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One Slimming World rule has left people confused for quite some time, but Dr Sarah Bennett, an expert nutritionist, has explained why they have this advice in place
It’s a brand new year, and with that comes many people wanting to shed a few pounds they may have put on over Christmas. Remember, you’re perfect just the way you are, but if you are looking to start eating a little more mindfully, places like Slimming World are renowned for getting you on track.
However, in the past, dieters have been left baffled by one of the rules that Slimming World introduced, which has been described as ‘odd’ by many, with others saying it makes no sense whatsoever. However, a doctor has explained the science behind the rule. So which rule is it?
It’s the banana rule. For those not familiar with Slimming World, some foods you can eat without thinking about them – and a banana is one of them. However, if you eat a mashed banana, that will cost you some of your ‘syns,’ despite the fact that there are the same amount of calories.
Slimming World captioned the video: “What’s the deal with mashed bananas? Dr Sarah Bennett, one of our expert nutritionists, is here to set the record straight”.
A load of comments about the banana came up at the start of the video, such as: “I can eat 20 bananas and not have to syn. But mash one and it’s five syns. Make it make sense” and “You don’t swallow a banana whole, you mash it with your mouth to swallow, so how does that work?”
Dr Sarah Bennett explained that, yes, mashed and whole bananas do have the same number of calories; however, there’s science behind the decisions of the healthy eating plan.
She said: “Mashed, blended, and juiced fruit goes down easier, and it has less volume, so it’s less filling. Also, the process of feeling full starts long before the food reaches our stomach.
“Chewing releases satiety hormones, as do the later stages of digestion. By mashing the banana, you reduce the impact of both of these steps, so you don’t feel as full. That’s when you might find yourself reaching for other snacks later”.
Dr Sarah Bennett explained that as a Slimming World member, “you can still eat mashed banana,” explaining that “nothing is banned”. However, “when it comes to weight loss, eating whole fruit has a bunch of benefits”.
According to research done in 2025 on whether whole fruit or fruit juices were better for people, scientists found that “fruit consumed in solid form provides greater satiety due to delayed gastric emptying and related physiological reactions”.
They also shared that the “synergistic effects of polyphenols and fibre in whole fruit benefit the gut microbiome by acting as prebiotics and producing short‐chain fatty acids that reduce inflammation”.
Overall, there are more “health benefits in whole fruit than fruit juice”.
Senior dietician at The British Heart Foundation shares: “Whole fruits generally contain less sugar than foods like cake, biscuits and chocolate, and come without the added fat. Because of their water and fibre content, they will fill you up for relatively few calories.
“A medium banana, for example, contains less sugar than a standard 50g bar of milk chocolate and half the calories, making fruit a good swap for sweet treats.”
