TOPICS IN NUTRITION Part 2
Geneva Coats, R.N.
FAT
Fat is the most concentrated
source of energy in the diet, providing nine calories per gram compared with four calories per gram from either carbohydrates
or protein. Studies with sled dogs show that those dogs fed diets high in fat and protein outperform those fed a greater proportion
of carbohydrates. Body fat itself serves a useful function; fatty layers provide insulation from the cold, provide an energy
reserve, and protect the nerve fibers in the body.
Fats are part of the structure
of the brain and cell membranes. Fat is required for maintenance of healthy skin, for regulation of cholesterol metabolism,
and as a precursor of prostaglandins, hormone-like substances that regulate many body functions.
Fats in the diet are necessary
for absorption of the fat-soluble vitamins A, D, E and K. Fats improve flavor and palatability of food. Fat is more easily
digested by dogs than either proteins or carbohydrates.
Is too much fat harmful?
Dogs do not develop atherosclerosis or heart disease from dietary fat as humans do. For overweight dogs, excess calories may
be a factor, but it is recommended to feed smaller portions of high quality food including fats, rather than reduce the total
percentage of fat in the diet. Fats must be limited for dogs with pancreatitis; however, fats do not cause pancreatitis in
dogs, they merely aggravate this condition if it is already present. For a healthy dog, fat in the diet is beneficial. Too
much dietary fat, however, may result in suboptimal intakes of protein, minerals and vitamins.
Bile is produced by the
liver, and stored in the gall bladder until needed. Dietary fats are emulsified by bile in the small intestine. Digestive
enzymes then break down the fats into glycerol and fatty acids. These components are then absorbed into the bloodstream through
the walls of the small intestines. Glycerol (a component of fat) can be converted into glucose by the liver. If the liver
is diseased and not producing sufficient bile, fats are difficult to digest, and fatty stools may result.
There are several basic
types of fats derived from foods; cholesterol, saturated fat, monounsaturated fat and polyunsaturated fat. All polyunsaturated
fats, including omega-3s and omega-6s, are considered important fatty acids because they are critical for good health.
FATTY ACIDS
Dogs cannot synthesize certain omega-3 and omega-6 fatty acids, they must obtain them from their diet. These
fatty acids are essential for healthy nerves, skin, coat, kidneys, heart, and to prevent inflammatory disease.
Omega-6 fatty acids are widely found in both animal and plant sources such as chicken, pork, beef, and vegetable
oils like sunflower oil. Omega-3 fatty acids are less common, and are found in fish, flax seed and marine sources, such as
spirulina and blue green algae. A high amount of omega-6 (in proportion to omega-3) promotes inflammation, poor coat, allergies
and skin conditions, so it’s generally advisable to supplement with a reliable source of omega-3 fatty acids.
There are at least
eight different types of omega-3 fatty acids. EPA and DHA are the most valuable. They are necessary for brain and nervous
tissue function, and are useful in prevention and treatment of inflammation and allergies. Heart health is supported by DHA
and EPA. Studies in humans suggest that diets rich in EPA and DHA are effective in relieving the symptoms of depression and
psychosis.
The richest sources of
DHA and EPA are cold-water fish and their oils, such as salmon, tuna, and mackerel. Aside from fresh seaweed, plant foods
rarely contain EPA or DHA.
Other sources of Omega-3
fatty acids include plant oils such as flax, canola, soy, hemp, and walnut. The omega-3 derived from these plants is a type
known as ALA. The problem is that ALA is inactive. It must
be converted by the body with special enzymes into the useful forms of DHA and EPA. Dogs cannot do this conversion reliably;
and as they age, they become even less efficient at converting ALA. Unconverted ALA
performs more like omega-6 fatty acids in the body, and can potentially provoke inflammation and allergies.
Many commercial dog foods
manufacturers rely primarily on soy, flax or flaxseed oil as their primary source of omega-3 fatty acids, due to its low cost.
Flax and soy also contain high levels of phytoestrogens, chemicals which can substitute for estrogen in the body. This can
potentially affect hormone balance. Unfortunately, it is difficult to find a commercial dog food that includes fish oil instead
of flaxseed oil or soybean oil.
SALMON and FISH OIL
You may have heard the
saying that “fish is brain food.” This is one old wives tale with a basis in scientific fact. Fish, fish oils
and marine greens contain the essential omega-3 fatty acid DHA, which is a component of brain, eye and nervous tissue. Salmon
oil or fish oil is something that you should definitely consider adding to your dog’s diet. The essential fatty acids
these oils contain are not found in most other foods. Intake of the omega-3 fatty acid DHA is particularly valuable during
pregnancy, because it is a key component of neural development.
Interestingly enough, in
nature, fish themselves do not produce omega-3 fatty acids. They obtain them from their diet of algae, plankton and smaller
sea life. Farm-raised fish are usually fed a diet of grains, not a natural diet of sea life. This means that farm-raised fish
are not as rich a source of omega-3 fatty acids as wild-caught fish. Wild salmon have red-pink flesh. Farm-raised salmon don’t
obtain the same micronutrients in their diet as wild salmon. Their flesh is not pink, and farmers must use artificial dyes
to give them a pink color! When checking labels, look for salmon oil from fish that are wild-caught, not farm-raised.
Before modern farming methods
came into practice, foods used to contain more EPA and DHA than they do today. Beef in modern feedlots are raised on corn
and grains, and don’t contain any ALA or DHA. Grass-fed
beef, bison, venison and other wild game will contain small measurable levels of DHA and EPA, but these levels are much lower
than those in fish…35 mg per serving compared to 1400 mg per serving of fish.
One concern with fish oil
is that fish may contain high levels of mercury, PCB, dioxins and other environmental contaminants. Wild caught salmon contain
lower levels of these chemicals than farm-raised salmon. If the label doesn’t say “wild” salmon, it is probably
farm-raised. Mercury contamination is mostly a concern in larger fish, such as tuna, swordfish and king mackerel. Salmon,
jack mackerel and sardines are all low in mercury. Also, the contaminants remain primarily in the flesh, and not the pressed
oils.
Pharmaceutical grade fish
oil capsules can also be used if contamination is a concern. Serve the whole capsule, or you can poke a hole in it with a
pin and squeeze the fish oil over the rest of the meal. Testing that has been done on a variety of fish oil supplements by
Consumer Reports and Consumerlabs.com found no traces of mercury, PCBs, or dioxins. Almost all brands regardless of price
were reliable in the amount of omega-3s they contained and were found to be fresh.
EPA and DHA are easily
destroyed by light, heat and oxygen, so fish oil capsules may be the better choice over fish oil jars with pumps available
at pet stores. Whichever form you buy, store in the refrigerator until used. It is best to add these supplements
immediately prior to feeding.
Sardines can be used to
replace fish oil supplements; one small sardine has over 100 mg of the omega-3 fatty acids EPA and DHA. Cod liver oil is not
as valuable as other fish oils, because it is lower in omega-3s. Since it is derived from liver, it is very high in vitamins
A and D. Excesses of Vitamin A and D are not beneficial and can actually be toxic, so cod liver oil should be used sparingly.
Many kibbles include fish
meal. Oil is extracted from the fish before it is processed and dried into a “meal”. Processing and lack of beneficial
oils means that foods made with fish meals will not provide the same nutritional benefits as feeding fresh fish and their
oils. Another concern is the fact that all fish meals are required by the US Coast Guard to be preserved with ethoxyquin at
their point of origin. This ethoxyquin is not required to be listed on the dog food label, since it was added to the fish
meal prior to its arrival at the production plant. The long-term health effects of ethoxyquin and other artificial chemical
preservatives are largely unknown.
VITAMIN E
Vitamin E was first identified
in the lab in 1936. It’s presence in the diet was found necessary for rats to maintain pregnancy; therefore Vitamin
E is also called “tocopherol”; derived from a Greek phrase meaning “to carry a pregnancy”. Vitamin
E is an essential fat soluble vitamin. It protects cell membranes from the damage caused by oxygen free radicals and the products
of fat metabolism.
A diet high in fish oil
also requires additional Vitamin E. Vitamin E is quickly depleted in the metabolism of omega-3 fatty acids. In the early
1960’s, it was noted that cats fed large amounts of canned tuna were becoming ill. This happened because canned tuna
is a rich source of essential fatty acids, but is deficient in Vitamin E. The cats developed a condition called “steatitis”
or “yellow fat disease”. This is characterized by abnormal waxy fatty deposits. Other symptoms of vitamin E deficiency
are hemolytic anemia, poor nerve conduction, muscle weakness and damage to the retina of the eye.
Therefore, when adding
fish oil or salmon oil to the diet, you will also need to add a good source of Vitamin E. Some natural sources rich in Vitamin
E are wheat germ, eggs, spinach, broccoli, romaine, and various nuts and seeds. These foods also contain the mineral
selenium, which is needed along with vitamin E.
Vitamin E can also be added
to food as a supplement. When shopping for a Vitamin E supplement, look for a source that states it contains “natural”
Vitamin E, or “d”-alpha tocopherol. The supplement “dl”-alpha tocopherol is a synthetic form of Vitamin
E that is manufactured from petroleum oil. There are other forms of vitamin E such as delta, beta and gamma tocopherols. A
supplement that contains natural, mixed tocopherols is the best choice. A small dog should receive Vitamin E, 50-100 IU at
least three times a week.
These Vitamin E supplements
are usually derived from soy. If your dog is allergic to soy, look for a cold-water dispersible or “dry” vitamin
E. It is more expensive than vitamin E derived from soy, but is also more readily absorbed.
Some commercial kibbles
include Vitamin E as a preservative, since it has potent antioxidant properties. The amounts used are relatively small and
are rapidly depleted by oxidation as the food sits on the shelf. Vitamin E is swiftly destroyed by heat, light and air, so
it should be added to the food at the end of preparation. Vitamin E is considered nontoxic, but in high doses may prolong
blood clotting.
In the next issue, we will
learn about carbohydrates, fruits and vegetables, prebiotics, and supplements. See you next time!
