More than Just a Hunger Hormone: Ghrelin Could Help Prevent Diabetes

Ghrelin may be best known as the hunger hormone, but a new study by researchers in the Department of Human Health and Nutritional Sciences has found that it also plays a significant role in fat metabolism, a discovery that could pave the way to using the hormone to prevent or treat insulin resistance in people with diabetes.

“Ghrelin is not just a hunger hormone as we thought,” says Prof. David Dyck, who led the study. “It can affect the uptake and breakdown of fat in the skeletal muscle, which in turn mitigates some of the factors that contribute to insulin resistance.”

Ghrelin is secreted mainly by the stomach and was first recognized for its role in driving food intake. It gets released when the stomach is empty, sending a signal to the brain that tells us we are “hungry”; as the stomach stretches during eating, secretion of the hormone stops, and the hunger feeling goes away. 

In recent years, researchers have discovered that ghrelin also functions in energy metabolism; however, its specific impact on energy metabolism in skeletal muscle was unknown.  As their name suggests, skeletal muscles are those attached to the skeleton, and they are a major site for glucose and lipid breakdown in the body.  Thus, understanding the impact of ghrelin on this group of tissues is paramount to understanding the full role of ghrelin in the body’s overall energy balance.

Dyck’s lab had previously found that ghrelin does not affect glucose uptake in rat skeletal muscle. This time, they focused on the effect of ghrelin on fat metabolism (including how it influences the uptake, burning and storage of fat) in two different types of muscle fibres found in skeletal muscle, one that prefers to use fat as a source of energy, and one that prefers to use glucose.  

Once again using isolated muscles from rats, Dyck and his team found that treating skeletal muscles with ghrelin led to a 15-42% increase in the uptake and burning of fat by the muscle.  The researchers were particularly interested to note that the same effect was observed in both types of muscle fibres (glucose burning and fat burning).

Because excessive fat storage in muscle tissue is linked to insulin resistance (where the tissues do not respond to insulin and are unable to remove glucose from the bloodstream), the increased burning of fat suggests that ghrelin might offer a new means to treat or prevent diabetes.  

Although ghrelin’s best-known role is to drive food intake, Dyck notes that obese people do not produce significantly more ghrelin than people of average weight.  This means that administering additional ghrelin could offer a feasible way to protect against the insulin resistance.  However, Dyck also cautions that there are many hurdles to overcome before ghrelin could be used as a preventative therapy for diabetes.  This includes a need to know more about the other roles ghrelin plays in the body and the influence of other nutrients, hormones, and neural input.

“We conducted this experiment on isolated rat muscle, which is away from its natural environment. It would be interesting to look into ghrelin’s action in the presence of other hormones and secondary responses in the body,” says Dyck.

Dyck’s study of this multi-faceted wonder hormone is far from over. Skeletal muscles may be important in maintaining blood glucose levels after a meal, but the liver has a significant role to play in regulating blood glucose during fasting and sleeping. This is why Dyck plans to next investigate ghrelin’s effect on the liver.

With some experts now calling the diabetes the largest pandemic in human history, one thing is certain: the hunger hormone is well-worth studying as a potential tool in the fight against this widespread disease.

This study was funded by the Natural Sciences and Engineering Research Council.

Read the full study in the journal Physiological Reports

Read about other CBS Research Highlights.