Metabolizable energy: why can two dogs of the same size need very different portions?

Reading time: about 7 min

My two German Shepherds remind me every day that the “average dog” on the food bag does not live in our house. Faddy has a sturdy build, and I have tended to need to watch his portions. Oscar, by contrast, used to be rather lean, even when he still weighed over 40 kilograms. At certain times Ossu ate as much as about 200 grams more per day than Faddy. If you rely only on weight and the feeding guide, that seems odd. Once you consider energy and body condition, it makes much more sense.

I think dog food manufacturers should state metabolizable energy as clearly as possible. Without that figure, it is very difficult for an owner to appreciate how much two seemingly similar foods can differ. But one distinction needs to be made from the outset: the metabolizable energy of a food and a dog’s daily energy requirement are not the same figure.

What does metabolizable energy actually tell us?

Metabolizable energy, or ME, describes the usable energy the body obtains from food after energy lost in faeces, urine and gases has been deducted. On dog food labels it may be expressed in kcal/kg or kcal/100 g. It does not yet tell you how many grams your dog needs to eat. It tells you how energy-dense that particular food is.

A dog’s daily energy requirement, or MER, is a different quantity. To estimate it, we first calculate resting energy requirement (RER), then adjust for factors including age, activity, reproductive status and health. A formula is a starting point, not a diagnosis or an automatic instruction for portion size.

First RER, then the individual dog’s needs

In veterinary medicine, an initial estimate of resting energy requirement is obtained using RER = 70 × (body weight in kilograms)^0.75. For example, a 40 kg dog’s RER is approximately 1,113 kcal per day. That does not mean a 40-kilogram dog should receive only 1,113 kcal. This figure covers the energy needed for basic bodily functions at rest.

An initial daily estimate for a neutered adult dog might, for example, be 1.4–1.6 times RER, or 1.6–1.8 times RER for an intact dog. Some inactive dogs or those prone to weight gain need less; working and sporting dogs need more. Requirements can differ surprisingly widely at the same body weight. Even veterinary guidelines emphasise adjusting multipliers according to the dog’s weight and body condition.

If we use a multiplier of 1.6 for a 40 kg dog as an example, we obtain 1,113 × 1.6 = approximately 1,781 kcal per day. A multiplier of 1.8 gives approximately 2,003 kcal. Both are mathematically valid starting estimates, but neither necessarily represents your own dog’s actual requirement.

How do you convert kilocalories into grams?

Suppose your dog currently needs an estimated 1,800 kcal per day and the metabolizable energy of its dry food is 3,600 kcal/kg. That is 3.6 kcal per gram. The initial daily portion would be 1,800 ÷ 3.6 = 500 grams. If another food contains 4,000 kcal/kg, the same 1,800 kcal would be supplied by about 450 grams. The bag may weigh the same, but the amount in the bowl is different.

More importantly, if Faddy and Oscar were eating foods of equivalent energy density and Ossu ate 200 grams more, that would correspond to an extra 720 kilocalories in the 3,600 kcal/kg example. I am not claiming that this was precisely how much more he needed every day. It shows why “they are both German Shepherds” is not an adequate way to calculate portions.

Is a 46 kg German Shepherd automatically overweight?

At one point Faddy weighed about 46 kg. When he lost four kilograms during leptospirosis, he already looked thin to me. Oscar weighed about 43 kg at the time, yet looked and felt much leaner. That quickly taught me that even within the same breed, ideal weight cannot be decided solely by the number in the breed standard.

Assessing body condition involves looking at and feeling the ribs, waist and abdominal tuck. Muscle mass also needs to be assessed, because a normal weight can conceal muscle loss. This is especially important in senior dogs and those with chronic illnesses. If a dog suddenly becomes thinner, “a fast metabolism” is not automatically the explanation; disease, food digestibility and actual energy intake may need investigating.

Small and large dogs do not follow one percentage rule

Small dogs usually need more energy per kilogram of body weight than large dogs. One reason is the nonlinear relationship between body size and metabolism, which the exponent 0.75 in the RER formula already takes into account. This does not mean that every small dog automatically needs a more energy-dense food or that every large dog has a slow metabolism.

A small dog’s limited stomach capacity, activity, appetite and health may make an energy-dense portion practical. Another small dog may instead need calorie control. The same applies to large breeds: a working German Shepherd and an inactive senior do not need the same portion simply because both weigh 40 kilograms.

When does age change energy requirements?

Puppies use energy for growth and development, so higher multipliers are often used. An older dog’s energy requirement may decrease as activity and muscle mass decline, but this is not automatic for every senior. If an older dog develops pain or osteoarthritis, it may move less while also losing muscle. Simply reducing calories is not enough: nutritional completeness, adequate protein and the most suitable activity possible also need to be maintained.

For weight loss, weight gain, growth, pregnancy or illness, the usual adult-dog multiplier must be used cautiously. For example, AAHA guidelines give an initial weight-loss factor of approximately 1.0 × RER calculated from ideal body weight, but this does not replace an individual plan. Rapid weight loss and muscle loss are not a good outcome simply because the number on the scales falls.

What about food quality and ingredients?

Kcal/kg is an essential figure, but it does not describe the entire quality of a food. Two foods can provide the same energy yet differ considerably in protein sources, fatty acids, vitamins, minerals, digestibility and ingredients. A familiar brand, the word “premium” or a high price alone does not establish that the formulation is suitable. Nor does a lower price automatically indicate a poor product. I want to see both the recipe and data supporting its nutritional value.

A suitable food must supply the nutrients required for the dog’s life stage and actually be digestible and well tolerated by that dog. If the dog eats the recommended portion but loses weight, its stools change or its coat becomes dull, that is a reason to reassess the food and the dog’s health, not to keep adding grams indefinitely.

The bag gives you a starting point; the dog has the final say

I like calculations because they help prevent some substantial mistakes. But I do not trust a formula more than my eyes and hands. Faddy and Oscar have taught me that choosing a portion means bringing together three things: the food’s energy content, the dog’s actual activity and its body condition.

To judge whether a portion is appropriate, do not compare your dog only with the chart on the bag. Measure the same food for a few weeks, monitor weight and muscle, and check whether the trend is moving in a suitable direction for your dog. That is much more meaningful than arguing over whether it “should” eat 350 or 450 grams.

Sources

AAHA (2021). Energy Requirement Calculations, Nutrition and Weight Management Guidelines for Dogs and Cats.

Merck Veterinary Manual. Nutritional Requirements of Small Animals.

AAHA (2021). Weight Reduction in the Obese Pet.

FEDIAF (2025). Nutritional Guidelines for Complete and Complementary Pet Food.