If you're a java-lover who's looking to lose weight, the coffee diet might sound like the ultimate dream. After all, it promises to harness the power of this bean brew to boost your metabolism, decrease your appetite and burn fat.
Intrigued? Here's what you need to know before you fire up the Keurig.
How the Coffee Diet Works
The coffee diet is a relatively new diet plan made popular by medical doctor Bob Arnot's 2017 book The Coffee Lover's Diet. In it, Dr. Arnot says that drinking a least three cups of light roast coffee daily and eating a fiber-rich diet are the keys to weight loss. While the plan is generally safe for most people and encourages healthy food choices, there's a lack of consistent evidence that coffee helps with weight loss, and the plan may be difficult to stick with long enough to see results.
Dr. Arnot recommends drinking light roast coffee due to its higher amount of polyphenol, antioxidants that help protect our cells from damage by free radicals. A March 2017 study in Phytochemical Analysis supports his claims: It showed that darker and slow-roasted coffees have a lower antioxidant capacity than lighter brews, most likely due to the antioxidants breaking down during the heat of the roasting process.
While following the diet, you can have as much coffee as you want throughout the day as long as the minimum limit is reached. Both caffeinated and decaf coffee are allowed.
In addition, Dr. Arnot recommends eating foods rich in fiber. The diet is similar to the Mediterranean diet in that it focuses on whole grains, fruits, vegetables, lean sources of animal protein, plant proteins and healthy fats (think olive oil, nuts and seeds, avocado and fish).
The diet's sample meal plans, laid out in the book, provide about 1,500 calories per day and limit processed foods. For most people, 1,500 calories is lower than their daily average intake and adequate for weight loss. In fact, Harvard Health Publishing advises that women should not consume fewer than 1,200 daily calories and men should not fall below 1,500 calories per day.
Possible Benefits of the Coffee Diet
Dr. Arnot claims that coffee suppresses appetite and boosts metabolism. But the research around these claims is conflicting.
Coffee as an Appetite Suppressant
A small study published in June 2013 in Obesity that included 33 participants who were overweight or obese found that drinking a moderate amount of coffee immediately before breakfast reduced calorie intake for that meal.
But another small study of just 12 participants, published in December 2014 in Appetite, found there were no significant effects of consuming coffee on energy intake or gastric emptying (the time it takes food to leave your stomach).
A review published in December 2017 in the International Journal of Food Science Nutrition suggested that timing might be the key factor. It found that caffeine given between a half hour and four hours before a meal may suppress calorie intake, but coffee administered three to four and a half hours before a meal had minimal influence on the amount of food eaten.
All in all, the research on coffee's ability to decrease food intake is limited and inconclusive.
Coffee and Weight Loss
There is more evidence that points to coffee's ability to boost metabolism, though.
A review published in October 2018 in Critical Reviews in Food Science and Nutrition evaluated 13 studies with a total of 600 participants. The research looked at caffeine intake and body weight, BMI and fat mass. Researchers noted that as caffeine intake increased, these other measures decreased. Specifically, when participants doubled their caffeine intake, their BMI, weight and fat mass decreased by 17 to 28 percent.
Caffeine may also contribute to an increased calorie burn immediately following a workout. A small study of 12 people, published in July 2016 in the Journal of Strength and Conditioning Research, had participants take either a caffeine supplement or a placebo before performing 30 minutes of sprint interval exercise. People who received the caffeine supplement had greater fat oxidation and calorie burn than those who were given the placebo. These results are promising for caffeine as a weight-loss aid, but more research needs to be conducted to confirm the results.
It's also important to note that there is no research showing coffee can help reduce fat in one area of the body. Fat oxidation is not specific to certain areas of the body, so if you're hoping to reduce stubborn belly fat with coffee alone, it is unlikely to help.
Read more: The 12 Worst Coffee Drinks to Order
Possible Drawbacks of the Coffee Diet
While coffee contains antioxidants, which provide a potential health benefit, upping your daily coffee amount could have some negative side effects as well.
Decaf coffee is allowed on the coffee diet, but most people aim to drink the minimum three cups in caffeinated form. This makes sense, since most of the research related to coffee's ability to help with weight loss is linked to the drink's caffeine content. However, excessive caffeine intake may cause certain health problems, such as high blood pressure.
A study of 1,100 people published in December 2016 in Clinical Nutrition found those who drank three or more cups of coffee per day had higher blood pressure than those who did not drink coffee at all. If blood pressure is a concern for you, it's best to speak with your doctor before increasing your coffee or caffeine intake.
Tummy troubles may also be a concern on the coffee diet. According to Johns Hopkins Medicine, caffeine, including coffee, increases the risk of diarrhea — part of the reason why caffeine is one of the top foods to avoid if you suffer from irritable bowel syndrome (IBS).
For those who are more sensitive to caffeine, the recommended three cups of coffee could cause jittery feelings or even disrupt sleep, according to the Mayo Clinic. And keep in mind that the Mayo Clinic recommends adults in general drink less than 400 milligrams of caffeine per day, which is roughly equivalent to four cups of coffee. Any more than that, and you may experience side effects such as headache, irritability and muscle tremors.
Is the Coffee Diet Healthy?
The coffee diet promotes a whole-foods approach to eating, which is similar to the Mediterranean diet. While focusing on whole, natural foods is a healthy approach, limiting all processed or convenience foods can be restrictive and unrealistic, making it hard to stick with.
The coffee diet's sample meal plans also come in low on their calorie counts, at around 1,500 calories per day, which may be unsustainable in the long term for most people.
The research on coffee's ability to decrease appetite and burn fat is limited and still inconclusive, which means it's not a magic bullet for weight loss. And while coffee is rich in antioxidants, it doesn't provide other nutritional benefits.
Coffee can also trigger digestive upset, including heartburn and diarrhea. Too much caffeine may increase blood pressure, anxiety and heartbeat, and it could also interfere with sleep.
Bottom line: Speak with your doctor or a registered dietitian before trying the coffee diet — or any diet, for that matter — to make sure it's the right approach for you.
- Phytochemical Analysis: "Understanding the Effects of Roasting on Antioxidant Components of Coffee Brews by Coupling On‐line ABTS Assay to High Performance Size Exclusion Chromatography"
- Harvard Health Publishing: "Calorie counting made easy"
- Obesity: "Effect of different amounts of coffee on dietary intake and appetite of normal-weight and overweight/obese individuals."
- International Journal of Food Science Nutrition: "Caffeine, coffee, and appetite control: a review."
- Appetite: "Coffee for morning hunger pangs. An examination of coffee and caffeine on appetite, gastric emptying, and energy intake."
- Journal of Strength and Conditioning Research: "Dietary Caffeine and Polyphenol Supplementation Enhances Overall Metabolic Rate and Lipid Oxidation at Rest and After a Bout of Sprint Interval Exercise"
- Clinical Nutrition: "Habitual coffee consumption and 24-h blood pressure control in older adults with hypertension"
- Johns Hopkins Medicine: "5 Foods to Avoid if You Have IBS"
- Critical Reviews in Food Science and Nutrition: "The effects of caffeine intake on weight loss: a systematic review and dos-response meta-analysis of randomized controlled trials"
- Mayo Clinic: "Caffeine: How much is too much?"