The Labs have a problem.

Actually, some Labs have a problem.

It’s in their genes: In 2016, a group of researchers at the University of Cambridge discovered a genetic anomaly in a small group of overweight Labrador Retrievers (1). Specifically, the modification is a short deletion sequence in a gene called POMC. The presence of this deletion was found to be positively associated with an increased tendency towards both the tendency to overeat and an increase risk of obesity. Technically then, because the problem is a deletion issue, this is not so much an “obesity gene” as it is the lack of a body weight control gene. The former description is more catchy, but less accurate.

In the study, the researchers examined all possible genetic sequences that were candidates for being an “obesity gene.” The POMC deletion was found in 10 out of 15 overweight dogs and in only 2 our of 18 lean dogs.  Moreover, the investigators tested dogs from 39 other breeds and did not find the mutation. The only other breed that was found to carry the gene deletion sequence was the Flat Coated Retriever (FCR). Although FCRs are not typically associated with obesity, when the researchers tested 200 dogs, they found that, just as in Labradors, the mutant POMC gene was positively associated with higher body weight and greater food motivation.

Confirming evidence: As we always like to see with good science, these results were subsequently corroborated by a separate and unrelated team of researchers (2). Like the earlier work, they found the mutation only in Labs and not in other breeds. One difference was that their results suggested that the POMC deletion variant may be inherited as a simple recessive gene rather than as having an additive effect, as suggested by the researchers in the initial study.

So, some (not all) Labs carry a fat gene that makes them more susceptible to obese conditions and to being highly motivated to overeat. Interesting information and, probably quite helpful for those Lab owners who have a tough time keeping their happy and energetic (and food-loving) Labrador Retriever from packing on the pounds.

But wait – there’s more! This year, overweight Labrador Retrievers once again became the focus of study (3). However, in this study, rather than focusing on the presence of a gene mutation, these researchers were interested in studying the flexibility of fat versus lean Labs.

What is metabolic flexibility? Metabolic flexibility refers to the ability of cells in the body (their mitochondria, actually) to shift back and forth between using glucose and fatty acids for fuel. In healthy animals, including those of the human variety, this shift occurs after eating and is orchestrated in part by the response to the hormone insulin. Overweight conditions are associated with a reduced ability to make this shift – hence – “metabolic inflexibility.” In humans, this change is associated with several of the pathological changes of overweight conditions, such as abnormal blood lipid (fat) profiles, insulin-resistance, and diabetes.

Carnitine may also be involved. Carnitine is a nutrient that can be obtained through the diet, but is also produced by the body. It is necessary for the transport of long-chain fatty acids into a cell’s mitochondria so that they can be used as an energy source. Because of its role in fat metabolism, it has been theorized that carnitine status may be involved both in the metabolic changes associated with obesity and more specifically, with metabolic inflexibility.

So: “What about overweight Labs? Do they show metabolic inflexibility and/or reduced carnitine levels? If so, are these changes related to the “fat gene” found in this breed?

A recently published study examines this question (3):

The Study: The researchers recruited 28 adult Labrador Retrievers living in homes. Of the 28 dogs, 16 dogs were overweight and 12 dogs were lean. Following an overnight fast, the dogs were fed a  high-fat meal that was composed of 50 percent of their estimated daily caloric requirement. Blood samples were taken before feeding (fasted) and hourly for a 4-hour period after the meal. Results: A group of several carnitine and phospholipid (fat) blood metabolites were measured. Fasting and postprandial measures of carnitine and acetylcarnitine were significantly lower in the overweight dogs when compared with lean dogs. Additionally, acetylcarnitine levels in lean dogs decreased in the first hour following consumption of a meal but this change was not observed in the overweight dogs. In those dogs, acetylcarnitine levels remained stable both before and after eating.

Conclusions: These results suggest that the overweight Labs in this study were experiencing a form of “metabolic inflexibility.” It was theorized that low carnitine status was slowing fatty acid oxidation (use) following a meal. While the authors suggested that  the overweight dogs were experiencing carnitine insufficiency, the design of the study did not allow determination of whether the low carnitine levels were a cause versus a consequence of overweight conditions. Regardless, these results do suggest a possible role of carnitine status in overweight conditions in dogs.

Take Away for Dog Folks: So, how does this information help the average dog and owner? First, it provides new information regarding metabolic changes that may be taking place in dogs who are overweight (Labs, anyway). These include changes in the dog’s ability to use fat as a fuel source and alterations in the body’s carnitine status.

Oddly, this new paper neither mentioned nor referenced the earlier work regarding identification of the POMC deletion and its connection to overweight conditions in Labrador Retrievers. My personal take-away from these two studies was to wonder if there exist differences in carnitine status and components of metabolic inflexibility between Labs who have the POMC deletion and those who do not. While the results of this new study are helpful in furthering our understanding of metabolic changes in overweight dogs, they also suggest a need to study possible connections with the POMC deletion sequence in the Labs who are unfortunate enough to be born without it.

Feed smart and exercise: The bottom line? Feed a high-quality food, provide your dog (all dogs, not just fat-prone Labs!) with plenty of enjoyable and stimulating exercise, and feed your dog a correct amount of food to achieve a lean and well-muscled body condition.

For those of you with a voracious Lab, remember, that part of his or her appetite could be in his genes……they may indeed be making him look fat.

Cited Studies:

1. Raffan E, Dennis RJ, O’Donovan, et al. A deletion in the canine POMC gene is associated with weight and appetite in obesity-prone Labrador Retriever dogs. Cell Metabolism 2016; 23:893-900.
2. Mankowska M, Krzeminska P, Graczyk M, Switonski M. Confirmation that a deletion in the POMC gene is associated with body weight of Labrador Retriever dogs. Research in Veterinary Science 2017; 112:116-118.
3. Soder J, Wernersson S, Dicksved J, et al. Indication of metabolic inflexibility to food intake in spontaneously overweight Labrador Retriever dogs. BMC Veterinary Research 2019;15:96-107.

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