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The necessary numbers in nutrition – how to implement them for weight management

There are many tools available to help you adequately assess the nutritional needs of your patient

Companion animal obesity is on the rise (PDSA, 2019). There are a huge number of pet foods on the market, all of which make various claims – including the ever popular “this is the best you can give to your pet”. Even as a veterinary professional, I find the plethora of foods available mind boggling, so one can only imagine how confusing this is for an owner.

The aim of this article is to help provide tools that can be used to identify what a pet food label means, to look at the various maths around weight loss calculations and to think on how we can use this in our day-to-day weight clinics, including the consistent use of body condition scoring (BCS), muscle condition scoring (MCS) and calculating the kcals in foods that are fed. We will examine how we can incorporate the management of food (therefore calorie) intake with some changes to lifestyle and feeding behaviours, to reflect the more natural feeding habits of our pets and how this can assist in a weight loss programme. I will refer predominantly to the weight management calculations of our canine companions; whilst principles from this can be used for all species, the dietary and behavioural feeding requirements differ hugely between species and need exploring on an individual basis.

Flexibility is key to assist owners in identifying a good diet. The European Pet Food Industry (FEDIAF) and the Pet Food Manufacturers Association (PFMA), the representative body in the UK, provide guidelines for the regulation of pet foods, including tools to help you understand labels. WSAVA also has a collection of nutritional toolkits that provide guidance on interpreting pet food labels. There are two important factors to focus on. First, whether a diet of choice is complete or complementary. Complete diets provide the nutrients required when following the feeding guidelines, whereas complementary foods do not and require feeding of a second source of nutrients to balance the diet. Another really important consideration is fixed versus non-fixed formulas (Case et al., 2011). Fixed formulas are often the premium diets that do not use a variable formula, which is dependent on the availability and market value of the ingredients involved. The consistency of fixed formula foods is advantageous for our calculations for weight loss and weight management. We also need to be aware that a protein source of animal origin in food is of a higher biological value (Case et al., 2011) than protein from a non-animal source.

Weight loss requires a calorie deficit (Pibot et al., 2008), but one balanced to ensure the pet is getting the right amount of all nutrients required. To create a calorie deficit, we need to know how many calories our pet is consuming. Most prescription diets provide their kcal/100g in the product books or online, though you can always call the manufacturer who can provide this information for you. However, if this information is not readily available you can use the modified Atwater calculation (Case et al., 2011). This calculation is useful for estimating the metabolisable energy contributed by carbohydrates, fats and protein in a diet. To carry out the calculation you need to identify the percentage of protein, fats and carbohydrates in the diet. You will find that protein and fats are listed as a percentage in the analytical constituents, but carbohydrates are not. Carbohydrate content has to be calculated. If we assume the analytical constituents add up to 100 percent, we can start by taking away the percentages that are provided to us: 100 percent – percent of protein – percent of fat – percent of fibre – percent of ash – percent of moisture = percent of carbohydrates. Once you have this value you can use your modified Atwater factors:

Percent of protein x 3.5 = A
Percent of carbohydrates x 3.5 = B
Percent of fats x 8.5 = C
A + B + C = kcal/100g of food

We now have an awareness of the kcal content of the chosen food, though be mindful that this is an estimate – it is an overestimation of a poor diet with less bioavailable nutrients and an underestimation of a premium diet (Case et al., 2011).

Now to calculate the kcal requirements of the pet in question. Our dog’s metabolic energy requirement (MER) ranges from 130 to 95kcal x BW(kg)0.75 and is responsible for maintaining weight. The higher value, 130kcal, is referring to a very active, working dog’s lifestyle and 95kcal is for the lifestyle of a more inactive dog (Freeman et al., 2011). For weight loss, I use resting energy requirement (RER), creating the calorie deficit needed for weight loss (Pibot et al., 2008) but providing the nutrient levels and kcal requirements at the lowest level. I calculate the RER on the actual weight, not the ideal weight, and recalculate this at every visit. The RER calculation for a dog is 70 x BW(kg)0.75, or 30 x BW(kg) + 70 if no scientific calculator is to hand. We expect a weight loss rate of 1 to 2 percent per week (Pibot et al., 2008), so I would always recommend initial weigh-ins every two weeks to ensure not too much weight is being lost and if it is, the diet can be adjusted accordingly.

I am a firm believer in the nine-point BCS as well as the animal’s weight. Whether you use the nine-point or five-point score for dogs and cats, you have to make sure everyone else in the practice is using the same scale. It’s also important to do an MCS, especially when looking at an animal with a BCS score that is under the five on the scale. This will indicate as to whether the dog is actually underweight or whether it is just exceptionally fit. An accurate BCS can assist us in determining how overweight a pet is and can give us an idea of the ideal weight the pet should be. A rough guide often used is that each score above 5 is equivalent to 10 percent overweight; 8 and 9 (30 percent and 40 percent respectively) are considered obese. We will still get pets who are more than 40 percent overweight in extreme circumstances, but the BCS gives us a starting point and an indication of where we want our target weight to be. It is also so important to teach the owner how to BCS their pet. I often start a consultation by firstly asking if they think their pet is overweight, and then by providing them with a nine-point BCS scale and asking them where they think their pet sits on this scale. This helps them adjust to the fact their pet is overweight and then aids compliance in the long run.

Once you have got your head around the maths and know how to do all of your calculations, history taking becomes important for any dietary adjustments. You need to understand the lifestyle and habits of a pet’s owner, so your suggestions will easily fit into their lives with only small adaptations. WSAVA provides a good example of a diet questionnaire, or you can create your own that’s more befitting of your individual style. Encourage owners to be open and honest so you can get the results you both want.

Weight loss can fail. You can calculate the perfect plan only to find that weight loss still does not occur – do not let that dampen your enthusiasm. Remember, you can refer back to a vet to check for any underlying conditions and check with owners that they are sticking to the plan. Equally, an owner might simply not return for a follow-up appointment or may decide that they do not want to carry on with the clinics; accept this as their choice. Some people will not be changed. This happens to all of us.

Finally, make sure everyone at your clinic is on board; questions about diet and feeding habits and the recording of BCS should become part of the normal clinical exam on all patients. Use the huge variety of tools available to help you navigate through the minefield of foods on the market and to adequately assess the nutritional needs of your patient.

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