and told The Sun that because glucomannan is a water-soluble dietary fibre, it acts as a "bulk-forming laxative".
"This means that people may get diarrhoea, flatulence and bloating as side effects."
Although the company says that the ingredient has been cleared by the European Food Safety Authority, Rhiannon says that we shouldn't just take that at face value.
"We should be careful about any claim taken out of context of a given study," she advises.
"We should remain sceptical over any 'miracle' weight loss claims here.
"Healthy weight loss is something that takes time, and from my experience, those who embark on any form of restrictive diet are often those who put the weight back on afterwards.
"As opposed to promoting diet culture and fads, we should be trying to promote a healthy relationship with food. Long term sustainable weight loss is best achieved through diet and exercise and this will always trump an instant fix!"
How do you account for all the celebs who have lost weight on Boombod?
It's just a matter of simple maths.
You might lose a little weight on BoomBod but "no more than reducing calories in any other way", nutritional consultant, Ian Marber, told The Sun.
"If you eat fewer calories then you will lose weight - how one does it is up to you, but these types of products do nothing to change habits, instead they promote the notion that hunger, appetite and eating are enemies that have to be fought."
Weight loss isn't a one-size-fits-all concept.
Some people may find that simply taking a shake helps them to focus on what else they put into their body and encourages them to work out more.
Others will try it and find that an increase in fibre makes them fuller because they don't get enough soluble fibre in their day-to-day diets.
Unless they overhaul what they eat in general, all that water weight they've lost will just pile straight back on once the week is up.
"Weight loss depends on the individual," explains Sarah Flower.
"When you don't feel hungry, you don’t eat as much and therefore you can lose weight - a very simple concept that for some can work, though for me it does not teach good eating habits and making long-term dietary changes for health.
"Some could lose weight in a week, others may struggle and have slower loses - it depends on metabolism, how much weight one has to lose and the diet used alongside aids like this.
"BoomBod is not something I'd use to aid weight loss in my clinics as I prefer to educate on food, diet and lifestyle changes, but for some, it could be a useful tool."
So, it might help you to feel fuller for longer but you could get that simply by upping your fruit, veg and wholegrains consumption.
If you want to lose weight and keep it off, you're much better off overhauling your diet so that it's healthy and sustainable - and filling.
BoomBod may help you shed a load of water weight in seven days but unless you commit to a lower-calorie, balanced diet that works alongside an active lifestyle, you'll just regain the weight - and possibly add more on.
A spokesperson for Olivia Buckland told The Sun that she hasn't used BoomBod for over six months and that like many women, she has tried quick-fix products in the past.
"She is now understanding and learning how important a mix of a healthy diet and exercise is for her and is really enjoying going to the gym and sharing that with her following."
Katie Price told us that she didn't want to comment on our claims, and The Sun has reached out to BoomBod and all the other brand ambassadors mentioned in this article for comment.
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