Chronic stress in cats and dogs activates the hypothalamic-pituitary-adrenal (HPA) axis and increases cortisol concentrations, leading to wide-ranging physiologic changes that affect gastrointestinal function, immunity, metabolism, and behavior. Nutritional interventions, especially tryptophan, alpha-casozepine, L-theanine, and omega-3 fatty acids, offer evidence-based options for modulating the stress response. This article reviews the effects of stress on nutritional physiology and summarizes practical nutritional anxiolytic strategies.
Clinical Note
Appetite changes (anorexia or polyphagia), GI disturbances, and immunosuppression are common in animals exposed to chronic stress. Nutritional intervention should be regarded as a complement to behavioral and pharmacologic management, not as a stand-alone treatment (Overall, 2013).
1. Physiology of Stress and the HPA Axis
1.1 Acute vs. Chronic Stress Response
The stress response is an evolutionary survival mechanism. But chronic activation produces pathological consequences:
- Sympathetic nervous system activation (fight-or-flight)
- Catecholamine release (adrenaline, noradrenaline)
- temporary appetite suppression
- Energy mobilization (glycogenolysis)
- Duration: Minutes-hours
- Chronic activation of HPA axis
- Cortisol level is constantly high
- Appetite irregularity (usually polyphagia)
- Muscle catabolism and fat storage
- Duration: weeks-months
1.2 Metabolic Effects of Cortisol
Chronic elevation of cortisol affects nutritional metabolism at many levels:
| Metabolic Parameter | Effect of Cortisol | Nutrition Result |
|---|---|---|
| protein metabolism | Muscle proteolysis ↑, Gluconeogenesis ↑ | Muscle wasting, negative nitrogen balance |
| carbohydrate metabolism | Insulin resistance ↑, Blood glucose ↑ | Risk of hyperglycemia, tendency to obesity |
| fat metabolism | Lipolysis ↑ (peripheral), Lipogenesis ↑ (visceral) | Visceral fat, dyslipidemia |
| GI function | Stomach acid ↑, Mucosal blood flow ↓ | Gastritis, risk of ulcers, malabsorption |
| immune system | Lymphocyte apoptosis ↑, Cytokine dysregulation | Immunosuppression, susceptibility to infection |
2. Stress-Gut-Brain Axis
2.1 Microbiota-Brain Communication
The gut microbiota directly affects brain functions through the vagus nerve, immune mediators and neurotransmitter precursors. This bidirectional communication is known as the microbiota-gut-brain axis (Cryan & Dinan, 2012).
Neurotransmitter Production by Microbiota
GI 95% of serotonin is produced in the intestine
Produces Lactobacillus and Bifidobacterium species
Bacillus and Serratia species synthesize
Produces Escherichia and Saccharomyces
2.2 Effects of Stress on Microbiota
Chronic stress dramatically changes gut microbiota composition. Galley et al. (2014) of chronic social stress in a mouse model lactobacilli It has been shown that while decreasing the population, it increases the potential pathogen species. Similar findings have been confirmed in the context of shelter stress in dogs ( Mondo et al., 2020 ).
- Decreasing species: Lactobacillus, Bifidobacterium, Faecalibacterium prausnitzii
- Increasing species: Clostridium, Enterobacteriaceae, potential pathogens
- Functional result: Short chain fatty acid (SCFA) production ↓, intestinal barrier permeability ↑
- Vicious circle: Dysbiosis → inflammation → stress response ↑ → more dysbiosis
3. Nutritional Anxiolytic Components
3.1 L-Tryptophan
Tryptophan is the rate-limiting precursor of serotonin (5-HT) synthesis. Dietary tryptophan intake directly affects brain serotonin levels. DeNapoli et al. (2000) showed that a low-protein, tryptophan-supplemented diet reduced dominance-related aggression in dogs.
Tryptophan → Serotonin Pathway
L-Tryptophan → Tryptophan Hydroxylase (TPH) → 5-Hydroxy-L-Tryptophan (5-HTP) → Aromatic L-Aminoacid Decarboxylase (AADC) → Serotonin (5-HT)
Clinical dose (dog): 10-20 mg/kg/day orally, in divided doses. The tryptophan/large neutral amino acid (LNAA) ratio is critical—high protein diets reduce the BBB passage of tryptophan (Bosch et al., 2007).
3.2 Alpha-Casozepine (Lactium®)
Bioactive decapeptide (α-S1 casein f91-100), obtained from the hydrolysis of milk protein casein with trypsin, has an anxiolytic effect by binding to GABA-A receptors. Beata et al. (2007) study showed that alpha-cazozepine significantly reduced anxiety scores in dogs compared to placebo.
- GABA-A receptor positive allosteric modulator
- Benzodiazepine-like effect without risk of addiction
- Lowers cortisol levels
- Calming effect on heart rate and blood pressure
- Dog dosage: 15 mg/kg/day
- Cat dosage: 15 mg/kg/day
- Onset of effect: 3-7 days
- Side effect profile: Minimal (GI tolerance is good)
3.3 L-Theanine (Suntheanine®)
from green tea (Camellia sinensisL-theanine, the isolated amino acid, crosses the blood-brain barrier, increases alpha brain waves and has a calming effect. Araujo et al. (2010) reported that L-theanine reduced anxiety symptoms in thunder phobia in dogs.
- Mechanism of action: Glutamate receptor antagonism, increasing GABA levels, dopamine and serotonin modulation
- Dog dosage: 2-4 mg/kg, twice daily
- Advantage: Calming effect without sedation, GRAS (Generally Recognized As Safe) status
3.4 Omega-3 Fatty Acids (EPA/DHA)
Long-chain omega-3 fatty acids (EPA and DHA) improve neurotransmitter function by reducing neuroinflammation and increasing cell membrane fluidity. Clinical studies have shown that omega-3 supplementation reduces symptoms of anxiety and aggression in dogs (Re et al., 2008).
| Source of Omega-3 | EPA (mg/g) | DHA (mg/g) | Bioavailability |
|---|---|---|---|
| Fish oil (salmon) | 180 | 120 | High |
| krill oil | 150 | 90 | Very high (phospholipid form) |
| Flaxseed oil (ALA) | - | - | Low (ALA→EPA conversion <10%) |
4. Nutrition Strategies According to Stress Situations
4.1 Shelter/New Home Stress
The shelter environment or moving to a new home are the most common sources of chronic stress for animals. Nutritional intervention can accelerate the adaptation process by:
Recommended Approach
- High digestibility diet (85%+ digestibility)
- Tryptophan fortified formulation
- Food containing prebiotics (FOS/MOS)
- Omega-3 rich (EPA+DHA >0.4% DM)
- Fixed meal times (circadian rhythm support)
Things to Avoid
- Sudden food change (GI increases stress)
- Irregular feeding times
- High carbohydrate diets (insulin spike)
- Competitive feeding in a multi-animal environment
- Excessive use of treats
4.2 Veterinary Clinic / Hospital Stress
Loss of appetite is common during hospitalization and delays recovery. Hospitalization anorexia in cats is particularly serious, with anorexia lasting more than 3-5 days increasing the risk of hepatic lipidosis (Valtolina & Favier, 2017).
- Warmed food: Heating to 37-38°C improves palatability by increasing aroma volatilities
- Hand feeding: Creates social bond and a sense of trust
- Wet food preference: More attractive in terms of smell and texture, provides hydration support
- Small, frequent meals: GI reduces load, stimulates appetite
4.3 Noise Phobia (Fireworks, Thunder)
Noise phobia is seen in 40-50% of dogs (Blackwell et al., 2013). Nutritional support should be started 2-4 weeks before the event:
Proactive Nutrition Protocol
- 4 weeks ago: Start alpha-casozepine + L-theanine supplementation
- 2 weeks ago: Increase omega-3 supplementation (EPA+DHA 40 mg/kg/day)
- Event day: Tryptophan rich, low protein light meal (2-3 hours before)
- After the incident: Create positive associations with high palatability food
5. Probiotic and Psychobiotic Approaches
Psychobiotics are live microorganisms that have a positive effect on mental health when taken in sufficient amounts (Dinan et al., 2013). Although psychobiotic research in veterinary medicine is still in its early stages, there are promising results:
| Probiotic Strain | Mechanism of Effect | Level of Evidence |
|---|---|---|
| Lactobacillus rhamnosus JB-1 | Vagal afferent activation, GABA receptor expression ↑ | Mouse model (Bravo et al., 2011) |
| Bifidobacterium longum BL999 | Cortisol lowering, anxiolytic | Canine clinical study (McGowan et al., 2018) |
| Lactobacillus casei Shirota | Suppresses stress-induced cortisol increase | Human RCT, veterinary extrapolation |
6. Pheromonal and Environmental Integration
Nutritional interventions have a synergistic effect when applied together with environmental enrichment and pheromonotherapy:
Tryptophan, alpha-casozepine, L-theanine, omega-3, prebiotic/probiotic combination
Safe area, puzzle feeder, elevated platforms (cat), fixed routine
Feliway® (cat F3 fraction), Adaptil® (dog DAP), diffuser or spray
7. Conclusion and Clinical Recommendations
The relationship between stress and nutrition is bidirectional and dynamic. While chronic stress impairs nutritional metabolism, appropriate nutritional interventions can modulate the stress response. Nutritional anxiolytics (tryptophan, alpha-casozepine, L-theanine, omega-3) and psychobiotics offer complementary strategies that increase the effectiveness of behavioral and pharmacological treatments. However, each case should be evaluated individually and the feeding plan should be customized according to the animal's species, age, health status and source of stress.
Related VetCriteria Tools
Source
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