One is made of fruit. The other is caffeinated. So a smoothie is a healthier option than a coffee, right? Don't be so sure, says Michael Mosley, as he weighs the evidence.
Which is healthier - coffee or smoothies?
It seems obvious that the answer must be a smoothie. After all, drinking coffee is a necessary evil while having a smoothie, made from fruit, is part of your five-a-day. But when you look into the scientific studies they reveal something much more surprising. Let's start with coffee.
There have been numerous claims down the years that drinking coffee will increase your risk of a whole range of terrible things from heart disease to cancer.
These claims have been largely based on case control studies, where you take a group of people who drink coffee and compare them with another matched group who don't.
The problem with this approach is that coffee drinkers are more likely than non-coffee drinkers to have other "bad" habits, like drinking alcohol or smoking, so it is hard to tease apart what is really doing the harm.
A more reliable way to get at the truth is to do what is called a prospective cohort study. You take a group of disease-free individuals, collect data about them, then follow them for a large number of years to see what happens.
When scientists collected data on the coffee drinking habits of 130,000 men and women and then followed them for over 20 years they found that coffee is rather a good thing (The Relationship of Coffee Consumption with Mortality, Annals of Internal Medicine, June 2008).
They crunched the numbers and concluded that "regular coffee consumption was not associated with an increased mortality rate in either men or women".
In fact, data from this study suggests that moderate coffee consumption is mildly protective, leading to slightly lower all-cause mortality in coffee drinkers than non-coffee drinkers. Based on this and other studies the most effective "dose" is two to five cups a day. More than that and any benefits drop off. There are hundreds of different substances in coffee, including many different flavonoids (compounds widely found in plants that have antioxidant effects). Which of these ingredients is beneficial, we simply don't know.
When it comes to the brain, however, the answer seems to be "caffeine". In research recently published in the World Journal of Biological Psychiatry (July 2013) they found that people who drank two to four cups of caffeinated coffee a day were half as likely to commit suicide as those who either drank decaff or fewer than two cups a day. This research pulled together data from three studies that had followed more than 200,000 people for more than 14 years, so it's pretty reliable. It is also supported by a number of other studies, which makes this claim even more plausible.
One reason why caffeine may be a mild anti-depressant is that as well as making you more alert, it increases levels of neurotransmitters in the brain, like dopamine and serotonin, that are known to improve mood.
The researchers don't recommend going overboard, noting that "there is little further benefit for consumption above two to three cups".
One note of caution is that these trials began many years ago so the sort of coffee consumption being tested is almost certainly good, old-fashioned coffee.
A simple mug of coffee delivers somewhere between zero and 60 calories, depending on whether it is black, white or white with one sugar. Cappuccinos, lattes and mochas contain coffee but they also contain a lot of calories - anything between 100 and 600 - so when it comes to fancy coffees I limit myself to the occasional tall, skinny cappuccino (70 calories).
But what about fruit smoothies? They may consist of pure fruit but by the time you've got rid of the peel and mashed the fibre then you have already lost many of the potential health benefits. What you are mainly left with is a sugary drink. In a survey published in early 2013, researchers found that out of 52 commercial smoothies, 41 had more sugar than Coca-Cola (a 12oz can contains the equivalent of about nine teaspoons), and all had more calories.
Fruit smoothies are acidic and the bits cling to your teeth, so dentists are not enthusiastic. An apple a day may keep the doctor away, but not when it's been peeled, blended, mashed and packaged.
In a study published in August 2013 in the British Medical Journal (Fruit Consumption and risk of type 2 diabetes) they found that while eating fruit cuts your risk of developing diabetes, drinking it appears to increase the risk.
This was another big study involving lots of people followed for many years. An interesting finding was that different fruits gave different levels of benefit. Three servings of blueberries, for example, cut the risk of diabetes by 26%, while eating apples, pears, bananas and grapefruits also had a positive, albeit much smaller, effect.
Overall those who ate fruit cut their risk of developing diabetes by 2%, while those who drank it (more than three glasses of fruit juice a week) increased their risk by 8%.
More bad news for fruit juice drinkers comes from a case-controlled study done in Western Australia that examined the daily diets of more than 2,000 people. They found that eating some types of fruit and vegetables (cabbage, broccoli, cauliflower and apples) cuts your risk of colorectal cancer, while drinking fruit juice was associated with an increased risk of rectal cancer. Sugary drinks lead to raised levels of the hormone insulin and persistently high levels of insulin are associated with increased risk of some cancers. The researchers point out that many things that protect against bowel cancer, such as antioxidants and fibre, are lost or diminished during the juicing process.
A smoothie may count towards your five-a-day, depending on how it's made
None of these studies specifically looked at the health benefits or otherwise of fruit smoothies, which are a relatively recent phenomenon, nor did they look at the impact of different types of juice - for instance, whether it was freshly squeezed or from concentrate, home-made or shop-bought. I would assume, for example, that drinking a home-made vegetable smoothie is going to be a lot better for you than a commercial fruit smoothie.
And I very much doubt that the occasional fruit juice or fruit smoothie is going to do any harm. Nonetheless, I've personally given up buying them and we rarely have them in the house. I eat whole fruit and when it comes to soft drinks I'm sticking to water, tea and, of course, coffee.
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