Why protein makes you feel full faster

Sara Suchy Jul 12th, 2012 (updated Apr 18th, 2016)
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High protein meals seem to fill people up faster. Now we know why.

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Feeling full, but why?
Feeling full, but why?

Scientists have long known that meals high in protein seem to make people feel full faster, but until now they have never been able to pin down exactly why. New research published in the journal Cell seems to have cracked the code.  But first, it’s probably helpful to understand how your body tells you it’s full. 

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All about communication
All about communication

The food you eat is modulated through mu-opioid receptors (MORs) on nerves found in the walls of the portal vein – a major blood vessel that drains blood from the gut. Food modulation is simply the process by which your body communicates to your brain that you have just eaten something.  How food is modulated will dictate how full a specific food makes you feel. 

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How you ‘feel full’
How you ‘feel full’

When stimulated, these MORs in the portal vein enhance food intake by telling the brain to eat more. When the MORs are blocked or suppressed, the brain is triggered to limit food consumption; resulting in that ‘full feeling’ after big meals.

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It’s in the proteins
It’s in the proteins

What scientists found in the Cell study is that the products of digested protein – peptides – can actually block the MORs, which, as we noted, curbs the appetite. Specifically, these protein-created peptides send signals to the brain that are transmitted back to the gut.  The gut is then stimulated to release glucose, which suppresses the desire to eat. 

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Proven in mice
Proven in mice

To tease out exactly what causes the protein-induced ‘full-feeling’, scientists used mice that were genetically engineered to lack the MORs. When these mice were fed high-protein foods, the peptides did not stimulate the normal release of glucose that would happen in mice with MORs, nor did the genetically altered mice show signs of being full. This pointed to the MOR response as the key in determining the body’s satiated, or “full”, feeling. 

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What you can do
What you can do

MORs are also present in the neurons lining the walls of the portal veins in humans, so high protein foods will make you feel full. To take advantage of your body’s food modulation response to proteins, make protein a part of every meal.  This can be done by adding lean meat, nuts or beans. Snacks that are high in protein such as almonds or peanut butter will also trigger the full feeling. 

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Slow down
Slow down

Finally, it also helps to enjoy your meals and snacks slowly. Food modulation takes time so there is a natural lag between the moment you start eating and the moment your brain begins to sense that it is full.  Eating slowly will help you avoid overeating.