Do you start your morning with a hot cup of coffee or a frothy latte? For some, the morning isn’t complete without a piping hot cup of java. Coffee has a stimulating effect on the nervous system that helps you wake up and get going in the morning. You might also wonder whether that invigorating effect that keeps you coming back for another cup boosts your metabolism and might help with weight loss. What does science say aout coffee, caffeine, and weight control?
How Caffeine Works
When you sip a cup of coffee, the caffeine enters your bloodstream and travels to your nervous system Here, it binds to receptors in your brain called adenosine receptors. By doing this, it blocks the activity of adenosine itself. That’s why it wakes you up. Adenosine is a chemical that promotes relaxation and calmness. So, when caffeine blocks the action of adenosine, you become more alert and sometimes a bit nervous and jittery. That’s because caffeine is acting as a stimulant. You might also wonder whether it has an impact on your resting metabolic rate?
Caffeine does appear to boost resting metabolism, although the effect is modest. A study published in the American Journal of Nutrition in the 1980s found that caffeinated coffee elevated resting metabolic rate and increased fat oxidation after participants drank it. Other studies show a spike in resting metabolism after drinking coffee as well and the effect lasts for up to 2 hours.
A more recent assessment found that drinking a 10-ounce cup of caffeinated coffee boosted resting metabolism in men by 7-11% for a few hours after they drank it. In women, the boost in metabolism was more substantial, up to a 24% increase. Still, even if you drink 3 or 4 cups of coffee throughout the day, you’ll only burn an additional 100 to 200 calories over the course of a day. That’s not insignificant, but if you enhance your coffee with sugar and cream, you’ll consume far more energy than the additional you burn off. So, skip the frou-frou drinks.
The Impact of Coffee and Caffeine on Appetite
Another way drinking coffee might work in your favor when you’re trying to lose weight is to blunt your appetite. However, a study carried out on 16 healthy men found that consuming 200 milligrams of caffeine with breakfast had no impact on appetite or how many calories the participants consumed with the meal. What they did find was the men who drank caffeinated coffee experienced a rise in circulating cortisol. Cortisol is a stress hormone that when sustained is linked with accumulation of fat around the abdominal region.
Interestingly, a study that compared water versus caffeinated coffee versus decaffeinated coffee found that decaffeinated coffee led to greater feelings of satiety. Drinking decaf was also linked with a greater increase in PYY, a hormone that suppresses appetite. So, if coffee does have appetite suppressing effects, it may not be due to the caffeine but some other component that’s present in significant quantities in decaf coffee.
Insulin Sensitivity, Cortisol, and Coffee
As mentioned, one study found caffeinated coffee was linked with a cortisol and, if sustained, this would not be favorable for body composition since cortisol is associated longer term with weight redistribution, more storage of fat in the abdominal region, and also breakdown of muscle tissue. Another issue is how caffeinated coffee impacts insulin sensitivity. If it reduces insulin sensitivity, more circulating insulin would promote fat storage and make it harder for your body to break down fat.
Interestingly, short-term, drinking coffee appears to decrease insulin sensitivity, and that’s not what you want if you’re trying to maintain a healthy body weight and avoid type 2 diabetes. However, habitual coffee drinking over a longer period of time boosts insulin sensitivity and appears to lower the risk of type 2 diabetes. So, overall the impact is likely positive.
Habituation to the Effects of Caffeine
On the plus side, caffeine appears to boost resting metabolic rate. However, this doesn’t necessarily lead to lasting weight loss. One study found that giving participants 200 milligrams of caffeine daily for 24 weeks did not lead to weight loss. Yet another study of 58,000 health professionals found those who increased their caffeine over the course of the 12-year study didn’t lose weight but actually gained/ Even studies that show weight loss with caffeine, the benefits are short-term and unassociated with successful weight loss maintenance longer term.
What it boils do to is this. Caffeinated coffee is a blend of thousands of chemicals, including caffeine and its impact on the human body is complicated. Plus, there are variations in how quickly people metabolize caffeine. Some people have a genetic variant of an enzyme that breaks down caffeine. In these folks, caffeine stays in their system longer and can have a variety of adverse side effects, including elevations in blood pressure, insomnia, anxiety, abnormal heart rhythms, as a result. Therefore, there are genetic differences in how your body handles caffeine.
The Bottom Line
Caffeine may modestly boost resting metabolic rate, but it alone is unlikely to lead to sustained weight loss. Your best bet is to eat a diet of whole foods and enjoy coffee for the other potential health benefits it offers. Preliminarily, studies show it may lower the risk of Parkinson’s disease, gall bladder, disease, and type 2 diabetes. Plus, a new study showed drinking four or more cups daily is linked with a 64% reduction in overall mortality. So, enjoy a cup or two of coffee but don’t count on it to help you lose weight. Eat a healthy diet instead and keep your body active. Those are tried and true ways to control your body weight.
Am J Clin Nutr. 1980 May;33(5):989-97.
Korr Medical Technologies. “Effects of Caffeine on Metabolic Rate”
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Precision Nutrition. “Coffee and Appetite”
American Diabetes Association. “Effects of Coffee Consumption on Fasting Blood Glucose and Insulin Concentrations”
Science Daily. “Higher coffee consumption associated with lower risk of early death”