SAN FRANCISCO (KPIX 5) -- In San Francisco, boutique juice bars have sprouted up everywhere with a little something for everyone.
Whether organic, raw, or cold pressed, advocates claim that, with juices, your body better absorbs nutrients.
"It's a real simple way to get a lot of healthy things," a woman in the Mission District told KPIX 5 News.
But, when pressed, some experts told us these claims about juicing are just too hard to swallow.
"There is no data, there is no data," exclaimed Dr. Robert Lustig, a pediatric endocrinologist at the University of California in San Francisco.
He says there's no good scientific evidence you absorb nutrients more quickly and, he warned, there's a much bigger problem.
"In the case of juicing, it's the loss of fiber," said Lustig.
Lustig explained how studies show how, when we eat fiber from fruits and vegetables, it travels down into our gut where it is then eaten by our "good bacteria."
That good bacteria helps keep us healthy.
"Fiber is the stealth nutrient. Fiber is one of the single most important nutrients we can put in our bodies and it's for our bacteria," explained Lustig.
"Research is showing that having enough good bacteria decreases your risk of heart disease and cancer, diabetes -- even obesity," said registered dietician Sonya Angelone.
Angelone is spokesperson for the Academy of Nutrition and Dietetics.
She has another issue with juicing: some may contain too much sugar. Not everyone is going to like pure kale juice.
"In order to make it palatable the first ingredient is juice -- like an apple juice -- which is just sugar," explained Angelone.
She says you have to juice a lot of fruit to get a single cup and that those naturally-occurring sugar calories can add up.
One bottled juice she looked at contained about 60 grams of sugar, about a quarter of a cup.
As for do-it-yourself juicing? Martin made a green juice drink.
The recipe called for 3 apples, 4 stalks of celery, a bit of ginger, half a lemon, a large orange and a handful of spinach leaves.
The drink was tasty but it contained 250 calories, as well as 13 1/2 teaspoons of sugar.
As for fiber? Only about 2 grams.
The vast majority of the fiber -- more than 30 grams -- ended up in the trash receptacle.
Lustig explained how juicers that keep the fiber in the drink still don't do the job in providing adequate fiber nutrients to our good bacteria.
He said there are two types of fiber that you need in your diet: soluble fiber (like the pectin found in apples) and insoluble fiber (called cellulose) that you can find in celery. Lustig said that, when eaten, the insoluble fiber forms a lattice-like barrier inside your intestines. The soluble fiber then fills in the holes of that lattice. This barrier of soluble and insoluble fiber slows down the absorption of sugar and then carries more nutrients into the right part of your intestines to feed your good gut bacteria.
With a juicer that keeps the fiber in the drink, Lustig explained, the insoluble fiber is destroyed and, without insoluble fiber, the slowdown in absorption to carry more nutrients to your gut bacteria is gone.
The soluble fiber is there but there is no lattice-like structure for it to adhere to. Lustig said the soluble fiber in the drink may increase the transit through the intestine and make you feel full. But you need to eat proper amounts of insoluble fiber.
Lustig says, without good fiber, excess juice sugars get into our bloodstream and are metabolized by our liver and are stored as fat on the liver.
"The only thing that stands in the way of that is the fiber that's contained in the fruit, and when you juice it, you're throwing it away," said Lustig, adding that if you're dumping the fiber in the wastebasket, you're sort of missing the whole point.
So while some fans love their juice, both Dr. Lustig and Angelone say consider eating the real thing.
KPIX 5 contacted the makers of bottled fresh juices and one referred us to the Juice Products Association. We submitted questions and received these answers from the Association's registered dietician, Diane Welland. Ms. Welland is the Nutrition Communications Manager of the JPA.
Here is an excerpt from our written e-mail conversation.
KPIX News: "UCSF Dr. Robert Lustig and Sonya Angelone, spokesperson for the Academy of Nutrition and Dietetics, say juicing removes significant fiber in our diet, that we don't get enough fiber in the first place, and that it's better to eat whole fruits and vegetables. How do you respond?"
Welland: "Studies show juice drinkers have either the same or higher total fiber intakes than non-juice drinkers. It's important to remember juice is high in potassium, vitamin C, magnesium and folate as well as polyphenols which are plant compounds that can protect against chronic illness."
KPIX News: Some fruit-based juices and smoothies have no sugar added but the sugar that's contained in the bottles can be significant in terms of calories. Should we be careful about drinking too many fruit based juices and smoothies because of the sugar content?
Welland: "According to the 2015-2020 US Dietary Guidelines, up to half of the recommended fruit intake goals can come from 100 percent juice. U.S. dietary pattern data shows people eat a 2-to-1 mix of whole fruit and juice, with more fruit than juice."
KPIX News: "Dr. Lustig says, molecule-for-molecule, the liver recognizes sugar from fruit juice as sugar and stores it as sugar; That, without the fiber, the sugar from the juice is more quickly absorbed into the blood stream. Is this a problem? Do you disagree with Dr. Lustig?"
Welland: "When nutrition researchers recently looked at this topic they found that 100 percent juice intake did not affect blood sugar and insulin levels."
KPIX News: Both Dr. Lustig and Ms. Angelone says we need to increase our intake of whole fruits and vegetables. Angelone says we should treat fruit-based juices as a "treat" because of the lack of significant fiber and sugar content. What is your opinion?"
Welland: "80 percent of Americans are not eating enough fruits and vegetables. Drinking juice can help them meet their goals and provides the same important vitamins and minerals. Research also shows that people who drink juice tend to eat more whole fruit."
Academy of Nutrition and Dietetics: eatright.org
Soluble and insoluble fiber: https://www.nlm.nih.gov/medlineplus/ency/article/002136.htm
Juice Products Association: juicecentral.org/latest-research
KPIX 5 also notes that 100 percent pure vegetable juice can be low in calories and sugar content, but check the nutrition label for sodium content.
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