Dietary Management of Pre-existing Obesity

8. Dietary Management of Pre-existing Obesity

The goal of the treatment is to lose body fat with minimal loss in lean tissue and without negative effects on health. Loss of adipose tissue depends on many factors: the initial body composition, the degree of energy restriction required, the rate of weight loss, the level of protein intake, the metabolic adaptations and the intensity of exercise. Recent work by one of the authors has suggested that cats that lose a higher percentage of body weight overall, tend to lose a greater proportion of lean tissue during weight loss (German, in press, 2008).

In theory, the strategy is simple: in order to achieve weight loss the cat must be fed less energy than it requires (Figure 16). In practice, this means feeding at a level below maintenance energy requirements. This is done by first calculating the energy requirement at ideal body weight and then feeding a proportion of this figure. It is essential to base the calculations on the target body weight and not the current weight.

Figure 16. Balance between energy supply and energy expenditure.  

How Do I Determine the Ideal Body Weight?

In order to make a correct calculation of maintenance energy requirements for an obese cat, the ideal body weight must already be known or be estimated.

When Ideal Body Weight Is Known or Can Readily Be Determined

The ideal body weight may have been recorded during a previous visit when the cat was a young adult in ideal body condition (e.g., a condition score of 3/5 or 5/9). It is by far the most accurate guide to optimal body weight in any individual.

Estimation of Ideal Body Weight from Current Body Weight and Body Condition*

In the absence of historical information, an estimate of ideal weight can be made from the current body weight and condition. Assuming that each point above 5 (on a 9-integer condition score) or half point above 3 (on a 5-integer condition score) correlates with 10 - 15% increase in body weight, a simple mathematical equation can then be used to estimate ideal weight e.g.,:

Current weight = 8 kg

Current condition score = 5/5 or 9/9 (~ 40% overweight)

Ideal weight = 100/140 x 8 kg = 5.7 kg

Recommending an Optimum Rate of Weight Loss

If correct energy restriction is applied, obese cats do lose weight (Butterwick et al., 1994; Butterwick & Markwell, 1996). However, the progress of weight loss must be carefully evaluated. A further question is: what rate of weight loss is best? Is rapid weight loss better than slow weight loss?

Many studies have focused on the ideal rate of weight loss because, for owners, rapid weight loss is more satisfactory. In a study (Szabo et al., 2000), obese cats lost 7 to 10% of their obese body weight (BW) during the first week, 3 to 5% during the second week and 2 to 4% for the remainder of the weight loss period. They were fed 25% of their maintenance energy requirement based on the target ideal body weight. However, at the end of the weight loss period, there was an increase in insulin and glucose concentration suggesting that glucose intolerance may be developing in these cats. Therefore, this level of energy restriction appears to be too strict and the authors concluded that the rapid weight loss might increase risk factors associated with the development of diabetes mellitus.

The recommended rate of weight loss remains a controversial issue in veterinary medicine. The weight loss rate must be consistent with relative sparing of lean tissue. Marked energy restriction (down to 45% of maintenance energy requirement at target weight) leads to more rapid weight loss (~1.3% per week) than moderate energy restriction (60% of maintenance energy requirements leading to ~1% body weight loss per week), but lean tissue loss is greater (18% compared with 8%) (Butterwick et al., 1994). Even if the optimal target rate of weight loss seems to be 1.0 to 1.5% of initial BW per week, the exact rate should be tailored to the exact needs of each individual case and slower rates of weight loss are acceptable if tolerated by the client and veterinarian (Figure 17a and Figure 17b).

At this rate, the majority of tissue lost is body fat and no adverse metabolic effects were noted in 14 cats (Center et al., 2000). Blood glucose and alkaline phosphatase significantly decreased between week 0 and week 18, but cholesterol, alanine aminotransferase and aspartate aminotransferase significantly increased. Nevertheless, absolute changes were small and within reference ranges for all the parameters except blood cholesterol concentrations. Nine cats developed hypercholesterolemia during the weight loss program (Center et al., 2000); this effect was also observed in another study (Szabo et al., 2000). Further, in a concomitant study (Ibrahim et al., 2000), changes in cholesterol concentration were found to be due to increased production of high density lipoproteins (HDL). This study also demonstrated that blood cholesterol concentration could be reduced by a diet containing corn oil, thereby confirming that the type of dietary fat could influence lipoprotein metabolism in cats.

How Do I Determine the Daily Energy Allocation to Achieve Weight Loss

Physiological Consequences of Energy Restriction

Decrease in energy expenditure is a universal response to energy restriction in all species. This adaptation is a survival strategy to protect the organism when the central nervous system detects a state of starvation; therefore, when body weight decreases, BMR decreases. In humans, changes in BMR when in negative energy balance vary between -5% to -25% depending upon the level of energy restriction (Prentice et al., 1991). Such reductions in BMR can make smooth and uniform weight loss difficult.

For humans, there are strong relationships both between the severity of energy restriction and the rate of weight loss, and also between energy restriction and suppression of resting metabolic rate. As a consequence, the greater the level of energy restriction applied, the greater the suppression of BMR. Hence, there may be a threshold below which the perceived advantages of rapid weight loss may, in the longer term, be counterbalanced by a more pronounced physiological defence against weight loss (Prentice et al., 1991). Therefore, the decrease in metabolic rate can be counterbalanced by using either pharmacological approaches or by increasing physical activity.

Optimum Energy Intake to Achieve Weight Loss

A study has determined the level of energy intake required to achieve an expected rate of BW loss of 1 to 2% per week in 7 neutered obese cats (Nguyen et al., 2002). In this study, energy expenditure was assessed by indirect calorimetry. The level of energy consumption during the weight loss period to obtain the desirable rate was 40 ± 2 kcal ME/kg ideal body weight e.g., approximately 66% of the energy requirement for an adult cat in optimal BW. Unexpectedly, resting energy requirement (RER) expressed as related to kg BW significantly increased whilst BW and body fat decreased. RER was measured during weight loss (Figure 18). Cats lost 37± 3% of their initial body weight, and the rate of weight loss varied along the study from 0.1 to 3.0% per week and was never linear. Mean RER was 32 kcal ME/kg BW [min 21- max 39] but RER was significantly lower in the obese state (27 ± 2 kcal ME/kg BW) than after weight loss (35 ± 1 kcal ME/kg BW, p=0.028).

Figure 18. Resting energy requirements in cats before and after weight loss.  

According to the current recommendations of the National Research Council (NRC 2006), an allometric coefficient was suggested to calculate the daily energy requirement for cats. The relationship between resting energy expenditure and body weight was best described with a coefficient of 0.65. When RER was expressed as kcal ME/ kg BW0.65, RER did not statistically differ between the obese and lean state, with a mean value of 58 kcal ME/ kg BW0.65 (Table 7).

For weight loss, the level of daily energy intake must be adequate to cover the basal metabolic energy expenditure but not the total daily energy expenditure. In practice, the level of energy restriction should not be lower than BMR, e.g., 21 kcal ME/kg BW or 39 kcal ME/kg BW0.65 as measured in experimental conditions. The initial energy allowance is estimated at about 60% of calculated energy requirement for the ideal body weight of the cat.

In general, weight loss will be faster at the start of the treatment and will decrease thereafter, but the physiologic response is quite unpredictable (Figure 19). Therefore, it may be necessary to adjust energy intake frequently during the weight loss period to achieve optimal body fat loss and to decrease the risk of hepatic lipidosis and insulin resistance.

Figure 19. Various weight loss curves.  

The initial allocation is only a starting point; during the weight loss program, the level of allocation has to be adapted to the rate of weight loss. This means a small (e.g., ~5%) reduction of the amount of food fed if the rate is too slow. Measuring cups are an unreliable method of measuring out food; instead, owners should be instructed to weigh the food on kitchen electronic scales which therefore enables small changes to be accurately made.

It is essential to ensure that, if possible, no additional food is given by the owner (or scavenged by the patient). Healthy treats may be allowed as this enables the owner to maintain their bond with the pet. This should, of course, be factored into the overall calorie provision and not on top of it. The caloric value of drinks (e.g., milk) must be also included as part of the overall plan.

How Do I Evaluate the Duration of the Weight Loss?

Once the clinician knows the target body weight, an estimate of the likely duration of the regimen can be determined (Figure 20). Such information has to be clearly explained to the owners, so that they are aware of the time commitment required for success.

Figure 20. Duration of the weight loss program for an obese cat.

How Do I Estimate the Daily Food Intake?

Calculation of the starting daily energy allocation is shown in (Table 8). To ensure compliance of the nutritional treatment, the presentation must look like the usual food: dry food, wet food or a home made diet. More than 2/3 of owners prefer to mix dry and wet foods. It is essential that the exact portion size is accurately measured at each meal time (Table 9). Their accuracy can be verified by weighing the first portion of the food at the clinic, and giving it to the owner to weigh on their own scales.

How Do I Monitor the Weight Loss Program?

It is essential to follow the progress of patients frequently during any weight management program, particularly during the initial period, when owners need the most support and when problems are most likely to be encountered. It also provides an opportunity to verify compliance, deal with any issues or concerns (e.g., excess begging behavior, problems with implementing play sessions), and to provide feedback, encouragement and support.

Regular Veterinary Checks

Owner motivation is the key to a successful outcome. Regular rechecks will help maintain compliance and owner motivation. A check every 2 - 4 weeks is recommended; if check-ups occur less frequently than every 4 weeks, compliance with the program will slip. It may also lead to a delay before a change is made, meaning that weight loss does not continue at an optimal rate.

Measurement of the Weight Loss

At each check-up, the cat should be weighed and a physical examination performed. Owner perspective on progress should be gauged and any problems with the program discussed. If necessary, changes to the dietary plan can be made and any issues identified and resolved.

Body weight is the principal outcome measure of interest and used to decide upon whether changes to the plan are required (reduction in amount of food fed, increase in dose of medication). In order to minimize variability amongst measurement, the same set of electronic weigh scales should be used, and regularly validated. Owners must not be discouraged by the fact that 1% weight loss per week is not very much (e.g., 60 g for a 6 kg cat).

The BCS chart can be used as a visual aid for leading discussion and providing owners with positive feedback. However, given that body condition is likely to change gradually, it is not essential to repeat the BCS at every visit.

Morphometric measurements are an additional means of monitoring outcome, and can be used to relay success in terms that the owner will understand (e.g., similar to a decrease in the size of the waist in people) (Figure 21).

Figure 21. Evolution of body weight change versus morphometric measurements. (Clinical case n°1).  

Periodic photographs provide an excellent visual demonstration of success, but should be taken in a standardized manner to enable comparison between time-points.

All measurements and comments should be recorded and used to provide positive feedback, wherever possible, for the owner. Veterinarians should also encourage owners to record daily food intake in a diary; this information can then be reviewed at each visit.

Follow-up by Phone

A first phone call within 48 hours after starting the regimen might be helpful to ensure the compliance of the owner. Then, regular calls from a technician responsible for overseeing the program, is an excellent means of checking on progress, enhancing compliance and addressing any problems as early as possible. The involvement of other members of the veterinary team is a good way to boost success and make owners appreciate the commitment of the practice.

What Should I Do at the Time of First Reassessment?

Regular revisits are made to assess progress throughout the weight loss regimen. Having interim target weights (in addition to the final target) can help maintain the owner’s motivation throughout the process. There are three possible scenarios at the time of the first weigh-in.

Successful Outcome

The cat loses weight at a normal rate and the owner is satisfied. One can then renew the regimen and fix the time of the next appointment.

The Cat Did not Lose Weight or Even Worse, Gained Weight!

In this situation, it is necessary:

• To verify that the calculation of the daily amount of food is correct. If this is the case and there is no other possible explanation, a reduction (usually 5 - 10%) in food intake may be necessary.
• To re-evaluate family environment without making the owners feel guilty. How is the motivation of the owner? Are instructions clear enough? Are there any neighbors likely to feed the cat? Verify whether any non-compliance (e.g., feeding additional items) has occurred. If this is the case, it may not be necessary to alter the amount fed.
• To consider additional diagnostic investigations such as to examine for possible hormonal disorders. In cats, hyperprolactinemia and acromegaly are common and alter the ability of the cat to lose weight. Until recently, medical treatment has not been available to correct this situation.