Energy & Water: Nutrition Guide for Dogs and Cats

To stay healthy, all pets require a well-balanced diet. A balanced diet provides nutrients in the proper amounts and proportions. There are two major categories of nutrients:

• Essential Nutrients have to be received from diet.

• Non-essential nutritients can be made in the body. 

Pets need six main categories of nutrients in addition to energy: water, carbs, proteins, fats, minerals, and vitamins.

Despite not being a nutrient in itself, energy powers every bodily function. In the end, a significant portion of the diet is consumed to meet energy expenditure of bodily functions.  After meeting energy needs, the remaining nutrients support growth, tissue repair, reproduction, and immune system health.

Energy Intake & Feeding Behavior

Many dogs and cats will adjust their food intake to meet their energy needs if they are given a moderately palatable, balanced diet. Pets typically regulate the amount of food they eat for their energy needs. 

Unrestricted access, extremely high palatability, and indoor/lower-activity lifestyles, however, can interfere with self-regulation and make pets more likely to overeat and become obese. Dogs and cats are now primarily companion animals rather than working or hunting animals, which lowers daily energy expenditure. As a result, pet owners need to be aware of both diet composition and portion control.

How Energy Is Expressed

Pet food's energy content is commonly expressed in kilocalories (kcal) or kilojoules (kJ). In addition to crude protein, crude fat, and other analyses, labels typically include energy. Metabolizable energy (ME), the amount of gross energy left over after losses in urine and feces (and gases, if applicable), is the energy value you see on a label.

Energy in Food − Energy in Feces − Energy in Urine (± gases) = Metabolizable Energy (ME).

For instance, ME = 1000 kcal if a food has 3000 kcal of gross energy and 2000 kcal are lost through urine and feces.

ME can be calculated analytically using composition data and atwater factors, or it can be measured in feeding trials by gathering and examining excreta.

Modified Atwater Factors

The Modified Atwater Factors, which are widely used in North America, can be used to estimate ME after gross energy is corrected for digestibility and urine losses:

• 3.5 kcal/g of protein

• 8.5 kcal/g of fat

• 3.5 kcal/g of carbohydrate (NFE).

The AAFCO method for predicting ME through proximate analysis is based on these factors.

 

Energy Density

Energy density is defined as calories per unit weight or volume, such as kcal/kg, kcal/100 g, kcal/cup, or sometimes kJ/kg in Europe. Low energy density diets may limit intake through gut fill, while high energy density diets may promote overconsumption if portions are not watched. Intake is influenced by palatability, moisture content, and fiber content.

Calorie analysis is provided with the label. It is important to understand how much certain parts of pet food, such as protein, constitute of total calories per serving. 

Key insight: Wet foods have a lot more water and fewer carbohydrates per gram than dry foods,which typically have a higher percentage of protein by weight. On an energy basis (per 1000 kcal), a wet food can provide similar protein per calorie as a dry food. Labels can look very different while delivering comparable nutrient density per calorie.

In order to make good choices for pets, consider nutrient density, which is expressed as nutrients per 1000 kcal ME, as well as moisture content and caloric density.

Example of Nutrient Density with Table 1–2 (wet food):
If a wet food has 7% protein (as-fed) and 98 kcal per 100 g, then

Calculating Energy Density from a Label

 

An example of dog food (as-fed):

The mass balance of proximate components (≈100%) allows you to estimate carbohydrates by difference:

• 26 percent crude protein

• 15% is crude fat.

• 5% crude fiber

• Ash (estimated minerals): 5–8% (calculate using a single value, such as 6%).

• 10% moisture

With 6% ash, the estimated carbohydrate content:

Carbs = 100 - 26 - 15 - 5 - 6 - 10 = 38% (approximately 39% if 5% ash is assumed).

The Modified Atwater Factors can then be used to estimate ME.

How Much Food Is Enough?

You can estimate the daily portion once you know the diet's ME density, i.e., 348 kcal per 100 g.

Example (adult dog): Food provides 348 kcal/100 g; required energy = 1100 kcal/day.

Tip: Round to practical measures (e.g., cups) using the product’s kcal per cup if provided.

Energy Imbalance

Problems arise from both too much and too little energy.

• Excess energy (overfeeding): causes fat cell hyperplasia, which promotes adiposity and later-life obesity. It also raises the risk of skeletal disorders (such as osteochondrosis and hip dysplasia) in certain breeds. 

• Inadequate energy causes weight or muscle loss in adults and slowed growth in young ones. Shortfalls in healthy pets typically happen during illness or in high-demand situations (working dogs, late pregnancy, lactation).

Water

The most important nutrient is water. It serves as a transport medium, lubricant, and solvent. Its high heat capacity and evaporative loss through panting help to support thermoregulation.

• When the body loses about 10% of its water content, it can be fatal.

• Water plays a crucial role in digestion, enzymatic reactions, and excretion (the kidneys filter blood and eliminate waste in urine).

• Daily requirement: water needs to be replaced every day because it is continuously lost through breathing, urine, and feces.

Moisture in the Diet

• Dry foods usually have less than 10% moisture.

• Wet foods: usually 80% moisture.

While cats may still underconsume water even on wet diets, some studies indicate that dogs can have enough water when dietary moisture is extremely high (e.g., >67%). Provide free access to fresh, clean drinking water at all times, regardless of the type of diet.

Metabolic Water

Although metabolic water is produced by the oxidation of fat, carbohydrate, and protein (typically 5–10% of daily requirements), this is insufficient on its own.

Practical Takeaway

Give pets unrestricted access to drinking water so they can adjust their intake to their daily activities and the environment, taking into account both dietary moisture and caloric density.