Are Green Smoothies Healthy, Or Not?

Some critics say blending ruins the fiber

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Do fruits and vegetables lose nutrition when blended?. Robert Daly / Getty Images

In some small circles of the plant-based diet community, a controversy is brewing.  The claim is that blending fruits and vegetables - mainstays of a healthy anti-aging diet - to create a thick green smoothie actually destroys the healthy dietary fiber within the ingredients. As a result, the critics contend, the smoothie is less nutritious than the sum of its healthy components. Is this really true?

The origin of the "debate":  The discussion seems to originate with a statement by Caldwell Esselstyn, surgeon, author, former Olympic gold medalist, and champion of the plant-based diet's ability to halt and reverse heart disease.  On his website, Esselstyn warns that smoothies should be avoided, thanks to the potential sugar load and because by blending:

"... the fiber is so finely pureed and rapidly swallowed without the benefits of mixing with helpful bacteria in the mouth. The sugar is separated from the fiber of the fruit, bypasses salivary digestion and results in a surge of glucose. The fructose enhances inflammation, hypertension and endothelial injury. Chew your food."

I've researched the relationship between fiber and greater longevity, and was surprised to see the suggestion that chopping fiber up into smaller pieces could render it less valuable to the body.  After all, what's unique about insoluble fiber found in the cell walls of plants and vegetables is that its greatest benefit is a mechanical one: its ability to bulk up stool, speed up the time it takes for us to excrete waste, lowering blood cholesterol and improving insulin sensitivity along the way.

  Would pureeing it make a difference?

Food scientists weigh in:  For an answer, I consulted two food scientists well-acquainted with the nutritional benefits of fiber.  First, Donald Thompson, Professor Emeritus of Food Science at Pennsylvania State University, whose research has focused on the nutritional effects of food processing treatments, among other aspects of nutrition.

"'Fiber' is actually a rather large and diverse category," he tells me. "To say anything categorically about the effect of shear forces on the health effects of "fiber" would be either ignorant or irresponsible."

While the health effects of one type of fiber - beta-glucan in oats and other grains - seem to be related to its molecular weight, a property which could theoretically be reduced with enough "shear" (as in forceful blending), Thompson says there's no beta-glucan in fruit and vegetables in any case. 

With some exasperation, Thompson continues:

"I find the sloppy and unsubstantiated thinking of bloggers and others not knowledgeable about the topic to be a rabbit hole down which a responsible scientist could vanish for extended periods, spending far more time exploring the possible validity of an unsubstantiated claim than the person who made the claim ever devoted to it in the first place.  The burden should be on the person making the claim to provide evidence or retract the claim.

  To me this issue is one of the ethics of science."

My next expert source was David Jacobs, epidemiologist and professor in the University of Minnesota's School of Public Health. 

As co-investigator of CARDIA, a national study of the evolution of cardiovascular risk in young adults, and co-investigator of MESA, a national longitudinal study of middle-aged and older adults, he's investigated the links between nutrition and age-related illnesses like coronary artery disease and diabetes

Jacobs explains that the benefit of dietary fiber lies not only in its effect on digestion and eliminating waste from the body, but also for the nutrition that comes along with it.

"Fiber from plant foods is the nonstarch polysaccharide cell walls of cells that contain lots of varied phytochemicals," he tells me.  "Some people call these phytochemicals "copassengers": you get them automatically with the fiber.  Besides fiber effects on laxation and digestion, the more important aspects is ingesting the phytochemical copassengers   Phytochemical molecules are very small (as are all molecules); blending could not physically damage them."

In effect, says Jacobs, blending is simply another preparation method to help us consume highly nutritious foods.

Esselstyn's response:  Finally, I spoke directly with Caldwell Esselstyn, the man who got the discussion started in the first place.  No slouch in the nutrition or heart disease department, Esselstyn has been profiled by CNN's Sanjay Gupta, featured in the 2011 documentary Forks Over Knives and is credited with helping former US president Bill Clinton recover after heart bypass surgery.

When I asked why he holds this position against smoothies, Esselstyn described his patients as being seriously ill with cardiovascular disease.  His plant-based diet approach requires them to eat kale and other greens up to six times a day, chewing them thoroughly to “maximize the nutrition, including extracting the nitrates from these whole vegetables." 

Why not blend those greens, to make them easier to consume, especially if mixing them together helps you eat an extra three or four servings of fresh produce each day?  Esselstyn seems to be concerned that if his patients gulp back a fruit-laden smoothie - with or without greens - they’re less conscious of what they’re eating.

Still, on the fiber point, Esselstyn doesn't offer any scientific proof that blender blades make this nutritional component less, well, nutritious.

“I seem to have backed myself into a corner with my anti-smoothie stand, maybe too vigorously, trying to be tough on my own patients who have severe illness. For the same reason, I never tell them to eat nuts, because they couldn’t eat just 3 or 4, they’d have them in every room of the house”.

Bottom line:  There's considerable evidence that eating more fruits and vegetables can help you ward off disease and disability, including helping you avoid a first heart attack. Beyond boosting the amount of fiber in your daily diet, smoothies are also a way of incorporating more water and air into your food - both of which (curiously) can help you feel more satisfied, and likely to eat less at subsequent meals.

Finally, a small study published in 2013 in the British Journal of Nutrition found that blood markers for cardiovascular disease improved among subjects who had a blended vegetable and fruit beverage daily (essentially a green smoothie), compared with those who had a beverage of fruit alone with similar sugar content.

So, until future research proves that fiber is indeed ruined by your Vitamix or Nutribullet blender, continue to boost your consumption of daily greens by tossing them in.  Just limit the amount of juice or fruit you include at home or at the smoothie bar - since some of these would-be healthy beverages can contain upwards of 50 or 60 g of sugar apiece (about 12-15 tsp)!  And (as Esselstyn advises) that's not good for your heart, your brain health, or your longevity.

Sources

Caldwell B Esselstyn Jr. "Prevent and Reverse Heart Disease" Penguin 2008. Interview with the author conducted by phone November 5, 2014.
http://www.penguin.com/book/prevent-and-reverse-heart-disease-by-caldwell-b-esselstyn-jr-m-d/9781583333006

David R Jacobs, Jr, Lene Frost Andersen and Rune Blomhoff. "Whole-grain consumption is associated with a reduced risk of noncardiovascular, noncancer death attributed to inflammatory diseases in the Iowa Women's Health Study." Am J Clin Nutr June 2007, vol. 85 no. 6 1606-1614.

David Jacobs. Professor, School of Public Health, Division of Epidemiology & Community Health. Correspondence conducted November 5, 2015.

George TW, Waroonphan S, Niwat C, Gordon MH, Lovegrove JA. "Effects of Acute Consumption of a Fruit and Vegetable Purée-based Drink on Vasodilation and Oxidative Status. Br J Nutr. 2013 Apr 28;109(8):1442-52.

Thompson, D. 2010. Natural Food and the Pastoral: A Sentimental Notion? J. Agr. Environmental Ethics April 2011, Volume 24, Issue 2, pp 165-194.
Correspondence with Donald Thompson conducted November 5, 2014.

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