Sunday, 21 December 2008

Carbohydrates: Dogs' Doodads or Spawn of Satan?

Depending on which side of the fence you're on, Carbohydrates are either the Dogs' Doodads or the Spawn of Satan. As I get older, I prefer to sit on the fence. Let's start with the basics.


What are Carbohydrates?

Carbohydrates are so named because they have the generic formula (CH2O)n. C is carbon and H2O is water hence Carbo-Hydrate. There are several different types.

1) Sugars. There are monosaccharides, the most common being Glucose (a.k.a. Dextrose), Fructose and Galactose. There are disaccharides, the most common being Sucrose, Lactose and Maltose. Disaccharides are 2 monosaccharides linked by a glycosidic bond formed by a condensation reaction (removal of a water molecule, usually by an enzyme). Disaccharides have to be hydrolysed (have a water molecule added back in, usually by an enzyme) into monosaccharides before they can be absorbed in the gut.
Sugars are simple carbohydrates.

2) Starches. These are chains of glucose molecules linked by glycosidic bonds. Starches have to be hydrolysed into glucose molecules before they can be absorbed. There are unbranched chains like amylose which is also known as resistant starch. There are branched chains like amylopectin and maltodextrin. Glycogen is a branched chain "animal starch" that is synthesised inside muscle and liver cells and which can be rapidly converted back into glucose inside cells.

3) Non-Starch Polysaccharides (NSPs). These are also known as fibre/fiber and there are 2 types: soluble (e.g. pectin, beta-glucan & cellulose) and insoluble (e.g. bran). These aren't absorbed, but gut bacteria can feed on soluble fibre/fiber. Starches and NSPs are complex carbohydrates.

For more information, see http://en.wikipedia.org/wiki/Carbohydrate

The amount of carbohydrate that someone needs varies from person to person and increases with the intensity and volume of exercise done. See Everyone is Different. What are the best carbs to eat? "Complex" ones from "wholegrain" cereals? Not necessarily.


Simple vs Complex

TV ads for breakfast cereals bang on about the wholegrain goodness of complex carbohydrates releasing energy slowly. The terms "Simple" and "Complex" actually refer purely to the chemical structure of a carbohydrate and have nothing to do with how quickly they turn into blood glucose in the body. The Glycaemic Index (GI) (or Glycemic Index if you're American) relates to how quickly carbohydrates turn into blood glucose in the body. See http://www.mendosa.com/gilists.htm for a list of 750 foods and their GI & GL (GL = Glycaemic LoadGI/100 x carb content per serving). Here are a few extracts. Note: a GI of 55 is low; a GL of 10 is low.

The last three items in the list are all simple carbohydrates. As you can see, some wholegrain complex carbohydrates turn into blood sugar faster than simple carbs. This is because the wholegrains have been ground into powder which is rapidly digested and absorbed, despite the presence of fibre/fiber.

As fructose has such a low GI, does this mean that we can eat as much of it as we like? No! When we eat fructose, it passes from the small intestine into the portal vein and goes straight to the liver. As liver cells contain an enzyme called fructokinase (which has a high affinity for fructose), all dietary fructose is absorbed by the liver where it tops-up liver glycogen. Liver glycogen is also topped-up by glucose (obtained from the digestion of starchy carbohydrates). Once liver glycogen stores are full, any further fructose is converted into fats, which are stored as ectopic liver fat and also exported as triglycerides. High serum triglycerides are heart-unhealthy. See Cholesterol And Coronary Heart Disease.

Why is GI important? When we eat carbohydrates
, they raise blood glucose levels. Pancreatic beta cells secrete a hormone called insulin, which allows more glucose to pass into cells (by moving Glu-T4 transporters inside the cells). When more glucose enters cells, glucose levels in the blood fall. It's a negative feedback loop. For millions of years, we lived on a diet of natural, unrefined carbohydrates and so the secretion of insulin never had to change blood glucose levels very rapidly.

When unnatural, refined, high-GI carbs are eaten, blood glucose levels rise much faster. This results in over-secretion of insulin (hyperinsulinaemia). This shuttles too much glucose into cells and results in.......low blood glucose, followed by low blood insulin. Rapidly-falling and low blood insulin levels cause feelings of severe hunger and cravings to eat more carbs. It's a vicious circle. Hyperinsulinaemia also has other bad effects on the body. See http://www.mercola.com/2001/jul/14/insulin.htm to learn about Insulin and its Metabolic Effects.

GI has a weakness because adding fats and some proteins to high-GI foods lowers the GI but can increase the insulin response. Saturated fats, monounsaturates and omega-6 polyunsaturates raise the insulin response to carbs.

There is another index called the Insulin Index (II). See http://www.mendosa.com/insulin_index.htm.
The II contains a few surprises. Some proteins (e.g. the whey in milk & yoghurt) produce a large insulin response.
Insulinogenic proteins are also glucogenic, so they don't cause low blood glucose.

On the other hand, refrigerating some foods lowers their GI & II by changing the starch in them into resistant starch, even if the food is subsequently re-heated. Rice & potatoes are two such foods.

As the terms "simple" and "complex" are meaningless in terms of carbohydrates' effects in the body, I prefer to use the terms "slow" and "fast". In a nutshell, slow carbs are good and fast carbs are bad. These terms can be applied to proteins, too. Egg is slow and whey is fast. Sticking to mostly slow foods keeps blood glucose and insulin levels stable, which results in better appetite control and better health, too.

It was soaring serum insulin levels that were sending me to sleep after carby meals years ago. Postprandial hyperinsulinaemia results in amino acids from digested foods being shuttled into cells. However, L-tryptophan isn't shuttled into cells, so the level of this amino acid
in the blood rises relative to others. As L-tryptophan competes with other amino acids to cross the blood-brain barrier, now that the competition has been removed, more L-tryptophan enters the brain. It's converted into 5-hydroxytryptophan (5-HTP), then serotonin & melatonin. High melatonin levels in the brain cause sleepiness.

So remember, "Right carbs, right amounts, right times."

7 comments:

Rosso said...

Few moments of your time Nige if I may,

1.What are your views on using low GI fruit in place of starchy carbs as a main source of carbs?

I've got wild cherry, dried apricots, lychee and a few others on mind. Some seem to have incredible anti-inflammatory properties

Am I headed for a fatty liver on this route? I've had digestive problems on oats and wholemeal breads and pastas.

2. When you say Omega 3 lowers insulin production, are we talking EPA, DPA, DHA or the parent ALA here?

The reason I ask is because I've started taking a fish oil (DHA, EPA) with most meals on days I don't take powdered linseed(ALA).

3. Resistant starch - you briefly touched on it. Is it a yay or a nay from yourself? How about an article on it at a later date? The infamous Japanese banana diet seems to be working on this principle.

And your last paragraph on 5HTP was great. The penny really dropped. It all makes sense now.

All the best,
Ross

Nigeepoo said...

1) Fresh/frozen/tinned in juice fruit is fine as it's mostly water. Dried fruit is all too easy to "nom" your way through a lot in a short space of time, though you may regret it 4 hours later when you're sitting on the loo clutching your tummy!

2) I don't know which particular omega-3 fat lowers insulin production (IP). Omega-3 fats lower IP by temporarily increasing the insulin sensitivity of muscle & fat cells (but not liver cells IIRC). Increasing the amount of feedback lowers the output in a negative feedback loop. The other types of fat temporarily decrease the insulin sensitivity of muscle & fat cells.

3) I have no problems with resistant starch (RS). I can eat cold potato/rice salad without any tummy trouble at all. Others may not be so fortunate. RS may aggravate inflammatory bowel conditions. However, omega-3 fats and Vit D3 are anti-inflammatory.

A slump can occur if a large amount of anything is eaten as large protein meals also produce an insulin response (as insulin is the storage hormone for carbs & proteins). Fat doesn't produce a slump as it doesn't directly produce an insulin response, though it modulates the insulin response produced by carbs & protein. Acylation Stimulating Protein doesn't cause a relative increase in serum L-tryptophan level.

Thanks for your comments.

Rosso said...

Cheers mate!

Been looking at the opposite extreme today, a certain Arachidonic acid.

Tanya said...

So...can I infer that to be anti inflammatory one can eat potatoes and rice in moderation esp. if you don't eat them until the next day, reheating after refrigeration?

Nigel Kinbrum BSc(Hons)Eng said...

Hi Tanya.

I don't know whether GI/GL correlates with inflammation so cannot directly answer your question.

Cooked & refrigerated potatoes/rice have a very low GI/GL due to the formation of resistant starch, which remains even after re-heating.

This is good if you are prone to wildly fluctuating blood glucose & insulin levels.

This is not so good if you are prone to gastrointestinal distress.

ProudDaddy said...

I was under the impression that the insulin spike caused by whey (from the leucine?) is accompanied by a glycogen spike that nullifies any effect on serum glucose. Nobody has yet convinced me one way or the other whether hyperinsulinemia or hyperglycemia (or both) is the culprit, but I'm leaning towards glucose-only because, I'm thinking, otherwise bodybuilders would be drpping like flies!

Nigel Kinbrum said...

That's a good point. This post is quite old and needs updating. If there wasn't a glucogenic response to insulinogenic proteins, we'd all keel over with hypos!