Weight loss coffee: what black coffee does, and what it cannot

Does coffee actually help you lose weight?

By a small amount. The clearest summary comes from Reza Tabrizi and colleagues, who pooled 13 randomised trials with 606 participants in 2019. People given more caffeine lost a little more weight and fat than those given less, and the effect rose with the dose. The trials were small and varied a great deal in design, so the size of the effect is uncertain.

Those trials mostly gave caffeine as a measured dose, often as capsules, so they say little about a cup of filter coffee with sugar. Coffee bought as a weight loss product promises far more than this evidence supports. A cup works on the margins, slightly raising calorie burn and helping a workout, while what you eat decides the result.

Take Kavya, 34, who runs the office of a school in Chennai and is an example rather than a patient. She has three tumblers of filter coffee a day, each with two spoons of sugar, and a cousin has told her to switch to black. The switch will help her, though mostly because of the sugar she drops.

Sources: [1]

How much extra does caffeine make you burn?

Dulloo's team measured it in a room-sized calorimeter in 1989. A single 100 mg dose of caffeine, about one ordinary cup of coffee, raised resting metabolic rate by 3–4% for about two and a half hours.

When volunteers took 100 mg every two hours across a 12-hour day, daytime energy use went up by 8–11%. Over the full day that came to about 150 extra calories in lean volunteers and 79 in people who had previously lived with obesity. The volunteers who had previously lived with obesity got about half the effect of the lean ones. That dosing schedule also adds up to more caffeine than the 400 mg a day that safety reviews accept for healthy adults.

With two or three ordinary cups spread through a day, a fair guess from these figures is a few dozen extra calories. A short walk after dinner burns about as much. Regular drinkers also grow partly tolerant to caffeine, which may be one reason the long-term studies find smaller changes than the lab did.

Sources: [2], [12]

What does a lifetime of coffee drinking do to body weight?

Esther Lopez-Garcia and colleagues at Harvard followed 18,417 men and 39,740 women for 12 years, asking about caffeine every two to four years. Everyone gained some weight over that time. Those who increased their caffeine gained slightly less than those who cut back, but the gap between the extremes was only about 0.4 kg.

An increase in coffee and tea drinking was also linked with less weight gain. Because this was an observational study, it cannot prove the caffeine caused the difference. What it does show is the scale: in a large group followed for twelve years, the difference linked with caffeine was well under a kilo.

Coffee drinkers may have other reasons to keep drinking it. A 2014 meta-analysis of 28 cohort studies, covering over a million people, found each extra daily cup linked with a 9% lower risk of type 2 diabetes for caffeinated coffee and 6% for decaf. Again, these are associations, but they suggest the habit is not working against you.

Sources: [3], [4]

Black coffee, filter coffee or cold coffee: which one helps?

This is where most of the gain or loss is decided. A cup of black coffee or an americano has close to nothing in it. A South Indian filter coffee made with half a tumbler of full-cream milk and two teaspoons of sugar carries roughly 90–110 calories. A large café cold coffee with ice cream or syrup can carry several times that.

Kevin Hall's energy balance model, published in The Lancet in 2011, gives a way to size this. Each lasting change of about 24 calories a day eventually shifts body weight by about 1 kg, half of it within a year. Kavya's three sweet tumblers hold roughly 100 calories of sugar alone. Dropping the sugar and keeping the milk could, on that arithmetic, move her weight by around 4 kg over a few years, without touching her meals.

So a gradual cut works better than a sudden switch to bitter black coffee that she hates. Go from two spoons of sugar to one for two weeks, then half, then none. Use toned or double-toned milk if you like it milky. Leave the chicory blend alone if that is what you enjoy, because it adds taste, not calories.

Sources: [5]

Is green coffee extract worth taking?

Green coffee capsules are made from unroasted beans and are sold for their chlorogenic acid. Igho Onakpoya and colleagues at Exeter reviewed the human trials in 2011. They found five, could use three, and judged all of them at high risk of bias. Pooled, the capsules took about 2.5 kg more off than placebo, but the authors wrote that the studies were of poor quality and more rigorous trials were needed.

Green tea extract has a slightly better record. A 2009 meta-analysis by Rick Hursel and Margriet Westerterp-Plantenga found catechins with caffeine lowered weight by about 1.3 kg on average. The effect looked smaller in people who already took in over 300 mg of caffeine a day, though that difference did not reach significance. If you drink three or four cups of coffee, the extract has less left to add.

Some ready-mixed slimming coffees add herbs such as garcinia to instant coffee, so read the label. Onakpoya's group also reviewed garcinia, pooling nine trials, and found about 0.9 kg more loss than placebo, with stomach upsets more common in one study. Butter or ghee coffee goes the other way: a tablespoon of fat adds around 100 calories to a cup that had almost none.

Sources: [6], [7], [8]

Should you drink coffee before a workout?

If you exercise, an hour before is the best time for your cup. The International Society of Sports Nutrition reviewed the trials in 2021 and found that caffeine at 3–6 mg per kg of body weight helped endurance, strength and sprinting in many of them. For a 60 kg woman the low end is 180 mg, which two ordinary cups will cover.

Kavya's school day ends at four, and she does squats, lunges and rows with a backpack of books on her building's terrace at five. On days she has a coffee at four she manages a third set. Those extra sets matter more than the few calories they burn, because lifting while eating less is how the body is persuaded to keep its muscle and give up fat.

Muscle is also how we judge a good result at Metaboliq. The plans aim to lose up to 20% of body weight while keeping muscle, and they are set by a doctor after a home blood test. For someone like Kavya, a pre-workout coffee is one small part of that.

More caffeine does not mean a better workout. Around 9 mg per kg, jitters, a pounding heart and an unsettled stomach become common and performance does not improve. If coffee on an empty stomach gives you acidity, have it with a banana or a handful of peanuts.

Sources: [9]

Why does the time of your last cup matter for fat loss?

Caffeine stays in the body for hours. Christopher Drake's group gave people 400 mg at bedtime, three hours before or six hours before, and checked their sleep at home with a monitor. All three cut sleep compared with a placebo, including the dose taken six hours early. The authors' advice was to avoid substantial caffeine for at least six hours before bed, so a 4 pm coffee is about the limit for an 11 pm sleeper.

Lost sleep costs more than energy. Arlet Nedeltcheva's team in Chicago put ten overweight adults on the same reduced-calorie diet twice, once with 8.5 hours in bed and once with 5.5. With short nights, the share of weight lost as fat fell by 55% and the loss of lean mass rose by 60%, and people felt hungrier. It was a small, two-week study, but the direction is hard to ignore.

For Kavya, that means the last tumbler comes from the school canteen around three, and the after-dinner cup with her husband becomes warm milk with a pinch of elaichi. She grumbled for a week. By the second week she was falling asleep before eleven, and her evening snacking had eased off too.

Sources: [10], [11]

How much coffee is safe, and who should drink less?

A large 2017 safety review led by Daniele Wikoff found that up to 400 mg of caffeine a day is not linked with harm to the heart, bones or behaviour in healthy adults. For pregnancy the review used a lower ceiling of 300 mg, and many obstetricians advise less, so follow your own doctor. A cup can vary a lot: in one US study, single servings of café coffee held between 58 mg and 259 mg.

Robin Poole's umbrella review in the BMJ found coffee more often linked with benefit than harm, with the largest risk reductions around three to four cups a day. The clear exception was pregnancy, where high intake was linked with low birth weight and pregnancy loss. Women at higher risk of fractures may also want to keep intake moderate. For counting at home, treat an ordinary cup of instant or filter coffee as one, a large café coffee as two, and an energy drink as one, and stay at four or fewer.

One more point for vegetarians. Coffee drunk with a meal reduces how much iron the body absorbs from plant foods. In Morck's study, a cup with a meal cut absorption by 39%, while coffee taken an hour before the meal had no effect. Coffee an hour after the meal blocked iron just as much, so if your iron runs low, have your cup between meals and at least an hour before you eat. People with acidity, palpitations, anxiety or high blood pressure should check with a doctor before drinking more.

Sources: [12], [13], [14], [15]