There may be some health benefits related to drinking coffee, such as lowering the risk for Type 2 diabetes in adults, but coffee drinks that have added sugar and cream or specialty drinks such as flavored lattes or mocha drinks are often high in calories and sugar and are best thought of as an occasional treat. Diet soda, on the other hand, does not have calories and sugar. As a replacement for regular soda, diet soda may help with weight control. However, diet soda is sweetened with sugar substitutes. Sugar substitutes taste very sweet, often many times sweeter than regular sugar. Some research studies suggest that having sweet-tasting things regularly (such as drinking diet soda throughout the day) can cause you to prefer and actually seek out this sweet taste, which could also make you crave sweet foods.
Coffee (unless it’s decaf) and many diet sodas have caffeine. For teens, it’s important to limit the amount of caffeine to less than 300 mg per day (some sources recommend no more than 100 mg per day). One 12-ounce cup of brewed coffee, a tall at Starbucks® for example, may contain anywhere from 140 to 300 mg! And while soda is lower in caffeine than coffee, you can still overdo it (a 12-ounce can of Pepsi® or Coca Cola® has about 35 mg of caffeine).
So which is better, diet soda or coffee? It’s actually important to limit both. One cup of coffee or one can of diet soda per day is usually fine. If you’re having more, consider gradually switching to drinks lower in caffeine and higher in nutrients. For example, consider adding an 8-ounce glass of milk (skim, soy, almond or rice) or kefir (a yogurt drink) to your daily routine, exploring the many flavors of herbal tea, or choosing bottled water (sparkling or plain) to replace the 12-ounce soda.