Of all the strange things we're told about diet and eating -- 'don't eat carbs are 5pm', 'drink lemon water before breakfast', 'fat is bad for you', 'only eat one type of fruit per meal' -- this one is really fascinating:
Don't drink your smoothies. Chew them instead.
What? How? Why?
Because it's good to stay open-minded and get the facts before completely dismissing weird trends, The Huffington Post Australia spoke to someone who can give honest, credible information: Zane Andrews, associate professor in physiology and a neuroscientist who studies how food affects the brain at Monash University.
"The main role chewing plays is that it prepares our gut. In doing that it actually releases gastric secretions and enzymes into the gut and stomach, which helps to break down food that's coming in. It's like turning the oven on before you put something in. You're preheating it," Andrews told HuffPost Australia.
It's not just the stomach which is involved in the digestive process -- the mouth and brain are equally as important.
"Anything we put into our mouth is going to elicit a response in the brain. You'll get responses from the taste and texture of food, or you could have water in your mouth. All of these things will be registered by the brain," Andrews said.
"Then it will signal the gut -- so either the stomach or intestines -- and it will tell it what's going on and what to prepare for.
The theory of chewing smoothies is that the chewing action helps digest the smoothie and makes you feel full more quickly. But is this really effective enough to warrant chewing smoothies over drinking them?
"My feeling is that [this theory] is probably not based on biology. It might not be as effective as people think," Andrews said.
"What we know, and what's crucial, is when that smoothie actually gets to your gut (or the stomach), that's when you start to release what we call 'satiety hormones'. These satiety hormones are released into the blood in response to the types -- and amount -- of nutrients that have just come into the stomach and then into the gut."
Some of these satiety hormones include glucagon-like peptide-1 (GLP-1), cholecystokinin (CCK) and peptide YY (PYY).
"What they do is, when nutrients come into the gut, they are released into the blood and they feedback to the brain, and they actually tell the brain that 'we've received some nutrients and you can probably turn off feeding now'. They are classic satiety signals, or meal termination signals," Andrews explained.
So, it doesn't matter whether you're chewing the smoothie not -- you're still going to experience those satiety hormones when the smoothie reaches your stomach.
"The chewing doesn't really come into it. It's more about the nutrient load," Andrews said. "Different types of nutrients will elicit different types of satiety hormone responses. Generally, protein will elicit the strongest response for meal satiety.
The most important factor is the nutrients hitting the gut to release those satiety hormones and then telling the brain they're full, rather than chewing your smoothie.
"Fibre is also really important. If there's one thing that I would suggest with smoothies, is to maintain the fibre in it. People will juice up oranges, carrots and apples, and while that's good because it's relatively healthy, you're losing the fibre."
Instead of using fruit juice in your smoothies, blend the whole orange or apple with the other ingredients to ensure you keep all the fibre.
"Fibre in the gut helps to regulate the way that nutrients are absorbed. More importantly, I think, than chewing your smoothies is to try and have fibre where possible," Andrews said.
As for whether the rate you drink the smoothie plays a role in how well (or badly) you digest the drink, Andrews said it's not a significant amount.
"I don't think [timing] would do anything. I wouldn't speed drink your smoothie, just drink it at a normal pace. And I don't think chewing is going to do much," Andrews said.
The bottom line is feel free to keep drinking your smoothies, and drink it at a normal pace. To get the most out of your smoothie, and to ensure you feel full for longer, make sure your smoothie is packed with whole fruit, as well as protein (e.g. yoghurt, nuts, seeds, protein powder).
"It's a complex process because the amount of nutrients in your gut and the type of nutrient will determine how strong that signal is back to the brain. You can kind of amplify that signal depending on what the makeup of the smoothie is," Andrews said.
"Try not to pull out all of the fibre. The most important factor is the nutrients hitting the gut to release those satiety hormones and then telling the brain they're full, rather than chewing your smoothie. That must look weird."
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