Want to be 'skinny'? Doctor explains why you actually need 3 different types of fibre in your diet

A doctor has advised focusing on a balanced diet that includes three main types of fibre: soluble fibre, insoluble fibre, and resistant starch. Here's why.

UK doctor Dr Karan Rajan, an NHS surgeon and social media, shared in an Instagram video on February 23, 2025, that to support optimal gut health, it's essential to consume a diverse range of fibre types. He also suggested increasing your fibre intake gradually to allow your gut microbiome to adjust.

Dr Karan Rajan was reacting to a woman's video in which she said, “I don't know if a majority of people know this, but the fibre is what keeps you skinny, and there are two different types of fibres – there is soluble fibre, and there is insoluble fibre; and you want the insoluble fibre.”

Here's what Dr Rajan said: “If you want to improve your gut health, you actually need three different types of fibre in your diet – soluble fibre, insoluble fibre and resistant starch.”

Here's a breakdown of the 3 main types of fibre

He then went to explain each of them, saying:

1. Soluble fibre absorbs water and forms a biological jelly inside. It bulks up your poop, so it is juicy and soft; and it feeds bacteria in your large intestine, so they can poop out anything beneficial anti-inflammatory metabolites. In fact, soluble fibres like the one found in psyllium husk can actually improve IBS (Irritable Bowel Syndrome) symptoms.

2. Insoluble fibre acts like a rake to sweep through your digestive tract. It acts as a mild form of human drain cleaner.

3. Resistant starch is a carbohydrate that acts like a fibre to feed your gut bacteria. There are a few different types, but you can usually find them in unripe mangoes and green bananas or cooking and cooling carbohydrates like potatoes or rice.

Dr Karan Rajan added, “Most fibre containing foods will contain at least two types of fibre. For example, in a kiwi, the skin is mostly insoluble fibre and the flesh is mostly soluble fibre. And if you like eating hairy fruits, you get both.”

Tips for increasing fibre intake

He then went on to list '3 basic rules of fibre newbies':

1. Figure out what works for you. Increase your fibre intake slowly. I suggest going no quicker than 5 grams a week.

2. If certain fibre-rich foods trigger your symptoms, see if it is high in fodmap.

3. Diversify your sources of fibre. This way, you can benefit from a range of different prebiotics, antioxidants and nutrients.

By incorporating a diverse range of fibre types into your diet, you'll be supporting a healthy gut microbiome, promoting regular bowel movements, and reducing the risk of chronic diseases. Prebiotic foods play a crucial role in maintaining a healthy gut. Click here for the ultimate gut health guide and discover the top prebiotic foods for optimal wellness.

Note to readers: This article is for informational purposes only and not a substitute for professional medical advice. Always seek the advice of your doctor with any questions about a medical condition.