Behavior and nutrition in dogs

Leptin is a hormone produced primarily in adipose tissue that signals to the brain (especially the hypothalamus) that sufficient energy is available in the form of food. High leptin levels reduce hunger, while low levels increase appetite. It thus helps maintain a balance between food intake and energy expenditure and counteracts obesity. Leptin is also responsible for mobilizing energy from fat reserves in times of nutrient deficiencies. At the same time, leptin plays an important role in the immune system. Deregulation can lead to inflammation and autoimmune diseases (allergies).

Complex carbohydrates provide a stable energy supply. Foods such as sweet potatoes, oatmeal, and brown rice ensure consistent insulin release, thus stabilizing leptin levels. Studies show that omega-3 fatty acids can help reduce leptin resistance—a problem commonly found in overweight dogs (Zicker et al., 2012). High-sugar processed foods can lead to insulin overproduction, disrupting leptin balance and promoting cravings. A balanced protein intake helps regulate leptin levels. Lean meat, eggs, and fish are particularly suitable.

Overweight and obesity aren't just human problems. Up to 60% of domestic dogs are now overweight (Chandler et al., 2017). The consequences can be diverse, but above all, there is an increased risk of premature death (Kölle & Ziese, 2021). The hormone leptin plays a crucial role in controlling food intake. Leptin is produced in white adipose tissue and signals to the brain when the dog is full. It is thought to suppress appetite and stop food intake. It also influences:

• ✅ Energy level and metabolism
• ✅ Stress resistance
• ✅ Impulse control

A disturbed leptin balance can lead to:

• ❌ Obesity and binge eating
• ❌ Restlessness or increased aggressiveness
• ❌ Concentration problems lead

When food is consumed, leptin levels in the blood fluctuate. A drop in leptin leads to a reduction in heat production and food intake, while a rise in leptin leads to heat production and a cessation of food intake. The body can then lose the ability to detect leptin concentrations in the blood, resulting in a loss of satiety. These dogs exhibit increased begging for food and always appear hungry. This can be due to age, but also due to a one-time increase in body fat, especially due to overfeeding. Of course, there are also dogs with increased food motivation. It is therefore very important to feed dogs a restrictive/controlled diet and avoid overfeeding. Obesity also has lasting effects on behavior. A measurement of the stress hormone cortisol showed that overweight dogs tend to have higher stress hormone concentrations. Continuously elevated cortisol levels can, in turn, lead to insulin resistance (type 2 diabetes). Pogany et al. (2018) also demonstrated that overweight dogs are more pessimistic than normal-weight dogs. This plays a key role in successful behavioral therapy. Physical consequences of obesity also include acute and chronic orthopedic conditions, such as osteoarthritis, cruciate ligament rupture, herniated discs, heart problems, and respiratory problems. The resulting psychological consequences are obvious. Pain or difficulty breathing often lead to behavioral changes because they disrupt general well-being and develop into symptoms such as nervousness, reduced concentration, or even aggression.

Corn is a common ingredient in commercial dog food because it's a cheap source of carbohydrates. However, it has some properties that can indirectly affect the production of the neurotransmitter serotonin. Serotonin is an important neurotransmitter in the brain that regulates emotional stability, stress management, and impulse control. Serotonin is a neurotransmitter that plays a key role in:

• ✅ Relaxation and emotional balance
• ✅ Anxiety management
• ✅ Impulse control and stress resistance play a role.

Low serotonin levels are associated with:

• ❌ Increased irritability and aggression
• ❌ Anxiety behavior
• ❌ Associated with susceptibility to stress.

Serotonin is produced in the body from the amino acid L-tryptophan. Although corn contains L-tryptophan, it does so in small amounts and in an unfavorable ratio to other amino acids, particularly leucine. These amino acids compete with L-tryptophan for transport across the blood-brain barrier. As a result, less L-tryptophan reaches the brain, which can lead to lower serotonin levels (Pérez-Camargo, 2004). Studies show that aggressive dogs have lower serotonin levels than non-aggressive dogs. The researchers concluded that a tryptophan-rich, corn-free diet (e.g., with turkey, egg, or salmon) can help reduce impulsive behavior (Rosado et al., 2010).

Corn consists largely of rapidly digestible carbohydrates . These lead to a rapid rise in blood sugar levels , followed by a rapid fall . Fluctuations in blood sugar can exacerbate stress reactions and excitability, which in turn can lead to unwanted aggressive behavior (Reisner et al., 1996).

Corn contains relatively high amounts of omega-6 fatty acids, which can be in an unbalanced ratio with omega-3 fatty acids. An excess of omega-6 can promote inflammatory processes in the body, which in turn affect the nervous system and lead to increased irritability (Zicker, 2008). A pro-inflammatory environment in the body can disrupt hormone balance and thus negatively impact neurotransmitter production.

Alternatives with a better influence on serotonin levels are:

• ✅ Tryptophan-rich foods: meat (e.g. turkey), eggs, salmon, cheese
• ✅ Complex carbohydrates with a low glycemic index: sweet potatoes, oatmeal, brown rice
• ✅ Omega-3-rich foods for anti-inflammatory effects: fish oil, flaxseed oil, chia seeds

Nutrition has a direct influence on a dog's hormonal balance and can positively or negatively influence behavior such as aggression, anxiety or hyperactivity.