Are smoothies healthy or not? Experts examine the latest evidence

Posted on Oct 24 2017 - 10:42pm by admin

SMOOTHIEGETTY

Recent research puts fruit juice and smoothies on the same nutritional footing

This daft dietary double standard stems from official guidance which puts fruit juice and smoothies on the same nutritional footing, flying in the face of the latest research. 

A recent study by scientists at the University of Leeds found smoothies are actually much closer to crushed fruit because they retain fibre, which probably explains why they do not produce the same spikes in blood sugar levels as juice

Public health nutritionist Dr Emma Derbyshire says: “The clear and confirmed benefits of many smoothies are being lost in a fog of confusion surrounding government advice on free sugars and the one-size-fits-all approach taken by the UK’s Eatwell Guide.”

 So-called ‘free’ sugars are defined by the Scientific Advisory Committee on Nutrition (SACN) as all added sugars “plus sugars naturally present in honey, syrups, squashes and unsweetened fruit juices.”

Dr Derbyshire adds: “SACN does not actually mention smoothies, which contain useful amounts of pulped fruit.”

She points out: “Juices and smoothies are made differently and have different nutrient profiles. 

“Smoothies are typically made by blending whole fruits and vegetables which preserves fibre, while juicing usually leaves the pulp, and with it the fibre, behind.

“This is confirmed by studies showing smoothies retain their fibre and have a lower glycaemic index, yet the Eatwell Guide ignores the evidence and includes smoothies in its advice to restrict consumption of juice.” 

Dietitian Dr Carrie Ruxton agrees: “At present, smoothies are lumped together with juices which are flagged for their high sugar content, but this is unfair as some of the sugars in smoothies are clearly not ‘free’.”

The fibre findings are important as the Government advisers at SACN recently shifted the goalposts on recommended intakes. 

Dr Derbyshire says: “Because it is most commonly associated with maintaining healthy bowel movements, fibre has been seen as something of a Cinderella nutrient. But we now know it also reduces the risk of heart disease, diabetes, stroke and bowel cancer.” 

Having a smoothie once a day could help to plug nutrient and fibre gaps that most of us have

Dr Derbyshire

That’s why SACN now say we should get 30g a day, 20 per cent more than the previous recommendation and almost 40 per cent above the current average intake of 18.5g a day.

In a new research review, just published in the Journal of Nutrition & Food Sciences, Dr Derbyshire argues that smoothies could have a role to play in helping meet this new target and also plug worrying vitamin and mineral gaps in the British diet. 

After analysing data from more than 800 adults who took part in the official National Diet and Nutrition Survey, she identified a number of nutritional shortfalls.

“When intakes were compared with recommendations, up to 40 per cent of people were failing to consume the bare minimum for several nutrients,” she warns. 

The worst shortfalls were vitamin A, which is important for immunity and vision; folate, which is needed to form healthy red blood cells; selenium, which helps protect cells against damage and supports immune function; potassium, which regulates blood pressure and supports cardiac function; iron which is needed for memory and cognition; and magnesium and calcium, which are vital for healthy bones.

Dr Derbyshire says: “Smoothies that are made from real fruit, with no added extras or nasties, have a valuable role to play. Having a smoothie once a day could help to plug nutrient and fibre gaps that most of us have.” 

University of Leeds researchers tested a commercial smoothie, and found that cell wall structures in the fruit, which are the most fibrous parts, remained intact even when the smoothie was subjected to simulated digestion. 

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Scientists believe smoothies are much closer to crushed fruit because they retain fibre

When they compared it to samples of orange and apple juice and crushed or pureed banana, apple, mango and orange, the scientists found the structure of the smoothie was much closer to the crushed fruit than the juices. 

Their study concluded: “This indicates that smoothie processing would offer similar benefits to whole fruit.”

The quality and quantity of fruit used in smoothies will vary, but Dr Derbyshire says: “While this study only looked at one commercial smoothie, it is safe to assume that the others are likely to confer similar benefits.”

A two-phase study at Oxford Brookes University, which used the same brand of smoothies, found a 250ml bottle of mango and passionfruit would provide 11 per cent of the recommended intake for fibre and the strawberry and banana smoothie would provide five per cent of the 30g target.

Fibre is known to reduce the glycaemic index (GI) of food and drinks, which measures how quickly they reach the bloodstream as sugar, and how likely they are to cause unhealthy spikes in sugar levels.

Both smoothies had low GIs of 36 and 39, which were largely in line with the GI of the fruits used in them.

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Smoothie processing would offer similar benefits to whole fruit, a study claims

Satiety, the feeling of fullness we get from food and drinks, aids weight control because the longer we stave off hunger pains, the lower the likelihood of snacking.

A University of Bristol study, which recruited 47 adults to compare the satiety of fruit salad, smoothies, milk, blackcurrant squash and water found that, as expected, the fruit was the most fi lling.

But the smoothies were found to be the second most satisfying, slightly ahead of milk and considerably better than squash or water.

Dr Derbyshire says: “These results show that young adults see these as being more ‘food like’ which means that other foods are less likely to be eaten.”

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