Carbohydrate Digestion and Metabolism UPDATES

Dietary Carbohydrates —

Joint FAO/ WHO scientific update on carbohydrates in human nutrition


FAO / WHO Scientific Update on carbohydrates in human nutrition: introduction

C Nishida & F Martinez Nocito


Carbohydrate terminology and classification

J H Cummings & A M Stephen

Nutritional characterization and measurement of dietary carbohydrates

K N Englyst, S Liu & H N Englyst

Physiological aspects of energy metabolism and gastrointestinal effects of carbohydrates

M Elia & 3 H Cummings

Carbohydrate intake and obesity

R M van Dam & J C Seidell

Dietary carbohydrate: relationship to cardiovascular disease and disorders of carbohydrate metabolism

J Mann

Carbohydrates and cancer: an overview of the epidemiological evidence

T J Key & E A Spencer

Glycemic index and glycemic load: measurement issues and their effect on diet-disease relationships

B J Venn & T J Green

FAO/WHO Scientific Update on carbohydrates in human nutrition: conclusions

J Mann, J H Cummings, et al

Carbohydrate Digestion and Metabolism
Glycaemic Index —

The low glycaemic index diet Ludwi: Lancet 2007, vol 369, March 17, 890-892

David Ludwig has written a thought provoking article on the glycaemic index(GI) This concept has been around for more than 20 years. The argument for this measure is that it is a guide allowing the classification of health providing properties of carbohydrate meals. Eating simple sugars which are rapidly absorbed is a challenge to the body hormonal system.

GI is determined by measuring the 2 hour incremental area under the glucose curve after taking 50 g of carbohydrate and comparing this with a white bread or glucose load. The higher the GI the greater the potential hormonal challenge to glucose homeostasis. Glycaemic load (CL) is the average GI multiplied by the carbohydrate amount.

It is also claimed that in times gone past that we ate a diet that was characterised by a lowGI. It is a absolute necessity for any theory that the central element is unchallengeable by measurement. Who knows how our primeval ancestors ate. Feast and famine, hunting ,gathering , good weather ,bad weather, fierce carnivores hunting for the same food. No shop until you drop but hunt and gather before you drop. Early death from all manner of pestilences.

The bolus of food can be seen as a sponge. The glycaemic curve will be dependent upon

time of chewing .
length of time spent ingesting the food or drink e.g. sipping. A simple experiment is sipping a glass of wine or gulping it down.
Eating communally is important. In contrast to the snatched meal.
gastric emptying time. This is determined by the chemistry of the food ingested e.g. fat has the greatest retarding effect. So a piece of white bread coated with butter and a protein paste will have a lower GI than white bread on its own
How the ingested food was prepared .
Each of us has two experiments going. One’s own eating habits and that of people we are advising. What do we really enjoy?

Perhaps GI should only be part of a dietary regime. That the forbidden treats be eaten slowly and in discrete amounts. Food is a real treat in life. There is such a contrast between the snatched sandwich and a couple of pints in a Pub before an important game and the slow meal eaten amongst family and friends for Sunday lunch. Both are fun and should live together. A mix is all important.

The European Journal of Clinical Nutrition 2007 vol 61 has published a supplement. S1-137

Kidney and Glucose Homeostasis —

The kidney contribute to glucose homeostasis in three ways

Gluconeogenesis 15-55 g per day

Utilisation of 25-35 g glucose a day

Reabsorption of glucose

In healthy adults 180 g of glucose is filtered by he kidneys each 24 h through sodium-glucose transporter 2 (SGLT2) in proximal tubules

Hanefeld, Forst 2010 Dapagliflozin an SGLT2 inhibitor, for diabetes Lancet vol 375 pp 2196-2197

Japanese colonic bacteria —

Marine algae contain sulphated polysaccharides that are absent in terrestrial plants. These unique polymers are used as a carbon source by marine heterotrophic bacteria that produce specific CAZymes. In comparison to the accumulating knowledge on the degradation of plant polysaccharides little is known about the enzymes acting on polysaccharides from marine edible algae such as Porphyra (nori), Ulva (sea lettuce) or Undaria (wakame).

Gut microbes supply the human body with energy from dietary polysaccharides through carbohydrate active enzymes, or CAZymes, which are absent in the human genome. These enzymes target polysaccharides from plants that dominated diet throughout human evolution

The array of CAZymes in gut microbes is highly diverse, exemplified by the human gut symbiont Bacteroides thetaiotaomicron, which contains 261 glycoside hydrolases and polysaccharide lyases, as well as 208 homologues of susC and susD-genes coding for two outer membrane proteins involved in starch utilization.

The question of how this diversity evolved by acquiring new genes from microbes living outside the gut. In this paper by Hehemann et al in Nature April 2010 the authors characterize the first porphyranases from a member of the marine Bacteroidetes, Zobellia galactanivorans, active on the sulphated polysaccharide porphyran from marine red algae of the genus Porphyra. They show that genes coding for these porphyranases, agarases and associated proteins have been trans¬ferred to the gut bacterium Bacteroides plebeius isolated from Japanese individuals

Their comparative gut metagenome analyses show that porphyranases and agarases are frequent in the Japanese population and that they are absent in metagenome data from North American individuals.

Seaweeds make an important contri¬bution to the daily diet in Japan (14.2 g per person per day), and Porphyra spp. (nori) is the most important nutritional seaweed, traditionally used to prepare sushi

This indicates that seaweeds with associated marine bacteria may have been the route by which these novel CAZymes were acquired in human gut bacteria, and that contact with non-sterile food may be a general factor in CAZyme diversity in human gut microbes.

Hehemann et al 2010 Transfer of carbohydrate-active enzymes from marine bacteria to Japanese gut microbiota Nature vol 464 pp 908-912

Sonneburg Genetic pot luck 2010 Nature vol 464 837-8


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