Fibre has long been praised for supporting gut health – from keeping digestion regular to nourishing beneficial gut bacteria and regulating appetite-related hormones. But beyond better digestion, can it actually help with weight loss? And if so, how does it work?
Dr Karan Rajan, a UK-based surgeon and widely followed health content creator, has broken down what fibre can and cannot realistically do for weight loss, explaining which works better: whole foods or supplements. In an Instagram video shared on February 19, the surgeon outlines five key mechanisms that are triggered when you eat fibre, explaining how each one can support weight loss and improve overall metabolic health.
1. Gastric distension
According to Dr Rajan, fibre physically expands in the stomach, increasing volume and triggering stretch receptors that signal fullness to the brain – helping you feel satisfied while consuming fewer calories.
He explains, “Fibre physically stretches your stomach. This triggers mechanoreceptors to send a signal to your brain stem via your vagus nerve so you feel satisfied on fewer calories.”
2. Slowed gastric emptying
The surgeon points out that soluble fibre absorbs water and forms a gel-like consistency in the stomach, which slows down the movement of food through your intestines, keeping you feeling fuller for longer.
He states, “Soluble fibre forms a gel in your stomach. Food exits more slowly, so you stay fuller for longer between meals and do less snacking.”
3. Gut hormone release
Fibre also stimulates the release of gut hormones such as GLP-1 and PYY, which help regulate appetite. These hormones signal to the brain that you are full, working in a similar way to medications like Ozempic.
Dr Rajan explains, “The presence of fibre in your intestines stimulates L-cells to release GLP-1 and PYY, the same hormones that Ozempic mimics. These cross the blood-brain barrier and suppress appetite at the brain level.”
4. Microbiome fermentation
When fibre is fermented in the colon, gut bacteria produce short-chain fatty acids, which help suppress the production of the hunger hormone ghrelin – further supporting appetite regulation and satiety.
The surgeon highlights, “Fibre reaches your colon and bacteria ferment it producing short-chain fatty acids, and these reduce the production of the hunger hormone ghrelin.”
5. Reduced absorption efficiency
High-fibre meals can also modestly reduce calorie absorption, as some nutrients bind to fibre and pass through the digestive tract without being fully digested – meaning the body takes in slightly fewer calories overall.
Dr Rajan explains, “High-fibre meals have lower effective calories because some nutrients bind to the fibre and pass through undigested. It’s a small effect, but it compounds the more fibre you eat.”
Fibre doesn’t override thermodynamics
Fibre supports weight management indirectly by enhancing appetite regulation and amplifying fullness signals – but it does not override the basic principles of energy balance. As Dr Rajan points out, calories still count. If your maintenance intake is 2,500 calories and you consistently consume 3,000 calories – even from high-fibre foods – weight gain is still likely.
He explains, “If you eat 3,000 calories of high-fibre foods and your maintenance calories is 2,500, you still gain weight. Fibre can’t override thermodynamics. What fibre does is make a calorie deficit easier to maintain. You’re less hungry. You have fewer cravings. And your gut hormones are working with you. In fact, studies show that higher fibre diets lead to a spontaneous calorie reduction of around 10 percent without conscious restriction.”
Do fibre supplements help?
According to Dr Rajan, fibre supplements can be helpful – but only when used as a supportive tool, not a substitute. They should not become an excuse to skip naturally fibre-rich foods altogether. Instead, supplements are best reserved for situations when access to whole foods is limited. He stresses that whole foods remain essential because they provide a full spectrum of nutrients that supplements alone cannot replicate.
The surgeon emphasises, “Fibre supplements are a tool, but not a replacement. They’re useful in lots of scenarios, like when you’re travelling, and whole food fibre is limited, or you’re sick, and appetite is low, or you can’t be bothered to cook, or you’re on a GLP-1 medication and still need to hit your fibre goals at lower calories, or you just want more fibre but not more food. Whole foods are excellent because they come with polyphenols, vitamins, minerals, nutrients, and the food matrix effects. Ultimately, any fibre you can get into your diet is still a net positive, whether it’s a supplement or a whole food. But do not use supplements as an excuse to never eat fibre-rich foods.”
Note to readers: This article is for informational purposes only and not a substitute for professional medical advice. It is based on user-generated content from social media. HT.com has not independently verified the claims and does not endorse them.
