Besides nutritional requirements, ferrets have to meet their energy
needs; that is, their caloric requirements.  A Calorie is a measurement,
or unit, of energy and different nutrients have different amounts of
energy contained within in them.  (scientific standards now require the
use of kilojoules (kJ) rather than Calories, but it is confusing to most
people; one Calorie equals 4.186 kJ).  For example, the energy (rounded
off) contained within carbohydrates is 4 Calories per gram, protein has 4
Calories per gram, alcohol supplies 7 Calories per gram, and fat contains
9 Calories per gram.  Scientists used to believe ferrets, being long
skinny mustelids, had higher energy requirements because they had a
higher metabolism (you can read it in nearly every book on ferrets or
mustelids), but recent studies have shown that the metabolism of ferrets
and polecats is essentially the same as other small mammals of the same
size and are not elevated as previously thought.  Earlier differences in
metabolic rate have been attributed to procedural problems and stress
during testing conditions, NOT real metabolic differences.  This means a
2 lb ferret's metabolism is roughly the same as that of ANY other 2 lb
mammal.
 
There are some significant implications of this finding, the first being
that the idea that ferrets need food every four hours or harm will come
to them is false.  If they did, then so would every other mammal of the
same size and that idea is patently absurd.  It is patently absurd
anyway; polecats feed once or twice a day (if lucky) and have so for
millions of years; it is extremely unlikely a domesticated derivative
would be different in this regard.  This finding actually makes
evolutionary sense how many carnivores the size of a ferret can depend on
finding and killing prey every few hours?  The larger the prey the fewer
of them there are, and polecats have to struggle to find enough food a
couple of times a day, much less every four hours.  It is so difficult
that polecats would have had to evolve some sort of coping mechanism to
survive, and they did--both behavioral and physiological.  The difficulty
of finding prey has created a deep instinct in polecats to kill surplus
prey and stash it for later, a behavioral trait reflected in ferrets that
impulsively hide toys.  Also, if the animal doesn't consume carbohydrates
for energy, then a very efficient method of utilizing protein for energy
would have had to evolve, and it did, which is why ferrets have no need
for carbohydrates.
 
Also, realizing the idea that ferrets need frequent feedings is false
confirms what non-American ferret owners have known for centuries:
ferrets do just fine when fed a couple of times a day and they do not
require a constant, ad lib source of food for optimal health.  A
combination of leaving food out all the time (called ad libitum -- ad
lib -- feeding) and high carbohydrate load have trained many ferrets to
eat small, frequent meals, but that in no way proves healthy ferrets have
to eat that way.  If someone tells you otherwise, demand they present
their evidence in the form of published, scientifically approved studies,
or shut their mouth.
 
Like all mammals, the ferret can obtain caloric energy from
carbohydrates, fats, alcohols, or proteins.  Carbohydrates are nipped
apart and converted into a series of sugars that are ultimately converted
into glucose (blood sugar).  This is a very simple, easy procedure and
you harvest 4.1 Calories (kcal) per gram of carbohydrate.  It costs the
body 6 Calories to metabolize 100 Calories of carbohydrate, giving the
body a surplus of 94 Calories.
 
Fats are broken down into monoglycerides, diglycerides, free fatty acids,
and glycerol, absorbed and then rebuilt as triglycerides and brought into
the body via the lymphatic system into the circulatory system.  If they
are not needed, they are converted into fats and stored for future needs.
When the ferret needs energy, fats are broken down into fatty acids and
glycerols, both of which can be used for caloric energy.  One of the
breakdown products of fat metabolism is ketones (ketone bodies), which
are preferentially used by the heart, muscles and brain as a source of
energy.  Using fat for energy is not as simple a procedure as using
carbohydrates, but it provides much more energy, giving you 9.1 Calories
(kcal) per gram.  It costs 4 Calories to metabolize 100 Calories of fat,
giving the body a surplus of 96 Calories.
 
Alcohols are rarely used by ferrets for energy.  Because of their small
size and the ability of their stomach to expand to hold a large volume of
food, it is feasible a ferret could consume so much alcohol in a single
sitting to reach toxic levels and die, so alcohol should not be left out
where it could be knocked over and consumed.  It is possible that on rare
occasion a wild polecat may chance upon fermenting fruit and consume it
for the alcohol and sugar, but such instances would be rare and alcohol
levels small.  The body utilizes alcohol preferentially over fat, so if
you are dieting and drinking alcohol, your chances of loosing weight are
slim.  Alcohols are converted into acetate in the liver, and then further
metabolized to give you 7.1 kcal per gram in energy.  It costs 6 Calories
to metabolize 100 Calories of alcohol, giving the body a surplus of 94
Calories.
 
Proteins are broken down into amino acids that are converted into
keto-acids.  This is generally the most complex of the metabolic
reactions to create caloric energy and you get approximately 4.1 Calories
(kcal) per gram.  Once proteins are converted to keto-acids, they can
be used directly for energy in the TCA cycle (AKA: tricarboxylic acid
cycle, citric acid cycle, or the Krebs cycle), converted into glucose by
gluconeogenesis, or converted into fat by lipogenesis.  When you burn
protein, you harvest 5.3 kcal per gram, but in most animals (including
humans), some of the protein is converted into urea and is not completely
oxidized, so protein only yields between 4.1 and 4.2 kcal/g.  It is
possible that some hypercarnivores, the ferret included, have specialized
mechanisms for metabolizing protein, so the energy yield may be somewhat
higher.  It costs 30 Calories to utilize 100 Calories of protein for
energy, leaving a surplus of 70 Calories.
[Posted in FML issue 4595]