Transcript: Are Green Smoothies Good for You?
Unhealthy lifestyle behaviors associated with increased risk of premature death include things like smoking, and excessive drinking, and not eating enough greens. The best way to get your greens is in whichever way you’ll eat the most of them, and one way to sneak extra greens into your daily diet is with whole food smoothies, a potent blend of good nutrition in a quick, portable, delicious form. The Mayo Clinic offers this as a basic green smoothie recipe, combining the healthiest of fruits—berries—with the healthiest of vegetables, dark green leafies. Two ounces of baby spinach is about a cup and a half. Curly parsley is another mild beginner green to start with. Surprisingly, the sweetness of the fruit masks the bitterness of the greens, such that the pickiest of children love them, along with any adults who would otherwise not consume dark green leafy vegetables for breakfast.
Or even fruit for that matter. The average teen may only get about 1/20th of a serving of fruit, otherwise—and Loops don't count. But offering smoothies can have a dramatic effect on fruit consumption for students who do not want to take time peeling or chewing fruit—who doesn’t have time to chew fruit? But the milkshake-y texture of smoothies may not just boost the quantity of fruit and vegetable consumption, but also the quality.
Carotenoid phytonutrients, like beta carotene and lycopene, can exist as microscopic crystals trapped within the cell walls of fruits and vegetables, and they’re released only when the cells are disrupted; that’s why we need to chew really well. (“Mastication” is doctor-speak for chewing.) We either have to chew better or choose plants that are easier to chew. For example, while tomatoes have more beta-carotene than watermelon does, the watermelon’s beta-carotene is more bioaccessible, because it has kind of wimpy cell walls. But the cells of other fruits and vegetables are smaller and tougher. To maximize nutrient release, food particle size would ideally be reduced to smaller than the width of the individual plant cells, but you can’t do that with chewing. Most vegetable particles end up greater than two millimeters when you chew them, which corresponds to way up here, whereas if we broke open all the cells we could release much more nutrition. We can never chew as well as a blender. The particle size distribution from chewing is about what you’d get blending in a food processor for about five seconds, or one of those high speed blenders for maybe half a second. 40 seconds in a blender and you can break spinach down to a subcellular level.
Why does that matter? Take folate, for example: the B vitamin in greens that is especially important for women of childbearing age. Feed people a cup of spinach a day for three weeks, and their folate goes up compared to control. But even just chop it up finely with a knife first before chewing it, and you end up with more than twice as much in your bloodstream—and the same absorption boosting effect with lutein, the green nutrient so important for our eyesight. It’s not what you eat; it’s what you absorb.
But for lutein, the boost was only 14%; so, a few extra bites of the whole leafy greens would have gotten you just as much. And some other nutrients, such as vitamin C, aren’t affected by pre-chopping at all. And this is less of an issue with cooked vegetables. This is for raw carrots. Boil the carrots for three minutes first, and even just regular chewing can release about ten times more, but not as much as blended. Intense cooking—boiling for 25 minutes—so damages the cell walls that even gulping down large particles can result in significant absorption. But even then, blending may double carotenoid availability, explaining why we may be able to absorb three times the alpha- and beta-carotene from puréed cooked carrots compared to mashed cooked carrots. So, blending vegetables—raw or cooked—into soups, sauces, or smoothies can maximize nutrient absorption. You went to the store and bought it, or toiled in your garden to grow it; you might as well take full advantage of it.
Might there be a downside to enhanced absorption, though? We’ll find out, next.
To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video. This is just an approximation of the audio contributed by Katie Schloer.
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