Nuts appear to boost one's metabolism, such that when we eat nuts we burn more of our own fat to compensate. In my 2-min. video, Testing the Fat Burning Theory, I show that people who don't eat nuts tend to burn off around 20 grams of fat a day-about 5 pats worth of butter, but those eating walnuts averaged more like 31 grams-7 or 8 pats of butter. In Fat Burning Via Arginine, I explore one theory as to why this may happen (and where arginine can be found in our diet).
It may also be the flavonoids, phytonutrients found in nuts as well as citrus, berries, red onions, beans, green tea, grapes, and cocoa, that may boost our metabolism enough to significantly slim our waistline. Based on what kind of evidence? I showcase a study done on purple grape juice in my video Fat Burning Via Flavonoids.
Just like nuts are calorically dense yet don't seem to cause much weight gain, Welch's was hoping that the same would be found for their grape juice. They had people guzzle down 2 cups a day for three months. Keep in mind that Welch's grape juice has more sugar than Coca Cola. Two cups of purple grape juice contain the equivalent of 20 spoonfuls of sugar. The control group was basically given grape Kool-Aid instead, with the same number of calories and same amount of sugar, but no detectable phytonutrients.
At two cups a day study subjects were getting hundreds of extra calories a day. Surely after 3 months they'd gain a couple pounds. Indeed that's what happened in the grape-flavored sugar water group--how could they not with all that extra sugar in their diet? The grape juice group, on the other hand, did not. In fact, their waist circumference shrunk significantly. Drinking grape juice appeared to burn away significantly more tummy fat. So maybe there is something to the theory put forth by the nut and green tea researchers that flavonoid phytonutrients are capable of helping the body burn fat. If true, then it's just one more reason to eat nuts and drink green tea--not grape juice. Instead of the juice, I'd recommend eating concord grapes, the source of purple grape juice that you may be able to find at a farmer's market near you.
-Michael Greger, M.D.
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