Over the years, studies have alternately suggested that coffee is both good and bad for health. A few studies have even suggested that it might help you lose weight. While the current scientific thinking on the topic is anything but settled, there’s some evidence that coffee might be helpful for dieters.
There’s been such enthusiastic support for some of the early findings of studies about coffee’s role in weight loss that there’s now a diet plan called the coffee lover’s diet, which is laid out in a book of the same name by Dr. Bob Arnot, a physician and bestselling author of numerous diet and wellness books. That diet encourages drinking at least three cups of light-roast coffee per day, while restricting calories with an eating plan that looks a bit like the Mediterranean diet to lose weight.
Other high-profile celebrity diet gurus have also recently pushed green coffee bean extract, a pill-based supplement, to help people lose weight. A 2017 study conducted in Iran found that women with obesity who took 400 milligrams per day of this supplement for eight weeks while following a low-calorie diet lost more weight than those on the same diet who did not take the extract. The extract comes from unroasted green coffee beans and contains caffeine and other components of coffee that may promote weight loss. The use of this supplement has been deemed a fad by some nutritionists.
However, there is something to the idea that coffee and its constituent components could help support weight loss.
“There have been various studies looking at the effects of coffee consumption for weight loss,” says Katherine Mitchell, an oncology dietitian at the Ohio State University Comprehensive Cancer Center – Arthur G. James Cancer Hospital and Richard J. Solove Research Institute in Columbus. For example, one 2020 study conducted at the Harvard T.H. Chan School of Public Health “found that people who drank four cups of coffee per day saw a 4% decrease in body fat, believed to be linked to an increase in metabolism due to caffeine intake,” she explains.
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If you’re among the millions of people who reach for an eye-opening cup of coffee each morning, you’re certainly not alone, and that jolt of caffeine may be good for more than just getting you ready to tackle the day; it might actually be helping jumpstart your metabolism and support weight loss efforts.
“Coffee may improve weight loss due to caffeine’s effect on increasing metabolism,” says Dr. Eric Pham, a weight loss expert with St. Joseph Hospital in Orange County, California.
Caffeine does this by stimulating the nervous system and releasing the hormone epinephrine. Also known as adrenaline, epinephrine signals fat cells to break down and release fats into the blood. This makes the fat more available to be used as fuel.
This increase in fat metabolism “occurs in all people regardless of race, sex or age,” says Dr. Brian Quebbemann, a bariatric surgery specialist based in Newport Beach, California, and author of “World’s Greatest Weight Loss: The Truth That Diet Gurus Don’t Want You to Know.” However, these effects appear to be lower in people with obesity.
Caffeine can also boost your resting metabolic rate, which means you may end up burning more calories around the clock. Quebbemann says drinking coffee regularly “decreases the amount of weight a person gains over time. The reason for this is likely due to not only decreased calorie intake but an increase in resting metabolism.”
But, he notes that “the details are important.” For example, “If you drink coffee 30 minutes to three hours before eating, you’ll generally consume fewer calories. The decrease in appetite diminishes significantly after four hours.” This trick works for both caffeinated and decaffeinated coffee, “so, the appetite suppression effect is not completely dependent on caffeine.”
Mitchell notes that for some, “consuming coffee before a meal may lead to an enhanced feeling of ‘fullness’ and less calorie intake at the time of that meal.”
Both the metabolic boost and the suppression of hunger that coffee can provide are dose-dependent, meaning how much you ingest makes a difference. Drinking up to about four cups per day may optimize those effects, Quebbemann says.
One 8-ounce cup of coffee contains about 100 milligrams of caffeine, so four cups puts you at about 400 milligrams of caffeine. Stacey L. Pence, a registered dietitian at the Ohio State University Wexner Medical Center says this has been determined to be a safe amount. “According to the U.S. Dietary Guidelines Advisory Committee and a large meta-analysis, consuming up to four cups of coffee per day with up to 400 milligrams of caffeine daily is not associated with significant adverse effects or development of chronic diseases in healthy (non-pregnant) adults,” she says.
In addition to speeding your metabolism and encouraging fat-burning, coffee might make you a little more able to stick with a diet or get moving more because it can combat fatigue.
“Caffeinated coffee or other caffeinated beverages have been used for their effectiveness in improving mental alertness and reducing physical fatigues as well as improving sports or exercise performance, which may contribute to achieving weight loss,” Pence explains.
Mitchell also points to findings from a meta-analysis published in 2020 that found coffee intake was linked with improved exercise performance. “Exercise along with a balanced diet is an integral piece of the puzzle when it comes to weight loss.”
Coffee is also a mild diuretic that encourages the kidneys to release extra sodium and water from the body. In other words, it makes you pee more. This could reduce the amount of water in your body, which may register as weight loss – also known as water weight.
Beyond caffeine, compounds called mannooligosaccharides are also thought to support weight loss, Pence says. These indigestible compounds, dubbed MOS for short, have “prebiotic properties that may promote the growth of beneficial bacteria in the intestines. MOS has been found to possibly be effective in lowering total body fat in animal and human studies – with increased consumption of MOS causing increased fat excretion in feces, producing a mild laxative effect. This would create a lack of absorption of fat calories, which could promote some weight loss.”
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Other Health Benefits of Coffee
But there’s more to coffee than just a jolt of energy and potentially a little weight loss support. For starters, it might help you focus more. “Coffee intake has been associated with improvement in alertness and mental function as well as memory,” Mitchell says.
What’s good for the brain is usually good for the heart, an old medical saying goes, and that appears to be true with coffee too.
“Some research shows drinking caffeinated coffee is possibly effective in reducing risk of developing Type 2 diabetes and may have cholesterol lowering effects,” Pence says. “Population research shows long-term consumption of coffee is associated with a reduction in cardiovascular mortality.” So, drinking that daily cup of coffee could be helping keep your heart a little healthier.
These effects appear to be “dose-dependent,” Pence says, “meaning the more you drink, the greater the effects. For example, some research shows drinking one cup of coffee daily is associated with a reduction of developing Type 2 diabetes by 6% to 9%. Other studies have found an additional 5% to 10% reduction in risk of developing Type 2 diabetes with each additional cup of coffee consumed per day.”
In terms of lowering cholesterol levels, drinking more coffee appears to be dose-dependent as well, Pence says. “Some research shows the greatest cholesterol lowering effects among those who consumed six to eight cups of caffeinated coffee daily for up to 11 weeks.”
However, this is a lot of coffee. “I would not recommend drinking more than six cups of coffee a day,” Pham says.
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Healthful Compounds in Coffee
While caffeine is certainly a main component of coffee and one of its keys for offering various benefits, there are a wide range of other compounds that have health promoting benefits.
Healthy compounds in coffeeH include:
- Chlorogenic acid. Also called CGA, this is a compound that causes the bitter, or acidic, taste with coffee. “CGA has an antioxidant effect that is likely responsible for the beneficial effects of coffee in terms of protection from heart disease and heart attack,” Quebbemann says. “The antioxidant effect of CGA also seems to protect your DNA and nerve cells.” CGA may also improve your ability to fight infections, from bacteria, fungus and viruses. It may also help stimulate the metabolism and slow the absorption of carbohydrates.
- Trigonelline. “Trigonelline may be beneficial in terms of fighting infection as well as in cancer surveillance, meaning our body’s ability to kill cancer cells,” Quebbemann says. “Trigonelline may also help to regulate blood sugar by decreasing the tendency for people with diabetes to develop an increased blood sugar level when they eat.”
- Polyphenols. Polyphenols are found in many types of plant-based foods and drinks. These antioxidants “have been shown to improve health, decrease inflammation and prevent illnesses,” Pham says. Mitchell adds that you can reap the tissue-protective benefits of polyphenols from a single cup of coffee.
The Downsides of Coffee
While it’s clear that there can be some benefits to drinking coffee, Mitchell recommends keeping intake to fewer than four cups (32 ounces) per day and notes that “not everyone can or should drink that amount per day.”
The same caffeine jolt that can make coffee help you feel better in small doses can overwhelm your system if you drink too much.
Signs of having consumed too much caffeine can include:
- Nervousness, restlessness or feeling jittery.
- Increased heart rate.
- Upset stomach and nausea.
- Muscle tremors.
- Frequent urination.
So how much is too much? The FDA says it’s safe to consume up to 400 milligrams of caffeine per day (roughly 32 ounces of coffee), but Mitchell notes that “caffeine tolerance and metabolism varies widely based on the individual and any health conditions you may have. For example, individuals who are pregnant, have heart conditions or caffeine sensitivity should limit their caffeine intake.”
In addition to the symptoms listed above, excessive consumption of caffeinated coffee or other caffeinated beverages can cause a variety of unwanted and potentially dangerous side effects, including:
- Heart arrhythmias.
- Gastric irritation.
- Diuresis (excessive urination and fluid loss) that could lead to dehydration.
- Gastroesophageal reflux disease or GERD.
- Frequent and more urgent urination.
- Bone loss.
Pham adds that you may also be able to get the same weight loss benefits of coffee without the side effects by drinking green tea.
Watch Out for Caffeine Toxicity
The FDA estimates that toxic effects, such as seizures, can occur after rapid consumption of about 1,200 milligrams of caffeine. That would be the equivalent of drinking 12 8-ounce cups of coffee in quick succession.
The FDA also warns about using caution when consuming caffeine products, such as pills, supplements or energy drinks that are labeled to help you pull that all-nighter and diet supplements that rely on large doses of caffeine to curb appetite and speed metabolism.
The risk of caffeine overdose increases with the concentration of caffeine in the product. It tends to be more difficult to overdose on coffee because there’s a large volume of liquid included with each hit of caffeine. For high-caffeine energy drinks or caffeine pills, however, it may be much easier to consume too much caffeine in a single sitting.
For women, the optimal amount may be a little lower than in men, particularly during pregnancy. “Women who consume large amounts of coffee during pregnancy have a higher risk of premature childbirth, a higher risk of having a low-birth-weight baby and a higher incidence of loss of the pregnancy,” Quebbemann says.
Because of these risks, the American College of Obstetricians and Gynecologists and other experts say pregnant women should limit consumption of caffeine to about 200 milligrams per day. The ACOG recommends one 12-ounce cup of coffee per day to stay under that 200-milligram limit.
Excess caffeine intake has also been associated with bone loss and osteoporosis, which is more common among women. “Some studies have shown that women who drink a large amount of coffee are at increased risk for bone fractures over time,” Quebbemann says.
And children should avoid caffeine altogether. The American Academy of Pediatrics suggests that kids aged 12 and older can safely take in 85 to 100 milligrams of caffeine per day, but recommends that younger kids avoid it completely. It can elevate blood pressure, increase heart rate and cause many of the same problems adults feel when they’ve had too much.
Should You Add Coffee for Weight Loss?
If you’re looking to lose some weight, should you up your coffee intake? Pence says she wouldn’t advise using coffee as your “sole strategy for weight loss, especially with the lack of sufficient, reliable evidence to rate coffee as a substance that helps reduce weight. However, it’s acceptable for the average, healthy adult to consume moderate amounts of coffee,” if you enjoy drinking it.
Mitchell agrees, adding that if weight loss is your goal, “coffee should not be relied upon as the sole strategy or consumed excessively to purposely curb appetite.”
The best advice for those looking to lose weight is to put in the work. To lose weight, you must create a calorie deficit by moving more and eating less. A combination of both exercise and healthy, low-calorie diet is best, Pence says.
Having a cup or two of coffee before a workout may be the best way coffee can help you lose weight, she adds. This is because caffeine can act as “an ergogenic aid to improve physical performance with sports or exercise,” which can help you get through a tough workout.
“If consuming moderate amounts of caffeinated coffee provides that boost you need to get through your workout or to provide more energy to plan and prepare a healthy meal, then feel free to do so, especially if you’re not part of an at-risk population for adverse reactions,” she notes.
While some folks are looking to increase their intake of coffee for weight loss or health benefits, others may be looking to cut back because of the side effects and dependency on caffeine that can develop. If you’ve been a regular coffee drinker for years but are looking to cut back your intake, go slow, Quebbemann says.
“Suddenly stopping all intake of coffee can result in a feeling of chronic fatigue and mental dullness. These effects gradually go away, but they can be quite obvious for a day or two if a hardcore coffee drinker quits cold-turkey.”
Black Coffee Is Best for Weight Loss
Finally, it should be noted that with all of this, we’re talking about unadorned, black coffee. “A cup of plain, black coffee has two to five calories,” Pham says, and “consuming a cup can cause you to burn up to 17 calories” because of caffeine’s metabolic boosting powers.
Mitchell adds that because black coffee clocks in at 5 calories or less per 8-ounce serving, “it’s considered a very low calorie food.”
However, “the potential weight loss benefits of coffee are negated when coffee is heavily sweetened with syrups and sugars.” And, if you add cream or milk, that will also substantially increase your caloric intake, which can halt weight loss or even result in weight gain.
“Some coffee drinks from Starbucks have up to 500 calories due to the additives,” Pham says. “People may also eat more while having a cup of coffee, thereby increasing their daily caloric intake.” While coffee might help you melt some excess weight, coffee cake certainly isn’t a diet food.