Takeaway:

Keeping a dog at a lean, healthy weight is one of the most well-documented factors linked to a longer life. Study A was a lifelong feeding experiment that followed dogs from puppyhood to old age. Study B reviewed veterinary records for over 50,000 dogs.

What the studies found:‍

Study A (lifelong controlled feeding experiment): Labrador Retriever littermates were paired up, with one dog in each pair fed 25% less than the other for their entire lives. The leaner dogs lived a median of 1.8 years longer and aged noticeably better. By 8 years old, only 10% of the leaner dogs had arthritis in multiple joints, compared to 77% of the normally fed dogs.

Study B (large-scale veterinary records comparison): Overweight dogs lived shorter lives than lean dogs of the same breed in every one of the 12 breeds studied. The gap ranged from about 5 months shorter in German Shepherds to about 2.5 years shorter in Yorkshire Terriers, and overweight dogs faced meaningfully higher odds of dying at any given age across the board.

Citations:

Study A: Kealy RD, Lawler DF, Ballam JM, Mantz SL, Biery DN, Greeley EH, Stowe HD. "Effects of diet restriction on life span and age-related changes in dogs." J Am Vet Med Assoc. 2002;220(9):1315–1320. https://pubmed.ncbi.nlm.nih.gov/11991408/

Study B: Salt C, Morris PJ, Wilson D, Lund EM, German AJ. "Association between life span and body condition in neutered client-owned dogs." J Vet Intern Med. 2019;33(1):89–99. https://academic.oup.com/jvim/article/33/1/89/8447813

Takeaway:

A peer-reviewed study came from McMaster University, UC Irvine, and the University of Kentucky, funded by the Alzheimer's Association and NIH/NIA. It found that a natural brain chemical tied to learning and memory (known as brain-derived neurotrophic factor or BDNF) rose to youthful levels in aging dogs. But that only happened when dogs got two things together: an antioxidant-fortified diet (added vitamin E, vitamin C, and other antioxidants, plus fruit and vegetable ingredients), and structured daily enrichment (a companion dog, regular walks, and ongoing mental training).

Note: Carrots, kale, broccoli, flaxseed, blueberries, wheat germ¹, sweet potatoes, pumpkin, and beets are among the foods commonly regarded as antioxidant-rich whole foods.²

Methodology & limitations:

Who was studied: 23 old Beagles (11 male, 12 female, ages 8–12.35 years), split into four groups — regular diet/no enrichment, regular diet/enrichment, antioxidant diet/no enrichment, and antioxidant diet/enrichment — plus 5 young Beagles (about 4 years old) as a comparison group.

What was in the antioxidant diet: added vitamin E, vitamin C, L-carnitine, and alpha-lipoic acid, fruits/vegetables

What "enrichment" meant: three things together — social (housed with another dog, not alone), physical (two 20-minute walks a week), and mental (ongoing training on simple discrimination tasks).

Length of study: 2 to 2.83 years

Limitations: This study found that aging dogs given both an antioxidant-rich diet and daily enrichment saw BDNF — a brain chemical linked to learning and memory — rise to levels typical of much younger dogs. Dogs in this study also showed improved memory-task performance, but the link between that improvement and the BDNF increase specifically was not statistically confirmed (just a trend).

Citations:

Fahnestock M, Marchese M, Head E, Pop V, Michalski B, Milgram NW, Cotman CW. "BDNF increases with behavioral enrichment and an antioxidant diet in the aged dog." Neurobiol Aging. 2012;33(3):546–554 (published online 2010 May 5). doi: 10.1016/j.neurobiolaging.2010.03.019 https://pmc.ncbi.nlm.nih.gov/articles/PMC2935515

1. Coates, J., DVM. "Vitamin E for Dogs: Benefits and Uses." Reviewed by Hart, H., DVM. PetMD. https://www.petmd.com/dog/nutrition/vitamin-e-good-dogs

2. Tanprasertsuk J, Tate DE, Shmalberg J. "Roles of Plant-Based Ingredients and Phytonutrients in Canine Nutrition and Health." Journal of Animal Physiology and Animal Nutrition 106, no. 3 (2022): 586–613. https://onlinelibrary.wiley.com/doi/abs/10.1111/jpn.13626

Takeaway:

Digestibility, how much of a food's nutrients are absorbed by the body rather than passed through in stool, is a widely used measure of nutrient absorption in animal nutrition science¹. Two peer-reviewed feeding trials found that fresh diets (both gently cooked and raw) are digested significantly more completely than kibble, and dogs eating kibble produced meaningfully more fecal waste per day than dogs eating fresh food in both studies.

What the studies found:

Study A (fresh cooked vs. kibble, single-brand comparison): When dogs ate a comparable amount of food, those on the fresh chicken diet produced about half as much stool per day as those on kibble, a sign their bodies absorbed more of what they ate rather than passing it through.

Dry matter, protein, fat, and caloric digestibility were all consistently higher for every fresh cooked diet tested (chicken, beef, pork, turkey) compared to kibble.

Study B (5-way feeding format comparison): Dogs in this University of Illinois-led study absorbed roughly 86% of the dry matter in a fresh, mildly-cooked diet, compared to about 82% for kibble — and a similar gap held for protein (86% vs. 82%) and fat (95% vs. 92%).

Dogs on the fresh mildly-cooked diet also produced significantly less stool each day than dogs on kibble — about 55 grams versus about 90 grams, roughly 40% less.

Methodology & limitations:

Study A: 12 Beagles for the chicken/kibble comparison plus 18 more dogs (6 per protein) for beef, pork, and turkey; 10-day feeding periods per diet.

Study B: 10 Beagles, rigorous 5×5 Latin square crossover, five 35-day feeding periods (Hill's Science Diet kibble, JustFoodForDogs fresh cooked, Primal frozen raw, Primal hybrid freeze-dried, Stella & Chewy's freeze-dried).

Both are small-sample, single-breed, short-term digestibility trials — standard for this kind of study, but they speak to nutrient absorption, not long-term health outcomes. Study B also found fecal microbiota shifted meaningfully by diet type (40+ bacterial genera affected).

Citations:

Tanprasertsuk J, Perry LM, Tate DE, Honaker RW, Shmalberg J. "Apparent total tract nutrient digestibility and metabolizable energy estimation in commercial fresh and extruded dry kibble dog foods." Transl Anim Sci. 2021;5(3):txab071. https://academic.oup.com/tas/article/5/3/txab071/6287114

Geary EL, Oba PM, Templeman JR, Swanson KS. "Apparent total tract nutrient digestibility of frozen raw, freeze-dried raw, fresh, and extruded dog foods and their effects on serum metabolites and fecal characteristics, metabolites, and microbiota of healthy adult dogs." Transl Anim Sci. 2024;8:txae163. https://academic.oup.com/tas/article/doi/10.1093/tas/txae163/7908844

1. "Digestibility is defined as the fraction of a nutrient ingested that is digested and absorbed by the animal." A Guide to the Principles of Animal Nutrition (Oregon State University), Ch. 20, "Measurement of Feed and Nutrient Utilization in Food-Producing Animals." https://med.libretexts.org/Bookshelves/Veterinary_Medicine/A_Guide_to_the_Principles_of_Animal_Nutrition_(Cherian)/01:_Chapters/1.20:_XX._Measurement_of_Feed_and_Nutrient_Utilization_in_Food-Producing_Animals↩

Takeaway:

A peer reviewed study from the University of Illinois compared four dog food diets built to contain nearly identical amounts of protein, differing only in where that protein came from: fresh chicken, chicken by-product meal (a rendered animal meal common in commercial kibble), wheat gluten meal, or corn gluten meal (two plant-based protein concentrates also used in some commercial dog foods).

In this kind of research, "protein quality" refers to how completely a dog's body can break down and actually use that protein's amino acids, rather than passing them through unused.¹ It is not a general judgment about how "good" or "clean" an ingredient sounds. By that definition, even with protein levels held equal on paper, the source of that protein made a measurable difference. Fresh chicken came out on top as a standalone ingredient.

What the study found:

Chicken by-product meal had significantly lower digestibility than every other diet tested for overall nutrients, protein, and energy. Corn gluten meal also underperformed, with lower dry matter digestibility than both the fresh chicken and wheat gluten meal diets.

Fresh chicken's protein digestibility percentage was actually a bit lower than wheat gluten meal's, but the researchers were clear that digestibility percentage alone isn't the whole story of protein quality. In their own words, protein sources "contain different amino acid profiles and vary in digestibility, affecting protein quality."

On that combined measure, fresh chicken won out: the researchers concluded, considering AA (amino acid) profiles and digestibility data, fresh chicken “provided the highest quality protein without additional AA supplementation". The other diets all required added supplementation to create a complete and balanced formula according to AAFCO standards.

Methodology & limitations:

20 adult female Beagles took part in a rigorous crossover design, rotating through all four diets so each dog contributed data to every comparison. Each diet was formulated to have nearly identical crude protein levels (39.8–41.7%). This study measured digestibility and protein quality as a strong proxy for how well a dog's body can actually absorb and use a food's protein. It did not measure longer-term functional outcomes like muscle maintenance. It's also a single study in one breed, standard limitations for this kind of controlled trial.

Citations:

Sieja KM, Oba PM, Applegate CC, Pendlebury C, Kelly J, Swanson KS. "Evaluation of high-protein diets differing in protein source in healthy adult dogs." J Anim Sci. 2023;101:skad057. https://pmc.ncbi.nlm.nih.gov/articles/PMC10066725/

1. For more on what "amino acid completeness" means and why it matters for protein quality: Templeman JR, Shoveller AK. "Digestible indispensable amino acid scores of animal and plant ingredients potentially used in dog diet formulation: how this protein quality metric is affected by ingredient characteristics and reference amino acid profile." J Anim Sci. 2022;100(11):skac279. https://academic.oup.com/jas/article/100/11/skac279/6677535

Takeaway:

A peer-reviewed study out of the University of Zurich found that dogs on a properly supplemented, self-made whole-food diet had higher omega-3s and lower cholesterol and triglycerides in their blood than dogs on a commercial kibble diet.

What the study found:

Dogs fed the commercial diet had consistently higher cholesterol and triglyceride concentrations than dogs fed the whole-food diet. Dogs fed the whole-food diet had consistently higher omega-3 fatty acid-containing lipid species and consistently lower saturated and monounsaturated lipid species.

Methodology & limitations:

16 healthy Beagles (8 male, 8 female) in this study, all fed a shared control diet for 3 months, then split into two groups for a further 3 months: one on a commercial dry diet (Purina Pro Plan), one on a properly balanced self-made whole-food diet (beef, veal sternum, beef liver, carrots, broccoli, apple, fennel, vitamin E, linseed oil, salmon oil, plus a commercial mineral/vitamin supplement).

Note: This study shows diet changes these blood markers. It doesn't establish what that means for a dog's long-term health, and the authors don't interpret the cholesterol/triglyceride difference as a health outcome.

Citation:

Boretti FS, Sieber-Ruckstuhl NS, Burla B, Deuel J, Gao L, Wenk MR, Liesegang A. "Serum lipidome analysis of healthy beagle dogs receiving different diets." Metabolomics. 2019;16(1):1. https://link.springer.com/article/10.1007/s11306-019-1621-3

Note: Better Than Me is formulated with appropriate amounts of wheat germ oil as a concentrated natural source of vitamin E. If you are feeding Better Than Me to your dog, there is no need to add additional Vitamin E supplementation.

Takeaway: A peer reviewed, controlled feeding study in geriatric Beagles found that vitamin E plays a measurable role in supporting immune function as dogs age, but the relationship isn't as simple as "more is better".

Dogs getting a low amount of vitamin E had a weaker immune response than dogs getting either a moderate or high amount. While a moderate amount actually outperformed the highest amount tested on some measures.

In other words, the study found that vitamin E matters for immune health, and there appears to be a middle range where it does its best work.

What the study found: Over 17 weeks, 32 female Beagles between 7 and 10 years old were fed diets containing either a low or high ratio of omega-6 to omega-3 fatty acids, combined with one of three vitamin E levels: low (17 mg per kg of food), medium (101 mg per kg), or high (447 mg per kg). To measure immune response, each dog received two immune-challenge injections partway through the study.

CD8+ T cells are a type of immune cell responsible for destroying virus-infected and cancerous cells, and one of the markers known to decline as dogs age¹. After 12 weeks, dogs on the low vitamin E diet had lower levels of CD8+ T cells than dogs on the medium or high amounts. At a later measurement point, the medium vitamin E group actually had the highest CD8+ T cell levels of all three groups, outperforming both the low-dose and high-dose groups.

Methodology & limitations: This study measured immune biomarkers, not actual illness or infection rates. The study is relatively small group size.

Citations: Hall JA, Tooley KA, Gradin JL, Jewell DE, Wander RC. "Effects of dietary n-6 and n-3 fatty acids and vitamin E on the immune response of healthy geriatric dogs." Am J Vet Res. 2003;64(6):762–772. https://pubmed.ncbi.nlm.nih.gov/12828263/

CD8+ T cells (also called "killer" T cells) provide direct cytotoxic activity against cancerous and infected cells, and their immune surveillance is considered crucial in controlling cancer occurrence and progression; their ability to proliferate is known to decline with age in dogs, a hallmark of canine immunosenescence. Takagi S, Yamauchi A, Yoshimoto S, Kudo A. "Negative Influence of Aging on Differentiation and Proliferation of CD8+ T-Cells in Dogs." Vet Sci. 2023;10(9):541.

Takeaway: A peer-reviewed study co-authored by researchers at Cornell University and The Farmer's Dog followed senior dogs for a year and found statistically significant differences in blood chemistry between dogs eating a fresh diet and dogs eating kibble.

These differences included markers tied to muscle maintenance, antioxidant activity, and AGEs (advanced glycation end products).

As the study's own authors put it, ‘AGEs are currently being studied in dogs and humans and appear to be at the foundation of inflammation seen in chronic diseases’.

Note: The Farmer's Dog funded the study and the company was involved in writing the manuscript.

What the study found: Dogs on the fresh diet showed higher blood levels of branched-chain amino acids, creatine, and two muscle-related compounds (carnosine and anserine) — nutrients generally tied to muscle maintenance, which matters more as dogs age.

They also had higher omega-3 fatty acids and lower AGEs than dogs on kibble.

Out of everything measured, 273 blood compounds showed a statistically significant difference between the two diets.

Methodology & limitations: 22 senior (12+ years) sled dogs, each eating a shared baseline diet for 4 months, then split between kibble (a research diet, not a commercial brand) and The Farmer's Dog's chicken recipe for 12 months.

Note: The study measured blood chemistry, not functional health outcomes.

Limitations: a small sample; a single, atypical dog population (working sled dogs, not average companion dogs); no control for individual health conditions dogs may have had. The two diets differ in ingredients and formulation, not just processing, so the study itself can't attribute the blood chemistry changes specifically to processing method rather than to the recipe overall.

Citation: Yamka RM, Sires R, Wakshlag JJ, Huson HJ. "Serum Metabolomics of Senior Dogs Fed a Fresh, Human-Grade Food or an Extruded Kibble Diet." Metabolites. 2025;15(10):676. https://www.mdpi.com/2218-1989/15/10/676