Although fad diets consistently disappoint, there’re exceptions. Remember the negative calorie diet plan? But lately, there has been a lot of buzz about “negative calorie� drinks.

Do they help you lose weight – and are they safe to try? Two new beverages — Enviga and Celsius — claim to boost your metabolism to burn more calories than they contain. Yawn!

Both have 5 to 10 calories per serving; drink one to three 12-ounce cans a day and you’ll expend up to an additional 100 calories, according to the manufacturers.

These products contain two ingredients that allegedly speed up metabolism: caffeine and epigallocatechin gallate (EGCG), an antioxidant found in green tea. It is known that caffeine may increase metabolic rate, but the jury is still out on a green tea extract.

“…it’s not clear that this increase will translate to weight lossâ€?, says Barry M. Popkin, Ph.D., a professor of nutrition at the University of North Carolina at Chapel Hill.

The beverages are safe, but if you’re sensitive to caffeine, know that each can contains the same amount as a cup or two of coffee.

Eager to sample them anyway? Go ahead… but if you need to lose some weight, remember that a healthy diet and regular exercise are pretty hard to beat. [via: Shape]