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The answer is simple. Even with weight control foods, pets are still eating more calories per day than their bodies need. Understanding why that is true is not so simple. I hope this post helps.

In every fat pet is a thin one. Releasing the thin pet requires feeding fewer calories than necessary for its ideal thin weight, not its present weight. Maintaining fat requires very few calories, and substituting “low calorie” food for regular food may still provide adequate calories for maintaining the present amount of fat.

The feeding instructions on the labels of these foods are generally too generous for significant weight loss. Weight loss requires calorie restriction greater than most owners realize, and is far greater than that found in weight control pet food. In fact a recent study of 95 brands of weight control diets for cats and dogs found that the calories varied as much as 200 calories in a cup of dry food and almost 100 calories per can of wet food. Changing weight control brands and feeding the same amount as the old brand could result in weight gain, not loss!

Serious weight loss requires a serious program under veterinary supervision. Blood testing prior to dieting will ensure that a pet’s liver and kidneys are healthy enough for the changes in metabolism that occur during dieting. Blood tests can also reveal conditions that cause weight gain, like hypothyroidism (under active thyroid gland), and make weight loss difficult if untreated. The veterinarian can also determine the safest level of calorie restriction necessary to promote weight loss for the individual patient. And most importantly, the veterinary staff can provide regular monitoring of weight loss progress in order to make necessary adjustments in calorie restriction during the dieting process.

Anyone who has dieted knows that weight loss is not constant during the course of a diet. Pets are no different. Weight plateaus with little change are common, as is temporary slight weight regain. The reason for this is the adjustments in metabolism that the body undergoes during calorie restriction. Both the resting metabolic rate and the non-resting metabolic rate slow down during dieting. This means the number of calories necessary to support bodily functions when perfectly still (resting metabolic rate) is less than before dieting. The number of calories required for muscles to perform their activities (non-resting metabolic rate) also decreases. Weight loss plateaus. Further weight loss requires fewer calories or increased exercise.

Losing fat during a diet also requires breaking down proteins for energy and replacing sugar. The body stores protein in muscles; muscles are the primary users of energy or calories. As the dieting body converts muscle tissue for energy it decreases calorie output. The decrease in calorie output by muscles contributes to the slowing of weight loss and the plateaus mentioned above.

These and other metabolic changes during dieting are the reasons why weight loss programs need to be closely supervised. Adjustments in calorie restriction during a diet are normal, not exceptional. Just feeding a set number of calories for a certain period of time is unlikely to result in successful weight loss. That is why there are so many fat pets eating weight control food. Owners seeking to help their pets lose weight need help from their veterinarian before simply purchasing “low calorie” food from the pet store and going it alone.

Dr. Ken Tudor

Image: Ruger by hoveringdog / via Flickr

Comments  10

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  • Vet Appointment
    02/23/2012 07:18am

    I agree that it's important to have the veterinarian monitor a weight loss program and especially important to assure the critter is in good health prior to a diet.

    Just like with humans, a healthy diet plan won't produce quick results.

  • Atwater Modified formula?
    02/23/2012 03:01pm

    Thank you, Dr. Tudor.

    Per this article on Truth About Pet Food:
    http://www.truthaboutpetfood.com/articles/pet-food-calorie-mis-information.html

    ... should calories be calculated based on the Atwater formula, or the Modified Atwater formula?

    Or, perhaps you don't agree with this article at all?

    I would appreciate your comments about Atwater vs. Modified Atwater.

  • 02/23/2012 03:06pm

    Hi again ... I should have included that I'm referring to the calorie calcs of the food being fed (for commercial foods), rather than calculating calories that the dog needs.

  • 3Dogs!Cat
    02/23/2012 09:55pm

    You ask a great question. When I first started studying dog food labels and comparing them to Atwater calculations based on protein, fat and carb content, the calculations never jibbed with the manufacturer calorie content. The label calorie content was always more than the calculations. I corresponded with many companies and none of the nutrition specialist could tell me why the difference. I suspect the difference may be in the calories absorbed from fiber conversion to fatty acids in the colon or the large margin of error in the guaranteed content label. I am still investigating. I basically take the label or web calorie counts at face value because they are higher than calculated so I am erring on the conservative side. With my homemade diets, I use the USDA database that uses the modified Atwater. Most nutritional data uses the modified and I am comfortable with that but I always choose the lowest calorie count in any given range for my weight loss patients. Does this help or answer your question?
    Thanks again for the question and I hope we didn't lose too many of our other readers in the discussion.
    Dr. T

  • 02/24/2012 05:03pm

    Thank you for your reply, Dr. Tudor.

    In the article I referenced it states that the Atwater Formula is what the food industry uses, and that the Modified Atwater is what AAFCO uses.

    You have stated that the food industry uses Modified Atwater, which is different than the other article.

    It leaves me a little bit confused, still.

    At this FDA pet nutrition link, below each chart, it is stated that Modified Atwater was used.
    http://www.fda.gov/animalveterinary/resourcesforyou/ucm047120.htm

    My only desire is to know how many calories I am feeding my dog, whom I am trying to help lose excess weight.

    I truly appreciate that you are one of the veterinary bloggers who are providing such wonderful information to readers. Pet obesity is a terrible problem, and I appreciate that you are on the blogging team here, and I look forward to your future blog entries!

  • 3Dogs!Cat
    02/24/2012 10:19pm

    Thanks for the clarification. Don't worry about Atwater or Modified Atwater. You don't need it. The article you reference is exactly what I mentioned in my first response. I had the same problem with my calculations and talks with representatives from the companies. But the author is creating a crisis where none exists. There are other factors for the difference in calorie counts that I also mentioned. Using guaranteed analysis and Atwater or modified Atwater calculations are full of pit falls because of the margin of error allowed by AAFCO. For dieting, take the company estimates as a starting point because they are required to use more accurate estimates than the simplistic calculations of the author of your article. All you need to know for calculating calorie requirements is the stated caloric density of the food you wish to use, i.e. kcal/cup or kcal/kg. But DO NOT use regular food for a weight loss program. As you will read in upcoming blogs, a calorie restricted diet has special needs. Because the pet is getting less energy the food must be fortified in protein, vitamins and minerals. We must feed less energy than needed for the ideal weight but meet the nutrient needs of the present weight. Only special weight loss diets will meet those requirements. Also make sure the calorie restriction is under veterinary supervision and all necessary pre-dieting labwork has been completed. You and your vet can then decide on the food to be used and calculate the quantity to feed based on the caloric content of the food and the daily caloric allotment.
    Dr. T

  • 02/25/2012 08:36am

    Ahhhh! Thank you so much for the additional information! I get it!

    I'm looking forward to future entries! I may also call your office to inquire if you accept long-distance patients (I am in the Seattle, WA area)!



  • overweight dogs
    02/27/2012 09:27am

    Hi I just wanted to mention that we have an "overweight" Puggle. Or so the vet says. Yes he is large for his breed at 55 lbs. But I was there the day he was born. He was the first to come out of his momma that fine day whom we also own as well as the daddy. And he was huge then. On the first day of life he was the fattest puppy in the litter. From day one we have called him Tubby, Mr Tubba Pants to be exact, recently the vet told us to stop feeding him so much. Well with three dogs in the house that is rather difficult. We have stopped filling the bowl twice a day now for 2 months. We only fill it once a day and they seem fine with it but not a pound lost on any of the dogs. Momma and Daddy both way about 25lbs each. We do not give them table scraps or snacks. So I have come to think some dogs are just made that way and will be bigger than some. I think we obsess to much on weght. Tubbs may be large but he is not in charge. He gets plenty of excercize too. So whats an owner to do. We just love him and he is a very important part of our family.

  • Russell Hoyt Sr.
    02/27/2012 11:18am

    I will warn you in advance that you will be unhappy with my response. With an obese prone pet in a multi-pet household, free feeding will not work. In addition you are "filling" the bowl. That is not precise enough for successful weight loss. Dogs are easily transitioned to scheduled feeding where the number of calories is carefully restricted for each animal. Vegetables and berries can be used as low calorie treats between meals. Owners always overestimate the amount the activity of their pets. Purchase a petometer and measure Tubby's time exercising and you will be shocked. A serious weight loss program must measure calories and time exercising. Until you are ready for such a program, Tubby will remain overweight. Fat is the largest endocrine gland (hormone producers) and overweight animals live in a constant state of inflammation 24/7/365 that will shorten their lives by two years. Show Tubby you really love him and work with your vet on a serious weight loss program. Sorry, in advance, if you find this response offensive.
    Dr. T

  • 02/27/2012 05:29pm

    Bravo, Dr. Tudor.

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