Weight is Not a Good Indicator of Fitness

Ken Tudor, DVM
Updated: July 18, 2012
Published: February 09, 2012
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For years, preoccupation with achieving a certain weight has been the goal of weight loss programs. But weight has proven to be an inaccurate measure of fitness.

In humans, the Body Mass Index, or BMI, has replaced weight. The BMI compares weight to height. Tall people have more bone and muscle, which weighs more than fat, so they could be "overweight" but not fat. A short person weighing the human average of 150 pounds could be carrying excessive amounts of fat and still be "normal weight." BMI corrects for these differences.

"Ideal weight" in pets has similar problems. Breeding practices have led to complicated breed weights. Blood lines within breeds often have very different body types, with differences as great as 20 pounds, and gender differences can have the same or greater weight variations. Cross breeding of different body types, like Labradoodles and Puggles, really stretch any notion of an ideal weight. "Mutts" resulting from multi-breed mixes allow only a guess for ideal weight because the major breed may be unknown.

Why is this important?

Because feeding recommendations are based on weight. Every overestimate of ideal weight by one pound will result in overfeeding by 53 calories! So an "ideal weight" difference of 2-5 pounds in a small breed could mean overfeeding by 100-250 calories. For larger breeds the difference could mean overfeeding by 500-1000 calories. Little wonder that half of the pet population is overweight. This is probably a major cause of failure in weight loss programs, since choosing a generous "ideal weight" can overestimate the calories fed during the diet.

What is the alternative?

In pets, the Body Condition Score (BCS) has proven to be a superior method for assessing fitness. It is a visual system, so scales are unnecessary, and experiments have confirmed that this simple method compares with techniques that are considered to be the gold standard for measuring body fat. Veterinarians use two BCS systems: a 5-point and a 9-point.

How does BCS work?

A BCS requires looking at a pet from the side, and from above looking toward the head. From the side, the perfect pet has a tight "tummy tuck" toward the hips; the ribs are not distinctly visible but are easily felt. From above, the same pet should have a gentle hourglass shape from the chest to the hips. This perfect pet is given a score of 3 in the 5-point system, and a 4-5 in the 9-point system.

A slightly sagging belly with ribs that are covered by a slight excess of fat and a straighter profile from the top is a 3.5 in the 5-point; 6 in the 9-point.

Greater difficulty feeling the ribs, loss of tummy tuck, and a straight to slightly bulging profile from above rates a 4 in the 5-point; 7 in the 9-point.

Inability to feel the ribs, abdominal sag, and a bulging profile from above with fat deposits on the hips and at the base of the tail scores a 4.5 in the 5-point; 8 in the 9-point.

Massive fat deposit on the chest, shoulders and neck, distended abdomen, and an extreme bulging profile from above with excessive fat deposits on the hips and tail base ranks a 5 in the 5-point; 9 in the 9-point.

Conversely, pets with a BCS of 1-2 in the 5-point system or 1-3 in the 9-point system are considered too thin.

Pets should be fed enough to maintain a BCS of 3 in the 5-point system, and 4 in the 9-point system. Dieters should have the same target BSC scores. A pet’s weight at a score of 3 or 4 is its individual healthy and ideal weight.

What is your pet’s BCS?

Dr. Ken Tudor

Images: HelleM / via Shutterstock; Body Condition Score Chart via Pet Food Direct

For downloadable BCS charts for dogs, cats, and rabbits, visit PFMA UK