Easy nutritional math? It was my understanding that there would be no math
Help conquer your fear of math with these simple and effective formulas that offer a more personalized approach to your patient's nutrition plan.
Are you intimidated by math? Do you find nutrition discussions difficult? During her talk at the Fetch dvm360® conference Robin Saar, RVT, VTS (Nutrition), puts these fears to rest by breaking down the math and presenting strategies for establishing client trust during nutrition discussions.
There are many aspects of veterinary nutrition that affect our patients throughout their lives, including weight loss, weight gain, gestation, lactation, neonates, and starvation cases. Saar presents approaches to all of these situations and breaks down the math into manageable pieces. Applying these formulas will allow you to provide more personalized care to your patients.
The most common math involved in veterinary nutrition is calculating energy requirements for various situations. The resting energy requirement (RER) is one of the basic calculations used in many applications. The RER is the requirement when the patient is awake but at rest. The formula to calculate RER is BW0.75 x 70, where BW is body weight in kilograms. Although there is a linear formula for RER (RER = 70 + (30 x BW)), Saar does not recommend its use, as it is not accurate for pets < 2 kg or > 30 kg. These days most smartphone calculators have the xy button (x to the power of y), where you enter the BW, push the xy button, and then enter 0.75, then multiply that result by 70.
To calculate the maintenance daily requirements (MER) we use the RER multiplied by a factor. In her Fetch presentation, Saar presents a detailed chart for the appropriate factors to use when calculating MER based on whether the patient’s activity is light/moderate/active, whether they are obese prone, whether the patient is intact or neutered, whether they need to lose weight or gain weight, and whether the patient is a dog or cat. From this chart, Saar highlights that cats tend to be slightly lower in their requirements than dogs and that neutered pets have lower energy requirements than intact pets.
When calculating the MER for weight loss, the factor is 1.0, effectively equivalent to the RER in these cases. Saar points out that for weight loss calculations, the BW used in the calculations should be the current weight, not the ideal or goal weight. She explains that this is partly because it is difficult to determine what the ideal body weight actually is, and partly because when using a regular diet for weight loss, cutting back calories will also result in reducing nutrients. Using the current weight avoids the risk of providing too few nutrients. This formula should be recalculated using updated weights frequently throughout the process of weight loss, so MER can be readjusted for the current weight. When calculating MER for weight gain, however, you should use the patient’s ideal weight (not current weight) so you can ensure that you are meeting adequate nutritional requirements.
In some cases, you may find that you need to calculate daily energy requirements (DER). DER is slightly different from MER. When using MER, the presumption is that energy requirements are similar every day. DER is used when there are specific short-term increases in requirements, such as in the case of sled dogs on long (100-mile) runs, gestation, or lactation, neonatal or pediatric animals, or certain disease states. Think of a DER as a special need for a lot of extra calories “on that day.” There are simple formulas for these DER calculating (if you are 16 weeks or younger, DER = RER x 3.0; if 17 weeks or older, DER = RER x 2.0); however, there are much more specific ways to calculate energy requirements for these situations that provide personalized care for each patient given their needs. Saar calls these “Robin’s Fun Equations.” They are a bit more complicated but can still be broken down into manageable steps, and provide a very tailored, personalized approach to caring for a patient. She presents these situations in detail in her Fetch seminar.
For example, when calculating the DER of a puppy, it is far more accurate to use the following equation: DER = 130 x BWC0.75 x 3.2 (2.71828-0.87(BWC/BWE) - 0.1) where BWC is current body weight, BWE is the expected adult body weight, and 2.71828 is a constant than to simply multiply RER by a generic factor. This more complicated formula considers that very young neonates have high energy requirements but lower body weight, and then as they grow their energy requirements increase, and then ultimately as they become closer to their adult weight, their energy requirements are lower. The formula for a kitten is very similar, but does have some minor differences (DER = 100 x BWC0.67 x 6.7 (2.71828-0.189(BWC/BWE) - 0.66).
By considering the current and expected weights, the feeding requirements increase at first with growth and weight gain, then decrease as you approach the expected adult weight.
Gestation is another life stage in which personalized nutrition can help your patients, although there is no need to increase DER until 5 weeks post-breeding. Again, there are minor differences between the formulas for dams (DER = 130 x BW0.75 + [26 x BW]) and queens (DER = 140 x BW0.67). For dams, this formula equates to an increase in MER by about 25% to 60%, and about 40% to 50% in queens. The goal during gestation is to maintain a normal body condition throughout pregnancy.
Lactation is another life stage that requires additional nutrition. Saar describes that lactation is one of the highest energy demands that an animal can have. The calculated DER for lactation is dependent on the number of puppies or kittens nursing. With 1 puppy the DER = 3.0 x RER; however, each additional puppy the factor of increase is an additional 0.5. For lactating queens, the DER is calculating per kitten by weekly intervals. For example, during weeks 1 to 2 of nursing, the DER for the queen is RER + 30% per kitten. In week 3 this factor is 45% per kitten, week 4 is 55% per kitten, week 5 is 65% per kitten, and week 6 is 90% per kitten.
Once these temporary phases are no longer active, energy requirements return to the typical MER formulation.
In terms of disease states, tracking weight loss and calculating the percent loss over time can be useful as an indicator of disease. An unexplained weight loss of 5% of more should result in further scrutiny as to any known factors or perhaps diagnostic tests to determine potential causes. An unexplained weight loss of greater than 10% is concerning. For smaller patients, a small change in body weight can be easily overlooked despite being a significant percentage change, so it is worth reweighing in a month to see if the trend is ongoing or perform further diagnostic testing to evaluate potential causes.
Other disease states that require tailored nutritional plans include patients at a risk for refeeding syndrome. An example of this would be a pet who was lost and then found a week or two later, thin and dehydrated. Blood work at first may appear normal. But if you offer food after a period of starvation, the body’s compensatory physiological processes that allow you to survive starvation will respond poorly to the abundance of food, and a day or two later result in electrolyte derangement and clinical signs. Refeeding, after these compensatory processes have been established and ongoing, acts as a trigger for cells to reuptake these electrolytes and glucose that previously had been shifted to the vasculature, and then blood concentrations of these substances get depleted. Although this sounds fairly complex, it is easy to combat these processes with a strict feeding plan. Saar presents a nutritional plan that is successful not only for refeeding after starvation, but also for diarrhea, diet changes, and other similar situations.
After calculating all these detailed energy requirements for specific patients in very specific situations, we still need to know what amount of food we feed. This can be calculated on a volume basis by using the kcal/cup data from each food, or by weight using the kcal/kg data. For foods where the amount of kcal/cup is not available, Saar shows us how to calculate this by using the metabolizable energy from the ingredients. NFE (nitrogen-free extracts) are carbohydrates. Proteins have nitrogen, so nitrogen-free extracts are carbohydrates. NFE = 100% - % crude protein - % crude fat - % crude fiber - % moisture - % ash. Note that ash is not typically listed but is 2.5% for canned diets and 8% for kibble. Metabolizable energy (ME) = 10([8.5 kcal/g x % crude fat] + [3.5 kcal/g x % crude protein] + [3.5 kcal/g x % crude NFE]). Adding these components gives kcal per kilogram of food. From here owners could then weigh the amount of food given instead of measuring it.
All of these methods of calculating energy requirements are really interesting nutritionally, and it is great to create such tailored plans for our patients, but how do we encourage owners to follow through? Saar presents several strategies for building trust and compliance:
- Develop trust. Why do some owners trust a 16-year-old pet store employee more than their veterinarian with years of training and a degree behind them? We need to build trust, and Saar reminds us that one of the best ways to develop trust is to share stories. Share client stories related to the recommendations you are making. Talk about other peoples’ experiences so they know there were others who did well and had good experiences on the diet you recommend. Then transfer that trust and information seamlessly to the rest of the team. Once you have your discussion and make your recommendation, communicate with the next person in line (the technician, the receptionist checking them out, etc). Clients want to see that we are all a team and organized, and not failing to share info or providing different opinions.
- Understand and listen to our clients. Sure, we know medicine and clients should know that, but in this day and age, they also hear all sorts of extraneous information. It helps to be sure to listen to what owners want. If they talk about kibble vs canned food, be sure to listen. If they talk about needing the convenience of getting food at the grocery store or having difficulty driving to the pet store across town, be sure to listen to these things. Do they talk about preferring homemade or fresh foods vs others? Pay attention to these details and adapt your conversation and recommendations to their needs.
- Give 1 clear recommendation. Saar realizes that we may have several options, but by already listening to owners you should have a clear recommendation that suits their needs and preferences. And reiterate this out loud so they hear it: “I have thought about your pet’s needs and the information you told me, and here is what I recommend.”
- Treat it like a prescription. “This will improve your pet’s health, so this is what we recommend.”
- Be open to offer another recommendation depending on the client’s needs in case there are other factors that affect your recommendation.
Packer is an associate professor of neurology/neurosurgery at Colorado State University College of Veterinary Medicine and Biomedical Sciences in Fort Collins and is board certified in neurology by the American College of Veterinary Internal Medicine. She is active in clinical and didactic training of veterinary students and residents and has developed a comparative neuro-oncology research program at Colorado State University.