A systematic approach to designing weight-loss plans for cats and dogs

Each pet must be assessed on an individual basis and will require a nutritional plan targeted to its specific needs

Obesity is defined as excess body weight that may contribute to impaired health and body function.1 Survey data suggest more than half of the cats and dogs in the United States are overweight or obese,2 making obesity the most common nutritional disease in companion animals. (This number is likely comparable to dogs and cats in Canada.) Pets with up to 20 per cent excess body weight are considered overweight (corresponding to a body condition score [BCS] of 6/9 and 7/9), while pets with more than 20 per cent excess body weight are considered obese (BCS 8/9 and 9/9).3 Obesity can result from animal factors, such as breed or spay/neuter status, or from considerations related to their owners, such as diet choice or feeding methods.4 As such, it can be challenging to discuss obesity with pet owners and to design and implement weight-loss plans. This article discusses obesity and offers a step-by-step approach to canine and feline weight loss. Using this system for appropriate patients can help standardize your care for the overweight or obese pet.

Why obesity is a problem

Obesity is not a concern simply because it’s common. On the contrary, it presents health hazards. Overweight and obese animals are at risk for a number of conditions, including diabetes mellitus, cardiac and respiratory disease, degenerative joint disease, inflammatory diseases, and neoplasia.1 Obesity is also associated with decreased quality of life and shorter lifespan in dogs.5-7 Obese animals are more difficult to examine (e.g. abdominal palpation can be further challenging) and excess body fat can interfere with diagnostic tests, such as radiography and ultrasound.

Designing a weight-loss plan for a cat or dog

For most overweight and obese patients, a standardized approach helps improve success. However, this methodology should not be applied to certain patients. Pets that have systemic illness requiring a specific veterinary therapeutic diet (e.g. formulas for chronic kidney disease), a diet formulated for growth (e.g. puppies and kittens), and those with severe illness (e.g. congestive heart failure [CHF] or neoplasia) should be treated with special care, even when obese. For those patients, consulting with a board certified veterinary nutritionist (acvn.org) may be needed.

A weight-loss plan for the uncomplicated overweight or obese patient should include the following seven steps:

1) Communicating with the owner about implementing a weight-loss plan

2) Performing a nutritional assessment

3) Estimating ideal body weight

4) Estimating energy requirements

5) Comparing current intake to estimated energy requirements for the pet

6) Selecting a diet and feeding plan

7) Monitoring and follow-up

Communicating with the pet owner about obesity

The communication piece is essential to a successful weight-loss plan, but it is often the most difficult part of the process. Some pet owners do not realize their pet is overweight, and it can be a sensitive subject to broach. When the pet owner is overweight themselves, it can become even more challenging to initiate the conversation. Focusing on the health effects of excess weight is the most important thing, as it puts the needs of the cat or dog first. Involving the entire veterinary team when communicating with pet owners regarding pet obesity can be useful and can help improve compliance.8

Diagnosis of obesity and nutritional assessment

A thorough nutritional assessment, including body weight, BCS, muscle condition score (MCS), and a thorough diet history is necessary, in addition to a standard medical history and physical examination.9

Body condition score

Body condition scoring provides an estimate of body fat mass. There are two body condition scoring systems: the nine-point scale and the five-point scale. Both range from emaciated (1/9 or 1/5) to obese (9/9 or 5/5). Ideal BCS is considered 4 to 5/9 or 2.5 to 3/5. Animals above ideal body condition are considered overweight or obese.

Muscle condition score

MCS estimates lean muscle mass independent of BCS. In addition to obtaining a BCS on each patient, muscle condition can be scored on a scale of normal, mildly decreased, moderately decreased, or severely decreased. A patient with a severe decrease in muscle mass can still be obese, and in these cases, body condition scoring may be more difficult because the animal will seem ‘bonier’ due to lost muscle mass.

Diet history

A thorough diet history provides insight into both the animal’s caloric intake and the owner’s feeding practices. Asking open-ended questions can frequently help the veterinary team discover more valuable information about what the pet is eating.

The components of a diet history include:

  • The pet’s main diet type, along with amount, frequency, and duration of feeding and how it is measured
  • All treat types, as well as amount and frequency
  • Recording human foods/table scraps with type, amount, and frequency
  • Food for medication administration
  • Food for training
  • Access to other pets’ food
  • Any other food the pet can access indoors or outdoors
  • Dietary supplements
  • Flavoured medications
  • Toothpaste

Estimating ideal body weight

Each body condition score point on the nine-point BCS scale is equivalent to approximately 10 per cent of body weight.10 Using that guideline, estimated ideal body weight can be calculated with the following formula:

Ideal body weight = Current body weight/division factor
(see Table 1)

Estimated ideal weight is a starting point for a weight-loss plan. In all cases, the patient will need to be monitored to determine if the ideal body weight calculation is appropriate. Asking the owner for information regarding previous weight can also provide insight into the pet’s ideal body weight.

Estimating energy requirements

While there are multiple formulas used to calculate resting energy requirements (RER), the exponential formula below is most accurate for all animals. This can be done using body weight in kilograms with the following:

RER (kcal/day) = 70 x (BWkg)0.75

Multiplying RER x 1.0 for dogs and RER x 0.8 for cats using ideal body weight calculations can help determine energy requirements for weight loss, although these equations should be used for overweight and obese animals without additional health complications. Energy requirements can also be determined by obtaining a thorough diet history and calculating current caloric intake, then decreasing intake by 20 per cent. Sometimes, one method works better than another, depending on the patient and other factors.

Comparing recommended intake to current intake

Some pets have a slower metabolic rate than others, and factors such as a low activity level, orthopedic disease, and spay or neuter status can impact how many calories a cat or dog needs each day. It is often helpful to go back to the diet history after calculating energy requirements and comparing current intake to the calculated energy requirement for weight loss. If the pet’s current intake is higher than the calculated amount, the veterinary team can proceed with the next step. If the pet is currently eating less than the calculated amount he or she needs for weight loss, it can be helpful to revisit the diet history. For canine patients, it can be beneficial to check thyroid hormone levels. It can also be helpful to consult a board certified veterinary nutritionist when the pet is eating less than the calculated amount for weight loss.

Diet selection for overweight and obese animals

Focusing on the health effects of excess weight is the most important thing, as it puts the needs of the cat or dog first.
Focusing on the health effects of excess weight is the most important thing, as it puts the needs of the cat or dog first.

Animals with excess body weight should ideally be placed on a therapeutic weight-loss diet. These formulas are nutrient-dense, meaning there is a higher concentration of protein, essential fatty acids, vitamins, and minerals per kilocalorie when compared to a maintenance diet. Therapeutic weight-loss diets also are lower in energy density, allowing the owner to feed the pet a larger volume of food. Other options include therapeutic ‘moderate calorie’ diets designed for obese-prone patients with other health conditions, as well as over-the-counter weight-management diets. These are typically used when the patient has concurrent disease or when the patient is not extremely overweight. Most obese patients require a therapeutic weight-loss diet for safe and successful weight loss. The goal is to provide adequate nutrition while restricting calories.

Treats can be included in a successful weight-loss plan, but should be considered when calculating total caloric intake. Additionally, they should make up no more than five to 10 per cent of total calories. Most owners are unaware of the high calorie content in treats, which can make up a significant percentage of calorie intake. Reducing the number of treats, as well as modifying treat type, is usually necessary when designing a weight-loss plan.

Monitoring the patient and adjusting the weight-loss plan

Patients should be weighed every two weeks during a weight-loss plan to allow for safe weight loss at a rate of 0.5 to two per cent of body weight per week. If the patient is losing weight too quickly or too slowly, the caloric intake should be adjusted in five to 10 per cent increments. Treat intake should be adjusted as well. Based on the rule of thumb that weight loss should occur at 0.5 to two per cent of starting body weight per week, the owner can be given a time frame in which weight loss would ideally occur. This can help provide them a sense of perspective and a realistic timeline.

In addition to feeding an appropriate diet for weight loss at an appropriate amount, monitoring patients is essential for success and will also improve client compliance. Once target weight is achieved and the pet is in ideal body condition, the patient should receive an average of five to 10 per cent more calories than what was necessary to achieve weight loss to maintain ideal body weight.


This systematic step-by-step approach helps manage many patients, but each pet must be assessed on an individual basis and will require a nutritional plan targeted to its specific needs. Use your nutritional assessment to help discover your patient’s requirements, to understand the owner’s feeding methods and practices, and to develop the most effective weight-loss plans for your patients.

Catherine Lenox, DVM, DACVN, is a nutritionist with Royal Canin USA. She also teaches online nutrition continuing education through the Veterinary Information Network (VIN). Dr. Lenox can be reached at catherine.lenox@royalcanin.com.


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