Fat: friend or foe? by Dr Mark Roberts PhD

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Dietary fat, not just regarding humans, but also dogs often conjures up images of sickness, obesity, and general lethargy, but are these views correct, or have they simply become ingrained in our heads, by clever marketing companies or other influencing parties? This article aims to look at the evidence and help you understand pet nutrition better.

Dr Mark Roberts

Hi there, my name is Dr Mark Roberts and I work as the Companion Animal Nutritional Scientist. I’ve been involved in companion animal nutrition for many years, both in the commercial sector and research. My PhD focused on the instinctive diet selection of dogs and the health benefits from consuming a diet rich in protein and fat. In addition to these studies, I’ve spent time conducting research in Alaska, examining the feeding habits of wild wolves, how this impact on markers of health, and
comparing this to domestic dogs, based on what they are fed. My goal, is to always help improve the health of dogs, by utilising my nutritional experience and research background, combined with robust science.

Fat serves numerous vital roles for a dog, including creating energy, helping with fat-soluble vitamin absorption, modulating inflammation, and promoting healthy growth.

How important is fat in a dog's diet?

Fat serves numerous vital roles for a dog, including creating energy, helping with fat-soluble vitamin absorption, modulating inflammation, and promoting healthy growth1. Beyond this, and the many more important functions fat has, nutritionally, although both protein and fat are deemed essential nutrients, carbohydrate is not required in a dog’s diet2, 3, 4.

In other words, fat is a lot more important than carbohydrates for dogs. This is an important point, because although our focus here is on dietary fat, it is impossible to disentangle the macronutrient from the others with which it interacts, in the presence, or not of carbohydrates.

Blood glucose control 

Having lower (without being hypoglycemic) and well-regulated blood glucose is much better for a dog, decreasing the risk of diabetes developing and issues such as urinary tract infections, enlargement of the liver and kidney disease5.

Any impact on blood glucose is commonly associated with the consumption of a carbohydrate source, however if a dog’s diet does not consist of carbohydrates, and is instead high in fat, then fat and protein serve as an alternative glucose source. This process is called gluconeogenesis, which when broken down in bits means gluco (glucose), neo (new) and genesis (creation).

With dietary fat, this involves a type of fat called triglycerides being taken apart, resulting in the release of fatty acids and glycerol6. Although both can serve as sources of energy, it’s glycerol, which contributes to glucose production in the liver. The liver is also the location where amino acids (which come from protein), more specifically alanine, glycine, and serine7 generate blood glucose after first being broken down by certain enzymes. In essence, using fat (and protein) as alternative sources of glucose in dogs, both results in lower, more stabilised blood glucose values, than dogs fed highly processed carbohydrate based diets7.

Energy

The best way to look at how fat is a great source of energy is to use a fuel tank analogy. If a dog is fed a high carbohydrate diet, then it’s primary source of fuel is carbohydrates. Using this macronutrient for energy involves it being broken down into glucose. From there, glucose is either used immediately or stored in the form of glycogen for later use, mostly in the muscle tissue and liver of the dog. The key issue from an energy perspective is that once the fuel tank (glycogen stores) get low, more carbohydrates are needed, otherwise the animal will fatigue.

In comparison, if a dog is on a high fat diet, low in carbohydrates, then it converts parts of fat and protein into glucose again for storage as glycogen (remember gluconeogenesis7). The main advantage this has over relying on carbohydrates for energy, is that fat is significantly more energy dense and plentiful in terms of bodyfat and depletes glycogen stores (the fuel tank) at a slower rate19, 20. However, using fat as the main source of energy has benefits beyond higher levels of fuel (glycogen). This involves a process called ketosis, whereby when fat is broken down for usage on a high fat, low carbohydrate diet, ketone bodies are produced from free fatty acids21. These ketone bodies are then able to provide energy at a more sustained level, without relying on the ups and downs typically associated with a high carbohydrate diet. Basically, meaning the issue of having to consume carbohydrates on an ongoing basis to reduce fatigue is negated.  

Pancreatitis

Pancreatitis is a common disorder in dogs, with the severity of the disease ranging from sub-clinical to fatal, and can be acute, relapsing, or chronic8. From a nutritional standpoint, a high fat diet has been linked with the increased risk of the condition in dogs9, 10, 11.

However, other studies have suggested that fat is not the key factor leading to the development of the disease 12. Due to these conflicting findings, and that in human research, diets high in fat and low in carbohydrate has been demonstrated to decrease fasting triglyceride levels 13, associated with the development of pancreatitis 14, I decided to investigate the subject. 

Over an eight week period, I fed two different groups of dogs a baseline extruded commercial diet, (with a high carbohydrate content) and then switched them to either a meat based diet also in high carbohydrates, or a meat based diet which had a neglectable carbohydrate content and was high in fat. Regarding the high fat diet fed group, I witnessed no increase in fasted and postprandial triglyceride concentrations or any other markers of pancreatitis 15.

This included pancreatic lipase, which in conjunction with triglycerides are main indicators of the disease. One really interesting finding from this study, was that the dogs fed the high fat diet, had significantly lower circulating fasted triglycerides compared to baseline measurements, when they had been fed the dry extruded commercial diet.

This result might seem strange, as it could be assumed that triglycerides ( a type of fat in blood) would increase if dogs are fed a high fat diet. However, because of a process referred to as carbohydrate-induced hypertriglyceridemia (HPTG) 16, carbohydrates are converted into fat, when excessive intake of carbohydrate occurs 17.

As a consequence of this, elevated triglycerides occur, the opposite to dogs fed high fat, low carbohydrate diets, whereby no synthesis of triglycerides happens with dietary fat used as the main energy source. Due to elevated triglycerides being associated with pancreatic disease and complications including seizures, ocular disease, and atherosclerosis 18, feeding a high fat, low carbohydrate diet to a dog, appears advantageous as a preventative measurement.

Obesity

Rates of obesity in dogs are rapidly increasing22, and although the finger of suspicion is often pointed at a high fat diet, is this correct? The first aspect to assume from this statement, is that the high energy a high fat diet has, is the fundamental factor in obesity.

However, as the NRC 2 and Waltham23 have feeding guidelines based on the energy density of a diet, this rationale is flawed if a high fat diet (or any other diet) is fed to the energy requirement of a dog. Feeding more than this will likely result in excessive weight gain, regardless of the macronutrient ratio of any diet.

In my own research, I found that after four weeks of dogs being allowed to eat as much as they want of a high fat diet, no significant bodyweight gain was observed, with body condition scores within the healthy range. This may be due to a high fat diet having a satiety effect, whereby the dogs felt full at a point similar to energy requirement. If this is correct, the potential exists, that dogs fed lower fat based diets might “beg’ for more food or treats from their owners24, increasing the potential for excessive energy intake and weight gain.

In Summary

This article has provided a snapshot into the role a fat based diet can have on a dog. We must remember that fat cannot be viewed in isolation. That is, if dietary fat content goes up, either protein or carbohydrates go down. Evidence clearly shows that a high fat, low carbohydrate diet results in lower, more stabilised blood glucose, both before and after a meal.

The common perception that a diet of this composition can increase the risk of pancreatitis is unwarranted, and indeed is more likely to reduce the likelihood of the disease developing. As an energy source, fat is plentiful and energy dense, having been demonstrated to outperform dogs lower in its dietary contribution. Finally, the risk of obesity, defies energy logic, that it, if energy requirements are met, no excessive bodyweight will ensue, regardless of a diet’s macronutrient composition.

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References

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