Many over-the-counter weight-loss supplements contain caffeine because of its potential effects on metabolism and weight. Whether or not caffeine can bring about a slight increase in weight loss, however, may depend at least in part on the source, and how long you've been consuming caffeine.
Caffeine and Weight Loss
Simply adding caffeine to your diet isn't likely to bring about a significant weight loss. You'll still need to eat less and exercise more to lose a substantial amount of weight. Caffeine may slightly increase your metabolism and may help you eat a little less at meal time, but eventually you may become less sensitive to its effects, according to a review article published in American Journal of Physiology - Regulatory, Integrative and Comparative Physiology in 2007.
Caffeine From Coffee
Drinking a moderate amount of coffee each day -- or about 2 to 3 cups -- may be helpful for weight loss. A study published in Evidence-Based Complementary and Alternative Medicine in 2013 found that chlorogenic acid -- a compound found in coffee -- may help limit the absorption of fat and it may improve the levels of hormones related to obesity. If you increase your daily coffee consumption to 5 cups, however, it could have the opposite effect. A study published in the Journal of Agricultural and Food Chemistry that same year found that high doses of chlorogenic acid given mice that were fed high-fat diets didn't protect against obesity, and that it could increase insulin resistance and the amount of fat stored in the body. The same is most likely true of high doses of green coffee bean supplements.
Caffeine From Tea
Getting your caffeine from green tea may be a good way to slightly increase your weight loss, according to the American Journal of Physiology review article, which notes that antioxidants -- called catechins -- in green tea may work together with the caffeine in the tea to provide greater weight loss benefits than either of these ingredients alone. Still, the increased weight loss is likely to be very modest, however. A review published in The American Journal of Clinical Nutrition in 2009 found that green tea with caffeine increased weight loss over the course of the study period by about 3 pounds compared to caffeine alone, and by about 1 pound when compared to drinking a control beverage that had no caffeine.
Caffeine From Sugar-Sweetened Beverages
Sugar-sweetened beverages -- in general -- tend to be more likely to increase weight than to help decrease weight, and adding caffeine doesn't offset these effects. In fact, a study published in the European Journal of Clinical Nutrition noted that beverages with caffeine needed to contain at least 10 percent more sugar to offset the flavor of the caffeine, making them even higher in calories and more likely to lead to weight gain. Don't think that switching to diet beverages will solve this problem, as another study -- published in the journal Obesity in August 2008 -- found that those who drink artificially sweetened beverages were more likely to be overweight than those who don't drink these beverages.
Potential Side Effects
Caffeine doesn't necessarily agree with everyone, especially when consumed in larger amounts. Some people experience acid reflux when they consume caffeine; it can interfere with some medications and it also may increase blood sugar and cholesterol levels. Other potential side effects include an increased heart rate, trouble sleeping, more frequent urination, depression, anxiety and nausea. It can also cause withdrawal symptoms if you suddenly cut back. These include vomiting, nausea, headaches, irritability and fatigue.