Carbohydrates Part 4: The Glycemic Load

Ok, time to finish this mess up because I have something special for next time.  Last time I looked at some of the major issues with the Glycemic Index including the fact that a single meal, typically of a single carbohydrate, was tested after an overnight fast which is really not how people eat in the real world.  People typically eat meals containing other nutrients (protein, fat, fiber) which impact on the GI, there is a second meal effect and, simply, the general approach to determining GI is a little bit contrived in the first place.

I also looked at one of the big assumptions regarding GI which has to do with the insulin response.   Given the impact of blood glucose on insulin release, it was always kind of assumed that insulin was responding similarly.  That is, a higher GI meant a higher insulin response.  But this does not exactly turn out to be true for reasons discussed in that part.

I had already mentioned that the GI for diabetics had been kind of abandoned due to being too complex and unrealistic with the focus being more on total carbohydrate intake than anything else.  That said, studies do find that lower GI diets have a small but measurable effect on metabolic parameters of diabetes compared to higher GI diets.

I’d note again that weight loss (and regular exercise) always improves issues related to insulin resistance and it’s often hard to tell whether effects are occurring from the low GI diet or the diet causing weight loss.  There is an additional issue related to this that I will come back to below.

And that brings me to perhaps one of the largest problems with the GI concept.

Problem 4: The Quantity of the Test Carbohydrate

When I first described how GI was determined/measured I mentioned that the test was invariably based around 50 grams of white bread (originally glucose) as the test carbohydrate and then 50 grams of the test food. Whether I mentioned it explicitly or not, it’s important to realize that the 50 grams refers to the amount of digestible carbohydrates, not just the mass of the food.

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Carbohydrates Part 3: Problems with the GI

So after a couple of weeks of nothing, it’s time to continue this series, which will invariably run to 4 parts because that’s just how I do things (tediously and in an overwritten fashion).

As an overview of last time, I described how the Glycemic Index (GI) is measured along with the implications that it had for diabetes treatment, potentially weight loss and for athletes.  The main take home is that, the development of the GI had an impact on diabetes treatment but was a huge hassle to use.

For weight loss, studies were about half and half on whether or not low GI foods (typically higher in protein and fiber) were more filling or not.  So far as athletes, the benefit of high and low GI are context specific while the physique athletes were the ones who really got hung up on the GI based on what would turn out to be an incorrect assumption about insulin dynamics (discussed today).

Problems with the GI

While the GI concept made a lot of sense in that carbohydrates would digest and impact on blood glucose differently, there were a lot of problems with the method.  Perhaps the largest was the most obvious: feeding someone 50 grams of digestible carbohydrate after an overnight fast isn’t really that relevant to how people eat in the real world in a number of ways.

Problem 1: Only One Meal is Eaten After Fasting

Yes, fine, breakfast by definition occurs after an overnight fast but are measurements made at that single time point indicative of the rest of the day?  It turns out that the answer is no.And it was found early on that there was a second meal effect, that how the body responded to the next meal of the day could be profoundly different.  In one study, a low glycemic dinner changed the glycemic response to breakfast on the next day.

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Carbohydrates Part 2: Glycemic Index

Ok, so I’ve clearly been delaying this article which continues from part 1 and talks about the Glycemic Index and I’ll apologize up front if it kind of sucks.  As usual, it wasn’t planned and the best structure flow has kind of eluded me.  So I’m just going to hammer it out and hope for the best.  But it will probably blow overall.

So  two weeks ago I looked semi-briefly at carbohydrate structure and classification and will summarize that even more briefly here.  There are three primary single sugars (glucose, fructose, galactose) which combine with each other to produce double sugars (sucrose, lactose, and maltose).  There is also High-Fructose Corn Syrup (HFCS) which for all practical purposes is identical to sucrose.  I should have also mentioned that glucose is sometimes called dextrose which explains the naming of maltodextrins, longish chains of glucose that are often found in sports and other food products.

Extremely long chains of glucose are called starch in food and glycogen in the body.  Very generally the above can be divided into simple (the sugars) and complex (starches) carbohydrates with maltodextrins being in a weird middle place (probably best to consider them as complex carbs I guess).  There is also fiber which, while a carbohydrate, is treated very differently in the body in terms of how it is metabolized and it’s effects.

Diabetes Treatment: Part 1

In the early days of nutrition, here I am talking about the first half and maybe a little bit later in the 20th century, it was generally thought that sugars were more or less ‘bad’ and starches/complex carbohydrates were ‘good’.

At least some of this was based on nothing more than the foods that each were found in were generally thought to be ‘healthy’ or ‘unhealthy’.  Sugar bad, complex carbohydrates good, ook ook. It’s worth noting that fruits contain simple sugars and, especially at the time, few would have considered those unhealthy.  That type of extremist stance would come later (thanks, Parillo).

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Carbohydrates Part 1: Classification and Digestion

On my Facebook group, someone mentioned that something about the GI of cooked versus raw carrots was moving through the fitness community (something like that) and that stimulated me to write this article series.  In it I want to ultimately look at the concepts of the Glycemic Index (GI) and Glycemic Load (GL) but today I need to give a quick primer on carbohydrates which I have done before so the next bits will make sense.

Classifying Carbohydrates

How to classify different carbohydrates in the human has been a topic for decades if not the better part of a century (I’m sure it goes back further than this but I’m not sugar historian) and to make this article make sense, I want to blather about the different types of carbohydrates.

Fiber

Let me start with fiber.  Composed of a variety of different compounds that I will not name but you can look at here if you really want fiber can be roughly divided into two categories.  The first are insoluble fibers.  These don’t mix in water, can’t be digested by humans and basically act as a broom in the gut.

The other are the soluble fibers, they mix in water (guar gum is a popular supplement, add it to water and wait and it will turn into a brick) and are digested in the body.  However, unlike other carbohydrates these are fermented in the gut by bacteria into short-chain fatty acids (SCFA).  These have a number of profound health benefits and actually provide 1.5-2 cal to the body (although it’s not considered carbohydrate grams of calories).

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A Primer on Dietary Carbohydrates – Part 2

In a Primer on Dietary Carbohydrates – Part 1, I took a brief look at what carbohydrates are and listed the three primary categories of dietary carbohydrates which are monosaccharides, oligosaccharides and polysaccharides.  As well, I looked in some detail at the monosaccharides (simple sugars) which are glucose (dextrose), fructose and galactose.  Today, I want to examine the other two major categories of dietary carbohydrates: oligosaccharides and polysaccharides.

Oligosaccharides

The term oligosaccharide is used to refer to any carbohydrate chain between 2-10 molecules long (‘oligo’ = ‘several’ or as I like to call it ‘a buncha’; ‘saccharide’ = sugar).  Chemically, that is, an oligosaccharide, is a buncha monosaccharides that are chemically bonded together but there are only 2-10 of them in the chain (this will make more sense when I discuss polysaccharides).

And while some of the longer chains may be found in small amounts in the diet or in specialty food products (e.g. some maltodextrins which are a combination of maltose and dextrose may be about this length) by and large the primary oligosaccharides are the disaccharides, two sugar molecules bound together.  I’ve listed the primary dietary disaccharides in the table below including what two sugars they are made up of along with where they are generally found in the diet.

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Name Combination of Where Found
Sucrose Glucose + Fructose Too many places to list
Lactose Glucose + Galactose Dairy products
Maltose Glucose + Glucose Malt Beverages (Beer!)

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