Some amino acids cannot be used to make glucose; those that can are called glucogenic. A smaller number can only be used to make ketones and are called ketogenic; these can also be used to make energy. Four amino acids are both glucogenic and ketogenic; one of these is tryptophan, a precursor for both seratonin and melatonin. Only two amino acids, leucine and lysine (not so coincidentally are essential amino acids), cannot be converted to TCA cycle intermediates and used as an energy source. Animals cannot convert fat directly back into glucose, instead making fatty acids and glycerols. Both fatty acids and glycerols are eventually converted into acetyl-coenzyme A (acetyl-coA), which are used for energy in the TCA cycle. Glycerols can also be converted to glucose through several intermediate steps. When non-carbohydrate sources such as protein or fat are used to make glucose, it is called gluconeogenesis. It is clear from this discussion that ferrets can create energy from four different sources: carbohydrate, fat, alcohol, and protein, but the same is true of any mammal--even humans. The difference is that ferrets are superbly adept at converting protein into energy and do not suffer the same problems as humans, or many other mammals for that matter. Rather than suffering rabbit starvation as would a human on a lean prey diet, ferrets would thrive and become fat little carnivores on a diet of nothing but Mr. McGregor's vegetable patch nemesis, Peter. In terms of the energy requirements during exercise, they of course would be higher in exercising animals. Muscles require energy to work, so the more you work them, the more energy you need. This is one reason why all carnivores lounge around or sleep so much; it is to conserve energy. The need for additional energy would be much greater in an exercising ferret than their corresponding need for nutrients. In the wild, because polecats and New Zealand feral ferrets use protein for energy, what this means is they simply eat more food--that is, prey. All mammals, humans included, eat to meet caloric needs, but will adjust food preference -- whenever possible -- to satisfy particular dietary cravings. The catch is, eating to meet caloric needs is a misnomer, as is the idea that ferrets are trying to regulate blood sugar. In reality, even when fasting, blood sugar levels are remarkably stable. If they weren't, then a human or a ferret sleeping for six hours would have extreme hypoglycemia because the amount of glucose in their blood would be used up in less than an hour. Two hormones, insulin and glucagon, regulate blood sugar by reacting to increased or decreased levels in the blood. Simplistically, insulin makes muscles and other cells store blood sugar, so it is removed from the blood and stored in the liver, muscles and other tissues. Glucagon makes those same cells give up blood sugar, increasing their levels in the blood. Because both mechanisms are always in the on position , they react very rapidly to changes in blood sugar levels, so, unless some disease or pathological condition is in play, or if there is a heavy workload while fasting, the blood sugar level is remarkably stable--even during long fasts. Ferrets, as well as humans, essentially eat to maintain insulin levels; when they drop (and glucagon increases), you get hungry. Consuming carbohydrate, which is essentially a long chain of sugar, inundates the blood stream with glucose, so insulin levels are increased to regulate the flood. When the blood glucose levels drop, so does the amount of insulin, which is part of the hunger trigger . So, ferrets on a diet of carbohydrates tend to eat frequent, small diets in their attempt to regulate insulin levels. They do it NOT because they need to, but because it is an adaptation to a diet the ferret is not designed to eat. The ferret pancreas is not adapted to such a diet and the long-term effect is that a large number of them develop insulinoma. If asked, at a future time I can post about the carbohydrate-pancreatic connection to insulinoma, how they relate to stress, and how both have possible influences on adrenal disease. Ferrets are designed to eat a high protein diet and to use that nutrient source to provide them with adequate sources of energy, so why do some people insist ferrets require carbohydrates? Part of the problem is most studies are on humans and extrapolated to other species. In humans, the amount of glucose that can be made from protein is limited because the process primarily takes place in the liver (and about 10% in the kidneys). The liver requires oxygen for gluconeogenesis, but most of its oxygen for that purpose comes from oxygen-poor venous blood in the hepatic portal system. Between this oxygen poor system and the cost in energy to convert protein to glucose, humans can only make enough glucose to barely supply basal metabolic needs; that is around 1400-1500 kcal per day (good luck if you are a large guy). This is not enough calories for active humans and they experience energy malnourishment; that is, they suffer from rabbit starvation. Ferrets, however, evolved eating a high protein, moderate fat, low carbohydrate diet. It is clear that ferrets have no carbohydrate requirements, so their primary source of energy MUST be proteins and fats; the amounts of carbohydrates consumed are essentially scientifically insignificant. If you assume the ferret is no more efficient than a human in converting protein to glucose, how do they meet their energy needs if they do not require carbohydrates? One reason is that ferrets have a brain far smaller in proportion to their body size than a human, and the brain sucks up a lot of energy. Another reason is because the ferret has a liver that is proportionately larger than those in humans, so they have proportionately more area for gluconeogenesis. There are indications that more gluconeogenesis takes place in the ferret kidneys, and that ferrets are slightly more efficient at recycling nitrogen, so not as much is lost as urea. Finally, ferrets are just a lot smaller than people, so the internal volume of body tissues that require energy are proportionately smaller. All these reasons, and likely more, allow the ferret to live a carbohydrate-free life, using nothing more than protein to create the glucose necessary for life. Bob C Communication? [log in to unmask] Questions? [log in to unmask] [Posted in FML issue 4595]