Surprise Diet Sabotage: Are Smoothies Actually Healthy?

A breakdown of smoothies and the health benefits of the breakfast trend.

— -- Smoothies are a fun and quick food fix for breakfast. But when it comes to the health benefits behind the trend, the blended drinks might not be as filling or as healthful as some people think.

Nutritionist Sarah B. Krieger, of St. Petersburg, Fla., stirred the controversy after her presentation to the Academy of Nutrition and Dietetics. Her hypothesis: pulverizing fruit reduces fiber and lets sugar from fruit speed into the blood stream.

She asserted that quick release of sugar spikes the blood sugar, speeds through your system and you get hungry sooner. Hello, snacking!

I decided to break down the health differences between drinking the ingredients that have been blended together as a smoothie, versus consuming them separately.

New York-based dietitian Maya Feller explained, "When you get a dump of sugar into the blood stream ... it spikes the blood sugar. Then you get a drop."

The fiber in fruit slows digestion and acts as a time release, gradually distributing fuel into the body. When fruit is blended into a smoothie, that release occurs sooner than it would with whole food.

"You could say that fiber is like a mesh-netting ... it slows the sugar absorption down, so that it's not going rushing in," Feller said.

To test this, I ate the raw ingredients of a smoothie, including 4 and a half ounces of mango, 4 and a half ounces of pineapple, 2 ounces of bananas, 3 ounces of vanilla yogurt and 6 ounces of apple juice. It took me about 15 minutes to chew the ingredients. I sat down at the table and felt like I had a real meal.

Then, over the course of the next two hours, I checked my blood sugar levels every 15 minutes.

The next day I made a smoothie with the same exact ingredients and drank it. Because it was a smoothie, I could walk around while I drank it. It took me less than five minutes to drink. Then I followed the drinking of the smoothie by the same blood sugar tracking.

Drinking the smoothie caused my blood sugar to spike to 129 milligrams per deciliter within the first half an hour. But at the 1:15 mark, it dropped a lot lower, below the 80 mg/dl it was when I first woke up.

At that point I felt hungry and lightheaded. Feller explained that my body was "really trying to get itself back up to normal with a high and then a low."

My results from the blood test after eating the fruit were very different. When I ate the fruit, my blood sugar never got above 112 mg/dl. It also stayed consistently above my waking baseline. More importantly, I wasn't hungry for two hours and I never felt lightheaded.

Feller estimates that the smoothie was about 300 calories. Less than two hours after drinking the smoothie, I was hungry and snacking, accidentally adding more calories to the day through smoothie diet sabotage.