Ask Tufts Experts

I make smoothies using only fresh-squeezed OJ, yogurt and fresh or frozen fruit (mostly bananas and berries). Is the fiber in the fruit lost by blending them into the smoothie? What about other vitamins and minerals?

Not to worry, says Alice H. Lichtenstein, DSc, Gershoff Professor of Nutrition Science and Policy at Tufts’ Friedman School. You’re losing some fiber from the orange by squeezing out the juice and discarding the rest. Otherwise, however, all the fiber should remain, even after combining into a smoothie, and the fruits’ vitamins and minerals should be intact. Heating can destroy some nutrients, but not blending. (We trust, by the way, that you’re using low- or non-fat yogurt in that smoothie?)

Is there a difference in the effect on the body between natural (l-alpha tocopherol) and synthetic (d,l-tocopherol) vitamin E?

Vitamin E (as alpha-tocopherol) can exist in two configurations, like a right and left hand (the d and l forms, respectively), explains Jeffrey B. Blumberg, PhD, chief of the Antioxidants Research Laboratory and Senior Scientist at Tufts’ Jean Mayer USDA Human Nutrition Research Center on Aging. Dietary vitamin E is always found as the l form while synthetic vitamin E is generally an equal mixture of the d and l forms. A vitamin E binding protein in the liver transfers the l form into lipoproteins for transport throughout the body and discriminates against the d form such that it is rapidly excreted. Thus, milligram for milligram, the natural dietary l form is about twice as potent as the d form that’s mixed into synthetic vitamin E. This difference is partly compensated for, however, by the way International Units (IU) are used to measure vitamin E: One IU of vitamin E contains 1.0 milligram of the d,l mixture, but it takes just 0.74 mg of the l form to equal 1 IU.