Research Review: Green Tea, cayenne & your metabolism | Precision Nutrition

Research Review: Green Tea, cayenne & your metabolism

By Helen Kollias, Ph.D.


I’m a spicy food lightweight. Pathetically so. I ask for “super mild” at Indian restaurants with a tub of yogurt. I think black pepper is spicy.

And I figured I wasn’t missing much beyond a burnt tongue until I started looking at the benefits of spicy food. Yes, there are benefits beyond watery eyes, a possible out-of-body experience, and bragging rights for consuming the most “suicide” wings.


There are actually foods that can increase your metabolism and increase how much energy you use. These are known as thermogenic foods, since they get your body to burn more calories, which is a measure of heat/energy use (“therm” refers to heat) [1].

I guess “foods” isn’t really the right word for them, since they’re actually chemicals such as caffeine, the “hot” in hot peppers (capsaicin) and compounds in green tea (catechins). All these compounds can increase how much energy you use (up to 4-5% or 70-100 calories/day) and how much fat you burn (10-16% more).

Capsaicin: feel the burn

You know the “ate a hot pepper” feeling, right? Your eyes tear up. Your nose runs. You break out into a sweat. You grab for ice water.

Well, the good news is that that capsaicin, the chemical that’s kicking your ass, is actually increasing your metabolic rate. (The bad news is that your glass of water isn’t going to help put out the fire in your mouth. Try cold milk next time – capsaicin is fat soluble.)

How does capsaicin work? It triggers the “fight or flight” response hormones (catecholamines like epinephrine/adrenaline, norepinephrine/noradrenaline and dopamine). Some of the effects of these hormones are:

  • Your heart beats harder and faster
  • You breathe faster and deeper
  • Your body moves fat and glucose into the blood for your muscles to use

Catecholamines get your body ready for a fight or to run away. (Oddly enough, catecholamines don’t help much when trying to speak in front of a large audience – damn the slow wheels of evolution!)

How hot is hot? Measuring spiciness

The Scoville scale is a way to measure hot pepper heat (or spiciness) based on capsaicin content. The higher the number, the hotter the pepper.

Sweet peppers (bell peppers) have the lowest score of 0 Scoville heat units (SHU). Pure capsaicin has the highest score: 16 million SHU. (Just for reference, law enforcement pepper spray comes in at 5 million SHU.)

The hottest pepper is bhut jolokia (sometimes known as the “ghost pepper”) at 1 million SHU. Apparently in India, where this pepper is grown, locals smear it on fences as elephant repellent. Habanero & Scotch bonnet peppers have a score of around 250,000 SHU. Other peppers like cayenne and jalapeño peppers have scores of 50,000 and 5,000 SHU, respectively.

Gee, I was hoping to gain some respectability in the world of heat and to work my way up to jalapeño peppers, but now that’s looking pretty wimpy compared to the head-popping bhut jolokia.

Green tea: Caffeine and catechins

Green tea has two thermogenic compounds: caffeine and catechins.

Caffeine, yup I’ve heard of that, took too much during university. I need it in the morning to… zzzz.

Okay, now that I’ve had my coffee, on to catechin, which are antioxidant phytochemicals (literally plant chemicals) found in teas. Green tea has four types: epicatechin (EC), epicatechin-3-gallate, epigallocatechin (EGC), epigallocatechin gallate (EGCG). (For more on tea, see What You Should Know About Tea and All About Rooibos.)

In your body, catechins increase fat oxidation (burning of fat) by activating fat metabolizing enzymes (acyl-CoA oxidase/medium chain acyl CoA dehydrogenase) though a cellular chain of events [1].

Green tea (catechins and caffeine) together increase norepinephrine, by blocking an enzyme (catechol-O-methyltransferase; COMT) that reabsorbs noreinephrine. More norepinephrine means you’re getting ready for a fight or to make a mad dash to safety, just like with capsaicin.

But there seem to be genetic differences in how well green tea works. For instance, Asian populations appear to have a version of COMT that responds better to green tea than Caucasians [2]. See also Bryan Walsh’s article on whether green tea is right for you.

Research question

This week’s review looks as how capsaicin, green tea and sweet pepper affect people’s appetite when they try to lose or gain weight. Do capsaicin, green tea, and/or sweet pepper make you feel fuller?

Reinbach HC, Smeets A, Martinussen T, Møller P, Westerterp-Plantenga MS. Effects of capsaicin, green tea and CH-19 sweet pepper on appetite and energy intake in humans in negative and positive energy balance. Clin Nutr. 2009 Jun;28(3):260-5.


Twenty-seven people risked their taste buds to see whether spiciness helped with controlling appetite or whether it was something else. Keep in mind that these people didn’t need to lose much weight since they were considered “normal” using BMI (average 22.2 kg/m2.)

What? Only 27 people!?

Yup, that’s it. After doing a mathematical calculation (called a power calculation) the researchers figured that they only need 24 people to see if spiciness changed people’s appetite, so they had 3 extra just in case.

Let the fun begin

Hmm, if you want to figure out if something controls appetite, what should you do? Maybe put people on a diet and give them the supposed appetite suppressant? That’s what the researchers did: They put people on a calorie restricted diet for three weeks with various foods that could help suppress appetite.

Then, the researchers also put everybody on a bulking diet for three weeks to see if the same supplements would have an effect when there was no hunger involved.

Thus, they were able to compare the effect of the foods in both a caloric deficit and caloric excess.

In both diets everybody got the same breakfast and lunch, but with smaller portions in the calorie restricted condition. Then, for supper they got the same food, but they could eat as much as they wanted.

Everybody got to try all the different supplements that included:

  • capsaicin – 510 mg of cayenne pepper capsules (40,000 Scoville heat units)
  • green tea – 350 mL of green tea drink (598.5 mg catechins & 77 g caffeine)
  • CH-19 sweet pepper – 2.3 mg capsiate capsules
  • capsaicin + green tea together
  • placebo


Not surprisingly, eating less food during the day makes you more hungry — well, actually less full (or satiated). Big surprise! During the calorie-restricted period, people also rated food as tastier, when compared to the bulking condition. Also not really rocket science. If all you get to eat is an apple, that’ll be the best apple ever.

Okay, now to the interesting stuff. Capsaicin + green tea reduced cravings for fatty, salty, bitter and hot tastes, and capsaicin only reduced cravings for sour – don’t ask me why green tea seems to counteract capsaicin’s sour craving powers, because I have no idea.

What else is weird is that with the exception of bitter, these craving-fighting powers of capsaicin and green tea only happen during the dieting (calorie restriction) part of the study. During the bulking, none of the supplements made a difference to whether the volunteers felt more or less full – except bitter cravings, where capsaicin and green tea helped.

OK, so if you’re on a bulking diet, you should keep drinking green tea and eating at your favourite Indian restaurant, right? Not so fast! Even though capsaicin and green tea didn’t do much for cravings in the bulking diet they did increase feelings of fullness – not so good if you’re trying to gain weight.


Combining green tea and capsaicin while on a calorie-reduced diet actually helps reduce savoury cravings and hunger more than either one alone. That’s a bonus, since these compounds are already known to be thermogenic.

Green tea and capsaicin together suppress appetite on bulking diets, but not at much as in the weight loss condition.

Neither green tea alone nor capsaicin alone did much to suppress appetite.

Sweet pepper didn’t do much either, but without a green tea + sweet pepper condition we can’t say whether the combination of the two would work.

Bottom line

If you’re having problems losing weight and you’re following the PN habits, then try adding more spice to your foods.



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

Learn more

To learn more about making important improvements to your nutrition and exercise program, check out the following 5-day video courses.

They’re probably better than 90% of the seminars we’ve ever attended on the subjects of exercise and nutrition (and probably better than a few we’ve given ourselves, too).

The best part? They’re totally free.

To check out the free courses, just click one of the links below.