Coffee and appetite:
Does coffee make you more or less hungry?

By Jennifer Koslo, PhD

Our hunger and appetite are controlled by complex systems within our bodies, which can be profoundly affected by what we eat and drink — including coffee.

While people often use caffeinated coffee to control their appetite, new research shows that if you want to reduce your bodyweight, you might be better off sticking to decaf.

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Introduction

Billions of people worldwide drink coffee to get more energy, feel more alert, and improve their athletic performance. Coffee also suppresses appetite, so many people drink it to lose weight.

According to Dr. Mehmet Oz, if you want to lose weight, then you should skip brewed coffee and take green coffee bean extract instead. However, if you aren’t an Oz fan, and prefer to drink your coffee instead of taking it in pill form, could it still help you lose weight?

Is coffee healthy? It depends.

Thanks to Famous TV Doctors and media attention to coffee’s health effects, our worries bubble up like a well-formed espresso crema: Should we drink more java? Or does every drop float us closer to a well-caffeinated grave? The truth seems as muddy as truck stop joe.

One reason: People metabolize coffee at different — and genetically determined — rates. And coffee affects many neurotransmitters and hormones (such as cortisol and insulin).

Coffee’s mixed effects also depend on the type of coffee, the amount you drink, when you drink it, your overall biological makeup, and so on.

For more details on the diverse benefits and risks of coffee see All About Coffee.

What’s in that cuppa joe?

Coffee is a complex mixture of chemicals.

It’s a major source of caffeine, the world’s most widely used stimulant drug. Caffeine is a xanthine alkaloid, a central nervous system and metabolic stimulant. A little bit of caffeine can improve health; a lot of caffeine can harm it.

Caffeine is an effective ergogenic — something that improves athletic performance — it spares muscle glycogen and delays fatigue. For more on caffeine, see All About Caffeine.

Coffee also contains phytochemical compounds called chlorogenic acids, an important group of biologically active and antioxidant dietary phenols. Chlorogenic acids are also found in apples, pears, artichokes, strawberries, pineapple, sunflower and blueberries (1).

Chlorogenic acids have recently caught the attention of obesity researchers and dietary supplement manufacturers alike, as they can help decrease hunger. Mouse studies to date have produced mixed results, so I wouldn’t run out and buy green coffee bean extract just yet (2,3).

Chlorogenic acids, found in coffee, are antioxidants that may also decrease hunger.

Unlocking appetite control secrets

Hunger and satiety: Every obesity researcher seeks for the key to unlock their secrets. It’s tricky, as appetite, hunger, and satiety are influenced by dozens of interacting hormones.

This week’s study looks at three of those hormones: ghrelin, leptin, and peptide YY. Ghrelin is an orexic, or appetite-stimulating, hormone. Leptin and peptide YY are anorexic, or appetite-diminishing, hormones.

Ghrelin & leptin

Ghrelin is secreted mainly in the stomach. It stimulates appetite and increases food intake. Leptin is a hormone, synthesized primarily in fat cells, that has been shown to decrease food intake and increase energy expenditure.

As a side note, an easy trick to remember the difference between these two: ghrelin = stomach GRemlins and GRowling.

For more on how leptin and ghrelin work, see Leptin, Ghrelin, Weight Loss: It’s Complicated.

Peptide YY (PYY)

Cells of the intestinal mucosa of the ileum and large intestine release the third hormone, peptide YY (PYY).

PYY lowers appetite and food intake, perhaps by acting on neurons in the hypothalamus to help people feel full or satisfied. Other researchers speculate that PYY may delay gastric emptying (4).

Research question

So how does coffee work?

If coffee can help people to lose weight, how does it do it? Does it increase PYY and leptin and decrease ghrelin? And is it the caffeine or something else like chlorogenic acid that acts on the hormones?

Well, this week’s review asks three related questions:

How do caffeine, caffeinated coffee, and decaffeinated coffee affect people’s feelings of hunger and fullness?
How might coffee affect blood levels of hormones such as ghrelin, PYY, and leptin?
Does a glucose load change the drinks’ effects? (In other words, does a donut with your coffee change the game?)

Initial hypotheses

Hypothesis 1: Decaffeinated coffee, caffeinated coffee, and caffeine will decrease hunger, ghrelin, and leptin and increase satiety and PYY

Hypothesis 2: These effects would occur during the 60 minutes after subjects drank the test beverage and during the subsequent 120-minute period following glucose ingestion.

Let’s see how it turned out.

Greenberg, J.A., Geliebter, A. Coffee, hunger, and peptide YY. J. Am. Coll. Nutr. 31(3), 160-166 (2012).

Methods

This study used a placebo-controlled, randomized, four-way crossover trial. In other words, there were four drinks total — a placebo plus three test drinks:

caffeinated coffee
decaffeinated coffee
a caffeine-water solution

The 11 study subjects drank each of the four drinks during the study period (hence the term “crossover”).

The study was also single-blinded: Subjects didn’t know what they were consuming (i.e. they were blind to it) but the researchers did.

This type of design allows researchers to compare the drinks more effectively without being concerned about variation between subjects. They can compare Person A drinking Beverage X to Person A drinking beverage Y and so on.

Subjects

Because there were four test conditions (placebo drink, caffeinated coffee, decaffeinated coffee, caffeine in water) the subjects visited the lab four times for testing, 1-2 weeks apart (so that there would be no potential interaction between drinks). During the 48 hours before a test, subjects were not to exercise or drink alcohol.

The lab visits were scheduled for the afternoon. Subjects ate the same identical light breakfast before each visit, then nothing else — no lunch and no snacks. I am guessing they were pretty hungry at the start of testing.

Each visit followed a similar procedure:

Before testing, each subject was weighed and asked to fill out a questionnaire on caffeine, food and alcohol intake; illness, stress and exercise; and any possible side effects from the previous visit.
Subjects rested in a chair while a catheter was inserted into a vein for blood sampling throughout the study. An initial blood sample was collected.
Subjects rested for 30 minutes.
Subjects were given a randomly selected beverage: placebo drink, caffeinated coffee, decaffeinated coffee, or caffeine in water, and asked to drink it within ten minutes.
Researchers drew blood a second time.
More resting for 60 minutes, after which subjects were asked to drink a ten ounce bottle of flavored water containing 75 g glucose. (Ick — strong coffee, numerous blood draws and drinking glucose? My belly sure wouldn’t be happy! Most likely the combination on an empty stomach would have me looking for a place to barf. Ah, what people do in the name of science!)
Meanwhile back at the lab… glucose ingestion was followed by six more blood draws over a two hour period. If you add in the other blood draws, we are now up to eight total. During each of those eight draws, the subjects were asked to rate their levels of hunger and satiety (fullness) on visual analog scales (VAS).

Measures

Subjects’ ratings of hunger and satiety

The visual analogue scale (VAS) is a well-validated and often-used tool that researchers use for more subjective or nebulous things like pain or fatigue (5). VAS let people rate things on a continuum — in this case, from 1 to 100.

To assess subjects’ hunger, researchers asked them: “How hungry do you feel?” with 0 being “not at all” and 100 being “I have never been more hungry.” They were also asked to rate their satiety with 0 being “I am completely empty” and 100 being “I cannot eat another bite.”

An example of a Visual Analog Scale (VAS) measuring hunger and satiety.

Objective measures

So what did the researchers do with all that blood? Well, they also tested levels of three internal peptides (the term peptide refers to two or more amino acids linked by chemical bonding between their carboxyl group and their amino group): ghrelin, PYY, and leptin.

To recap:

Hormone	Found in / secreted by	Effect on hunger
Ghrelin	Stomach and pancreas	Increases hunger
PYY	Lower bowel (ileum & colon)	Decreases hunger
Leptin	Adipose (fat) tissue (primary) as well as GI tract; ovaries; bone marrow; muscle; pituitary; liver	Decreases hunger

Preparation of the test beverages

My mom thinks I am a coffee snob, and I must admit I laughed when I saw that Chock Full O’Nuts Original was the brand that was used in this test.

Coffee snob or not, the $200 participation fee would keep me stocked with my favorite organic fair trade coffee beans for at least a month or two.

Researchers wanted to maximize the concentration of non-caffeine coffee compounds, yet achieve a brew that wasn’t tar-thick. They scanned the literature and found that a brew equal to 6 mg of caffeine per kg of body weight was about right.

This amount equals about 16-20 ounces of coffee, which is about what your average coffee drinker consumes these days considering the ginormous mugs we all use.

And then — seriously — they used their research staff as testers, making the highest concentration that their staff could tolerate. I can just picture a lab full of jittery, hyper-alert scientists, slapping the invisible bugs off their skin.

Researchers used a run of the mill drip-filter coffee maker, Chefmate. You might have one sitting on your kitchen counter.

Here’s how the drinks broke down:

For the caffeinated coffee, 40 g of ground coffee was used to achieve 6 mg/kg body weight caffeine. The caffeine content was measured by high-performance liquid chromotography to be 0.73 mg/ml coffee.
For the decaffeinated coffee, 57 g of ground coffee was used to achieve the same strength.
For the caffeine in water, they still used the coffee maker, but instead of grounds, researchers used food-grade caffeine powder to yield 6 mg/kg body weight of caffeine.

Results

So, remember:

Hypothesis 1: Decaffeinated coffee, caffeinated coffee, and caffeine will decrease hunger, ghrelin, and leptin and increase satiety and PYY

Hypothesis 2: These effects would occur during the 60 minutes after subjects drank the test beverage and during the subsequent 120-minute period following glucose ingestion.

The results may surprise you.

(If you want a quick summary, skip to the conclusion.)

Results were reported two ways: plotted as a graph of time vs beverage effect, and calculated as area under the curve or AUC. AUC is a statistical means of summarizing data from a series of measurements on one individual.

Ratings of hunger (at 180 minutes): For time vs. beverage effect, decaffeinated coffee yielded statistically significantly lower hunger levels than placebo and caffeine during the whole study period. Hunger AUC yielded similar results and was statistically significantly lower following consumption of decaffeinated coffee vs. placebo and caffeine.Hunger AUC for caffeinated coffee was not significantly different for caffeinated vs. decaffeinated coffee. However, hunger after caffeinated coffee was not significantly lower than after placebo or caffeine.

Hunger AUC was not significantly different for caffeine than placebo or for decaffeinated coffee vs. caffeinated coffee. The difference between hunger after decaffeinated coffee and placebo did not vary significantly over time after glucose ingestion and did not diminish toward the end of the study.

Ratings of satiety (at 180 minutes): While there were no significant beverage effects detected, ratings of satiety produced a similar pattern to those of hunger. In other words, ratings of satiety were higher after the decaffeinated coffee than any of the other beverages, just not high enough to reach statistical significance.

PYY (pmol/l at 90 minutes): PYY was significantly higher after decaffeinated coffee than after both placebo and caffeine within 60 minutes of ingestion and during the 90 minutes following beverage ingestion. PYY AUC in the 90-minute period was significantly higher for decaffeinated coffee than for placebo and caffeine.

PYY (pmol/l at 180 minutes): There was a trend for PYY AUC to be higher for decaffeinated coffee than for caffeine.

Ghrelin (pmol/l at 180 minutes): There were no significant effects of any of the beverages.

Leptin (nmol/l at 180 minutes): There were no significant effects of any of the beverages.

Conclusion

While caffeine has long been used as an appetite suppressant, in this study it was decaffeinated coffee that resulted in significantly lower hunger levels and higher plasma levels of PYY than placebo (plain water) and the other caffeinated beverages.

More PYY means less hunger. Not only that, but the decrease in hunger lasted for the full 3 hours of the lab visit, even though, after 1.5 hours, levels of PYY decreased.

Another interesting finding was that the decrease in hunger and increase in PYY persisted through and after the glucose ingestion.

We can speculate here that there is something – one or more noncaffeine components (coffee includes hundreds of them) – that can decrease hunger and increase PYY. It could be chlorogenic acid, or maybe other satiety hormones. We don’t have the whole picture yet, especially since leptin and ghrelin didn’t seem to be affected.

Now remember: This study has limitations, including a very small sample size. Future studies could include a fifth beverage: decaffeinated coffee with supplemental caffeine; this would help to assess any interaction between caffeine and the noncaffeine components.

For rating hunger and fullness, food measurements could be used, and maybe researchers could even measure brain waves.

Regardless, this study providing some interesting data that may lead to practical applications for increasing feelings of fullness and decreasing feelings of hunger.

Bottom line

Coffee is full of antioxidants and provides numerous health benefits, though not everyone responds to it equally well. (If you’re wondering whether you metabolize caffeine well, check out 23AndMe or a similar genetic analysis service, which can test your caffeine metabolism abilities.)

If you’re relying on a lot of caffeine to suppress your appetite, consider another strategy: Try switching out your high-test for decaffeinated coffee and tune into your feelings of hunger and satiety. You might be pleasantly surprised at what you find.

(And maybe the people around you will be pleasantly surprised that you’re no longer a psychotic grouch!)