The problem; if you get a "Trenta" lemonade, it will have 21 teaspoons of sugar. Yes, 21. That's not only more sugar than you should have in a single drink, it's more than you should have in a single day.
We're not trying to pick on Starbucks. If you buy any prepared beverage, you are paying for sugar. According to the U.S. Department of Health and Human Services, people who consume drinks with added sugars consume more total calories, and studies have found that drinking sweetened beverages is related to weight gain. Though it can obviously be the other way around - people who are fat like to buy junk food, including sugary drinks.
Not everyone accepts that coffee is good for you. The Mayo clinic says it is just not bad for you, in moderation. A 'Trenta' coffee at Starbucks is 5 cups of coffee at one time, which is quite a bit of caffeine, including resulting irritability and difficulty sleeping. And Starbucks is able to market to children guilt-free in a way that tobacco and liquor companies are not, so they have no issue selling kids and teens anything they want. It remains the difficult task of parents to fight large corporation marketing.
“Energy and coffee beverages are subject to the same nutrition rules as other foods and drinks; it’s all about moderation,” says Ellen Schuster, a University of Missouri nutrition expert. “Ideally, it’s best to avoid drinking calories, because drinks leave you less full than solid foods. By eating calories in the form of high-calorie, high-sugar drinks, people crowd out other nutritious foods. However, like any indulgence, it’s fine to order a ‘Trenta’ drink as an occasional treat.”