Serotonin Deficiency and Weight Gain

Serotonin is a neurotransmitter, meaning it is a chemical messenger that is able to send signals throughout the body and central nervous system. Its main role in the brain is in stabilising mood as a result, it is often called the ‘happiness hormone’. 

It can have other functions in the rest of the body, for example, it is able to control the contraction of the stomach, can induce vomiting, plays a role in organ development, and regulates bone mass.

In recent times, there has been growing evidence that the levels of serotonin in the brain can be linked to weight gain, especially in cases of depression. This is because it is able to affect a person’s appetite.¹

When there is enough serotonin, it can suppress the appetite and promote calorie use. It is, however, thought that having a decreased amount of serotonin in the brain can cause a person to overeat, meaning that it can cause weight gain.²

Understanding serotonin deficiency

Serotonin is important in the normal function of the body, and it has many roles throughout. A deficiency in serotonin occurs when there is not enough to maintain this normal function. 

Serotonin deficiency can occur through many routes:³

• Other vitamin and mineral deficiencies
• A naturally decreased amount of serotonin receptors, which are small structures onthe surface of cells that can ‘sense’ how much serotonin there is
• Chronic stress
• Age-related changes to the brain
• Lack of sunlight exposure

A deficiency of other vitamins and minerals, is the one that is most in our personal control as this is typically dictated by our diets, rather than genetic and external environmental factors.

The main factor that can result in serotonin deficiency is a tryptophan deficiency. Tryptophan is a precursor to serotonin. This means that it is modified by a series of processess in the body to produce serotonin.

If your diet is low in tryptophan, the body may not be able to produce adequate amounts of serotonin. This can lead to signs and symptoms of serotonin deficiency (see below):³

There are also some other nutrients that have been linked to serotonin deficiency if there is not enough of them in the body:

• Vitamin B₆ – this helps the body convert tryptophan into serotonin – this process is called serotonin synthesis
• Vitamin D – this is usually gained from sun exposure but in places like the UK, winter can mean there is not enough sun to supply the body with adequate vitamin D
• Omega-3 fatty acids

How does serotonin deficiency affect weight gain?

As mentioned above, serotonin can affect a person’s appetite. However, depending on where in the body the serotonin is acting, the effect can change.

If the serotonin acts in the central nervous system, it can suppress appetite and increase the expenditure of calories, and therefore energy. However, if it acts in the rest of the body (peripheral), it can promote the absorption of food and storage of energy this balance is vital for survival.³

The peripheral effects of serotonin (meaning the effects of serotonin in the rest of the body) can explain why, counter-intuitively, people who are on anti-depressant drugs, specifically serotonin selective re-uptake inhibitors (SSRIs) may experience weight gain.

A study was performed on  rats, wherein the the subjects were fed an obesogenic diet (meaning a diet designed specifically to induce, or promote, obesity in these rats). A week into this diet, it was found that the signalling of serotonin had decreased, resulting in lowered energy expenditure. ⁴ This suggests that certain foods, particularly those high in fats, may cause changes to serotonin signalling that can create a cycle of overeating and weight gain.

Interestingly, this study also highlighted the link between insulin (which is a hormone, or messenger in the blood, that controls blood sugar), leptin (which is a hormone that is produced by fat cells to help maintain body weight) and serotonin. Increased insulin and leptin in the blood appears to decrease serotonin signalling, which may also contribute to obesity.

This study is important as it suggests that changes in a person’s diet can affect the signalling of various hormones and neurotransmitters in the body, which, in turn, can cause the person to become obese through reduced serotonin signalling, as this causes the person to overeat even more.

Signs of low serotonin levels

The signs and symptoms of serotonin deficiency include:

• Fatigue
• Finding that you suddenly crave carbohydrates
• Issues with concentration
• A low mood
• Mood swings
• Anxiety
• Weight gain

How to boost serotonin levels

The level of serotonin in the body can be affected by diet, as mentioned above. There are several foods that can be eaten to help increase a person’s serotonin levels, whether this be to help increase the levels of tryptophan (serotonin’s precursor), or to increase other vitamins and minerals which are involved in serotonin synthesis.

The following foods are rich in tryptophan:⁵

• Milk
• Chicken
• Pumpkin seeds
• Fish
• Peanuts
• Cheese
• Eggs
• Sesame seeds

Eating these foods may help increase the levels of serotonin in the blood as they will increase the amount of tryptophan available to be converted into serotonin.

The following foods are rich in vitamin B₆:

• ^Beef liver
• Tuna
• Salmon
•  Chickpeas
• Poultry
• ortified cereals – these are cereals that have been altered slightly to increase the amount of vitamin B6 in them
• Bananas
• Dark leafy greens
• Papayas
• Cantaloupe
• Oranges

Eating these foods may help increase the levels of serotonin in the blood as vitamin B₆ plays an important role in converting tryptophan to serotonin – without it, the necessary reactions cannot occur and tryptophan will not effectively be synthesised into serotonin.

The following foods are rich in omega-3:

• Fatty fish such as salmon, mackerel, herring, sardines and tuna
• Flaxseeds
• Chia seeds
• Walnuts
• Plant based oils

It has been suggested that omega-3 also plays a role in serotonin synthesis, therefore it is important to ensure that there is enough of this in the body.

Summary

Serotonin is a very important neurotransmitter that has many roles and functions in the body. These include mood stabilisation, control of appetite, control of stomach contraction, and the development of bones and organs.

However, serotonin deficiency can cause a variety of issues.There is increasing evidence for serotonin deficiency causing weight gain – the appetite-suppressing function of serotonin is diminished, meaning that the affected person may overeat. Serotonin deficiency can also cause people to emotionally eat, which increases the risk of weight gain.

There are several vitamins and minerals that can boost the levels of serotonin in the body, and these are tryptophan, omega-3 and vitamin B₆.  Eating a balanced and varied diet is important in maintaining overall health as it will ensure that your body gets the nutrients that it needs.