Author Topic: Dry weight - comparing foods  (Read 5101 times)

Dottie

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Dry weight - comparing foods
« on: Oct 09, 2014, 14:56 »
We are currently having a discussion on a suitable dog food for pancreatitis - link.  This has led us into the area of calculating and comparing fat level in dry and wet food. I do not want to hijack that particular thread so I thought it might be useful to continue the discussion as a separate topic.

Dry matter basis is a measuring tool for the key constituents of dog food. On the All About Dog Food website, the dry matter measurements are given for protein, fat, fibre, carbohydrates and ash.  As I understand it these figures are reached after all the moisture is removed from the product. 
Here is a quote from David lifted from the aforementioned thread:
Quote
In order to compare fat contents in different types of foods (dry vs wet vs raw etc) you do indeed have to work out the dry weight value which can be a real headache. Fortunately, we've thought of that and every product on the AADF website has a dial for the dry weight fat level in the Nutrition section of the review page. No matter what type of food you're looking at, these dials can be directly compared.

You can also go to the Dog Food Directory and select the exact dry level fat levels you are looking for in the panel on the left under 'Nutrient levels'. Again, since these are dry-weight, they work for all foods so no maths is required on your part.
* It is worth noting that we are talking about protein and other constituents in this thread, not just fat.

Manufacturers will give the typical analysis of their food which is different to the dry matter but the dry matter figure comes into play if you want to compare perhaps a wet canned food with a kibble.  Most of us would struggle to do the necessary calculations but with the dry matter dials there is no need. I would imagine that the dry matter figures are particularly useful for those who have dogs with special dietary needs. 

I have struggled to get my head around this - it does seem complicated, especially as the food that I am giving to my dogs today (Turkey Nutriment) has a dry matter fat level of 28.9%.  I'm watching their weight so at first glance it is a bit alarming.  However, the guaranteed analysis is 9.6% and they have lost weight.

There is more about the subject here.  If I've got anything wrong I apologise but I am only just learning myself and look forward to understanding it a bit better so if anyone can help, it's over to you...........
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David

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Re: Dry matter - comparing foods
« Reply #1 on: Oct 13, 2014, 15:45 »
Hi Dottie and thanks for starting this thread as it is certainly a subject that causes a lot of confusion in dog owners. I will try to make it a bit clearer.

The first thing to point out with nutrient levels is that, if your dog is well, then you don't really need to worry about them.

If not, nutrient levels can be a very important part of choosing the right diet, but without converting the numbers on the pack to their 'dry weight' values, comparing different foods (or at least different types of foods) is almost impossible.

The difficulties arise from the water that is present in the food, usually listed as 'moisture'. Let's look at an example:

Food 1: Dry food. 8% moisture, 25% protein.
Food 2: Wet food. 70% moisture, 15% protein.


To the untrained eye, the wet food looks like it's quite a lot lower in protein than the dry but, in reality, it contains almost twice as much! Here's why:

The dry food is only 8% moisture. That means, in 100g of food, 8g is water. This leaves 92g of 'dry matter', 25g of which is protein. As a percentage that is 25 / 92 x 100 which comes to 27%. This is the 'dry matter protein' value.

The wet food, on the other hand, is 70% moisture meaning that 100g of food only contains 30g of dry matter. Of that 30g, 15g is protein. 15 / 30 x 100 = a whopping 50% dry matter protein.

If you are comparing two foods with different moisture levels, dry matter is the only way to be sure that you're doing it right.

As Dottie kindly points out, we have already done the maths on all of the foods listed on the AADF site but if you're struggling with the calculations for any other foods or if there's anything else I can help with, please feel free to post here.

Pegasus

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Re: Dry matter - comparing foods
« Reply #2 on: Oct 20, 2014, 13:31 »
On a separate line - I would like to see the calorific content labelled on dog foods, currently it is only the weight loss ones that label this, although all the N American ones seem to have the calorie content on the label.

Dottie

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Re: Dry matter - comparing foods
« Reply #3 on: Oct 20, 2014, 14:50 »
Good point. Very few of the light versions have a calorie count. I was told that it is difficult to judge the calorie requirements of dogs so maybe that is why.
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Dottie

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Re: Dry matter - comparing foods
« Reply #4 on: Oct 20, 2014, 21:18 »
I forgot to ask this in my previous post:  When assessing the nutrition  in different foods, should we be looking more to the dry weight rather than the percentages in the analysis? The reason I ask is that last year a few of us started to feed Naturediet but almost all of us have had to stop because of weight gain in our Cairns.  I never could understand it because the analysis of protein and fat looked OK.  However, now that I am 'into' checking dry weight, I see that the protein is 35.7 and the fat 28.6 (both above average).  I understand that dry weight is useful for comparison, but is it also best to use that when making our choice of dog food? 
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David

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Re: Dry matter - comparing foods
« Reply #5 on: Oct 21, 2014, 10:47 »
I forgot to ask this in my previous post:  When assessing the nutrition  in different foods, should we be looking more to the dry weight rather than the percentages in the analysis? The reason I ask is that last year a few of us started to feed Naturediet but almost all of us have had to stop because of weight gain in our Cairns.  I never could understand it because the analysis of protein and fat looked OK.  However, now that I am 'into' checking dry weight, I see that the protein is 35.7 and the fat 28.6 (both above average).  I understand that dry weight is useful for comparison, but is it also best to use that when making our choice of dog food?

Since the moisture levels of different wet foods and even dry foods can can vary considerably, it is indeed best to assess nutrient levels on a  dry matter basis.

Dottie

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Re: Dry matter - comparing foods
« Reply #6 on: Oct 21, 2014, 12:31 »
Thank you - it is very helpful to know that. 
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Dottie

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Re: Dry weight - comparing foods
« Reply #7 on: Mar 20, 2017, 13:07 »
This is an online calculator for dry matter. It is provided by the Feline Nutrition Awareness Effort. It makes the job of calculating dry matter much easier.
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