Treatments for Obese Animals

2. Treatments for Obese Animals

Pharmacological Treatments

A large pharmacological arsenal has been developed to treat human obesity. It should be noted that some of these pharmaceuticals have been developed for dogs. Some studies have been conducted with these agents to reduce the body weight of obese dogs (Bomson & Parker, 1975). These trials have not been successful.

Dehydroepiandrosterone (DHEA) administered at a large dose (60 mg/kg of body weight /day) reduces the deposition of fatty tissue and has been used as an agent to facilitate weight loss, in combination with a low-energy diet in obese dogs (MacEwen & Kurzman, 1991; Kurzman et al., 1998). DHEA also exhibits hypolipemic and hypoglycemic properties. Its mechanism of action has yet to be fully clarified. Due to the many uncertainties as to the various effects of this hormonal precursor, its utilization in dogs can not be recommended at this time.

Injections of human recombinant leptin have also been used in dogs. The administration of leptin to healthy or obese dogs induced a significant loss of weight proportional to the duration and the dose used. Weight loss is nevertheless greater in healthy dogs. The dogs start to gain weight a week after the end of the treatment, gradually returning to their initial weight. The weight loss is essentially due to a reduction in body fat mass. In a study comparing the effects of leptin administration in obese males and females, a similar loss of weight was observed in the two groups at doses of 0.5 mg/kg BW/d and 5.0 mg/kg BW/d (Lebel et al., 1999). This type of specific trial does not argue in favor of the use of leptin in obese dogs, especially due to the lack of long-term data and the presence of the rebound effect after the end of the treatment.

Whatever place pharmacological treatment will have in the future, it should not be forgotten that in a global approach (behavioral and dietary) of obese dogs, medication should never be used as it does not change the owner's behavior.

Surgical Treatments

In human medicine various surgical interventions help limit food consumption. These techniques are not used on animals at this time.

Approach of the Owner

The psychological approach of the owner is essential. The objective is to motivate the owner by explaining the causes and the damage caused by obesity as well as the advantages of having a healthy animal. Clear explanations, regular checkups and the establishment of a weight curve are steps that will contribute to successful treatment (Lewis et al., 1987; Norris & Beaver, 1993). No diet is possible without the cooperation of the owner.

Clinical trials conducted on obese dogs provide various findings. The first is that in a weight loss program initiated by the owner, over 50% of those owners did not return for checkup visits. It must therefore be concluded that over 50% of dog owners abandon the diet in the month following the first visit (Remillard, 2000). In another study, 75% of dogs registered stopped losing weight (Gentry, 1993). These details will be addressed from a more practical perspective under Clinical Food.

Nutritional Treatment

Two techniques can be used to reduce the dog's weight. Fasting is applicable and effective provided the animal does not present with a concomitant pathology like hepatic insufficiency or diabetes mellitus. It is necessary to hospitalize the animal and to give it daily mineral and vitamin supplements. Many authors have shown that the dog can easily bear complete nutritional privation (De Bruijne & Lubberink, 1977; Brady & Armstrong, 1977), but according to Abel et al. (1979) prolonged fasting past 36 days can lead to heart lesions. Furthermore, this method is not to be recommended for ethical reasons and because it does not bind the owner to long-term dietary modifications.

The restriction of energy intake is accordingly the only truly valid option. The dietary balance must be established with the owner. In the absence of precise information on the quantities of food ingested, it should be possible to estimate the total daily energy typically consumed by the animal. A very strict protocol must then be established with the owner's full cooperation.

Level of Energy Restriction

The choice of the ration's energy level depends on several criteria, including the degree of weight excess, the animal's sex and the projected duration of the diet. The first step consists of defining the ideal weight; the second is setting the energy restriction level. The diet is generally calculated to provide 40% - a very severe restriction - (Markwell et al., 1990) to 60% (Edney, 1974) or 75% (Dzanis, 2000) of the energy needed to maintain the optimal weight. Table 10 provides an overview of the various clinical and experimental trials. Theoretically, the higher the energy restriction, the shorter the restriction period needed.

The practitioner may be tempted to opt for very severe energy restriction to limit the duration of the diet. This is not recommended. Too severe a restriction may lead to a significant feeling of hunger in the animal, generating an augmentation of activity after meals (Crowell-Davis et al., 1995b) and consequently the dissatisfaction of the owner and a lack of cooperation with respect to following a strict diet. The diet runs the risk of being abandoned after a few weeks or even a few days. Additionally, the loss of muscle mass can also be exaggerated by a sudden loss of weight, as has been shown in humans (Pasanisi et al., 2001). In experimental conditions, the rebound effect (weight gain after the end of the diet) is so much more intense and fast when the energy restriction is severe (Laflamme & Kuhlman, 1995). The explanation advanced for the severity of the rebound effect is that the dogs present a reduction of metabolic activity associated with an increase in energy efficiency during the diet. The more severe the energy restriction, the less the physical activity is of the dog (Crowell-Davis et al., 1995a). This reduction in activity constitutes a second risk factor for muscle mass loss.

Lastly, the long-term modification of the owner's behavior is more desirable than a rapid change. As a consequence, a very severe energy restriction is not recommended for all animals, but should be reserved for the most severe cases of obesity, when the weight gain is more than 40% and there is a medical indication for rapid loss, such as serious respiratory, cardiac or orthopedic problems. The same applies if the animal has to undergo anesthesia in the short or medium term.

Various experimental and clinical trials show that a reasonable objective is to maintain a loss of 1 - 2% of the initial (obese) weight per week, or 4 - 8% per month. There is a wide consensus on this degree of weight loss. Table 11 proposes various degrees of energy restriction based on several parameters: body weight excess, sex and desired weight loss period.

For weight loss of 1.5% per week, at least 3.5 - 4 months are needed to change a body score from 7/9 to 5/9 (or from 4/5 to 3/5). (© I. Jeusette)

Differences between Males and Females

A study conducted on Beagles showed that it was more difficult to induce and maintain the weight loss in obese females - neutered or unneutered - than in neutered males. The initial degree of obesity was comparable, as was the weekly loss of weight.

In the course of time, the adjustments to the quantities were more severe for the females compared with the male dogs. For female dogs, an energy intake limited to 54% of the calculated maintenance energy need based on the ideal weight did not lead to the attainment of the target weight. The 60% level used at this time appears to be inappropriate for females. The development of body composition was not affec-ted by sex (Diez et al., 2002). The maintenance food of obese dogs needs to be exa-mined to understand this difference between the sexes. At comparable weight, obese bitches consume an average 15% less energy than males by unit of ideal metabolic weight and their lean mass is generally inferior. It is therefore illogical to apply the same weight-loss protocol to individuals of different sexes (Jeusette et al., 2004c).

Modification of the Food

It is totally contraindicated to achieve energy restriction by simply reducing the quantity of the food typically consumed. This will lead to deficiencies in essential nutrients and will have little probability of success. An animal that is denied food may develop unpleasant behavior: nervousness, theft of food and sometimes even aggression (Branam, 1988). These behaviors discourage the owner and the diet will be highly unlikely to succeed. Crowell-Davis et al. (1995a) relate the effects of the restriction on the behavior of a group of dogs in the kennel: during the first few days of calorie restriction the animals showed a greater propensity to chew objects, heightened aggression among some subjects and an increase in the frequency of barking. The selection of a food specially adapted for weight loss is therefore imperative if deficiencies are to be avoided and the dog is to receive sufficient food, while simultaneously limiting energy intake.

Low-calorie Foods

There are various ways to reduce the concentration or energy density of commercial dog food. The simplest way of effectively reducing the energy concentration of a commercial food is to reduce the fat content and increase the dietary fiber content. These two major changes are indeed essential, but all nutrients (amino acids, fatty acids, minerals and vitamins) must be given due consideration in the formulation of a food, as described in more detail below.

In addition, it should be noted that the production of extruded dry food containing large quantities of air will help increase the volume of the ration. This method mainly has a psychological impact on the owner and less on the dog, since the weight of the daily ration is reduced. The change in the size, texture and shape of the kibble may be a way to increase the ingestion time and satiating power. In the case of wet food, very high hydration (over 80% water) also helps maintain a relatively large volume. Nevertheless, the impact on satiation is dubious, as the water - or the liquid fraction of the food - is evacuated from the stomach in 20 - 30 minutes depending on the size of the particles. The addition of viscous dietary fiber that binds water does on the other hand slow down gastric emptying (Russell & Bass, 1985).

The essential nutrient content of low-calorie foods is extremely important. A more or less severe restriction imposed on an animal must never be accompanied by any deficiencies of proteins, essential amino acids, essential fatty acids, minerals, vitamins or trace elements.

The protein concentration of low-calorie foods must be greater than those of maintenance foods to provide the essential amino acids. Figure 6 illustrates the necessity of increasing the protein content in the food to avoid the energy restriction causing a protein deficiency.

The same reasoning is valid for all essential nutrients. High-protein diets have been used successfully for several years in humans and have demonstrated many benefits.

Figure 6. Adaptation of the diets's protein level based on the energy restriction.

• Positive effect on body composition by maintaining lean tissue mass. High-protein diets minimize muscle wasting and facilitate the loss of fat (Durrant et al., 1980; Piatti et al., 1994).These effects have also been observed in dogs as part of a low-calorie diet. Three similar diets differing in protein concentration (20%, 30% and 39% of energy intake) were fed to 42 obese dogs. The diet with the highest protein content led to increased loss of fat mass and minimized the loss of lean tissue (Hannah, 1999). These results have been confirmed in another trial comparing two low-energy diets. The high-protein diet contained 157 g of protein/1000 kcal or 47.5% of dry matter (Diez et al., 2002).
• Lower yield in terms of net energy intake for proteins compared with carbohydrates. At the same weight, digestible carbohydrates and proteins provide comparable levels of metabolizable energy, but proteins provide lower net energy levels (Rubner, 1902). This means that the use of proteins costs the organism energy. The energy expended is accordingly not stored in the form of fat, which is advantageous for obese individuals.
• Satietogenic power of proteins (Louis-Sylvestre, 2002): the increase in the prevalence of obesity has fueled interest in foods with a strong satiating power. The results of many studies conducted on humans have shown that the absorption following the consumption of high-protein foods was lower than after consumption of foods with a high carbohydrate or fat content. The amino acids from the digestion of proteins are absorbed slowly and the main path of their metabolism is gluconeogenesis. Therefore, proteins are sources of glucose that induce little insulin secretion and they slow down the appearance of hypoglycemia, which contributes to the feeling of hunger. The speed of digestion varies from one protein to the other and amino acids induce the secretion of insulin to varying degrees, so the satietogenic power may also differ from one protein to another. This certainly merits studies specific to the dog.
• Beneficial effect on palatability. This property is particularly significant when using low-calorie foods.
• Improved conservation of weight loss after the diet. This effect has been shown in humans (Westerterp-Plantenga et al., 2004).

The quality of the protein is also important. It is necessary to increase the protein content of the ration when significant quantities of mixed dietary fiber (association of soluble and insoluble fiber) are added, due to the reduction in the digestibility of the dry matter (DM) (including the protein) caused by some fiber.

The fat content of low-calorie foods is generally reduced to less than 25% of energy intake. Nevertheless, a minimal fat concentration is necessary to ensure the intake of essential fatty acids and the transport of fat soluble vitamins. The most recent recommendations are at least 5.5% of DM (for a food containing 4000 kcal/kg of DM, or 14 g/1000 kcal). Low-calorie commercial foods never contain less than 5% of fat. In addition, the choice of fat sources of different origins (vegetable oil, linseed oil or fish oil) ensures the intake of essential long-chain fatty acids.

The use of dietary fiber has fueled a wide debate in both human and animal nutrition. The incorporation of fiber is not universal rather it is one of many approaches (Diez & Nguyen, 2003). Fiber can be advantageous for the nutritional management of obesity in dogs.

• Fiber is generally a dilution element and allows a reduction in the energy density of a food. A standard dry maintenance food has an energy concentration of 3500 -  4000 kcal per kg of DM, but several authors (Lewis, 1978; Hand, 1988) advocate a low energy concentration. It is however difficult to formulate a food with an energy concentration lower than 2800 kcal/kg of DM.
• Soluble fiber slows down gastric emptying and induces slower absorption of nutrients in dogs (Russel & Bass, 1985).
• Insoluble fiber acts as a bulking agent, increasing the volume of the food and accelerating dietary transit (Burrows et al., 1982; Fahey et al., 1990).
• Fiber leads to a feeling of satiation: a diet containing at least 20% total dietary fiber (Total Dietary Fiber (TDF); Prosky et al., 1994) reduces the voluntary energy intake in dogs (Jewell et al., 2000).

But fiber also presents some inconveniences, which vary according to the nature of the fiber and the rate of incorporation:

• Fiber increases the quantity of feces and the frequency of defecation (a general effect of dietary fiber)
• Fiber causes a reduction in the digestibility of certain nutrients like proteins and minerals, which demand their incorporation in greater quantities
• Fiber adversely affects palatability (Meyer et al., 1978), which can be easily corrected by the addition of palatability factors
• Fiber may lead to gastro-intestinal problems, such as flatulence and diarrhea.

Figure 7a. Crude cellulose does not predict nutritional value.

Dietary fibers, in purified form or in high-fiber food like vegetables or whole-grain cereals, have a universally acknowledged satietogenic effect in humans, but they may lead to gastro-intestinal problems, such as flatulence and diarrhea.

Fiber and Chemical Analysis

From a legal perspective, the fiber content shown on pet food labels is crude cellulose (also known as crude fiber). This fiber content arises from an analytical method that does not fully reflect the actual fiber content of the food. A chemical analysis of the crude cellulose only measures part of the insoluble fiber, primarily the cellulose and some hemicelluloses (Figure 7a & Figure 7b). Yet other types of fiber are also used by the pet food industry including soluble fiber (psyllium, guar gum), and mixed fiber (mixtures of soluble and insoluble fibers).

The preferred method for measuring any dietary fiber (soluble and insoluble) is to measure the enzymes in the total dietary fiber. This is the only way to acquire significant nutritional information. The difference between crude fiber and total dietary fiber is much greater than in food containing more mixed fiber or soluble fiber content. Table 12 for example shows that in the case of cereals, the ratio of the two values is 1 to 4. At the extreme, a food containing significant quantities of soluble (non-cellulose) fiber will have negligible crude cellulose content.

Figure 7b. Presentation of the various dietary fiber dosing methods in relation to the chemical composition: application to beet pulp.  

Fiber and Satiety

In obese humans undergoing low-calorie diets the ingestion of a daily supplement of insoluble fiber (Ryttig et al., 1989; Astrup et al., 1990), soluble fiber (Krotkiewski, 1984; Di Lorenzo et al., 1988) or mixed fiber (Burley et al., 1993) induces better satiety or reduces the feeling of hunger.

It is much more difficult to evaluate the feeling of satiety in dogs than it is in humans. Various indirect methods are used to evaluate satiety, by measuring ingestion or the speed of gastric emptying. In the case of the latter, it is postulated that the distention of the stomach inhibits the physiological mechanisms leading to ingestion and as a consequence acts as a signal of satiety (Jewell et al., 1996, 2000). However, the methodology for measuring gastric emptying in dogs has not been widely standardized. The repeated measurements in the hours following the meal necessitate manipulation of the animal that may slow down gastric emptying.

Butterwick et al. (1994) reported that the addition of insoluble fiber in moderate concentrations did not have any affect on ingestion in dogs. A group of dogs presenting 15% overweight were given a food rich in various types of dietary fiber (from 6.6% TDF for the control group to 15.6% TDF of DM). The quantities of food were calculated to cover 40% of the energy requirements for maintaining optimal weight, which corresponds to severe energy restriction. Three hours after the main meal, a highly palatable second meal (wet food) was made available to the animals for 15 minutes; consumption was then measured. The trial was conducted twice in a 12-day period. The quantities consumed during the second meal were comparable for the different groups (Butterwick et al., 1994). It is nevertheless difficult to draw any conclusion from these results as the control diet contained 6.7% TDF and the effect of the severe energy restriction had to dominate with respect to the dietary fiber. Lastly, it must be noted that most of the dogs are unable to control their consumption when they are given a highly palatable food.

Fiber and its Effect on Weight and Body Composition

Energy restriction associated with the provision of a high-fiber, low-fat diet (23% and 9% DM respectively) leads to a greater reduction in body fat mass and blood cholesterol concentrations, in comparison to a high-fat, low-fiber diet (Wolfsheimer et al., 1994a). The reduction in body weight and blood pressure are also greater in the case of the former, although the differences are not significant (Borne et al., 1996). The two diets provide 35% of metabolizable energy in the form of protein, which is around 10% higher than a maintenance diet. The use of DEXA has made it possible to collect evidence of modifications in body composition following low-calorie diets, although the weight losses are statistically comparable. Nevertheless, conclusions should be carefully considered because the effects of the two parameters (fat content and fiber content) are confounding in this study. Furthermore, low-fat diets that are not supplemented with fiber produce the same effects in rats (Boozer et al., 1993).

In humans, spontaneous loss of body weight (Krotkiewski, 1984) and body fat (Raben et al., 1995) has also been reported following the ingestion of soluble or insoluble fiber in obese and non-obese patients. Furthermore, the addition of a supplement of insoluble (Solum et al., 1987; Ryttig et al., 1989) or mixed fiber (Godi et al., 1992) produces a greater reduction in weight in obese patients subjected to moderate energy restriction (1200 kcal/day), compared with a control diet.

The results of the studies reported above suggest that dietary fiber plays a beneficial role in the weight loss of obese patients. The effects of fiber are summarized in Table 13a & Table 13b.

Carbohydrates

The content and quality of the digestible carbohydrates - primarily starch - of low-calorie diets has also been the subject of some studies. In human food, the concept of the glycemic index (GI) was developed by Jenkins et al. (1981) as a means of predicting the glycemic response following the ingestion of food containing established quantities of carbohydrates. The GI of a food is defined as the ratio (in %) of the glycemic response following the ingestion of a 50 g portion of digestible carbohydrates to the response after ingestion by the same individual of a 50 g portion of starch in the form of white bread.

The GI is a concept utilized in the dietetic treatment of diabetic patients and in some diets (including the Montignac diet) that confirms the utility of sources of non-refined cereals or dietary fiber (Wolever & Jenkins, 1986). The GI is controversial however, because individual responses can be variable and the development of glycemia after a complete meal is different from the changes induced by the absorption of a single type of carbohydrate (Jenkins et al., 1988). Nevertheless, it would appear that the consumption of non-refined cereals plays a part in the prevention of human obesity, especially by acting on the hormonal regulators of obesity (Koh-Banerjee & Rimm, 2003).

The application of this concept in diets for diabetic or obese dogs is fairly logical. The principle is to use sources of starch that stimulate the production of insulin only to a limited degree. This limits the storage of energy in the form of triglycerides in the adipocytes. The complete food that limits glucose production does not stimulate the production of insulin - a lipotrope hormone - as much. From a practical perspective, white rice is not recommended as a main cereal in low-calorie foods, whereas barley and corn constitute the best sources of energy (Sunvold & Bouchard,1998) (Figure 8).

Figure 8. Comparison of the postprandial secretion of insulin obtained with various sources of starch. (From Sunvold & Bouchard, 1998)

Minerals, Vitamins and Trace Elements

The mineral, vitamin and trace element concentrations of low-calorie foods must be higher than those in maintenance foods, similar to protein. Restricting energy intake and the quantities given must not lead to deficiencies of these essential nutrients.

Special and Nutraceutical Ingredients

Several special ingredients (food additives or other nutritional supplements) are added to low-calorie foods to induce certain benefits. They are principally various sources of dietary fiber, antioxidants, L-carnitine, chromium and even chondroprotective agents. At this time, the addition of chromium to foods is not permitted in Europe. A non-exhaustive list of these products and the benefits identified are presented in Table 14.

L-carnitine is an amino acid synthesized de novo in the liver and the kidney from lysine and methionine and in the presence of ascorbate. L-carnitine is an agent that facilitates the transportation of long-chain fatty acids in the mitochondria where they are subjected to b-oxidation (Figure 9). Adequate levels of L-carnitine are therefore needed in muscle to produce energy from fatty acids.

L-carnitine is not synthesized in muscle but provided by the blood following hepatic or renal synthesis or via the intestinal absorption of the L-carnitine present in food. The main dietary sources are red meat, fish and dairy products, whereas white meat is less rich in L-carnitine and vegetables do not contain any L-carnitine. L-carnitine is not considered to be an essential nutrient, because it is synthesized by the organism. L-carnitine deficiency is responsible for dilated cardiomyopathies in a small population of dogs. Several studies on monogastric animals have suggested that the provision in the diet of L-carnitine improves nitrogenous retention and modifies the body composition in favor of muscle mass. This effect has been shown in growing dogs (Gross & Zicker, 2000).

Because muscle mass requires more resting energy than fat mass, augmentation of muscle mass may prevent obesity. The incorporation of L-carnitine into low-calorie diets for obese dogs is recommended to modify body composition (Allen, 1998; Sunvold et al., 1998; Caroll & Côté, 2001). The addition of L-carnitine to a low-calorie diet increases the weight loss in obese dogs and stimulates the maintenance of muscle mass (Sunvold et al., 1998). In this trial, no significant differences were noted between the two supplemental levels (50 and 100 mg/kg of food).

Figure 9. Mode of action of L-carnitine.  

The incorporation of L-carnitine is recommended for obese dogs fed a low-calorie diet to prevent the rebound effect. In home-prepared rations the choice of ingredients naturally rich in L-carnitine is recommended. (© Faculty of Veterinary Medicine of Liège).

Conjugated fatty acids derived from conjugated linoleic acid (CLA) have been widely studied in animals due to their various beneficial properties, with effects on neoplasias, atherosclerosis, obesity, the immune function and diabetes mellitus. CLAs are naturally found in ingredients that come from animals, such as dairy products, meats and fats. They are synthesized in the rumen by certain microorganisms and by some animal enzymes. The two isomers identified as being biologically active are 9-cis, 11-trans and 10-trans, 12-cis (Figure 10). Some specific CLA isomers prevent the development of obesity in mice and pigs. Nevertheless, the properties of CLAs to modulate obesity in humans and monogastric animals remains a subject of controversy, as clinical trials have produced contradictory results (Azain, 2003). It has however been shown that the 10trans, 12-cis isomer prevents the accumulation of triglycerides in human pre-fat cell cultures. This antiadipogenic action is partly due to an effect on the regulation of the metabolism of glucose and fatty acids in the fat cells (Brown & McIntosh, 2003).

In humans, the effect found is a reduction of fat mass. The work also supports the fact that the CLAs do not help reduce the body weight of obese patients but do increase the lean mass at the expense of the fat mass (Kamphuis et al., 2003). The doses used in the clinical trials on humans were of the order of 1.4 - 6.8 g of CLA per day (Blankson et al., 2000; Kamphuis et al., 2003).

Figure 10. Comparative structure of conjugated linoleic acid and linoleic acid.

In dogs, the addition of CLA (0.6% DM) in a low-calorie high protein diet (55% DM) has helped limit the augmentation of the plasma nitrogen concentration typically observed when this type of diet is used (Bierer & Bui, 2003). A second study shows a positive effect of CLAs on body composition and the ingestion of food in dogs fed ad libitum. Lastly, an in vitro fermentation trial shows that CLAs are produced in very low quantities by the intestinal bacteria in dogs. The authors therefore recommend the addition of CLA to low calorie diets (Fukoda et al., 2002).

Garcinia Cambogia extract is used to limit lipogenesis in humans (Cha et al., 2003; Hayamizu et al., 2003). The active ingredients are hydroxycitrates or AHA (alpha hydroxycitric acid), commonly known as "fruit acids". The expected benefits include inhibition of hepatic lipogenesis and a reduction of energy ingestion (Westerterp-Plantenga & Kovacs, 2002). The mechanisms of action have not been clearly established.

Garcinia Cambodgia. The sole source of alpha hydroxycitric acid (AHA) in a concentrated form is found in certain plants, such as the fruit of Garcinia Cambogia, which comes from Southeast Asia.

Low-calorie Home-prepared Diets

Obese dogs can be fed home-prepared diets. However, the conditions described above must be respected. Lean ingredients should be selected (lean meat), high-fiber sources of starch (complete cereals), vegetables, dietary fiber supplements in purified form (bran, soy fiber) and the diet must be carefully formulated to ensure it is complete and balanced. Compared with a maintenance diet the protein-calorie ratio will be higher as will the micronutrient concentration and the dietary fiber percentage. Nevertheless, this last point may pose problems if the animal sorts and leaves the vegetables needed to provide fiber. This can be avoided by using complete starchy food (bread, rice or pasta). The intake of crude fiber of the ration may then be raised to 4 - 5% DM. By using dietary fiber supplements it is possible to increase the concentration to 7 - 10% DM.