not only your performance but also your general health and well-being.
"By eating a low-GL diet you gain more energy," says Holford. "It gives you more stamina and, provided you choose foods with a high nutrient content, faster recovery."