Most people find that drinking a cup of coffee in the morning increases their alertness, and others may find that coffee also reduces their hunger. While many people, increasingly on social media, say that coffee is their go-to drink for weight loss, studies are only beginning to uncover how caffeine and other compounds in coffee affect body weight.
Coffee loophole
In her report published in Scientific American, writer Lori Youmchajikian said that many diet trends and recipes have spread under the name “coffee loophole” since early this year, which has sparked renewed interest in consuming coffee (or caffeine in general) to lose weight.
These sources claim that adding homemade spices or commercial supplements to a cup of coffee, or even sipping the mixture within 7 seconds of feeling hungry, can enhance the weight-loss effect. Experts are still confused about this: Does coffee—especially caffeine—contribute to weight loss in the first place? And how long do any weight-loss effects last?
Coffee and other caffeinated products are rumored to be a quick and easy solution to weight loss. The rationale is partly related to coffee’s ability to stimulate the digestive system. The caffeine in coffee can increase muscle contractions in the colon that stimulate bowel movements. This means your digestive system gets rid of its contents a little faster than usual. Caffeine is also a diuretic, which means it increases urine production, and urinating more can lead to water weight loss.
These combined effects on digestion and water weight occur quickly after drinking coffee, but are short-lived and do not cause permanent weight loss. However, drinking coffee over longer periods of time appears to have different effects.
the study
According to the writer, drinking coffee regularly does not lead to significant weight loss, but it may prevent weight gain, albeit slight. The average person typically gains weight as they age—about a pound a year during middle age—but heavy coffee drinkers appear to experience less age-related weight gain.
A 2023 study that tracked the coffee habits of more than 150,000 participants found that drinking unsweetened coffee was associated with a small reduction in weight gain over four years after adjusting for other lifestyle variables. With each additional cup, coffee drinkers gained about a quarter pound less than their peers. Most people probably won’t notice such a small difference in weight, though. Other studies have reported similar results.
Coffee has also been linked to a small amount of body fat loss, the author reports. In one study, people who drank four cups of instant coffee a day had 4 percent less body fat and lost a small amount of overall weight after about six months. That compared with a control group who drank a placebo that looked and tasted like coffee and maintained their same diet and exercise habits.
Does caffeine help reduce weight gain?
The author notes that caffeine, the main biologically active compound in coffee, appears to be a key factor in the reduction in weight gain. This compound is known to stimulate diet-induced thermogenesis, or the energy used to digest, absorb, and store nutrients from food. On average, people spend about 10% of their total energy expenditure processing food.
Studies have shown that caffeine can increase this amount by raising a person’s metabolic rate. A higher metabolic rate causes the body to use more energy at rest. Digestion speeds up, causing organs in the intestines to use slightly more energy and burn more calories. However, this energy boost is generally small; coffee drinkers may burn an extra 80 to 150 calories a day, according to one short-term study.
Caffeine is also thought to stimulate the sympathetic nervous system, which regulates the body’s fight-or-flight response, the author notes. It blocks receptors that bind adenosine, a neurotransmitter that induces sleepiness and promotes relaxation. Caffeine then triggers physiological responses in the sympathetic nervous system, such as increased heart rate and alertness. This, in turn, burns a few more calories, explains Marilyn Cornelis, an assistant professor of preventive medicine at Northwestern University.
The author pointed out that caffeine may also increase fat oxidation – the process of breaking down fat stored in tissues for energy – which may explain why coffee consumption is linked to lower fat mass.
Aside from caffeine, coffee also contains a lot of polyphenols — a type of antioxidant — which may affect weight. Chlorogenic acid, the polyphenol that gives coffee its distinctive bitter taste and strong aroma, has been shown to help keep blood glucose levels stable.
Since cravings can be linked to blood sugar fluctuations, keeping your blood sugar stable may help regulate appetite, Cornelis says. The bitter taste itself may also play a role, as there’s evidence that the gut senses bitter compounds and modulates appetite hormones to reduce food intake.
Coffee and appetite hormones
Scientists are only beginning to understand how chlorogenic acid might enhance coffee’s effect on hormones that control appetite and hunger, the author notes. One small study that followed 126 overweight people found that coffee had a regulating effect on satiety hormones, with people eating slightly less food and feeling fuller after drinking the beverage.
After drinking coffee, participants had higher levels of serotonin, a brain chemical that can, among other things, suppress appetite, and lower levels of the hunger-stimulating hormone ghrelin. These effects were stronger in those who drank the coffee blend that contained more chlorogenic acid. Evidence suggests that coffee may influence appetite and hunger, but its effects may vary widely from person to person.
So drinking coffee to curb an immediate spike in hunger may not be a realistic expectation. Scientists are also still trying to understand whether additives, such as cinnamon and cayenne pepper, contribute significantly to coffee’s modest weight-loss effects, but they say these ingredients are harmless when added.
The author believes that the effects of coffee on health in general seem beneficial, but if it is drunk in moderation, research has consistently linked long-term coffee consumption to a reduced risk of type 2 diabetes and heart disease, improved cognitive function, and even a lower death rate. But increasing coffee intake just to achieve these effects is not for everyone.
“It’s not like more coffee is better,” says Rob Van Dam, a professor of exercise science and nutrition at George Washington University. Drinking more than about 400 milligrams of caffeine a day can cause difficulty sleeping, increased stress and some anxiety, she adds. To put that into perspective, a single shot of espresso typically contains about 60 milligrams of caffeine, though popular coffee drinks can contain much more, depending on the size and roast.