During pregnancy, your body works hard to supply your growing baby with the energy and nutrients it needs to develop organs, put on weight, and add a healthy layer of fat under the skin. Weight loss programs, pills, teas, and other mechanisms for losing weight typically undermine your need for extra nutrition in pregnancy, and aren't recommended.
During pregnancy, you need more calories and far more vitamins and minerals than your body normally requires. This is because you have to provide for your own cellular needs, for the nutritional needs of a growing baby, and also for the changes taking place in your body as you adapt to pregnancy. For instance, you need to increase your blood volume by nearly 50 percent, and women who were at a healthy pre-pregnancy weight need to increase fat stores for breastfeeding, notes Dr. Miriam Stoppard in her book "Conception, Pregnancy and Birth."
To provide for your changing needs, most women should gain 25 to 35 pounds during pregnancy, explain Drs. Michael Roizen and Mehmet Oz in their book, "You: Having A Baby." Doing this generally requires consuming an extra 200-300 calories each day, plus taking a prenatal vitamin to provide additional nutrition. While women who were heavy before pregnancy may not need to gain as much weight, obstetricians almost never advise women to lose weight during pregnancy.
When you lose weight, by definition, you're taking in fewer calories each day than your body needs in order to function. Weight loss teas work in different ways, though many increase metabolic rate so that you're burning more calories each day. If you consume a weight loss tea during pregnancy with the goal of losing weight, not only are you not providing for your own nutritional needs, you could be denying your baby the energy it needs to grow appropriately.
Another concern with many herbal supplements -- including weight loss teas -- is that they're not regulated by the FDA, explain Drs. Roizen and Oz. This means that they may contain ingredients that aren't safe for use during pregnancy, and could cause harm to you or to your developing baby. Furthermore, many weight loss teas include caffeine or caffeine-like ingredients -- these ingredients help the teas boost your metabolic rate. Drs. Roizen and Oz recommend limiting caffeine during pregnancy, since consumption in large quantities can lead to miscarriage and other complications.
During pregnancy, your safest strategy for selecting a healthy diet and lifestyle is to talk to your obstetrician, explain Heidi Murkoff and Sharon Mazel in their book "What To Expect When You're Expecting." Based upon your pre-pregnancy weight and health status, your doctor can help you figure out how much weight you need to gain, and how you should go about gaining it. Avoid using any herbal medications, teas, or weight loss aids unless your doctor specifically sanctions them for pregnancy.