However, the clinical preparations prepared from such insulins differ from endogenous human insulin in several important respects; an example is the absence of C-peptide which has in recent years been shown to have systemic effects itself. Novo Nordisk has also developed a genetically engineered insulin independently using a yeast process.According to a survey that the International Diabetes Federation conducted in 2002 on the access to and availability of insulin in its member countries, approximately 70% of the insulin that is currently sold in the world is recombinant, biosynthetic human insulin. A majority of insulin used clinically today is produced this way, although clinical experience has provided conflicting evidence on whether these insulins are any less likely to produce an allergic reaction. Adverse reactions have been reported; these include loss of warning signs that patients may slip into a coma through hypoglycemia, convulsions, memory lapse and loss of concentration. However, the International Diabetes Federations position statement from 2005 is very clear in stating that "there is NO overwhelming evidence to prefer one species of insulin over another" and "[modern, highly purified] animal insulins remain a perfectly acceptable alternative. "Since January 2006, all insulins distributed in the U.S. and some other countries are synthetic "human" insulins or their analogues.
The result is that the blood glucose level rises somewhat after eating, and within an hour or so, returns to the normal fasting level. Even the best diabetic treatment with synthetic human insulin or even insulin analogs, however administered, falls far short of normal glucose control in the non-diabetic.Complicating matters is that the composition of the food eaten (see glycemic index) affects intestinal absorption rates. Glucose from some foods is absorbed more (or less) rapidly than the same amount of glucose in other foods. In addition, fats and proteins cause delays in absorption of glucose from carbohydrates eaten at the same time. As well, exercise reduces the need for insulin even when all other factors remain the same, since working muscle has some ability to take up glucose without the help of insulin.Because of the complex and interacting factors, it is, in principle, impossible to know for certain how much insulin (and which type) is needed to cover a particular meal to achieve a reasonable blood glucose level within an hour or two after eating. Non-diabetics beta cells routinely and automatically manage this by continual glucose level monitoring and insulin release. All such decisions by a diabetic must be based on experience and training (i.e., at the direction of a physician, PA, or in some places a specialist diabetic educator) and, further, specifically based on the individual experience of the person. But it is not straightforward and should never be done by habit or routine.