So after a couple of weeks of nothing, it's time to continue this series, which…
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.
And this is relevant as some of the test foods were well, damn near impossible, to get 50 grams of digestible carbohydrates into the person. For example, 1 medium carrot (61 grams of carrot) contains about 4 grams of digestible carbohydrate. This means eating 12 of them (720 grams of carbohydrate) to get 50 grams of digestible carbohydrate.
That’s a lot of carrots. And was part of why it was so absurd for physique people who got obsessed with the GI to worry about putting carrot slices on a salad or whatever. We’re talking about tiny amounts of carrot and digestible carbohydrate.
Now, compare that to the roughly 3 pieces (90 grams weight) of white bread (15 grams carbs apiece) that provide the same ~50 grams of digestible carbohydrate. Or sweet potatoes that take two 5″ sweet potatoes to provide the same digestible carbohydrates. Sugars are more or less 50 grams total weight to 50 grams of carbohydrate but even 50 grams of fructose (GI of about 20) will make most people sick to their stomach. 50 grams of sucrose is just delicious.
But there was just a huge disconnect with the way the GI was being measured in terms of realistic portions. Because if it takes 50 grams of digestible carrot to have a certain GI, that raises the big question: how much of an impact will say, 10 grams (2 medium carrots) have on blood glucose, health, etc. And this is really the biggest issue with the GI. It’s simply not relevant to what actual food portions or amounts are.
Enter the Glycemic Load
To deal with the problems inherent in the GI, the concept of the Glycemic Load or GL (no, not this one) was developed. The GL is just a weighted measure of the GI of a food and the actual number of carbohydrates that are being consumed.
Mathematically the GL is defined as
GL = GI of a food * grams carbohydrate of that food eaten/100
So if a food has a GI of 70 and you eat 10 grams of it
GL = 70 * 10 = 700 / 100 = 7.
If a food has a GI of 20 and you eat 100 grams of it
GL = 20 * 100 / 100 = 20
Which means that eating more of the low GI food actually has a larger impact on all of this than eating less of the high GI food. Strictly speaking eating 50 grams of a food with a GI of 10 has the same GL as eating 10 grams of a food with a GI of 50; both have a GL of 5.
Of course, this points out that clearly it takes far less of the high GI food to have the same GL as the lower GI food and from various standpoints, this can be considered a negative. But it also points out that eating a controlled/small amount of high/higher GI food (IIFYM anybody) might be no better nor worse than eating a ton of lower GI foods instead.
There are other factors that contribute to the GL of a food. Total carbohydrate is really the key one but the fiber and protein content, starch content, how the food is cooked/prepared, the amylose/amylopectin ratio (don’t worry about this, it’s just an issue with the types of starches in the food) and a host of others. So while the above is a really quick approach to determining GL (GI * amount of carbs), other factors play a role, just like GI. There are, just as with GI, individual response to any given food and this interacts with the person’s underlying physiology (see below).
The Glycemic Load and Everything
While researchers continue to bother with the Glycemic Index, there has been a real shift towards the glycemic load concept. And at a fundamental level, they are of course linked. Lowering the GI of the diet will reduce the glycemic load to one degree or another so long as carbohydrate intake doesn’t go up. How much will depend on the degree of change in the GI but, to a first approximation, a lowered GI diet IS a lowered GL diet.
And in that vein, lowered GL diets have been shown in at least some studies to provide benefits in terms of lowering the risk of heart disease, developing obesity (rather high GI diets may increase risk), treating diabetes by lowering the glycemic response (i.e. less carbohydrate coming into the system at once) and improving things like HbA1c (a marker of diabetic problems.
I actually am not aware of anything (translation, can’t turn anything up on a Pubmed search) on the GL per se and fullness although the components of low GL foods; like the GI any effect would be variable and could just as easily modulated by other components of that food or meal. Protein, fat, fiber always contribute and you can’t consider just the carbohydrate content and GI of the food.
Low GL diets possibly facilitate weight loss. Keeping in mind that research on this is always done in the overweight, the data on this is very mixed and some studies show no benefit of lowering the GL of the diet to enhance weight loss. In one study, a lower Glycemic Load diet only improved weight loss in people with high insulin secretion to begin with; people with low insulin secretion gained no advantage.
Actually, the data on the impact of GL on most of the above is always extremely mixed and this is likely due to a lot of factors.
Problems with the Glycemic Load
Just as with GI, any studies that compare high and lower Glycemic Load diets are not just looking only at changes in carbohydrate content: fiber, protein, etc. all play a role and diets different in GL may differ in those and more. Frequently all macronutrients (protein, total carbohydrate, fat and fiber). There are also likely to be vast changes in the intake of other nutrients such as vitamins and minerals. Many of them play a role (for example, magnesium improves insulin sensitivity) and changes in the diet could be working through any and/or all of those mechanisms.
In a practical sense, this may not be that important in the sense that eating higher protein/fiber foods is usually a good thing. But it means that the Glycemic Load PER SE may not be providing the benefit (also see below). It’s easy to lose sight of the forest for the trees here and just as people lost the plot looking at the Glycemic Index in isolation, the same can happen with Glycemic Load. Unless someone is eating carbohydrates by themselves (which does happen mind you), every other component of the meal, etc. may be playing a role.
Yes, total carbohydrate intake and GI is a key factor but there are others.
Altering Glycemic Load
At a fundamental level, there are two ways to alter the diet to reduce the glycemic load. The first would to keep carbohydrate intake the same and lower the average GI by choosing less refined generally), high-fiber (almost always foods). And in a lot of studies showing that high carbohydrate diets work for certain things (such as diabetes, Poly Cystic Ovary Syndrome and others), they invariably use a lower GI diet.
And this is fantastic in the research realm where the diets are being prescribed, provided and even sometimes followed. When people read this research they invariably conclude that there is no difference in high- and low-carbohydrate intakes. And while strictly true, I think it fails the reality check.
Because we know that most people aren’t going to eat low GI foods on a high-carbohydrate diet. There are exceptions, make no mistake. But in the aggregate, in the modern Western World it’s not happening. As Dan Duchaine used to say “Good advice not followed is bad advice” and I think this is a case of that. Telling the general public to lower Glycemic Load by eating only lower GI foods clearly isn’t happening for most.
Especially given that there is another way to effectively lower the glycemic load which is to reduce total carbohydrate intake. Assuming the GI of the foods chosen stays roughly the same, this alone will reduce the Glycemic Load of the diet and probably works better in the aggregate. Earlier review papers concluded basically that, that lowering total carbohydrate intake while increasing dietary fat (from predominantly monounsaturated sources) was the optimal diet for the treatment of the metabolic syndrome.
Similar results have been seen in Poly Cystic Ovary Syndrome (PCOS) a condition seen in woman that is usually associated with insulin resistance especially if they are obese (about 95% of obese PCOS women are insulin resistant). Here lowering carbohydrates moderately and increasing fats improves metabolic outcomes. Lowering carbohydrates also causes a decrease in visceral fat (the fat around the organs in the gut) that cause so many health problems. Full blown ketogenic diets have been shown to beneficial.
In contrast, low GI (which again are low GL diets) also improve things for these women. But I still maintain that most people in the real world simply don’t/won’t eat that way and lowering/moderating carbohydrates while increasing protein and fats is the easier/more effective approach. Let me note that weight loss and exercise in and of itself always improves outcomes as well.
The Glycemic Load in Other Populations
As noted above, most research into topics like these tend to deal with the general population and many of the diseases of modernity such as heart disease, obesity, Type II diabetes, etc. And while GI has been examined in terms of athletes (mostly in terms of pre-, during-, or post-workout nutrition), I am not aware of a single study looking at Glycemic Load in athletic or even lean populations.
And, while this is speculation, I would tend to doubt that it matters in the big scheme. Most health issues with diet such as high sodium and blood pressure, saturated fat intake (within reason), etc. tend to be kind of irrelevant in a lean highly active athlete. A high refined carbohydrate/Glycemic Load diet is a big issue for someone carrying excess fat who is insulin and pre-diabetic. For someone lean and insulin sensitive who is burning a ton of calories/carbohydrates in training, probably not so much.
Yes, fine there is the fiber, protein, micronutrient issue, I’m not denying that. But a diet has to be pretty imbalanced in one or the other direction or this to matter much. I wouldn’t suggest an athlete eating 80% carbs from nothing but high GI sources but concluding that an athlete should only eat lowered carbohydrates from low GI sources all the time is equally mistake.
Don’t exclude the middle: if protein intake is where it should be and fat is moderate, carbohydrate intake can only be so high to begin with. That is, if protein is 25-30% and dietary fat is 25%, that means carbs can’t be higher than 50-55% of the total diet. Mind you, percentages suck but even the total gram amount of carbohydrate won’t be that high unless activity is super high and that eliminates any issue.
So consider someone who weighs 180 pounds at 10% body fat eating 16 cal/lb per day (which is a decent estimate of maintenance). 30% protein is 4.8 cal/lb of protein. At 4 cal/lb that’s 1.2 g/lb protein or 216 grams per day. If their fat intake is 25%, that’s 4 cal/lb of fat. At 9 cal/g that’s 0.44 g/lb which is 79 grams per day. That only leaves 45% for carbohydrate which is 7.2 cal/lb. At 4 cal/g that’s 1.8 g/lb carbs. At 180 lbs, that’s 324 grams of carbs. Which sounds like a lot but 1.8 glb is only 4 g/kg which most sports nutritionists would consider a fairly low intake (it is for an endurance athlete, not so much for a bodybuilder).
This is broadly similar to the moderated carbohdyrate diets I mentioned above for treatment of metabolic syndrome and PCOS although dietary protein is often lower in those approaches. This isn’t really a surprise in the big scheme. Not really a surprise. Combined with the right kinds of activities and you have a winning combination….
My point being that unless the diet is totally imbalanced and comprised of insane amounts of high GI carbohydrates, the generally lean athlete probably needn’t worry excessively about any of this. I already explained why GI kind of doesn’t matter to anything due to improves insulin sensitivity in trained people, the fact that the insulin response doesn’t really matter and that low GI foods often have a higher initial insulin response, etc.
Don’t misread this, I’m not saying it’s ok to eat high GI foods so long as the total amount is lowered. But pretending like a diet exists at one of two extremes is missing the point. I could go off on a rant about how people present or misinterpret If It Fits Your Macros (IIFYM) but this isn’t the time nor the place. The point is that a meal with dietary protein, moderate carbohdyrates, fat and fiber (whether in the carbohydrate itself or from added veggies) isn’t going to have a high GL no matter how you cut it.
Let’s Get to the Point
Let me be honest. Usually when I write series like this, they flow fairly naturally and I do one part a week. That didn’t happen this time. I recall having a fairly strong idea about the purpose of all of this when I started but kind of lost the plot somewhere around the way. I’m not even happy with this piece but I just want the series to be done.
So far as I can recall, my point had to do with the once again recurring idea that carrots or some other high GI food shouldn’t be eaten by athletes or bodybuilders. This even a new idea but it’s ludicrous on a number of levels. The first is that the GI’s relevance to much of anything outside of a few specific situations (i.e. during workout, post-workout for athletes who are training twice a day) and is impacted by the other macros, training status and everything else.
That led into the concept of the Glycemic Load (GL) which, while better, is still problematic. At the very least it takes into account the total carbohydrate amount. Eating a few grams of a high GI food doesn’t matter. Putting 3 grams of some high GI vegetable on your salad doesn’t matter in the least since the amount is so small. Quite in fact, 30 grams of a lower GI food could impact on blood glucose to a much larger degree.
So don’t lose sight of the forest for the trees, hope I can stay focused the next time I do a series like this and make sure to check in for my next update since it’s gonna be a doozy.