Caffeine: The Weight Loss Drug You Didn’t Know You Were Taking?

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Most of us drink it, and some of us can’t even function without it – caffeine is the most widely consumed psychoactive drug in the world. Whether in tea, coffee or other drinks, around 90% of adults consume caffeine every single day. Caffeine is best known for being a stimulant, boosting alertness and suppressing sleep. Yet caffeine might also have a whole range of other benefits, one of which is weight loss. But is taking more caffeine really a worthwhile approach to shedding those kilos? Let’s take a look at the science.

What is it?

Caffeine is a naturally occurring chemical found in plants like tea, coffee and cocoa. Plants produce caffeine mainly as a defensive mechanism, since caffeine is toxic to insects and other small animals that might eat the plant. Caffeine may also inhibit the growth of nearby competing plants.

What does it do?

Caffeine’s main effect is to prevent a neurotransmitter called adenosine from binding to its receptor in the central nervous system. Adenosine builds up throughout the day, especially during exercise, and affects the secretion of other neurotransmitters like dopamine and serotonin. The result is that higher levels of adenosine suppress alertness and motivation while promoting fatigue and sleep. Adenosine is then cleared during sleep. Caffeine also has some secondary effects, like boosting calcium release in muscle cells (which allows them to contract harder) and triggering the release of adrenaline and noradrenaline.

What does this have to do with weight loss? Firstly, adrenaline and noradrenaline increase the body’s resting metabolic rate (RMR) – the rate at which the body expends energy when not exercising. This includes stimulating the breakdown of stored fat. Secondly, caffeine may help people exercise harder. As mentioned previously, exercise increases adenosine levels, which suppresses the release of dopamine and reduces mood and motivation. Blocking the action of adenosine may therefore improve motivation to exercise harder and for longer, and may also improve exercise performance thanks to caffeine’s effects on muscle tissue and metabolic rate.

What’s the evidence?

This all looks good on paper, but does caffeine actually lead to meaningful weight loss? Let’s look at the effect on resting metabolic rate, since this tends to be the most appealing – who doesn’t want to burn fat without lifting a finger? Studies suggest that people consuming caffeine do indeed burn more Calories, but not by much. This meta-analysis, for example, looked at studies in which participants took various doses of caffeine, with the average dose tested being equivalent to around 6 cups of coffee per day. They found that people taking caffeine expend around 100 Calories more per day than those taking a placebo. For reference, this is roughly the amount of Calories spent in 30 minutes at normal walking speed, or in 10 minutes at normal jogging speed.

While this isn’t nothing, it’s also not that impressive, especially when you consider that most people already consume some amount of caffeine and that the benefits of taking more caffeine did not seem to be very high. According to estimates, taking an extra coffee cup’s worth of caffeine only increases energy expenditure by about 10 Calories. So, chugging caffeinated drinks is unlikely to cause weight loss by itself.

Where caffeine might have more value is in aiding weight loss through other tried and tested strategies, namely exercise and dieting. There’s good evidence that caffeine taken before exercise not only improves performance, but also reduces perceived exertion, helping people to exercise harder and for longer. There’s also some evidence that caffeine suppresses appetite. Despite all this, we don’t really know if caffeine helps people lose weight in practice because not that much research has been done. Many studies that do exist don’t attempt to isolate the effects of caffeine, but rather study it in combination with other supplements, drugs, or alongside dietary restriction as opposed to more common forms of dieting.

Is it safe?

Caffeine is safe for most people below the maximum recommended daily dose of around 400 mg (about 4 cups of coffee), and is probably safe at much higher doses depending on how they are spaced out. Caffeine has multiple negative side effects, though these tend to lessen with regular consumption. The main long-term health concern when it comes to caffeine is its effects on sleep. When taken too late in the day, caffeine interferes with sleep and prevents the body from entering the deeper restorative sleep stages. This can happen without making it harder to actually get to sleep, so this negative effect may not be obvious. This results in increased tiredness throughout the subsequent day, leading to the consumption of more caffeine in a vicious cycle. Studies generally suggest that caffeine should not be consumed within 9 hours of bedtime.

It is possible to take a fatal overdose of caffeine, but this is extremely unlikely when caffeine is consumed in the form of drinks like coffee. You would need to drink somewhere between 50 and 100 cups of coffee in quick succession to receive a fatal caffeine dose. Caffeine-containing supplements are also safe, as they generally contain around 200 mg of caffeine – about half the recommended daily limit. However, some companies sell highly concentrated caffeine in the form of powder. This is actually illegal in many countries because it requires the consumer to measure out a safe dose. Since it only takes about a tablespoon of caffeine powder to kill someone, the risk of measurement error is considered to be too high.

The take home message

Consuming more caffeine without putting in any effort probably won’t have much of an impact on weight loss, but it might help you exercise by making exercise feel easier (if taken before or during exercise), and it could also help you stick to a diet. However, it’s important not to have caffeine during the second half of the day because of its effects on sleep.