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For example, I have 4 oranges. I can either eat them whole (assume I consume every last bit of the flesh) or blend them into a juice and drink it (assume I consume every last bit of it). Which is better?

One thing I've heard is that you get less fibre if you have fruit in liquid form.

Susan
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  • I seriously doubt digestive fiber can "disappear" with blending. Does this mean flax seeds lose their health properties when ground? – Lou Aug 04 '16 at 07:29
  • @Lou, even if the blended fruits contain the same amount of fiber (which probably do), they are more liquid then fruits, so they pass through the stomach faster and the glucose from them is absorbed faster, which results in higher blood glucose spikes. With other words - blended fruits have a higher glycemic index. – Jan Jul 10 '18 at 15:39

2 Answers2

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The simpler story is that it is better to eat whole fruit.

The problem with eating smoothies or even drinking fruit juice is that you are increasing the fruit's glycaemic index. For example, an orange has a glycaemic index of 40, while orange juice has a glycaemic index of 501. The theory goes that low glycaemic index foods lower the risk of metabolic disorders such as obesity and diabetes and there is indeed epidemiological data which confirms this specifically about fruit and fruit juice:

Greater consumption of specific whole fruits, particularly blueberries, grapes, and apples, is significantly associated with a lower risk of type 2 diabetes, whereas greater consumption of fruit juice is associated with a higher risk.

based on data from 3 studies which followed a total of ~150 000 women and ~35 000 men for 18 to 24 years.2. Note that the consumption of fruit juice increases the diabetes risk when compared to baseline, not just when compared to whole fruit.

Seeing that the average person in a Western culture has a higher chance of developing a metabolic disorder than of having difficulties digesting cellulose, we can conclude that, ceteris paribus, fruit is healthier for you than fruit juice. I did not find data on smoothies and purees, they should fall between whole fruit and fruit juice in glycaemic index.

The story gets murkier when we consider your diet as a whole. People are unlikely to eat a whole orange when they are thirsty. So if you are currently drinking orange juice and planning to switch to the same amount of whole oranges and switch to drinking water, this is probably going to be a healthy decision. But if you are going to switch to drinking Coca cola when thirsty, it will likely be worse. While I did not look for data doing this comparison, the glycaemic index of Coca cola is 631, and it also contributes many calories without them being paired with micronutrients.

There has been some debate on whether recommending diets based on GI makes sense, see these two 2002 reviews (paywalled): 3 and 4. Anecdotally, I'd say that they make sense, as I have seen people lose weight on them without complaining of hunger pangs.

1 http://www.health.harvard.edu/healthy-eating/glycemic_index_and_glycemic_load_for_100_foods

2 http://dx.doi.org/10.1136/bmj.f5001

3 http://dx.doi.org/10.1046/j.1467-789X.2002.00079.x

4 http://dx.doi.org/10.1046/j.1467-789X.2002.00080.x

rumtscho
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  • +1 for thinking alike, esp. on the part with the thirst. As @Iron Pillow also pointed out, you can drink, in a short amount of time, so many more calories and sugars than you'd probably have done with sticking to whole fruits. – cirko Jul 05 '15 at 19:17
  • These articles compare fruit to fruit juice, not smoothies, which is a bit different than what OP asked. So far I haven't seen any studies which would show what mechanism would alter the food's GI when mixing and drinking compared to simply chewing it. – Lou Aug 04 '16 at 07:27
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    @Lousy the mechanism is related to the speed of digestion. The less breakdown your digestive system has to do, the higher the GI. Nobody can predict the exact number, but the rule is that a whole fruit has a lower GI than a smoothie of the same fruit (because the step of breaking down cell walls is skipped) and that a juice has even higher GI than the smoothie, because the sugar doesn't have to be separated from anything else, it just gets into the bloodstream from its already-dissolved state without any more steps. – rumtscho Aug 04 '16 at 10:49
  • @rumtscho: the rule is that a whole fruit has a lower GI than a smoothie of the same fruit - that's exactly the rule I would like to see backed up. Also, many sites claim that "breaking cell walls" (if this is even a thing, since I don't see the difference between a thoroughly chewed apple slice and the same slice blended for a couple of seconds) actually helps release more nutrients. Again, I am not saying your answer is wrong, I am just saying there should be sources regarding smoothies. – Lou Aug 04 '16 at 11:28
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There is a simpler answer than others on this page.

Drinking the calories associated with 4 oranges can be done in about 5 seconds. This does not give your body's satiety mechanisms time to kick in and diminish your appetite if you are already tanked up on the calories you need for that day.

By contrast, eating the fruit (with peeling-time thrown in) is much slower, and gives your satiety mechanisms a chance to tell you that you don't really need the calories in that 4th orange.

The biggest nutritional danger today is not scurvy or any other vitamin deficiency. It's over-nutrition, i.e. too many calories. By eating the oranges, vs. drinking then, you reduce the danger of over-nutrition. Dr. Daniel Lustwig's editorial in JAMA first opened my eyes to this aspect of juice drinks.

Iron Pillow
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