Smoothies are not all equally healthy, and it’s not just the ingredients that make the difference, but also how they're made.

Did you know that how you juice your fruit and veg could make a difference to the amount of nutrients that end up in your glass?

That’s what researchers from Texas A&M University found in 2020 when they investigated three different methods of juicing.

They compared the phytochemical and antioxidant content of 19 vegetable juices when they were made with blenders, high speed centrifugal juicers, and low speed extractor juices.

In general, it was found that juices produced using a blender had the lowest amounts of beneficial compounds such as vitamin C, antioxidants and phenolics.

The team suggested this was probably due to blending producing more heat than the other two methods.

But before you consign your blender to the recycling centre, these juices were also found to have the highest amount of amylase inhibitors.

What are amylase inhibitors?

Found in the mouth and pancreas, amylase is a digestive enzyme that breaks down starch (a complex carbohydrate) so that it can be converted into glucose and used as energy.

If blood sugars are a concern, such as with insulin resistance, something that inhibits this process (i.e. an amylase inhibitor) may be beneficial because it lowers or slows the release of glucose into the blood stream.

The fibre found in vegetables and fruit is known to help slow down this process.

Antioxidants and phenols

When it came to antioxidants and phenols, however, it was low speed juicing that resulted in the highest amounts, although not for every vegetable.

Whilst green kale juice produced with the low speed juicer had the highest DPPH value (a measure used to predict antioxidant activity), the high speed centrifugal juicer produced better results for beetroot.

Professor Bhimanagouda S Patil at the Department of Horticultural Sciences, Texas A&M University, said that the findings were vegetable specific and there was a large variation of results based on the method used.

“Blenders and juicers have unique capabilities of extracting diverse compounds,” he said.

For those who want to get the most nutritional benefit, no single juicing method was better, and eating whole vegetables and fruit is preferable.

“Obviously, whole food is better since it contains fibre and other nutrients which are beneficial, but consumers are looking for quick accessibility and readymade products,” he said.

How to boost health of spinach

For spinach lovers, however, a veg smoothie may actually help to boost its nutritional value.

In a separate study from Linköping University, Sweden, researchers investigated how various cooking methods affected the lutein content of spinach.

An antioxidant found in a range of vegetables, particularly the dark green variety, lutein is a fat soluble pigment which is often taken in supplement form to help prevent age related macular degeneration in the eyes.

After prepping their spinach by baking, boiling, frying, microwaving, reheating and blending, scientists found the less heat, the better.

Because chopping spinach also releases its lutein, which fat helps us to absorb, they recommended blending it in a smoothie with fat from dairy such as milk or yoghurt.

What's the best approach?

However, what this all seems to show is that, for those of us who aren’t food chemists with a portable lab in our kitchen, a sensible approach might be to vary what we eat and how we eat it.

After all, variety is said to be the spice of life. So shaking it up, as well as a bit of blending or pulverising, might not be a bad thing.

Enjoyed this article?

Learn about the health benefits of brown rice

For articles and recipes subscribe to the Optimum Nutrition newsletter

Discover our courses in nutrition