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The Carbohydrate Roundtable, Part 1



John Berardi: Well Lonnie and Cy, here we are again, two years after our last roundtable. I hope you guys have been studying up over the last few years. I was getting pretty tired of carrying the both of you during that last one!

So why don't we get started? Since Jared's stepped into the can and it's been thirty minutes, I'm not waiting a second longer for that guy, weight-loss icon or not, he can just jump in when he comes back. And by the way, Cy, let's try to be nice to Jared. "Soy-boy" is not an appropriate way to greet our colleagues.

Let's quickly cover some familiar ground regarding carbohydrates. As most people know, carbohydrates were conventionally classified structurally as simple or complex, but these distinctions are relatively useless in terms of predicting the physiological response associated with consuming them. Can you guys explain why?

Lonnie Lowery: First, JB, you can study this. [Lonnie makes an inappropriate grab at his "package".] Just had to get that out of my system.

Secondly, you're calling the issue of carb complexity "useless"? That's pretty harsh, but yeah, it's mostly true nowadays. I do think historically there was some value to steering people away from simple carbs like table sugar. It's a source of "empty calories" as well as possessing some metabolically unfavorable effects. But now so much sugar is hidden in processed foods and beverages that the "complex vs. simple" distinction is less applicable to the average Joe. That is, teaching someone to avoid table sugar (sucrose) only gets him so far; complex carbs have become just as big a problem now.

JB: Why is that?

LL: So many complex carbohydrate foods are stripped, processed and refined that these choices don't offer the fiber and other nutrients they once did. Overall, I guess what I'm saying is that the simplistic notion of "complex equals good" and "simple equals bad" once had merit, but has become rather archaic, at least in application to real world (read as: fast, pre-packaged, yummy and artificial) choices. Now we have complex carbs that are heinous just as there are situations when good ol' simple sugars are great.

Complexity is just one way to classify a carbohydrate molecule, of course. Individual monosaccharide units (generally glucose, fructose and galactose) can be treated just as differently by the body as longer chains thereof. Fructose, for example, is absorbed at the intestinal wall more slowly (facilitated diffusion) than glucose (active transport). In the liver, fructose can also enter glycolysis (the metabolic pathway used to break down sugars in our cells) in such a way as to bypass its rate-limiting step.

Without enzymatic control (PFK for those who care), the pathway forms undue amounts of acetyl Co-A that are ultimately made into triglycerides. In other words, fructose, despite slower absorption and lesser insulin response, is itself lipogenic. That's quite different from the way glucose is metabolized, even though both are monosaccharides.

JB: Right you are, Dr. Fructose. Cy, how 'bout explaining the difference between what one might consider simple vs. complex carbohydrates or, in more scientific terms, monosaccharides vs. polysaccharides.

Cy Willson: Well, structural nomenclature such as monosaccharides, oligosacchardies and lastly, polysaccharides, which contain many linked units of monosaccharides, had classically been described as either "complex" or "simple" in terms of their structure. For example, since glucose or fructose are monosaccharides, they were classified as "simple" and thus were thought to be bad for you. The more linked units there were, the more "complex" it was considered and the better it was for you in terms of insulin release and overall health.

So, with this reasoning, they said that starch, a polysaccharide that is found in foods like rice, potatoes, etc., would be the most beneficial in terms of health and improving body composition. With this same reasoning, they assumed that fructose, a monosaccharide, was terrible since it should cause a high release of insulin.

The problem with these distinctions? Well, when you take a look at starch, it's merely a very long chain of glucose molecules that, once hydrolyzed, form free glucose or dextrose and cause a very high insulin response. As we know, insulin is a potent lipogenic hormone (fat building or generating) and if insulin levels are raised for a prolonged period of time, this doesn't allow lipolysis (fat breakdown) to occur. Thus a person will gain fat.

Now, fructose on the other hand doesn't require insulin in order to be stored as glycogen and thus it causes a very small increase in insulin secretion, making it better than starch in terms of the insulin response. In other words, an apple is better for you than a bowl of rice.

Also, they failed to consider the fact that fiber slows down the rate of digestion and thus allows for a smaller release of insulin. In other words, consuming whole wheat bread would be better than white bread due to the fibrous carbohydrates contained in the bread.

JB: Hey guys, don't forget the fact that classical distinctions leaned toward recommending complex carbs because nutritionists assumed that a long polysaccharide (many simple sugars joined together) would take longer to digest than a simple sugar and therefore would lead to a more gradual and lasting blood glucose response with a smaller insulin response. This would make "complex" carbs a wise nutritious choice.

However, while theoretically sound, this just doesn't pan out for many "complex" foods. Maltodextrin, for example, is a complex carbohydrate that digests more quickly than straight glucose (a simple carbohydrate) while causing more dramatic increases in blood sugar and blood insulin. Therefore it appears that classifying carbohydrates according to how they're processed in the body presents a better way to look at carbs than classifying them according to their structural characteristics (i.e. simple vs. complex). Enter the glycemic and insulin indices….

Jared, just entering the room: Hey guys, sorry I'm late. I had to stop at Tubway to grab a low fat sandwich. Do you guys mind if I eat while we do this roundtable thing?

JB: Go for it, Jared.

Jared: Good, 'cause if there's one thing I think we all agree on, it's the importance of a good post-workout meal. Since I just finished a grueling twenty-five minute walk, I know it's essential to eat something low fat and deliciously healthy to keep my heart rate up. And people say I don't know my nutritional physiology! When it comes to good nutrition, I choose to stop at Tubway.

CW: You're certainly a nutritional genius, Captain Olestra.

Jared: Olestra! Funny that you mention that since I've got some olestra chips right here in my Tubway bag. I just wanted to say that those chips with the olestra are awesome! I can eat and eat all that I want and not gain weight. You see, it's a rather neat thing, as the fat won't absorb so you only get the awesome nutritional benefits of potato chips!

As we know, those carbs are so good for you and they won't make you gain weight! Those potato chip manufacturers are sheer geniuses. If it were up to me, I'd have all my food deep-fried in olestra.

JB: Olestra, good for you? Um, how about… no. Lonman, help me get back on track here.

LL: Um, yeah. Anyway, the glycemic index, put simply, is a scale of how rapidly ingested carbs enter the bloodstream as glucose. It's one of the factors determining insulin response and metabolism of the substrate.

JB: But not the only factor that determines insulin response, as demonstrated by the insulin index. The insulin index, as I've discussed elsewhere at T-mag, measures the direct insulin response to an ingested food, whereas the glycemic index measures the glucose response to the ingested food.

LL: Right. Now back to the disparities between structural distinctions (simple and complex) and physiological responses… As with monosaccharides, we see large variations in the way the body handles various starches (technically, complex carbs). There's considerable variation between rice, bread, and potatoes, for example. Brown potatoes, in fact, are very similar in glycemic and insulinogenic response to simple glucose. This stuff isn't new. There were investigators reporting on these differences even back in the late 70s. Trickle down of such knowledge to dietitians and the general public has taken some time, however.

The truth is that the glycemic index is pretty much a moot point as we rarely consume a single type of starch or any other substrate. Mixed meals (with protein, various carbs and fats) result in way different glycemic and insulinogenic responses. Cy or Jared, care to comment?

JB: Let me jump in here for a second. While I agree that the GI only offers numbers for a single food, in a recent JAMA review (May 8, 2002) conducted by Dr. Ludwig, he stated that "In general, most refined starchy foods eaten in the United States have a high glycemic index, whereas nonstarchy vegetables, fruit, and legumes tend to have a low glycemic index. Co-ingestion of fat or protein lowers the glycemic index of individual foods somewhat but does not change their hierarchical relationship with regard to glycemic index. Despite initial concerns, the glycemic response to mixed meals can be predicted with reasonable accuracy from the glycemic index of constituent foods when standard methods are used."

Based on the literature, I think I agree to some extent with Dr. Ludwig in that meals containing a high GI carb, regardless of the other macronutrient constituents, will promote higher blood glucose responses than the same meal containing a low GI carb. In addition, I think the GI (and II — insulin index) can help us predict, with some accuracy, how our bodies will handle a mixed meal. Of course, there'll be some exceptions. But overall I think the GI (and II) offers a bit more predictive power than you suggest. Okay, Jared? Cy?

Jared: [still crunching his olestra-laced chips] Uh, I'll be right back, guys. Sometimes my vigorous walks give me the runs. Exercise isn't all that healthy sometimes.

CW: Hurry, Jared! Run! I'm sure glad we included him in our roundtable. Shall we get back to measures of insulin and glucose response?

I think it's important to use a combination of both the GI and II of foods to plan our diets. Essentially, if we're concerned about blood sugar and insulin, we can use the two to pick a food that has both a low GI and doesn't cause much of a release of insulin. Another strategy to modulate the response is to take a food that may rank fairly high in terms of causing an insulin release and add in some sort of soluble fiber to slow the absorption of glucose in the intestine. This will allow a higher GI carb to be eaten without the large burst in blood glucose.

One thing I can't understand are those individuals who want to reduce the glycemic index of a food by adding in fat.

JB: Right, that combination — high blood carbs, fat, and insulin — belongs in my Axis of Evil. Just like Jared.

LL: Okay, although I think John is just getting sassy and he sees my point, I'm gonna get ornery just to make the point that the GI debate is a longstanding one. Although I accept that Ludwig's new data are valid, I say hierarchy, schmiearchy — you guys are basically making an academic distinction.

Maintaining a hierarchy in relation to other carb foods, in itself, means little physiologically. The overall composition of a meal still matters regarding both humoral glucose and insulin responses (and thus nutrient partitioning). And that's to say nothing of frequent feedings, which also confound any religious interpretation of the glycemic index. Again, the individual glycemic index is mostly a moot point.

JB: But it's the best we've got to go on. One day there may be a better way to hammer in a nail, so should we conclude that hammers are useless? I've gotta get that nail in somehow so until that day, I'll use my hammer, thank you very much! It's the same here. We've got a way to classify carbohydrates that works fairly well (the GI). Of course, one day there may be a better one, but for now it'll do the job.

LL: Okay, hammerhead. But beyond that, first you guys cite research to imply that the GI holds regardless of co-consumption and now Cy suggests that adding soluble fiber is the ticket for controlled delivery. So which is it?

JB: Now you're just being a hairy, argumentative beast. Of course, it holds — relative to other foods. Add fiber to a food with a GI of 90 and fiber to a food with a GI of 70 and the 90 might become 70 and the 70 might become 50. Regardless of co-consumption the hierarchy remains. But now you're dragging us into that "academic" debate that you didn't want to get into so let's just leave it at that.

LL: Nope, I've got more to say. Listen, you're both acknowledging that dietary fat affects the insulin response. Isn't that co-consumption? I have to think that regardless of a "maintained hierarchy" among glycemic indices, the fact remains that various carbs are indeed affected, both in their delivery and their insulinogenic response, by factors such as soluble fiber, solidity, total caloric load, fat content, etc.

I don't disagree for a moment that Dr. Ludwig's new data are interesting but slower entry into the blood stream still matters physiologically. If a car is going fast enough to endanger pedestrians (say 50 mph), then slowing it down even 10 miles per hour helps reduce the risk (in this case screaming blood sugar). If another car (carb type) is slowed from 30 mph down to 20 mph due to co-consumed foods, great. In either case, co-consumption matters.

I think the practical interpretation of the (now becoming infamous) "Ludwig data" is obvious. Indulgence in yummy refined starches (in any food combination) over unrefined carbs (legumes, veggies, whole grains, etc.) is for guys who do twenty five minute walks as their "training session."

Why not just avoid refined starches and sugars pretty much all the time except for during and after exercise? Human beings aren't genetically programmed to handle too much of that stuff! Besides, all nutrition guidelines already suggest foods that happen to be low-GI (whole grains, legumes, most fruits, milk products, etc.) So again, it's not a huge deal.

JB: I'll agree with what you said there, except for the car stuff because I couldn't figure it out. Using low GI foods all the time is the best way to make the GI a moot point for sure!

CW: As I said earlier, instead of John's "Axis of Evil," why not add in a substance that will slow down digestion and absorption of glucose but at the same time doesn't possess any caloric value, i.e. soluble fiber? Just as the rate of absorption is a major factor in terms of protein accretion via ingestion of a protein supplement (casein), I think the same thing applies in terms of keeping plasma insulin levels low in response to ingestion of a food. Consuming a fair amount of fiber with each meal should accomplish this. You could also use the drug metformin, as one of its mechanisms of action may be slowing and/or reducing intestinal glucose absorption.

LL: Metformin! John, hide your Glucophage!

JB: Stand back everyone! He's making the transformation from the mild mannered Cy Willson to the indestructible Cy-Borg!

LL: Since John's pulling JAMA articles on us, it's worth mentioning that a recent article in said journal lists metformin as vastly over-prescribed. Whether this is cautionary or opportunistic depends upon one's mindset, I suppose!

JB: Picking fights again, you Bigfoot? Let's move right along. You're right Cy-Borg, metformin might help, as might Gymnema Sylvestre.

 
Part 2 will be posted next Friday.


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