Ingredient file // Plant protein
Soy Flour
Useful plant protein with a stool tradeoff
Soy flour is finely ground soybean, sold with its oil intact or with most of it removed. It supplies protein that dogs digest. In one feeding trial, the soy flour diet produced more stool than diets made with more refined soy proteins.
- What it is
- Finely milled, usually dehulled soybeans or soybean flakes, sold in full fat and defatted forms.
- Made from
- Dehulled soybeans or defatted soybean flakes
- Main job
- Plant protein for the recipe
- Typical amount
- No usual amount published; one trial used about 45%
- Watch for
- Soy allergy diagnosed by food challenge
- Not the same as
- Soy protein isolate
Our read // In our catalog
In 1 of every 105 foods we track
Share of foods that list it
1%
24 of the 2,523 foods with an ingredient list on file, from 4 brands. 14 wet dog food, 10 dry dog food.
Each square is 1% of the catalog
Where it sits on the label
Median position 8. In the top five of 6 foods, so it is usually a supporting ingredient.
Above the salt
Almost always listed before the salt, so there is more of it than a pinch.
Price per lb
Median of the cheapest bag price across 7 priced foods, 38% below the catalog. The price is the food's, not the ingredient's.
Who leans on it
79%
of the foods that list it are from Purina. 4 brands use it in total.
What it is
How it is made
Soy flour often comes from the same processing lines that make soybean oil. Full fat flour keeps the bean's oil. Defatted flour uses flakes left after oil extraction; both are milled into fine powder.4,5
- 01 // Source Soybeans Cleaned beans enter a processing line that also makes soybean oil and other soy ingredients.
- 02 // Process Hulls removed Processors crack the beans and separate the hulls from the protein rich inner parts.
- 03 // Process Oil extracted Defatted flour uses flakes after oil extraction; full fat flour skips this step.
- 04 // Process Heated and dried Heating reduces compounds that interfere with protein digestion, and drying prepares the material for milling.
- 05 // Output Fine soy flour The dried material is ground into a powder that a food plant weighs into its recipe.
What is in it
Composition, dry matter
46.6-59
% protein
Typical values for full fat and defatted flour. Removing oil raises protein's share, so the name alone does not tell you its concentration.
Why it is in the bag
What the manufacturer gets
-
01
Adds plant protein
Soy flour raises the recipe's protein content. Dogs digested protein well in a soy flour test diet, though that result belongs to the complete recipe.1,4,5
-
02
Holds water in mixtures
Soy flour absorbs water, a property food makers use when shaping mixtures. The amount used and the other ingredients still determine the finished texture.4,5
-
03
Uses an oil mill stream
Defatted flour turns flakes left after oil extraction into a protein ingredient. FAO described soy flour as economical, though its published price comparison is historical.5
How much A dog trial used 45.16% soy flour in one test diet; that is a tested amount, not a usual recipe amount.1,4
Our read // The claims
What the evidence supports
Strong: controlled studies in dogs agree. Some: small or mixed dog data. Thin: mechanism or lab work only. None: nothing, or the evidence points the other way.
-
Brands say
Soy flour gives dogs digestible protein
Evidence
- Strong
- Some
- Thin
- None
A controlled trial compared 6 protein sources. Its soy flour diet had 87.3% total tract protein digestibility. That supports its use as protein, but the result cannot stand for every flour or recipe.1,4
-
Critics say
Soy flour is a common dog allergen
Outruns the evidence
Evidence
- Strong
- Some
- Thin
- None
Soy triggered reactions in 18 of 297 dogs collected from food challenge reports. Those dogs were selected for food reactions, so the count does not show how often soy allergy occurs among dogs generally.2
-
Owners say
Soy flour harms a dog's thyroid
Outruns the evidence
Evidence
- Strong
- Some
- Thin
- None
A trial followed 20 dogs fed diets with different soy isoflavone levels for up to 1 year. Most measured hormones did not differ. It tested a soy isolate diet, not soy flour, and did not show thyroid disease.3
-
Critics say
Soy flour is just filler
Outruns the evidence
Evidence
- Strong
- Some
- Thin
- None
Typical flours contain 46.6 to 59% protein on a dry basis, and dogs digested protein in a soy flour test diet. More stool in that trial is a fair drawback; calling the ingredient filler ignores its protein.1,4,5
-
Owners say
Soy flour always makes dogs gassy
Outruns the evidence
Evidence
- Strong
- Some
- Thin
- None
The soy flour trial measured stool output, not gas. A separate study of soybean meal diets found no difference in flatulence. Neither result proves what every dog will experience with soy flour.1,4
Straight answers
What owners ask
-
Q01
Is it just filler?
NoSoy flour supplies substantial protein, and dogs digested it in a controlled feeding trial. Its drawback in that trial was greater stool output. Read it as a plant protein ingredient with a digestive tradeoff.1,4,5
-
Q02
Will it give my dog gas?
Not shownThe soy flour feeding trial found more stool but did not measure gas. A study of soybean meal found no flatulence difference, though meal is a different ingredient. Judge any change in your dog's stool against the whole new food.1,4
-
Q03
Is it soy protein isolate?
NoIsolate undergoes further processing that removes much of the carbohydrate. Soy flour retains more of the bean's other material. Hydrolyzed soy used in some therapeutic foods is processed differently again.4,5
Who uses it
Brands, best sellers and the company it keeps
Top brands, by foods that list it
Amazon best sellers that list it
Rank on Amazon's dog food best seller list, checked October 2026.
Usually listed with, share of the foods that list it
- Chicken 54%
- Beef 46%
- Wheat Gluten 46%
- Liver 46%
- Chicken Meal 38%
- Brown Rice 29%
- Chicken Broth 29%
- Whole Grain Wheat 29%
- Beef Fat 29%
- Corn Germ Meal 29%
- Carrots 25%
- Corn Starch-Modified 21%
On the shelf
Foods that list it
24 foods in our reviews list it. Here are some of them.
Show 18 more
4health Shreds Large Breed Adult Chicken Formula Dry Dog Food26.7% proteinPurina Pro Plan Bright Mind Adult 7+ Beef & Brown Rice Entrée Wet Dog Food48.0% proteinPurina Beneful Freshly Prepared Blends with Beef, Carrots, Peas and Barley Wet Dog Food50.0% proteinPurina Beneful IncrediBites Small Breed with Real Chicken in Gravy Wet Dog Food45.8% proteinPurina ONE Chicken & Brown Rice Brain & Heart Wet Dog Food50.0% proteinPurina ONE Chicken & Brown Rice Bone & Joint Wet Dog Food50.0% proteinPurina Beneful Freshly Prepared Blends with Turkey, Sweet Potatoes, Brown Rice and Spinach Wet Dog Food50.0% proteinPurina Dog Chow High Protein with Real Beef in Gravy Wet Dog Food50.0% proteinPurina ONE Chicken & Brown Rice Tender Cuts in Gravy Wet Dog Food50.0% proteinPurina ONE Beef & Barley Tender Cuts in Gravy Wet Dog Food50.0% proteinCesar Loaf & Topper in Sauce Rotisserie Chicken with Bacon & Cheese Wet Dog Food47.1% proteinCesar Loaf & Topper in Sauce Angus Beef with Bacon & Cheese Wet Dog Food47.1% proteinCesar Loaf Topper Sauce Filet Mignon Flavor With Bacon & Potato Wet Dog Food47.1% proteinAuthority Everyday Health Tender Blends Adult Dry Dog Food28.9% proteinPurina One True Instinct High Protein Real Chicken Duck Dry Puppy Dry Dog Food36.4% proteinPurina One True Instinct with a Blend of Real Turkey & Venison Dry Dog Food34.1% proteinPurina One True Instinct Grain-Free Formula with Real Beef Dry Dog Food36.4% proteinPurina One SmartBlend True Instinct High Protein with Real Beef & Salmon Dry Dog Food36.4% proteinOur read // On the bag
Count soy flour as protein on the bag
Ingredients are listed by weight, so soy flour near the top means it is a substantial part of the recipe. Count it as plant protein when you assess the other protein sources, then check the nutritional adequacy statement. If your dog has a diagnosed soy reaction, choose a food without ordinary soy flour.
Sources
What we read
Checked October 1, 2026.
- 1 Ileal and total tract nutrient digestibilities and fecal characteristics of dogs as affected by soybean protein inclusion in dry, extruded diets
- 2 Critically appraised topic on adverse food reactions of companion animals (2): common food allergen sources in dogs and cats
- 3 Effects of dietary soy isoflavones on health, steroidogenesis, and thyroid gland function in dogs
- 4 Evaluation of Soybean Ingredients in Pet Foods Applications: Systematic Review
- 5 Edible Soybean Flours and Grits