It is always important to with the basics. This page will briefly cover the basics of the six categories that make up all foods. Whenever we eat something, it will contain one, several or all of these categories.
All of these categories are important for life. The problem with any of these categories will be with respect to proper levels. Too much or too little of a nutrient can be very harmful.
When understanding nutrition it is important that we look at nutrient and nutrient levels as opposed to just ingredients. Focusing on ingredients alone can be misleading and can easily lead to imbalanced nutrients.
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"When the well is dry, we know the worth of water." - Benjamin Franklin Poor Richard's Almanac 1746
"Water is the driver of Nature." - Leonardo da Vinci
Without water we would all die as mammalian bodies are made 60-70 percent of
water. For puppies and kittens, this percentage is even higher. At ten percent body water loss, most pets will require hospitalization; at 12 percent, many can die.
Often we do not think of water as a nutrient, but all food is comprised of water. Most dry foods are often around ten percent water with 12% being the maximum. Cats will often prefer a drier food around five or six percent.
How much water is in the food we buy?
To legally place a title such as dry, semi-moist, etc, companies must adhere to specific percentages. Even with these restrictions, sometimes we do not know that we what we are buy!
- Dry - 3 - 11%
- Semi Moist - 25 - 35%
- Canned or wet - 60 - 87%
- Gravy - can be higher than 87%
So why is this important?
The water content is important for many reasons. First, when looking at pet water intake, the amount of water in the food can alter that the pet requires and thus alter how much they drink. Secondly the additional water in canned food is one of the reasons why many pets find canned food more tasty or palatable. For dogs, many people will add water to their dog's kibble for taste. I used to add warm water. However while we can add water to kibble, for pets where it is medically important to increase their food intake; this may not be an adequate method to "simulate" canned food. In order to come close to a canned food we would need to have 2.5 parts water to 1 part kibble. This fact, along with other palatability issues, make canned diets important in many situations.
Thirdly, there is a cost issue. For example lets take two different diets. Diet AB we shall say has 70% water and Diet XY will have 80% water. This means that Diet AB contains 30% food and Diet XY contains 20% food. This means that diet AB has 50% more food in it!!! This is important to consider when we look at price. Sure both diets have great labels and pictures but diet AB is cheaper. Or is it? If that cost does not make up for the difference of actual food in it, then it is often a more costly food! Beware or instead of saving money we could just be adding money to a company's bottom line and give less actual food to our pet.
A final note is to look for some diets that hide the fact that the food is actually considered a gravy and not canned food. Some diets, both prescription and over the counter will place a small label "in gel" next to the food name. This "in gel" is often of a very small font. This allows it to have higher water percentage than normal canned food. So the can may look great and have a great label but if it is actually 90% water, what type of savings is this? 10% food?? Some companies use this strategy for weight control; and this is true, if you fill a dog on water and not food, they could lose weight. However does this sound like a fun or healthy way to lose weight??
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| Glucose Molecule. Note the ring structure. This is the smallest unit of carbohydrates |
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"The foodstuff, carbohydrate, is essentially a packet of hydrogen, a hydrogen supplier, a hydrogen donor, and the main event during its combustion is the splitting off of hydrogen." - Albert Azent-Gyorgi, a Hungarian Nobel Prize winner in Medicine. He is famous for the discovery of Vitamin C
Carbohydrates, are you a good witch or a bad witch?
Carbohydrates, like all nutrients are good in proper amounts and types and bad in improper amounts and types. So what are the types of carbohydrates and how much does my pet need?
Forgive me while I get technical. If too boring, don't pass out, just skip to the next paragraph.  Carbohydrates are made of three atoms: hydrogen, oxygen and carbon and comes in the molecular formula of (CH2O)n.You will notice the "H2O" in the formula which is of course water where we get the name "hydro". Thus this compound is a hydrate of carbon or "carbohydrate." Fun huh?  Glucose is one of the most basic sugars with a molecular formula of C6H12O6. It forms a ring. When we have one or two sugar units (such as glucose) we have a simple sugar. (For technical people, a single unit would be called a monosaccharide and two units would be called a disaccharide). Saccharide comes from the Greek word for sugar and is synonym for carbohydrate (technically a saccharide is a carbohydrate of biologic use). When we have many sugar units linked together, more than nine, we call it a polysaccharide or complex carbohydrate. (for intermediate numbers we have an ugly huge word called oligosaccharides. Don't worry about remembering this one!).
So now we know the difference between a simple and complex carbohydrate/sugar. A simple sugar is made of one or two sugar units like glucose while a complex sugar is made of as many as nine to literally thousands. While there are many different types of sugar units, the most common ones that you will hear will be: glucose, galactose or fructose. Some common disaccharides are: Sucrose (glucose and fructose); Lactose (galactose and glucose); and Maltose (two glucoses).
Another important distinction with carbohydrates will be how these units are linked together. Depending upon how the units are linked will determine their function. The two main categories will be storage and structural functions. Storage function is primarily starch. (in animals we store it in a way called glycogen; and in plants it is called amylopectins or simply starch). In plants, when carbohydrates are used for structure (support to keep them upright) it is in a form called cellulose. Interestingly cellulose is simply a huge chain of glucose but because of how the plant links it; it is not digestible by dogs, cats or humans. Animals use carbohydrates for structure too! Shrimp, crabs,insects and spider's shell or ectoskeleton is made of chitin which is a carbohydrate. Our fingernails and hair though is made of protein and not carbohydrates. Glad you don't share the same type of hair as a spider?!
So what does the body do with carbohydrates?
For the most part, carbohydrates can be seen as fuel. Most starches and simple sugars eaten by dogs and cats will be used for either metabolic energy (creating ATP) or storage as animal starch, glycogen.
Carbohydrates are important however also for several metabolic pathways that make important chemicals in the body like Vitamin C, amino acids, glycolipids and glycoproteins.
What happens when a body "burns" the carbohydrate fuel?
When sugars are "burned" to create ATP (Adenosine TriPhosphate - the basic energy unit of the body), they are broken down into smaller components and since they are made of carbon, hydrogen and water, the resulting compounds are carbon dioxide (CO2) and water (H2O). The carbon dioxide is breathed out of the lungs and the water is used in other areas or urinated out. Feeding large amount of carbohydrates however does not eliminate the need to water.
What is the minimum amount of carbohydrates needed?
Interestingly carbohydrates are the one nutrient that do not have a minimum requirement. For growing, pregnant and lactating animals, carbohydrates are very important but for the adult dog and cat, they do not have minimum. However when we create food and need a balance of fats and proteins in relation to calories, the need for carbohydrates become important. Luckily both dogs and cats digest plant starches well. In fact in a feeding trial, cooked cornstarch was almost 100% digested in cats1.
For dogs and cats, when the carbohydrates are low it is even more important that the protein be of a high digestibility or quality. For dogs, if they eat a starch free food, they must have 33% Metabolized Energy (ME) from protein in order for the body to make the amount of carbohydrated needed for life2.
How much carbohydrate should a dog have?
Most dry foods contain 30-60% carbohydrate DMB (DMB stands for Dry Matter Basis and is the evaluation of a food after all the water has been taken out). Excess starch does not appear to create any problems in dogs.
Dogs that are pregnant or lactating (producing milk) are thought to have a minimum requirement of 23% carbohydrates DMB3.
Do I have to worry about too much simple sugars in pet foods like I do for my own foods?
Many people are worried about excess simple sugars for dogs and cats. Cats, technically, do not have sweet receptors in their mouth. So when you call them "Sweetie", this is why you get the strange look back from your cat! Luckily for both dogs and cats, excess simple sugars are rarely used and thus should not be considered a common concern when looking at commercial pet foods.
Should cats even have carbohydrates?
Like dogs, they have no minimum requirement for carbohydrates but it is important to note that carbohydrates serve important functions in cats and are well tolerated in cats if supplied in appropriate amounts. There is an extensive section on "Cats and Carbohydrates" on this site so I will not go into detail here. Suffice it to say, cats can have a reasonable level of carbohydrates and can serve to provide energy, the important nutrients that are included in the carbohydrate source (i.e. lutein and beta carotene in cooked, ground corn). If carbohydrate levels exceed 40% DMB4, then cats can begin to have problems. Externally we can see diarrhea and excess gas and internally we can detect elevated sugar in the blood and urine.
1) Meyer and Kienzle, 1991; Keinzle, 1993, 1993a. Cats were fed 4.7g/kg body weight of cooked cornstarch per day. The result was a digestibility of the cornstarch by the cats at almost 100%.
2) Kienzle et al, 1985
3) Small Animal Clinical Nutrition Fifth Edition Hand, Thatcher, Remillard, Roudebush, Novotny pg 71.
4) Small Animal Clinical Nutrition Fifth Edition Hand, Thatcher, Remillard, Roudebush, Novotny pg 72.
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| What the neighbor dog steals off your grill. |
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When we look at the make up of a animal, the most abundant substance is water which is followed by protein. So if you are called a "meathead" you can tell them that protein is indeed the second largest component of your head. Well... maybe if you don't want to get beat up, you shouldn't say that.
So what is protein?
Protein is any molecule that is made up of amino acids. There are 21 amino acids in plants and animals. Each amino acid is a smaller molecule made up of carbon, hydrogen, oxygen and nitrogen. Some also have phosphorus and selenium atoms.
What do proteins do in the body?
What don't they do?! Not only does protein make up the majority of muscle but also of skin, finger nails, and hair. They make up all of our hormones, enzymes and hemoglobin. They are used as support structures for most organs.
What does the body do with them?
Hormones are messengers used between cells. So besides estrogen and testosterone, there are hundreds of hormones that your body used to communicate between cells. Hemoglobin of course carries oxygen to our cells and another protein called albumin forms the most common blood protein and helps carry nutrients to the cells. Antibodies which are an important part of our immune system are also proteins. Proteins help maintain our blood pressure and blood pH (pH can be thought of as "acid level"). They also are used for structural support like the collagen in our skin or the collagen and elastin in our cartilage, joints and ligaments.
Would you be surprised to know that our muscle makes less than half of our total body's protein?!
Cats need another amino acid that dogs don't right?
That is correct, just as dogs have an additional amino acid requirement than people; cats need an additional amino acid from dogs (and thus two more when compared to people). This is one of many reasons why we cannot feed dogs and cats like people. Each species is different, with different requirements.
The additional amino acid required by dogs and cats when compared to humans: Arginine
The additional amino acid required by dogs when compared to cats: Taurine.
So how much protein does a pet need?
Unlike carbohydrates, there are specific requirements not only of protein but also of certain amino acids. There is more information on specific amino acids but keep in mind that both dogs and cats have specific requirements for specific amino acids. In general dogs have 10 amino acids that they cannot create and must be consumed. Thus they are called Essential Amino Acids (EAA). Cats have 11 EAA with the additional amino acid being Taurine. Luckily virtually all cat foods are supplemented with taurine. This however is one of many reasons not to give cats dog food.
Minimum protein requirement for Dogs.
The dog's minimum protein requirement is 8% DMB of high quality digestible protein1. AAFCO (Association of American Feed Control Officials) recommend that dog food contains a minimum of 16% DMB2.
Minimum protein requirement for Cats.
The cat's minimum protein requirement is 16% DMB of a high quality digestible protein3. This is twice the amount of dogs because cats are true carnivores where dogs are omnivores. AAFCO recommends that adult cat food contains 26% protein DMB4.
How much is too much?
Unfortunately with the push for whole meat at the top of the ingredient list, the view of high protein equating to higher quality, many pet foods have excess protein. Once the minimum requirement has been met for a particular pet, there is no benefit to giving higher levels of protein. The maximum amount of protein in food for adult dogs should be 30% DMB and for adult cats 45%DMB5.
Unfortunately many pet food exceed these levels. For healthy pets, this excess protein is not stored but processed by the liver and excreted in the urine. Other than muscle mass which is based upon overall health and physical activity, there is no "protein store" like there is for carbohydrates. When the body needs to make more proteins (muscle, enzymes, hormones, etc.) the next day, it needs to obtain it from the next meal. So giving high protein today, does not prepare the pet for tomorrow. In fact if the body needs more protein and it is not delivered in the food, then the body can start to take the protein from its own muscle which leads to a loss of muscle mass if continued.
Additionally, any disease that disrupts the breakdown of protein and the filtration of the nitrogenous waste that comes from protein breakdown, can lead to a rise in these toxins. Many conditions, like liver or kidney disease, can have a slow onset in dogs and cats and can initially occur without having clinical signs. Thus a cat with some non-clinical liver disease can be made worse with excess dietary protein.
For this reason, in adult dogs, the protein on a dry matter basis (DMB) should be between 16 - 30%. For adult cats, the protein should be between 26 - 45%. One method of keeping these levels within these levels while maintaining proper caloric intake is to supplement with levels of carbohydrate and fat.
1) NRC (National Research Council), 2003.
2) AAFCO 2007
3) NRC, 2003
4) AAFCO 2007
5) Small Animal Clinical Nutrition Fifth Edition by Hand, Thatcher, Remillard, Roudebush and Novotny page 95
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| Basic Amino Acid Structure - CLICK HERE for more |
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| First 11 amino acids of dogs and cats - CLICK TO ENLARGE |
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| The other 10 - CLICK TO ENLARGE |
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| Butter |
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In a world that is constantly looking for "low fat" and "no trans fat" labels, we often think of fats or lipids as "bad" nutrients. Like carbohydrates, as long as lipids are not taken in excess are not bad. Unlike carbohydrates, there is a minimum requirement of lipids that are needed. Furthermore there are many different types of lipids. Each type is very different.
What atoms make up lipids?
Just like carbohydrates, they are made of carbon, hydrogen and oxygen. What makes a lipid versus a carbohydrate is the same as the difference between a cat and a tree, it all has to do with how the atoms are arranged!
Because of these atoms, the breakdown compounds include water and carbon dioxide. Unlike carbohydrates though, the configuration of fats allows for far more energy to be released from fat than carbohydrates.
What does the body do with lipids?
- Many can be utilized for energy.
- Many are used as necessary components of cells and cannot be manufactured by the body. These are called Essential Fatty Acids (EFA).
- At least 1-2% of the food must contain fat in order for the body to be able to absorb the fat soluble vitamins.
What type of lipids are there?
We will simplify these in a little bit.
- Nonesterfied fatty acids
- Simple lipids
- Complex lipids
- Prostaglandins
- Sterols and steroids
- Fat-soluble vitamins
Nonesterfied Fatty Acids
These include three main categories: saturated, monounsaturated and polyunsaturated. See below for some helpful diagrams. What makes the difference between these molecules all has to do with the "extra" bond between some of the carbons. Instead of a single bond, they have one or more double bonds. The more bonds, the more "unsaturated" a fat becomes. The presence of an extra bond or two can have some huge effects on the lipid's function and character. Unsaturated fatty acids have lower melting points (easier to melt) than saturated fats. Also this is what makes the difference between Omega 3, 6 and 9 fatty acids. The number refers to where the double bond sits. It is sits on the third carbon, it is an Omega 3. If it sits on the ninth carbon, it is a Omega 9. The length of the fatty acid is typically between 4 and 28 carbons long.
Thus Omega 3, 6 and 9 fatty acids are all unsaturated fatty acids. Olive oil is made primarily of one saturated fatty acid, called palmitic acid which has no double bonds and on monounsatured fatty acid called oleic acid. "Oleic" comes from the word for oil or olive.
Simple Lipids
The most common one is called Triglycerides. I have a diagram below. It looks like a giant letter "E". The back of the "E" is called a glycerol molecule with the three lines being made of long fatty acids. Triglycerides make up the major component of the fat molecule and fat storage. So a "love handle" is made primarily of triglycerides. No, this does not make me feel better either... 
Complex Lipids
Many of the structural lipids are found here. The walls of our cells are made of a long sheet of molecules called phospholipids. These are interesting compounds because one side of the molecule is fat soluble (hydrophobic) and the other side is water soluble (hydrophilic). Thus the two layers of phospholipids in the cell wall have a water soluble outside with a fat soluble inside. See picture below.
Lecithin comes from the Greek word for egg yolk and is one of its major components.
Another major group here are the glycolipids. Glyco refers to the fact that the lipid has a carbohydrate attachment. These are also present in cell walls and often used as cell markers. They tell a cell who they are. Think of them as little addresses on the cell. Cerebrosides are also types of glycolipids and as the name implies are major components in nerve cell membranes. Cerebrosides are also heavily present in muscle cell membranes Gangliosides are present in the ganglion brain cells.
Prostaglandins
These super important chemicals in the body and there are hundreds of them. They all have the similar characteristics of having 20 carbons including a 5 carbon ring. They are chemical messengers that act locally and have strong physiologic affects. Because they are produced and act locally (within an organ) they are called paracrine mediators instead of hormones which act between one organ and another.
One prostaglandin that you may have heard of is the one made by the enzyme (protein) called COX-2. This prostaglandin that is responsible for inflammation and is what the drugs like advil, aspirin, and motrin try to suppress. These drugs are called NSAIDs (Non-Steroidal Anti Inflammatory Drugs) and for dogs include previcox, deramaxx, rimadyl and metacam. This category of drugs is not handled well by cats. Metacam has just been recommended against any chronic use in cats.
Sterols and Steroids.
Yes... those steroids. ROAR!!! Steroids however include more than just body building steroids which are called anabolic steroids but also corticosteroids like corisone (like the cream) or prednisone, dexamethasone and triamcinolone. Corticosteroids have numerous physiologic effects but its most common feature is to reduce inflammation.
Sterols include cholesterol. Cholesterol is a precursor to fat soluble vitamins and sex hormones. So cholesterol has both good and bad effects. Again, it comes to balance.
Fat soluble vitamins
These include A, D, E and K. Please see the last section for more information.
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| Types of Nonesterfied Fatty Acids |
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| Triglyceride - CLICK TO ENLARGE |
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| Cell walls are made by phospholipids. CLICK TO ENLARGE |
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| A macro shot of salt crystals taken in the Natural History Museum of Vienna. Courtesy of Wikipedia |
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Many times we forget that we need minerals as much as we need the other nutrients. In fact there are 18 essential minerals for which we need in order to stay alive. Seven of them we need more of and eleven of them we need less of. This broad distinction breaks them into the Macrominerals (those that we need in larger amounts so that we can look at basic percentages in food) and into Microminerals (those that we need in smaller amounts and are measured in either parts per million (ppm) or milligrams per kilogram (mg/kg). Macro and Micro do not refer to the physical size. Minerals can be defined as all inorganic elements in the food.
In the past, the amount of "ash" was very important because this could help indicate minerals that were not supposed to be eaten. Ash is what remains after a food is incinerated. In the past, fish that was not properly cleaned was often high in sand or silica. This lead to silica stones in the bladder and other problems. The problem with ash is that it does not tell us what the ash is made of. Are they good minerals or bad minerals? So while this measurement is not completely worthless, it needs to be looked critically in light of other factors. Super high ash levels could indicate a problem.
The Seven Macrominerals
- Calcium
- Phosphorus
- Sodium
- Magnesium
- Potassium
- Chloride
- Sulfur
The Eleven Microminerals
- Iron
- Zinc
- Copper
- Iodine
- Selenium
- Manganese
- Cobalt
- Molybdenum
- Flourine
- Boron. Has this page begun to boron you?
- Chromium
To find out more about each mineral, please click on the picture below.
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Finally we make it to the vitamins and the final group of basic nutrients.
What is a vitamin?
"Vital - Amines" are amines, or nitrogen containing compounds, that are vital to life. This term was shortened to "vitamin" which is helpful since not all of them contain nitrogen. What we now know as a vitamin must have five characteristics1:
- It is organic and cannot fit into one of the other nutrient categories
- It is found in food
- It is essential for life
- Without it, the body will exhibit symptoms
- It cannot be synthesized in large enough quantities to support normal function
Vitamin Like Substances
These are compounds that "like" vitamins but do not fit the precise definition of a vitamin. They are never the less very important. They include:
- L-Carnitine
- Carotenoids and Bioflavanoids
- These contain literally thousands of compounds. A commonly mentioned one is resveratrol from grapes. It is present in red wine and has a number of salubrious effects.
- Lipoic Acid
- ubiquinones
- Orotic Acid
- Inositol
- p-aminobenzic acid
There are two main types of vitamins: water and fat soluble:
- Water Soluble Vitamins
- Vitamin C - Ascorbic Acid
- Vitamin Bs
- B1 - Thiamine
- B2 - Riboflavin
- B3 - Niacin
- B5 - Pantothenic Acid
- B6 - Pyridoxine
- B7 - Biotin
- B9 - Folic Acid
- B12 - Cobalamin
- Choline is also grouped as a B vitamin although it does not meet the requirement of that of a vitamin as many animals synthesize it in their livers.
- Fat Soluble Vitamins
- Vitamin A - Retinoic Aciud
- Vitamin D
- D2 - ergocalciferol
- D3 - cholecalciferol
- Vitamin E - tocopherols and tocotrienols
- Vitamin K - Phylloquinone (AKA phytomenadione or phytonadione)
How are Vitamins absorbed?
Fat soluble vitamins (A,D,E,K) require bile salts produced by the liver. Bile salts are made from cholesterol and conjugated (joined) with the amino acids taurine or glycine. Cats can only conjugate bile salts with taurine and this is the main reason why taurine is an essential amino acids for them. In dogs and humans, when taurine is scarce, the body will switch to conjugating the bile salts with glycine instead. (bile salts can also be conjugated with sulphate or gluconate but the amino acids are the most common).
Think of bile salts as having the same properties as soap. It breaks up fat into small little bubbles called micelles. These small bubbles (fat on the inside, water soluble on the outside) are then passively absorbed through the intestines at the level of the duodenum or ileum. (the duodenum is the beginning of the small intestine and the ileum is the end of the small intestines before the colon). Once absorbed the body used fat-protein molecules (called chylomicrons) to join the micelles as they pass through the lymphatic system to the liver. Once in the liver the fat soluble vitamins are then processed there.
The water soluble vitamins (B's and C), in contrast to fat soluble vitamins, require active transport into the blood stream from the intestines. This means that there are pumps that are made out of protein in the intestine that use electrolytes or other proteins to help "pump" or transport the vitamins into the blood stream.
Where are they stored?
Fat soluble vitamins are able to be stored in the fat of an animals. This gives the advantage of being able to store larger amounts of these vitamins but it is this large storage capacity that also makes toxicity of these vitamins a risk. Water soluble vitamins have very limited storage and for this reason run the common risk of deficiency and have low risk of toxicity. It is always a trade off!
Each of these are described in greater detail. Please click on the link below to learn more.
1) Small Animal Clinical Nutrition Fifth Edition. Hand, Thatcher, Remillard Roudebush Novotny
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