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Originally Posted by dwiley  Amylase is certainly not the only enzyme that breaks down carbohydrates, but it is the one that catalyzes the breakdown of polysaccharides into monosaccharides, disaccharides - which can then be broken down into glucose molecules. Monosaccharides are broken down into glucose, galactose, and fructose. Disaccharides are broken down into maltose and lactose. It is only after these polysaccharides are broken down (by amylase) that monosaccharides and disaccharides can be broken down with aid of other digestive enzymes (maltase, sucrase, and lactase). It's been a long time since I took Cell Biology, but this is my understanding. Please, feel free to chime in with the whole story. Sorry if this is too "science-sounding" but there really is no other way to explain it. |
First off, I don't mind science sounding stuff. I love science. I don't like it when science sounding language is used but scientific principles are not.
Amylase does catalyze the breakdown of polysaccharides. In humans, there is a brief window in which it happens
before the stomach because we produce it in our saliva, but it doesn't—as far as we understand—continue significantly in the low pH of the stomach. It begins again with pancreatic amylase in the small intestine.
Glucose, galactose, and fructose
are monosaccharides, and maltose and lactose
are disaccharides. So some of what you're saying doesn't make sense.
You're also missing a big player in the realm of starch digestion: hydrolysis. Amylase facilitates the breakdown of complex starches, but the key component is the water of the digestive system. So the amount of an enzyme isn't a simple measurement of an animal's ability to digest a sugar.
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Originally Posted by dwiley Actually, amylase doesn't function at a low pH. Acidic = low pH. |
Yes, you're totally right. I had written "high acidity" and then revised the word "acidity" without changing the adjective. My typo.
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Originally Posted by dwiley Salivary amylase is very important in chemical digestion and begins the breakdown process in the mouth and esophagus. Additionally, the chewing motion that humans use due to their flat molars (teeth that dogs do not have) mechanically help break up long polysaccharide chains. If dogs do not have salivary amylase, then the food must wait until it reaches the intestines to be exposed to pancreatic amylase. The chemical digestion doesn't start until much later in the digestive process, and also has less time to finish due to the shortened intestinal tract. |
Humans do prep their starches pre-stomach with grinding and salivary amylase. That proves that humans are more herbivorous than dogs—not in dispute—but does not prove that dogs are carnivores rather than omnivores.
Certainly, dogs are not as good at an herbivorous diet as people. That's not in dispute either. What I'm disputing are claims that dogs are obligate carnivores or that they somehow cannot access nutrition of plant sources. I'm also disputing that a grain is somehow inferior to a potato.
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Originally Posted by dwiley Where is this clear evidence you keep referring to? Yes, dogs survive eating foods that have wheat and corn. Explain to me the "lots of nutrition" dogs get from them. |
If wheat and corn were "filler" with "no nutritional value" or "low nutritional value," then dogs who ate food consisting mostly of corn or wheat would die. The millions dogs doing fine on such foods disprove those claims. I think dogs do better when the corn and wheat don't provide the vast majority of their calories, and I do think dogs need lots of meat in their diets. I'm just not buying these claims that an appropriate amount of of corn or wheat is just "filler" and it's somehow incompatible with a dog's biology. I also dispute the idea that corn or wheat is somehow less "nutritious" than a potato.
Mammals thrive on a wide range of nutrients. A dog on the right proportion of meat and corn is probably better off than a dog who's on pure meat. In fact, if a dog were fed only muscle meat, he would eventually die from malnutrition.
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Originally Posted by dwiley I beg to differ. My dogs were fed prey-model raw for years and always got an absolute glowing bill of health from the vet. Their bloodwork was always perfect, their coats were soft and shiny, their poop was a perfect consistency, and they never struggled with eye gunk, ear infections, or any kind of skin allergy. Nobody makes all meat kibble because it would be outrageously expensive to produce... |
My understanding of even prey-model diets is that they are typically supplemented. All the recipes I've ever seen online call for things like flax seed, yams, brewer's yeast, pumpkin, and vitamin supplements. Perhaps you simply fed carcasses, but I don't know of any people whose dogs thrive on just meat, bone, and organs.
And, fyi, my dogs do not struggle with eye gunk, ear infections, or skin allergies. And coats get shiny when you give dogs fat. Whether it's animal fat or vegetable fat is largely irrelevant. In fact, that's the first thing I'd often suggest for somebody with an itchy dog: more fat.
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Originally Posted by dwiley I'm curious to know what food you feed - as I'm sure the majority of your food is not corn and wheat. Unless you are only feeding them corn and wheat, the argument that your dogs are thriving on them is invalid. More than likely, there is a considerable amount of animal protein that contributes to the health of your dogs. |
Eukanuba PP 30/20. It's certainly not "mostly" corn and wheat, but it has substantial amounts of corn, rice, and sorghum (ingredients 3, 4, and 5) in it. If they had "no" or "low" nutritional value, it would be hard to see how my dogs could be thriving.
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Originally Posted by dwiley I don't recall saying anywhere in my post that I was feeding my dogs ALL meat and no corn or wheat. Also, I'm pretty sure pumpkins, apples, and spinach aren't grains... |
But your points have repeatedly been that dogs are carnivores and not omnivores. So it's weird to make that argument and then to turn around and feed your dogs an omnivore's diet. And pumpkins, apples, potatoes, and spinach aren't grains, but you haven't made a single argument about the difference between root vegetables, fruits, leaf vegetables, gourds, and grains. Your points have all been about how dogs can't digest starches properly. So why feed your dogs so much vegetable matter?
I assume it's because the dogs do great on it! An appropriate proportion of vegetable matter isn't just acceptable, it's good! Dogs have been co-evolving with people for at least ten millennia. They've adapted somewhat to our diets in that time period, since the proto-dogs who could would be able to reproduce better. Their needs aren't identical to ours, but neither are they identical to wolves'.
Mammalian evolution has shown, in independent branches, that members of the carnivora order adapt quickly to omnivorous diets—and even once or twice in the tree, they've gone full herbivore like the Giant Panda did.
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Originally Posted by dwiley Again, I stated that dogs thrive on a diet that consists primarily of protein. I also recall stating that it's the owner's prerogative to feed what they choose. My post was to show that there IS scientific evidence to support that wheat and corn is less easily digested by dogs, and therefore has a lower (relative) nutritional value, compared to animal protein. |
The evidence you posted was about starch, not about grains. Most of the nutrition in a potato is locked away as starch, just as it is in corn or wheat. Apples have more simple sugars, but I honestly don't think that's a selling point for their use in dog foods. For energy and health, you want lots of your carbs locked away in polysaccharide chains, because they break down over the course of hours instead of minutes, so you get more sustained energy. Why wouldn't that apply at least somewhat to dogs?
Nobody is arguing against the idea that dogs should be fed mostly meat. The argument here is against statements that certain ingredients have "low" or "no" nutritional value. If a potato or an apple is a good ingredient, so is an ear of corn.
01-24-2013, 06:47 AM
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