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The Ketogenic Diet: A Detailed Beginner’s Guide

A ketogenic diet is a diet very low in carbohydrates (less than 50g a day) and high in fat. This is thought to cause the body to break down fat into molecules called ketones to use as the main source as energy versus glucose from carbohydrates. It tends to exclude most fruits, starchy vegetables, grains and legumes.

Clinically, the ketogenic diet is largely used to treat children with drug-resistant epilepsy under management of specialist dietitians. However, this diet has increased in popularity for its perceived ability to provide weight loss in individuals. But there are several reasons why you may want to think twice before adopting this diet.

The weight loss is unsustainable long term

While studies have shown a reduction in weight on the ketogenic diet, this weight reduction is not sustained long term. Also, these studies have a high dropout rate which highlights just how difficult this diet is to stick to!

It is important to remember that weight loss is not the sole determinant of health. Someone in a smaller frame may have health issues internally while someone in a larger frame may be perfectly fine inside. 

Our body needs carbohydrates to function well

Carbohydrates are not only required for energy, but several processes in our body depend on them to function optimally. For example, carbohydrates are required to convert the amino acid tryptophan to the mood regulating hormone serotonin (also known as the ‘happy hormone’). Also, melatonin, a hormone that helps to regulate tiredness, is made by converting tryptophan first to serotonin (using carbohydrate) and then to melatonin.

Keto diets are often high in saturated fat…

Research found young healthy adults who followed a low carbohydrate/high fat diet had a 44% increase in low-density lipoprotein cholesterol (LDL) (the ‘bad’ cholesterol).

In the keto diet foods high in fat are encouraged, however it does not make a clear differentiation between saturated and unsaturated fats, hence the high LDL cholesterol intake. Saturated fats increase our risk of high cholesterol, heart disease and stroke, therefore should not be consumed in excess.

…and low in fibre

Many items excluded from the keto diet such as fruits, vegetables and grains are not only full of vitamins and minerals but also tend to be rich in fibre. Fibre has several benefits including improving blood sugar levels, digestion and reducing the likelihood of constipation. A study found that 65% of children on the keto diet experienced regular constipation – a side effect that may not sit well! Furthermore, ketogenic dieters may be missing out on beneficial microbiome support. The microbiome, which is often referred to as our second brain, has been linked to numerous health factors including immunity and mental health.

Overall, this restrictive diet that is high in saturated fat and low in fibre does not observe the nutritional guidelines and has the potential to do more harm than good in many individuals.

Rhiannon Lambert is a Registered Nutritionist specialising in weight management, eating disorders and sports nutrition. Founder of leading Harley Street clinic Rhitrition, bestselling author of Re-Nourish: A Simple Way To Eat Well and Food For Thought podcast host, Rhiannon’s qualified approach to nutrition and total dedication to her clients’ needs has seen Rhiannon work with some of the world’s most influential people


1) British Nutrition Foundation (BNF, 2018) Dietary Fibre

2) Freeman, J.M., Kossoff, E.H. & Hartman, A.L. (2007) The ketogenic diet: One decade later. Pediatrics. 119(3) pp.535-543.

3) Paoli, A., Rubini, A., Volek, J.S. & Grimaldi, K.A. (2014) Beyond weight loss: A review of the therapeutic uses of very-low-carbohydrate diets. European Journal of Clinical Nutrition. 68(5) pp.641.

4) Retterstøl, K., Svendsen, M., Narverud, I. & Holven, K.B. (2018) Effect of low carbohydrate high fat diet on LDL cholesterol and gene expression in normal-weight, young adults: A randomized controlled study. Atherosclerosis. 279pp.52-61.

5) Wibisono, C., Rowe, N., Beavis, E., Kepreotes, H., Mackie, F., Lawson, J., Cardamone, M., (2015) Ten-year single-center experience of the ketogenic diet: Factors influencing efficacy, tolerability, and compliance. Journal of Pediatrics, The. 166(4) pp.1036.


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