Good Carbs, Bad Carbs
Whenever I hear the standard positions from nutritionists, I keep hearing about the distinction between good and bad - sometimes good and evil - carbohydrates . What’s actually the difference?
What do they mean?
The usual suspects are very short carbohydrate molecules - sugars - and long ones - starch. Dietary fiber is rarely included, even though it’s sometimes implicitly part of the picture.
Why?
Sugar in its common food form has two parts: 1 part glucose (the stuff measured as blood sugar) and 1 part fructose. Both so-called ‘simple sugars’, which is why table sugar is a ‘double sugar’. The two molecules are easily separated during digestion, so sugar is absorbed very quickly. This produces what’s called a blood sugar spike, and is the difference between glycemic index and glycemic load (1) .
You can see quite clearly that 50g of starch produces a slower rise in the curves than 50g of sugar, but the rice curve also stays elevated for longer, and you reach normal and fasting levels much later. In the end the body has the same blood sugar load to handle, just spread over a longer period.
Comparing Apples and Oranges
The comparison of starch with sugar has a very well-hidden aspect: starch consists of long chains of glucose molecules. 100g of starch is therefore digested as 100g of glucose. Breaking starch down into glucose takes a while. That’s the reason for the slower blood sugar rise. Sugar, on the other hand, is a molecule made of glucose and fructose. 100g of sugar is digested as 50g of glucose and 50g of fructose (2) . Only glucose is responsible for blood sugar levels.
What’s bad, what’s good?
In the classic sense, a high glycemic index (the high spike) is bad. But in the end, the same glycemic load still has to be handled: the same amount of blood sugar has to be processed. In that sense, I find it more useful to talk about ‘bad’ and ‘slightly less bad’: ‘good’ would mean avoiding the load altogether, and providing a higher proportion of actually bioavailable nutrients.
If we now only treat this rating as relative, where do these carbohydrates land on the scale between ‘actually good’ and ‘actually bad’? Let’s bring in another type of carbohydrate that was only briefly mentioned once: dietary fiber - indigestible carbohydrates that have taken their fair share of criticism elsewhere on this site - but in the context of this article, they come off considerably better.
Fiber is fermented in the large intestine, where some short-chain fatty acids are released that can genuinely benefit the gut (with the caveats covered in some of the linked articles above). In the context of this article I’m therefore placing fiber in the ‘relatively good’ carbohydrates group, but that’s not what most people mean when they mention this goroup.
My own frame of reference is a strong preference for fat-based metabolism, which leads me to draw a wide gap before the bad carbohydrates, because all others produce a large flood of glucose that the metabolism has to process. In other contexts the gap may be smaller, but I don’t see a high glycemic load as metabolically beneficial under any circumstances.
We now need to distinguish between starch in its ‘complete’ form - from whole grains, for example - and refined starch, such as white flour. Since the outer layers of grains come with a substantial load of antinutrients (not just fiber), I file both under ‘pretty bad’. From a metabolic standpoint, whole-grain starch ranks slightly better than pure starch. When it comes to digestibility and antinutrients, that can even reverse. But that’s a different topic.
Simple sugars are unambiguously ‘very bad’. True, the glycemic load of 100g of sugar is only half that of 100g of starch, but the second half (fructose) has such an immediately harmful effect on the body that nothing good comes of it: the glycemic effect is immediate: Sugar is broken down with virtually no delay and absorbed straight into the blood.
Conclusion
If any carbohydrate still earns (with other caveats) the label ‘good’, it’s fiber. But fiber is usually only implicitly included in ’the good ones’ because starch in mainstream recommendations comes from whole grains, and therefore brings a small amount of fiber along with it (relative to the usable starch).
Starch and sugar, in my book, don’t belong in the absolute categories ‘good’ and ‘bad’ - more like ‘pretty bad’ and ‘undoubtedly bad’.
Add to that the fact that carbohydrates are in every case non-essential , and I see no reason to consider them for my diet just because one gets a slightly better score in an oversimplified ranking.
I don’t smoke filtered cigarettes because they’re ‘better’ than unfiltered ones. The filter doesn’t make them ‘good’. I just don’t smoke.
