Research Review: 5-HTP (& turkey) for fat loss? | Precision Nutrition

Research Review: 5-HTP (& turkey) for fat loss?

By Helen Kollias


The “turkey coma” is a common occupational hazard of holiday dinners. The tryptophan in turkey converts to 5-HTP and serotonin, which helps relax us and make us feel fuller. Could 5-HTP also help us lose fat?

Are you planning on having a big turkey dinner in the next two weeks? Are you getting sleepy just thinking about your dinner?

We’ve all heard that the reason we get sleepy after eating a big turkey dinner is because is full of tryptophan. (Remember that Seinfeld episode where Jerry and George used a turkey dinner to lull a woman to sleep so they could play with her toys?)

What is tryptophan?

Tryptophan is an amino acid found mainly in animal products, though some higher-protein legumes, nuts, and seeds have some too. Soy and sesame, in particular, are relatively high in tryptophan, but many nuts such as pistachios and cashews also contain it. A few unprocessed grains, such as oats, have trace amounts in their unrefined forms.

Funny thing is, other foods are much higher in tryptophan.

Factoid! The best source of tryptophan is sea lion. However, sea lion is tough to find in your local supermarket.

Tryptophan in common foods (mg per 100 g)
Tryptophan in common foods (mg per 100 g)

To keep with the turkey eating season I’ve decide that this would be a good time to take a closer look at tryptophan.

Why does tryptophan make you sleepy?

After suffering a turkey-induced coma, I wondered how tryptophan could make me so sleepy.

After a little digging through my textbooks I found that though a series of biochemical reactions, tryptophan converts to 5-HTP, which can then become serotonin (see Figure 1). Ah ha!

Tryptophan to 5-HTP pathway. Click to enlarge.

Serotonin is a neurotransmitter that is responsible for mood, appetite and sleep. It’s present in both our brain and our GI tract.

Research question

This got me thinking: if eating tryptophan makes more serotonin, which makes me sleepy, would it also make me fuller? Or happier?

After years of wondering, this I review a study examining the tryptophan metabolite, 5-hydroxytryptophan (5-HTP) and how it affect appetite, mood and weight loss.

Rondanelli M, Klersy C, Iadarola P, Monteferrario F, Opizzi A. Satiety and amino-acid profile in overweight women after a new treatment using a natural plant extract sublingual spray formulation. Int J Obes (Lond). 2009 Oct;33(10):1174-82.


This study was a double-blind parallel study, meaning that neither the researchers nor the participants knew if they were in the control group or the group getting the treatment (double-blind). Both control and treatment happened at the same time (parallel).

Double-blind: Doesn’t somebody need to know what’s going on?

I’m sure you’re wondering: “Okay, I understand the participants not knowing what group they were in, but if the researchers don’t know… then how the heck do you do a study?”

Well, obviously somebody has to know or else it would be a completely blind study! Possibly hilarious, likely unethical, certainly useless.

Thus, usually in these double-blind studies a pharmacist is involved. The pharmacist provides the drug/supplement for the treatment and a placebo for the control group; and s/he keeps track of who is in what group.

The pharmacist only reveals the groups at the end of the study, after researchers have taken and analyzed all the measurements.

The placebo effect

Why bother with all this secrecy?

Double-blind studies try to eliminate both researcher and participant bias — in other words, whether researchers and/or participants believe that treatment X will or will not do Y.

Most of you have heard of the placebo effect. If study subjects believe a treatment will work, it sometimes does, regardless of what they were actually taking.

Well, the same is true of the researchers. Just like the participants, researchers can colour the results by knowing what should happen and skewing the experiment.

Is this manipulation on purpose? I’d say in most cases no, but science is littered with scientists that skewed or even plain made up their data.

If you want to know how bad things could be, or are thinking of going into science, you must read Betrayers of Truth: Fraud and Deceit in the Halls of Science by William Broad and Nicolas Wade (published way back in 1983).


Since this was a study looking at an obesity treatment the participants were, you guessed it, obese. They had a BMI between 25 and 35 kg/m2. All were female.

“Healthy” versus “disease-free”

All participants were “healthy,” though I’d say “disease-free” would be a better term than healthy.

After tossing out anybody that had hepatic disease, renal disease, unstable cardiovascular disease, uncontrolled hypertension, active cancer, an eating disorder, depression or surgery for weight loss, researchers were left with the healthy participants.

For example, subjects with controlled hypertension (controlled by drugs) and stable cardiovascular disease could be in the study — hardly what I would call healthy.

In total, there were 27 women between the ages of 25-35. Researchers randomly assigned participants to either the control group (13 women) or the treatment group (14 women) for 8 weeks.

All participants were also on a weight loss program that allowed them 2508 kJ/day with calorie breakdown of 25% from fat, 60% from carbohydrate and 15% from protein.

5-HTP supplementation

Women in the treatment group squirted 3 sprays of 5-HTP-Nat Exts under their tongues 5 times a day between meals.

The spray contained a mix of different plant extracts – Griffonia simplicifolia, Centella asiatica L.¸ Taraxacum officinale (aka dandelion), Cynara scolymus (globe artichoke), Paullina sorbilis L (guarana). Mart. and Alga Klamath.

I don’t know about you, but my botany is a wee bit rusty, so here is a chart explaining what is what:

Plant Known uses
Griffonia simplicifolia Rich in 5-HTP (increases serotonin production[1])
Centella asiatica L. Beneficial effects on blood and lymph circulation[2]
Taraxacum officinale (dandelion) Diuretic effect & antioxidative[3]
Cynara scolymus (globe artichoke) Detoxifying action[4]
Paullina sorbilis L Mart (guaranà) Stimulates fat metabolism[5]
Alga Klamath (Klamath algae) Rich in phenylethylamine (mood enhancer)[6]


Urine metabolites

The researchers indirectly checked that the spray increased 5-HTP and serotonin by testing urine for 5-HIAA (5-hydroxy-3-indoleacetic acid) 24 hours after taking the 5-HTP-Nat Exts spray.

5-HIAA is a major metabolite of serotonin. If it increases after administering the spray, then you can be pretty confident that the 5-HTP in the spray is getting into the blood.

If the 5-HTP is in the blood, it causes more serotonin to be made, which then degrades into 5-HIAA that ends up in the pee.

Body composition

To figure out whether the spray helped with weight loss, the researchers measured weight, skinfolds and waist girth before and after the 8-week study.

Eating behaviour and mood

To figure out how weight loss could have happened (yes, I’m tipping my hand), the researchers looked at appetite, binge eating, and depression.

To assess appetite, the participants fasted for 12 hours, took either the placebo or the 5-HTP-Nat Exts, and then recorded how hungry they using a 20 point scale. Then, after a standardized lunch, they re-assessed their appetite.

Using two question-based tests before and after the 8 weeks, the researchers quantified (put a number on) binge eating and depression.

Researchers assessed binge eating using the Gormally Binge Eating Scale (GBES) and depression with the Beck Depression Inventory.


After 8 weeks there was more 5-HIAA in urine of the treatment group, so it’s safe to assume that the 5-HTP in the spray was absorbed and increased serotonin levels.

This may seem unnecessary, but of all the measures it’s the most important in proving the hypothesis that 5-HTP does anything. No proof that 5-HTP was absorbed means no proof that 5-HTP did anything.

Appetite, binge eating & depression

The treatment group was less hungry after the 12 hour fast compared to the control, but there was no difference in appetite between groups after lunch.

After 8 weeks everybody was less likely to binge eat and were happier than in the beginning, but again there was no difference between groups.

What could have made the difference after 8 weeks? Weight loss.

Body composition

After 8 weeks of a moderately restrictive diet everybody had a slight improvement in BMI but the treated group had more of an improvement (not much either — around 1kg/m2).

The skinfold data is where it gets really interesting.

The control group had no decrease in skinfold thickness at any site, while the treated group every site had a decrease in skinfold thickness.

Now, many of you PNers know that skinfold thickness is a better way of tracking changes in body composition than a scale, so that means that the skinfold data is more compelling in proving 5-HTP helps with weight loss – well, fat loss, to be more accurate.


A spray containing 5-HTP and a few other plant extracts along with diet modification for 8 weeks was more successful for fat loss than diet only.

Bottom line

Before you decide to try 5-HTP you should remember that even though the treated group (5-HTP + extracts) did lose more fat they still had to watch their diet. You still need to modify your lifestyle.

I’d say if you have problems sleeping and want to take 5-HTP to help you sleep, you may end up with the added benefit of weight loss.

On the other hand, if you take 5-HTP in the form of a big turkey (or sea lion) dinner, all bets are off.



Click here to view the information sources referenced in this article.

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