Energy Balance Regulation Mechanism for Dogs and Cats
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All animals need energy to power their bodies. Growing animals require more energy than their bodies use because they are building new tissue, and mature animals need extra energy for reproduction. When food provides more energy than the body uses, the surplus is stored as fat. Adjusting a pet's energy intake means accounting for several factors — let's dig into the concept of energy balance.
Energy Expenditure
There are three major components of energy expenditure:
- Basal Metabolic Rate
- Voluntary Muscular Activity
- Dietary Thermogenesis
Basal Metabolic Rate and Resting Fed Metabolic Rate
Basal Metabolic Rate (BMR) is measured after an overnight fast. It represents the minimum energy the body needs to maintain cellular integrity. Resting Fed Metabolic Rate (RFMR) adds the thermogenesis that follows food intake on top of BMR. Together these are the body's main energy expenditures.
BMR and RFMR are directly proportional to the body's total lean mass and volume. A pet with more lean muscle needs more energy to maintain tissue function.
BMR and RFMR may account for around 60–70% of the total energy requirement.
Voluntary Muscular Activity
As the name suggests, this component is voluntary, and it can account for up to 30% of total energy expenditure. The more active the pet, the greater the energy required for muscular activity.
Dietary Thermogenesis
Also called the specific dynamic effect of food or meal-induced thermogenesis, this component can account for up to 10% of energy expenditure. The body generates heat while breaking large food components into smaller building blocks and converting one component into another. This is the cost of digestion, absorption, metabolism, and storage of nutrients.
In dogs, the process occurs in two phases: the cephalic phase (the moment food enters the body) and the postprandial phase (the six hours after food enters the body).
The rate of feed intake affects dietary thermogenesis. Cats eat more frequent meals, so they have higher dietary thermogenesis losses than dogs. Other factors, such as emotional stress, can also increase it.
Temperature matters too. In colder climates, the body uses more thermogenesis to warm up — this is called nonshivering thermogenesis.
General Factors Affecting BMR
BMR is affected by age, reproductive status, lean tissue, hormonal status, and calorie restriction. For example, eating fewer calories reduces lean tissue, so less energy is needed, which in turn affects hormone levels — something we recognize from our own bodies.
Reproductive status is also important. Neutered pets require less energy, which is why there are special diets formulated for them.
Regular exercise is essential for maintaining a healthy BMR. All animals need some physical activity to keep lean muscle and energy expenditure in balance.
Internal Controls for Food Intake
Food intake is regulated by both internal and external signals. This has been studied in lab animals and provides insight into other species as well.
General internal stimuli include gastric distention, the physiological response to the sight, sound, and smell of food, and changes in plasma concentrations of specific nutrients, hormones, and peptides.
External stimuli include food availability, the timing and size of meals, food composition and texture, and diet palatability.
Food causes stomach distention, which triggers the release of GLP-1 and cholecystokinin (CCK). These two hormones signal short-term satiety, and stomach distention also signals the vagus nerve.
The second physiological response is the ileal brake, which represents fullness of the small intestine up to the ileum.
Ghrelin, produced by the stomach, stimulates appetite and peaks just before a meal begins.
I cells in the duodenum and jejunum release CCK in response to protein and fat. L cells in the ileum and colon release GLP-1 and peptide YY to signal satiety; these hormones slow gastric emptying, which increases the feeling of fullness and activates the ileal brake.
Leptin, produced by adipose tissue, tells the body to stop eating — the more fat tissue, the higher the leptin. However, obese animals have lower leptin sensitivity, so it does not help them lose weight.
Insulin pushes glucose from the blood into cells, so smoothing out glucose peaks in the blood can help control appetite.
Reproductive hormones also influence satiety hormones. Neutered animals tend to gain weight by eating more, because reproductive hormones affect how leptin works.
External Controls of Food Intake
Palatable diets can cause overconsumption. Other factors such as texture, timing, and environment also matter. Dogs have a strong preference for wet, semi-moist, beef, and warm meals, and they tend to prefer sugary and salty flavors; palatability also rises with fat content. Social facilitation tends to increase how much dogs eat.