The involvement of circulatory glucose in the energy provision of skeletal muscle and heart of swimming carp was examined. Plasma glucose concentration varied  among individual carp, and estimates of glucose turnover rate (RT) were positively correlated with plasma glucose level in resting fish and in swimming fish.

Carp that were exercised at 80% of their critical swimming speed displayed a twofold higher RT at any plasma glucose concentration. Metabolic clearance rate also doubled in swimming carp relative to resting controls. Indexes of muscle glucose utilization (GUI), determined with 2-deoxy-D-[14C]glucose, indicated that glucose utilization in red muscle was not dependent on plasma glucose concentration; however, glucose utilization in this muscle mass was threefold higher in swimming fish than in resting control fish.

On the basis of whole body aerobic scope measurements in the carp, it was estimated that circulatory glucose potentially comprised 25-30% of the total fuel oxidation in the active red muscle mass. GUI in heart was positively correlated with plasma glucose concentration, and it is possible that glucose availability had considerable influence on the pattern of myocardial substrate oxidation in resting and active carp.

Carp are somewhat more reliant than rainbow trout on glucose for locomotor energetics, correlating with species differences in swimming capability and with the greater capacity of omnivorous carp to tolerate dietary glucose.
 

So what can we gain from the above information, besides a curious interest. Jack Blackford submitted this study when a debate on the carp-net-list concerning the lack of insulin levels in carp supposedly prevented them from using sugar found in many carp baits. The study suggests that they do metabolize carbohydrate, particularly simple sugars. So the carp has a sweet tooth for good reason. Oat even suggested that the carp got a glucose buzz from sweet baits, and indeed that is very likely. The addition of sugar to baits is substantiated by the experience of many who prepare their own baits. Sweet corn, particularly sweet canned corn with the instant release of sugar and corn syrup, are more powerful attractants than maize. The carbohydrate in maize is for the most part consisting of starch which requires complex enzymatic digestion, as compared to the simple sugars which dissociate in solution and are easily taken up into the carps bloodstream.

Do what you will with the information, but my suggestion is don't over sweeten your baits. Carp can taste well enough the offering and will have done so before it takes the bait into the mouth. Sweetening alkalinizes a bait reducing the attraction that carp have for acidic forage. Carp are able to detect items of a lower pH from the generally neutral background. Living and decomposing organic matter has a lower pH and is a homing signal for food.  The discovery of glucose is not a frequent matter in the aquatic environment, in other words it doesn't grow there, but usually is a landfall occurrence such as the falling of berries from overhanging vegetation. And sweet corn and maize are not naturally found broadcast into a water system.

The carp is an omnivore, utilizing a wide range of animal and vegetable matter for food. When carp feed, they become eating machines eating all food opportunistically, and competitively. Corn , boilies, tiger nuts, crayfish etc. in the most gluttonistic fashion. Animal and plant materials are effortlessly blended by the capable pharyngeals. Maize in some cases will pass through the vent as other indigestibles such as chitinous exoskeletons of crayfish or mussels. The carp do not think about this, they will eat boilies from end to end, dispatch a snail as it arises, gobble plants, mud and other indigestibles and continue to process all ingested items from one end of the alimentary canal to the other. One large carp may dispatch twenty boilies without being satisfied  because it vents as quickly as it eats. It will turn to more maize, blood worms, whatever comes down the path
 it follows. In it's wake it leaves many undigested particles which feed other animals or which generally enriches the ecosystem with nitrogen. When the feeding carp have harvested a feed area, they move on unless you keep them busy with introduced chum. When they are off feed they will prefer sanctuary in a temperature and surrounding which keeps their metabolic demands lowest, and at this time carp may suspend without interest in forage or baits.

A completely vegetable diet (grass carp) requires eight times the body mass of the fish to maintain itself in health. A carnivorous diet (pike) only requires five times body weight to arrive at maintenance. Omnivorous fish (carp) five to eight. A diet of boilies would allow homeostasis and maintenance at a lower weight, due to the nutritional advantages of their composition. But carp will still eat them until they vent them undigested along with the other items both good and bad. This gluttony to the point of negative return is observed in carp. And if your rig is not set wickedly to hook the carp, after a pull or two on the odd boilie which doesn't seem to vacuum up as the rest, it will mindlessly move on to the next hoovering, leaving the hook linked boilie for the next fish. It will not take a mind to persistently attack the stubborn boilie, and suspicious fish will avoid it. The alimentary canal is simple. Forage items are not intended to be held in storage, or in a churning or enzyme rich digestive system like land animals have. Nutrients are best processed in fast passage through the gut followed by a constant feeding situation, similar to the passage of organic soil through an earthworm. Boilie fed fish may be larger in mass which pleases the angler and specimen hunter, but size is not an adaptation benefiting health or survival of carp in the wild. Smaller carp from less nutrient rich waters are just as healthy, and perhaps even more so than over fed carp.

So if you need to make the bait a little more interesting and nutritious as well, a little glucose may be called for. And don't forget artificial sweeteners. Carp like them too.
 

Al