Smoothies and juices are healthy, right? Well, the answer is not always so straight forward.
Smoothies are made by blending ingredients, like fruits or vegetables with a liquid to make a thick, smooth drink. You drink the whole fruit because the entire thing has been pulverized. A juice is made by extracting the juice from fruits or vegetables, giving a much thinner liquid and a fibrous pulp which is discarded.
Smoothies and juices are thought of as very healthy foods. They both contain fruits and vegetables and therefore contain lots of vitamins and minerals. However a study looking at the absorption of three meals based on apples, showed that apple juice (devoid of fibre) could be consumed eleven times faster than whole apples and four times faster than apple purée (1). Juice was also demonstrated to be less satisfying than both purée and whole apples, with the latter being the most satisfying. Interestingly, blood sugar levels rose after all three meals, however after the juice, it dramatically dropped again and the juice also caused insulin levels to rise (1). Repeated juice consumption might not be so good for your blood sugar levels. Keeping the fibre intact seems to have a satiating effect. Eating the whole fruit might be the healthiest option.
However, another study showed that berries have a neutralising effect on blood sugar, preventing the blood sugar spikes often seen after consuming fruit smoothies or juices (2). The ingredients of your smoothie are an important factor in its effect on your blood sugar.
As with many foods, smoothies and juices can have their place in a healthy diet. Juices contain a lot of natural sugars and very little fibre, however if consumed soon after extraction, they contain many vitamins and minerals and can be useful for people who have very little appetite and need some readily absorbed nutrients. Including anti-inflammatory foods, such as ginger, turmeric and leafy greens, in the juice can really boost their nutrient value.
Smoothies contain fibre and many nutrients, and they can also be packed full of goodness with the addition of herbs, spices, vegetables, seeds and milk (dairy or non-dairy). The addition of milk, seeds or nuts also helps to lessen the effect on blood sugar as these foods contain protein. They are a good way to get nutrients into reluctant fruit and veg eaters.
The mistake many people make is to consume daily smoothies made just of fruit, thinking that it is helping them lose weight, when it may be doing just the opposite.
Eating your fruit whole, as nature intended, seems to be the optimum path, however if you can't manage without a smoothie, pack it full of veg and herbs, add some protein and berries and use other fruit as an accent.
(1) Haber, et al., (1977). Depletion and disruption of dietary fibre: effects on satiety, plasma-glucose and serum-insulin. The Lancet 310 (8040): 679-82.
(2) Törrönen, R., et al., (2012). Postprandial glucose, insulin, and free fatty acid responses to sucrose consumed with blackcurrants and lingonberries in healthy women. American Journal of Clinical Nutrition, 96(3), 527–533.