What Is Bad About Diet Green Tea?

If you like the taste, green tea may be the perfect diet beverage -- zero calories plus metabolism-boosting power. But if you like it sweet, a teaspoon of sugar adds 68 calories to the beverage. You can save calories by purchasing diet green tea beverages, but you'll lose out on many of the weight-loss benefits of green tea.

Processing

Green tea's ability to burn fat depends on the number of catechins it contains. According to the United States Department of Agriculture (USDA), green tea brewed from fresh leaves contains 127mg of catechins. Bottled green tea, diet or otherwise, contains an average of 12mg. The actual number of catechins varies by brand, but based on the USDA study, you'd have to drink 10 1/2 cups of diet green tea to obtain the benefits of a single cup of home-brewed green tea.

Caffeine Content

Diet green tea is a calorie-free drink, but it contains caffeine. Bottled diet green tea contains considerably less caffeine than home-brewed green tea, and much less than black tea and coffee. Two commercials brands of diet iced tea have fewer than 20mg of caffeine, about a fifth of the amount found in coffee. "The British Medical Journal" recommends that pregnant women consume no more than 100mg of caffeine a day, the amount in about five cups of diet bottled green tea.

Quantity

You may have to drink a lot of diet green tea to enjoy its benefits. One study comparing the fat-burning differences between green and black tea, for instance, involved consuming the amount of caffeine in about six cups of home brewed green tea or more than 65 cups of bottled diet green tea. The study, conducted by Kevin Maki and reported in 2009 in the "American Journal of Clinical Nutrition," involved male participants drinking 660mg of green tea catechins daily and others consuming 22mg of black tea catechins for three months.. The men drinking green tea lost more weight than black tea drinkers -- 5.3 lbs. compared to 2.8 lbs.

Alternatives

One alternative to trying to gain health benefits from drinking large quantities of bottled diet green tea would be to take green tea supplements. Meta-T Green Tea capsules, for instance, contain 90mg of catechins and Green Tea Slim capsules contain 60mg. Another solution would be to brew your own tea and add artificial sweeteners. Red wine, dark chocolate, blueberries, blackberries and black plums also contain catechins, but they also have calories that could contribute to weight gain.

Not a Substitute for Healthy Eating

It would be a mistake to rely exclusively on diet green tea to lose weight. A study in "Biotech Business Week" showing correlations between green tea consumption and weight loss included calorie-restricted diets. You can't expect green tea to burn away more fat than you accumulate by regularly eating fattening foods. One study involving rodents, did, however, provide hope for people looking for a free pass. M. Bose and other scientists at Rutgers University fed rodents green tea extract along with their fatty diets and found that obese mice lost weight and healthy weight mice didn't gain weight, according to the report published in September 2008 in the "Journal of Nutrition."