In the second article of our hunger and appetite addition, our expert is Jon Watkins, a PhD student from the Centre of Nutrition, Exercise and Metabolism at the University of Bath. Jon is going to talk about what gut hormones that make us feel full and how we might be able to use this knowledge for managing those cravings!
Key Question: What gut hormones make me feel full and how can this link to health?
Gut hormones are released in response to eating
The food that we eat is sensed and absorbed into our circulation by cells in the gut. This is important for providing our body with energy and essential nutrients, but also for the release of a number of gut hormones. These hormones perform a huge number of actions in the body, but for this article I am going to talk about their role for obesity and type 2 diabetes. I want to add at this stage, that many factors alter how hungry we feel, including psychological and other biological factors. It’s a complex topic so it’s best to take this in snack-sized bites, and today I am going to focus on hormones released from the gut.
Insulin release
Two particular hormones that are released after eating, called GIP and GLP-1, are able to increase insulin release from the pancreas (if you missed our introduction to insulin, check out Article #7 ). This effect is hugely beneficial especially after a sugar rich meal, to prevent a large spike in blood sugar. Importantly, these hormones don’t increase insulin release when blood sugar levels are normal or low, which protects against the potentially dangerous effects of having low blood sugar levels (click here).
Stomach emptying
A number of hormones including GLP-1, and two others called PYY, and CCK are also able to slow the rate of food emptying from the stomach. This is great for a few reasons. Firstly, food is better absorbed when it moves slowly through the small intestine compared to when it moves quickly. Secondly, this slows the appearance of sugar in the blood and can prevent a sharp rise in blood sugar levels. Finally, the slower clearance of food through the stomach can be sensed by the brain and results in feelings of fullness.
Reducing food intake
As well as affecting our feelings of fullness through delaying stomach emptying, certain gut hormones including GLP-1 and PYY have a direct effect on the brain to promote the feeling of fullness. By doing this, these hormones may reduce overall day to day energy intake by prolonging the time between meals and through eating less at a given meal.
Driving greater hormone release
So these hormones released from the gut can have benefits for blood sugar control and also for our feelings of fullness! The logical next question, is can we increase this response?
As a general rule, the greater the meal size (i.e. in terms of the energy content) the greater the release of gut hormones. However, eating more to drive a greater hormone release might not always make sense for keeping our energy intake lower to help manage our weight. We know that certain foods, including those high in protein and fibre are more filling than others, which could be linked to them increasing gut hormone release (click here). So eating more protein and more fibre in your meals is more likely to make you feel full.
As researchers, we are still finding ways to target different food sensors and transporters that are key for gut hormone release. For example, at the University of Bath we are studying the effects of feeding calcium on top of protein on the release of gut hormones. This is based on previous results which found that eating protein and calcium together increased the release of gut hormone by 25 % compared to eating protein alone (click here). It’s an exciting area to be involved in!
The take home message: Gut hormones are released after eating and help us control our blood sugar levels and also help make us feel full. As scientists we try to find ways to maximise this response due to the likely importance for obesity and other diseases.
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