You are already full, why do you continue to show off desserts?

Have you ever had this experience: after a big meal, you feel like you can’t eat anymore, but when you see dessert, you can still eat it. Just like Crayon Shin-chan, you are already full, but why can you still “make room” for dessert?

Image source: Crayon Shin-chan

Part 1

Desserts attract you not only because they are delicious

When eating, we don’t cook or buy many kinds of food, usually focusing on two or three kinds of food. When we eat more of the same food, the pleasure we get from it will decrease. This is a phenomenon called sensory-specific satiety (SSS), which is a sensory pleasure phenomenon proposed by French physiologist Jacques Le Magnen in 1956. Usually, after you eat a certain amount of the same food, the satisfaction produced by this food will decrease, resulting in a sense of fullness, and the pleasure obtained from this food will also decrease.

For example, if you listen to a nice song and keep repeating it for a while, you will find that the song is not so attractive. When we eat, we think that the food on the table is delicious, but as time goes by, the brain will eventually get "bored" with the food and feel full . If you replace it with dessert at this time, since dessert is a new flavor in this meal, it will lead to a renewal of appetite, so that the stomach can still make room for dessert, even if you already felt full before.

A study published in Brain in 2001 further proved this phenomenon. Scientists recruited volunteers to participate in a chocolate-eating experiment and observed the volunteers' brain activity. After each piece of chocolate was eaten, the volunteers were asked to rate their happiness and whether they wanted to eat more. Although the volunteers ate the same kind of chocolate (the volunteers themselves were not told), their scores gradually decreased. By observing brain activity, scientists found that when they were more willing to eat chocolate at the beginning, the subcallosal area of ​​the brain, the caudal medial orbitofrontal cortex (like/reward), etc. were more active, but when they were full, the parahippocampal gyrus and the caudal lateral orbitofrontal cortex (disgust/punishment) were more active.

From left to right, the chocolate eating condition increases. Panel C shows a decrease in rCBF in the subcallosal region, thalamus, and midbrain. Panel D shows an increase in rCBF in the caudolateral orbitofrontal cortex.

Image source: Reference [2]

The researchers also tested different types of chocolate and found the same results, so even if your brain is less attracted to meals, your brain may respond differently to other foods, such as desserts.

Ratings of pleasure (dashed line) and solid line (motivation) when eating chocolate in different states. The more you eat, the lower your pleasure level is, and the less motivated you are to eat chocolate.

Image source: Reference [2]

Part 2

Sugar does not have a strong satiety effect

For those who love sweets but don’t want to gain weight, there is another frustrating thing: desserts (mainly sugar) do not make people feel full.

When we are hungry, the stomach releases a hormone called hunger hormone , which stimulates the nerves to transmit signals to the brain to tell it that it is time to eat. When eating, complex carbohydrates, proteins, and cellulose will cause the level of hunger hormone to drop significantly, thereby alleviating hunger and increasing satiety .

But we have to admit that eating sugar is like drinking water, the feeling of fullness will not last long. The ingested sugar will quickly break down into monosaccharides and enter the blood, and the blood sugar level will rise, which will produce a feeling of fullness. This is why eating a piece of candy can quickly relieve hypoglycemia. However, insulin will also quickly lower the blood sugar level and make the feeling of fullness disappear. This process is relatively fast, and the stomach that secretes hunger hormones is still empty, so there will still be a feeling of hunger.

How does the brain sense fullness?

Image source: Reference [3]

Of course, in the real world, eating desserts will still make you feel full. This is because although desserts are high in sugar, they also contain other nutrients, so it is not the same as eating only sugar. In addition, the pulling sensation in the stomach will also increase, and these stimuli will also tell the brain that you are full. But because its main ingredient is sugar, the feeling of fullness will be weaker.

In summary, after a full meal, desserts are attractive to the brain under the influence of the SSS mechanism, and there is no strong sense of fullness after eating desserts, so we can still continue to "show off" desserts after a full meal~

Part 3

Why does the brain respond this way?

Some people who want to lose weight may find this distressing, but from an evolutionary perspective, this is actually an advantage. This mechanism allows us to not be limited to a few types of food when eating, but to tend to choose a wider variety of food. This expands the nutritional range to a certain extent and achieves the goal of a balanced diet. Eating a wider variety of foods will ensure that our bodies will not lack certain key nutrients, and this brain response also gives us a better survival advantage.

We can also use this mechanism in reverse. For example, preschool children generally have a low intake of vegetables and fruits, which is generally called picky eating. Scientists have found that if vegetables and fruits are made into snack foods and the variety is expanded, the proportion of children eating a variety of vegetables and fruits will be significantly increased. This result shows that preschool children may quickly get "bored" with one type of food. In order to ensure that children have a balanced nutrition, they should prepare as many types of fruits and vegetables as possible.

The number of vegetables and fruits selected by children is higher in mixed categories than in single categories. The four columns on the left are vegetables, the first three are single vegetables, and the fourth is mixed vegetables; the four columns on the right are fruits, the first three are single fruits, and the fourth is mixed fruits. The black ones represent the number of children who selected vegetables or fruits.

Image source: Reference [4]

In short, although knowing why we can still eat dessert after a meal cannot help us restrain ourselves from eating dessert, we can use the brain's response mechanism to help ourselves eat better, such as adding more types of foods when cooking, including those that we don't usually like to eat.

References:

[1]Wilkinson LL, Brunstrom JM. Sensory specific satiety: More than 'just' habituation?. Appetite. 2016;103:221-228. doi:10.1016/j.appet.2016.04.019

[2]Small DM, Zatorre RJ, Dagher A, Evans AC, Jones-Gotman M. Changes in brain activity related to eating chocolate: from pleasure to aversion. Brain. 2001;124(Pt 9):1720-1733. doi:10.1093/brain/124.9.1720

[3] Williams EK, Chang RB, Strochlic DE, Umans BD, Lowell BB, Liberles SD. Sensory Neurons that Detect Stretch and Nutrients in the Digestive System. Cell. 2016;166(1):209-221. doi:10.1016/j.cell.2016.05.011

[4] Roe LS, Meengs JS, Birch LL, Rolls BJ. Serving a variety of vegetables and fruit as a snack increased intake in preschool children. Am J Clin Nutr. 2013;98(3):693-699. doi:10.3945/ajcn.113.062901

[5]https://en.wikipedia.org/wiki/Sensory-specific_satiety

[6]https://baike.baidu.com/item/%E9%A5%B1%E8%85%B9%E6%84%9F/3846800?fr=aladdin

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