Begin by assessing the patient, the environment, and obtaining a full diet history as detailed in the American Animal Hospital Association Nutritional Assessment Guidelines for Dogs and Cats.²¹ Identify all household and environmental factors that impact feeding management (i.e., current diet, feeding schedule, treats, numbers and perceptions of household members involved with feeding), exercise (current and potential), and the environment (housing, environmental enrichment).²¹

Assess the patient

In addition to a complete physical exam, the patient health assessment may include relevant laboratory and imaging studies as appropriate to assess for comorbidities that may impact either caloric needs or require additional management (e.g., exercise limiting orthopedic disease, metabolic/endocrine disorders).

Evaluate the pet’s current body weight (BW), BCS, and muscle condition score (MCS) as part of the health assessment and for determining healthy weight.^21,33 Assessing the MCS along with the BCS will establish a baseline from which you may monitor muscle and fat loss, especially if there is either a comorbid condition (where either the weight loss rate may be lower or the patient is at risk for loss of muscle mass due to the catabolic impact of disease) or the patient is losing weight too rapidly (resulting in loss of muscle mass).

Estimating the pet’s ideal weight helps determine the pet’s caloric requirements and establishes a motivating goal. Some ways to estimate a patient’s ideal weight include the following:

• Historical. Check the medical record for the pet’s weight and BCS history to determine whether it shows a previous ideal weight that correlates to a BCS of 5 out of 9 or 3 out of 5.
• Calculate the ideal weight from the current BCS if historical weight information is not available. Each BCS ≥ 5 (on a 9 point scale) or half of a BCS ≥ 3 (on a 5 point scale) is equivalent to being 10% overweight.^34–37 For example, a 45 kg Labrador retriever that has a BCS of 8 out of 9 is 30% overweight and its ideal weight is approximately 32 kg (Table 1).
• Use the percent BF that correlates with the BCS scores to estimate ideal weight using the equation: [current BW x (100 – %BF)]/0.8.³⁷Note that lean mass is 80% of the ideal BW, assuming 20% BF.

Although there is not an established criterion in veterinary medicine, for the purpose of this document, the authors define obese as a BCS of ≥ 8 out of 9 (or 5 out of 5). Although studies often do not differentiate overweight pets from obese pets, health risks and clinically apparent disease seem greater in severity as weight gain increases. Long-term studies of pets with various BCS categories against controls are needed to verify that clinical impression. All overweight pets suffer from similar, yet less obvious morbidities, and should be treated with as much urgency for weight loss as obese pets.⁷

It is challenging to accurately determine ideal BW in obese patients that exceed the BCS scale (i.e., > 5 out of 5 or > 9 out of 9, correlating to being > 40% overweight). There is no proven method for adjusting the calculation for severely obese patients, and the above approach may cause an overestimate of the ideal weight. Reassessing the patient as their BCS improves during weight loss allows refinement and more accurate estimate of the patient’s ideal weight.

Assess the client and feeding management

Success for weight loss depends on the client’s willingness, interest, and ability to follow recommendations (i.e., adherence). Assess the client’s readiness to change his/her feeding habits and evaluate opportunities for changing the pet’s management and lifestyle.³⁸ Identify challenges the client has faced in the past with feeding management to effectively tailor the plan to the patient and engage the entire household.

Assess the current diet

The diet history can provide valuable information about current caloric intake that can serve as a starting point for the weight loss program and help the veterinarian anticipate potential challenges to the weight loss plan (discussed in detail below). Collect information about total daily intake (i.e., varieties and amounts of foods, treats, chews, and supplements; feeding management; and any use of food to administer medication), with sufficient detail to account for all calories ingested. Anticipate nutritional imbalances when treats and human foods exceed 10% of the total caloric intake.²¹

Evaluate how food plays a role in the client relationship with the pet, such as food used for training, nurturing, or bonding in specific situations. Assess “nonnegotiables” lifestyle aspects that the client seems either unlikely or unable to change and try to incorporate some aspect of those aspects into the plan. Such compromises can help increase adherence and trust moving forward with the weight loss program.

TABLE 1

Summary of BCS scales and their relationship with BF and BW^36,68–71

*Current body weight x (100 – % BF)/0.8. Lean mass is 80% of ideal weight (assuming 20% BF). BCS, body condition score; BF, body fat; BW, body weight.