You may have heard that prenatal vitamins can affect your weight--either that they help you lose weight or that they can make you gain weight. Neither of these is true. In fact, vitamins--regardless of type--don't affect your weight because they don't contain calorie-providing nutrients.
Prenatal Vitamins
While you might think, because they're available by prescription, that prenatal vitamins contain special ingredients, the truth is that they're actually very similar to regular multivitamin supplements. They contain regular vitamins and minerals that you'd find in a supplement for non-pregnant women, with quantities of nutrients adjusted to meet the needs of those who are pregnant. Specifically, prenatal vitamins have large quantities of iron and folic acid, which are especially important during pregnancy.
Your Weight and Pregnancy
If you're pregnant, you might wonder whether the prenatal vitamins you're taking are causing you to gain weight. It's natural to be curious about this, because generally you'll start to gain weight shortly after starting prenatals. However, this is mere coincidence; you gain weight during pregnancy as long as you're eating appropriately, whether you're taking prenatals or not. Stopping your prenatals won't slow or stop the weight gain, and you shouldn't stop taking your vitamins without talking to your obstetrician.
If You're Not Pregnant
If you're not pregnant, you might wonder whether prenatals can help you lose weight, as there's a common misconception to that effect. In fact, however, they will do nothing of the sort--at least not directly. There are no components in prenatals that prevent you from eating or speed your metabolism. However, they can be constipating and sometimes nauseating, which might make you reluctant to eat, and could result in you losing weight as a byproduct of your discomfort.
Rationale
The reason prenatals can't directly affect your weight is that the nutrients they contain--vitamins and minerals--don't provide you with calories, meaning you can't convert them into fat. Neither do they affect your processing of calorie-containing foods, meaning they can't cause you to burn fat. Instead of providing calories, vitamins and minerals assist in cellular reactions of various sorts, meaning that they play very different roles in health than do the energy-providing nutrients: carbohydrates, proteins and fats.
References
- "Biochemistry"; Reginald Garrett, Ph.D. and Charles Grisham, Ph.D.; 2007
- "Human Physiology"; Lauralee Sherwood, Ph.D.; 2004
- "Conception, Pregnancy and Birth"; Miriam Stoppard, M.D.; 2008
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