Caffeine is one of the most popular ingredients worldwide. Although it provides many benefits, caffeine can have negative effects as well. Whether caffeinated beverages are mostly helpful, potentially counterproductive, or neutral for people on keto or low-carb diets is somewhat controversial. This article explores caffeine's effects on health in the context of a carb-restricted diet and makes recommendations for consuming it in a way that maximizes benefits while minimizing side effects.
What is Caffeine, and How Does It Work?
The scientific name for caffeine is 1,3,7-trimethylxanthine. Caffeine is the most common stimulant in the world, consumed by an estimated 80% of people worldwide and 90% of Americans on a daily basis (1, 2).
Caffeine vs Other Stimulants
Although some consider it a psychoactive drug because it stimulates the central nervous system (CNS), caffeine's mechanism is different from that of cocaine and other stimulants. These stimulants work primarily by binding to the dopamine transporter. Dopamine is a neurotransmitter (chemical messenger that transmits signals between nerve cells in the brain) that allows us to perceive pleasure, excitement, and reward. When cocaine binds to the dopamine transporter, it prevents the removal of dopamine from the nervous system, thus amplifying its effects.
By contrast, although caffeine enhances dopamine activity, it works by blocking the effects of another neurotransmitter called adenosine, which causes relaxation and sleepiness. By binding to the brain's adenosine receptors, caffeine allows us to remain awake and alert (2).
Which Foods, Beverages and Medications Contain Caffeine?
Although caffeine occurs naturally in tea, chocolate, kola nut, and other plant foods, it's most often associated with coffee. In fact, its name comes from the German word “kaffee” and the French word “cafe,” both of which translate to “coffee.” Certain pain relievers: 30-65 mg (check labels for caffeine content)
Here is a list of the caffeine content in commonly consumed foods and beverages. In general, coffee from Starbucks and other coffee houses tends to be higher in caffeine than coffee brewed at home.
Caffeine Content in Coffee and Tea (8 oz/ 240 ml), except where noted
- Coffee, brewed: 100-180 mg
- Coffee, instant: 27-73 mg
- Coffee, decaffeinated: 3-15 mg
- Espresso: 60-75 mg per shot (30 ml)
- Black tea: 40-120 mg
- Green tea : 30-50 mg
- Yerba Mate tea: 65-130 mg
Caffeine Content in Other Beverages
- Cocoa powder: 12 mg per tablespoon
- Soft drinks: 35 to 55 mg per 12 ounces (350 ml)
- Energy drinks (Monster, RockStar, RedBull, etc.): 140 to 240 mg per 16 ounces (480 ml)
- 5-Hour Energy Shot: 200 mg per 2 ounces (60 ml)
The average US adult consumes about 4 mg of caffeine per kg of body weight, which is 270 mg for a person weighing 150 pounds (68 kg) (3). However, many people get much more than the average US adult, especially those who drink several cups of coffee daily.
Caffeine Increases Metabolic Rate and Promotes Fat Loss
Research has shown that caffeine promotes fat burning and helps suppress appetite, making it valuable for weight loss and maintenance (4).
In controlled studies, it's been shown to boost metabolic rate by up to 13%, depending on the person and the dosage (5, 6, 7).
In one study, people consumed 100 mg of caffeine every two hours for a total of 600 mg within 12 hours. During the study time period, lean adults burned an average of 150 extra calories, whereas formerly obese adults burned an extra 79 calories (7).
Caffeine May Increase Ketone Levels
Additionally, emerging research suggests that caffeine may help boost ketone levels.
In a small study of 10 healthy adults, consuming breakfast with caffeine dosages of 2.5 mg per kg body weight and 5.0 mg per kg body weight increased blood ketone levels by 88% and 116%, respectively, compared to having breakfast without caffeine (8). For reference, this would be about 170-340 mg of caffeine for a person weighing 150 pounds (68 kg).
Importantly, this increase occurred when caffeine was included with a breakfast totalling 85 grams of carb. It would be logical to assume that this effect would be equivalent or greater in people following low-carb or ketogenic diets.
In fact, it might be interesting to conduct a few n=1 experiments by measuring changes in your own ketone levels after consuming different amounts of carbs with or without caffeine.
Caffeine and Blood Sugar
Overall, caffeinated beverages seem to be protective against diabetes. What's more, higher caffeine intake has been linked to greater diabetes risk reduction.
In a meta-analysis of 26 studies and over one million people in total, for every 2 cups of caffeinated coffee consumed per day, the risk of developing diabetes was reduced by 12%, and every 200 mg increase in daily caffeine intake was shown to reduce diabetes risk by 14% (9).
Two additional reviews suggest that coffee itself may help prevent type 2 diabetes, given that both caffeinated and decaffeinated coffee seem to provide similar risk reduction when consumed on a regular basis (10, 11).
Conversely, other studies have found that caffeine raises blood sugar and insulin levels in both healthy people and those with diabetes or prediabetes (12, 13, 14).
And unlike diabetes risk, this effect appears to be due to caffeine itself rather than another component of coffee, because decaffeinated coffee hasn't shown the same ability to raise blood sugar (14).
However, it's possible that this response may occur mainly in people who aren't accustomed to consuming much caffeine.
One randomized, controlled study found that blood sugar and insulin levels didn't increase after prediabetic habitual coffee drinkers increased their daily intake to 5 cups of caffeinated coffee for 16 weeks. Indeed, their blood sugar levels were lower than the groups who drank decaffeinated coffee or no coffee at all (15).
This suggests that after adapting to caffeine's effects over time, blood sugar and insulin response may possibly even improve from baseline, although this likely varies from person to person.
And once again, it's important to point out that these studies were conducted in people who were not following keto or low-carb diets, so the caffeine was coupled with high carb intake.
This is another case where n=1 testing can provide useful information about your own body's blood sugar response to caffeine.
Other Beneficial Effects of Caffeine
Caffeine Enhances Physical Performance
Several studies have shown that caffeine enhances the body's response to strength and endurance exercise (16, 17, 18).
And contrary to popular belief, a recent study from July of 2017 found that heavy caffeine intake on a regular basis does not reduce the performance-enhancing benefits of high-dose caffeine prior to activity (19).
Caffeine May Improve Mood
Research suggests that caffeine has positive effects on mood, alertness, and levels of fatigue (20, 21).
In one study of mentally fatigued adults, consuming a large dose of caffeine (5 mg per kg of body weight) was found to both increase endurance performance by 14% and improve mood (20).
Caffeine May Protect Liver Health
Evidence from observational studies suggests that caffeine – particularly in the form of caffeinated coffee – may help protect against cirrhosis and fatty liver (22, 23).
Negative Effects of Caffeine
Unfortunately, caffeine also has some downsides. However, these responses are highly individualized and strongly influenced by the amount of caffeine consumed.
Here are some of the more common side effects of caffeine:
There's no denying that consuming caffeine on a regular basis can lead to dependence (24). Indeed, withdrawal symptoms such as headache and occasionally nausea and vomiting typically occur in heavy caffeine drinkers after going several hours without caffeine (25).
In a study in 25 healthy men, ingesting a modest dose of caffeine (3.5 mg per kg of body weight) prior to a stressful laboratory test increased levels of the stress hormones cortisol and epinephrine twice as much as ingesting a placebo. Moreover, effects were similar among those who regularly consumed coffee and those with less frequent intake (26).
Keeping cortisol levels within normal range is important for good health and to prevent weight gain. Research has shown that elevated cortisol levels may increase appetite, food intake, and fat storage around the abdomen (27, 28).
Because it stimulates the central nervous system and blocks release of brain chemicals that cause relaxation, caffeine can interfere with sleep in many people, especially when consumed later in the day. This occurs because its effects can remain in our system anywhere from 1.5 to 9 hours, with an average of 5 hours (29).
Increased Heart Disease Risk in "Slow" Caffeine Metabolizers
A case-control study of more than 2,000 people found that high caffeinated coffee consumption was linked to increased risk of heart attack only in those with the CYP1A2 genotype, who are predisposed to being “slow” caffeine metabolizers (30). Unlike “fast” caffeine metabolizers who eliminate the stimulant quickly, caffeine remains in the system of “slow” caffeine metabolizers longer. Another study showed that individuals with the CYP1A2 genotype are also more likely to see an increase in blood pressure after drinking caffeine (31).
How Much Caffeine Is Optimal?
How much caffeine should you consume in order to boost your metabolism, potentially reduce risk for diabetes and other diseases, and improve your physical performance without experiencing undesirable side effects?
A large analysis of 41 studies found that 38–400 mg of caffeine per day seemed to maximize the benefits of caffeine while minimizing the likelihood of adverse effects (32).
This is roughly third of a cup to 4 cups of coffee per day, depending on how it's made and how strong it is.
Admittedly, this is a large range. Some people will do best at the lower end, whereas others may need to consume significantly more caffeine to experience the same results.
Keto-Friendly Caffeinated Beverage Options
Drinking your coffee or tea black or with a tablespoon or two of heavy cream and/or adding a healthy sugar-free sweetener will provide 0-2 grams of carb, making these ideal choices for people who follow keto or low-carb diets.
This is by far the best way to order caffeinated beverages at a coffee house. The next-best option would be adding half and half, which contains 1 gram of carb per tablespoon. Unsweetened almond or coconut milk are other good possibilities, but be aware that many coffee and tea places use sweetened versions of these alternative milks.
Be sure to steer clear of “Light” or “Skinny” drinks, which are typically made with nonfat milk and contain sugar or other high-carb sweeteners. For instance, a 16-ounce (475 ml) Starbucks Skinny Mocha contains 20 grams of net carb, and a 12-ounce (350 ml) Coffee Bean Tea Latte made with almond milk, coconut milk and no-sugar-added vanilla powder has 34 grams of net carb.
Instead, stick with the basics when ordering out, and at home try these healthy, delicious caffeinated beverage recipes that contain less than 5 grams net carb per serving:
Keto-Friendly Decaf Beverage Options
If you avoid or limit the your caffeine intake, below are some keto-friendly decaf beverage options.
Take Home Message
For many of us, caffeine is part of daily life. Overall, caffeine been shown to have beneficial effects on our health. It's been shown to increase metabolism, enhance physical performance, improve alertness, and suppress fatigue. In addition, research suggests it may help prevent diabetes and protect against liver disease.
As long as caffeine intake doesn't go too much beyond the upper recommended level of 400 mg per day, it should be safe for most people.
On the other hand, some individuals are very sensitive to caffeine's effects and should consume it in very small amounts or avoid it altogether.
The key is taking an honest look at how caffeine affects you, which may include testing blood sugar and experimenting with how you sleep and perform at various doses. Finding the right amount of caffeine for you may truly improve your overall health and quality of life.
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