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Ask the experts: Low-carb fibre intake

Q I’ve heard new research says fibre decreases early deaths. I’ve been following a ketogenic diet so I eat very little in the way of carbs but, surely, I must get fibre from the low-carb vegetables, fruit and nuts I eat. Do you think I would get enough fibre?

A It’s unlikely, but not impossible.

You’re referring to a World Health Organization study by researchers from Otago University released in January 2019. It’s an important study as it pulls together nearly 40 years of research and the results are compelling.

Comparing the highest fibre eaters with the lowest fibre eaters, the study found a 15 per cent to 30 per cent decrease in deaths and occurrence of coronary heart disease, stroke, type 2 diabetes and colorectal cancer. The researchers recommend at least 25g-29g fibre each day, saying 30g or more would be even better. Basically, the lower the fibre, the worse the outcomes.

Low-carb fibre intake

On a very-low-carb diet, you’re likely not getting anywhere near 25g-29g fibre a day. To be fair, neither are the majority of Kiwis.

On average, we get around 20g. A 2017 master’s thesis from the UK investigated 40 people following very-low-carb diets and found they had an average fibre intake of around 12g a day. In a US trial, where over 70 people were encouraged to eat a low-carbohydrate diet but were eating around 90g-100g of carbs a day, their fibre intake averaged around 16g.

On a ketogenic diet, you’re encouraged to severely limit carbohydrate intake (usually to less than 10 per cent of energy intake, or 50g a day). Starchy fruit and vegetables, cereals and processed or sugary carbs are out, replaced with low-carb vegetables and fruit, nuts and seeds along with a focus on more protein and fat.

Downside of cutting foods out

While we applaud the limit on sugary and processed foods, it’s a shame about the fibre-rich whole grains and legumes. (And don’t start me on the sat fat.) There’s no cold potatoes or pasta either, both sources of resistant starch, a type of fibre we could do with more of. Just to be clear, fibre is a subset of the carbohydrate group, so the high amounts of protein foods and fats are of no help here.

Focus on fibre

To get enough fibre on a keto diet you’d need to concentrate. It’s certainly easier to get enough fibre when you can include more high-fibre carbs in your day. I analysed some keto menu plans I found online and they were pretty low in fibre. But if I upped the fibre with a good amount of nuts, seeds, chia seeds and plenty of vegetables (which these plans seemed disappointingly low on), I could get to the 25g-29g target.

Variety matters

The problem was the narrowed variety of fibre. The WHO study included fibre from all of these sources as well as grains, legumes and potatoes, so we don’t know what impact removing those could have. While our gut microbiome, which relies on this fibre for its health, loves variety, perhaps just getting enough is a good start.

First published: Apr 2019

Sources and References

  • Fraile, JG. 2017. Dietary fibre intakes among UK adults following very low carbohydrate diets and their expected long-term effects in cardiovascular disease risk. MSc dissertation, School of Biosciences and Medicine, University of Surrey
  • Hu T et al. 2016. The effects of a low-carbohydrate diet on appetite: A randomized controlled trial. Nutrition, Metabolism & Cardiovascular Diseases 26:476-88



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