What exactly is the Keto Diet?

With a diet where bacon and butter are considered ‘health foods’, it shouldn’t come as a surprise that the keto diet has built up such a hype! The diet has even been linked to celebs such as Kim Kardashian, Gwyneth Paltrow and Rihanna, having all sworn by the diet at one point or another.

Short for “Ketogenic diet,” this eating plan is extremely high fat (65-75% of your diet), low carbohydrate (<5% of your diet) and moderate protein diet (15-20%). This very low carbohydrate diet (around 20-50g per day or 5% total calories) causes the body to switch from burning mainly carbohydrates to burning fat as energy. As a result, the levels of ketones increases in your body.

What can you eat on the keto diet?

  • Fats such as avocado, cheese, butter, nuts, seeds, oils
  • Proteins such as meat, fish, eggs, cheese
  • Low carbohydrate vegetables, mostly greens

What can’t you eat on the diet?

  • Most dairy (apart from butter and cheese)
  • Fruit
  • Grains
  • Beans & legumes
  • Starchy vegetables such as sweet potato, squash, beetroot, carrot
  • Most processed food containing carbohydrates or sugar

Why did the keto diet become so trendy?


Believe it or not, the keto diet was initially designed as an effective tool in the treatment of drug-resistant childhood epilepsy. There is strong evidence to suggest that the keto diet can be suitable for those with epilepsy. A Cochrane review demonstrated a massive 30-40% reduction in seizures when compared with non-keto diet controls.

Neurological Diseases

There may also be some other health conditions in which the keto diet may be beneficial, for example, neurological diseases including Alzheimer’s, Parkinson’s and multiple sclerosis, however, the evidence is limited and more research is required.
Weight Loss

The most popular and trendy use for the ketogenic diet is weight loss and there are some review studies to suggest that a low carb diet can lead to a small but significant difference in weight loss in comparison to a low fat diet. However it’s important to remember that some of this weight loss will be down to water loss which accompanies a very low carbohydrate diet.

One large study showed that in the short term (3 & 6 months), a greater rate of weight loss was achieved on a low carb diet in comparison to a low-fat diet. It’s important to note, however, at one year they found little clinically significant differences in weight loss between the diets.

Whilst there is no proven mechanism for how the ketogenic diet may work when it comes to weight loss, some research suggests that ketosis help to suppress appetite, which may be useful for dieters who struggle with the discomfort of hunger.  Theoretically weight loss on the ketogenic diet may simply be down to a reduce energy intake rather than any special metabolic advantages for reducing carb intake.

Despite this, a more recent study has been published, looking at over 600 people who were told to follow a healthy low-fat diet or low carb diet. Each group were instructed to stick to 20g fat or 20g carbs per day. After the first 2-months, they were allowed to slowly increase the amount of fat or carbs they ate until they reached the lowest amount they believed they could maintain long-term. Interesting there was no significant difference between the low-fat and low-carb diets in relation to the amount of weight loss.

In summary, the ketogenic diet could be used as a weight loss tool for some, however, it can be difficult to sustain long-term due to its highly restrictive nature. There is also evidence to indicate that neither low carb or low-fat diets are superior and what really matters when it comes to weight loss is focusing on a diet which the individual can sustain.

Are there drawbacks from following the keto diet?

  1. Cutting out food groups also means cutting out vital vitamins and minerals increasing the risk of developing nutrient deficiencies.
  1. The keto diet may affect the health of our gut microbiome. This diet is extremely low in fibre, which is not only essential to health, but also to the health of our gut bacteria. By removing fibre, you also remove your main source of food for your gut bacteria. Research has shown changes in our gut microme when following the keto diet for long periods of time.
  1. The keto diet does come with side effects such as constipation, bad breath nausea, poor exercise performance, poor concentration and mood disturbances.
  1. Cutting out food groups may lead to fear around foods, which could lead to disordered eating.




  1. Paoli, A., Rubini, A., Volek, J. & Grimaldi, K. (2013). Beyond weight loss: a review of the therapeutic uses of very-low-carbohydrate (ketogenic) diets. European Journal of Clinical Nutrition,67, 789–796.
  2. Hession , M., Rolland  , C., Kulkarni  , U., Wise , A. & Broom, J. (2008). Systematic review of randomized controlled trials of low-carbohydrate vs. low-fat/low-calorie diets in the management of obesity and its comorbidities. Obesity Reviews,  (10), 36-50.
  3. Bueno, N., de Melo, I., de Oliveira, S. and da Rocha Ataide, T. (2013). Very-low-carbohydrate ketogenic diet v. low-fat diet for long-term weight loss: a meta-analysis of randomised controlled trials. British Journal of Nutrition, 110(07), pp.1178-1187.
  4. Dashti , H. M., Mathew , T. C., Hussein , T., Asfar , S. K., Behbahani , A., Khoursheed , M. A., Al-Sayer , H. M., Bo-Abbas , Y. Y. & Al-Zaid , N. S. (2004). Long-term effects of a ketogenic diet in obese patients. Experimental and Clinical Cardiology,9(3), 200-205.
  5. Foster, G. D., Wyatt, H. R., Hill, J. O., McGuckin, B. G., Brill, C., Mohammed, B. S., Szapary, P. O., Rader, D. J., Edman, J. S. & Klein, S. (2003). A Randomized Trial of a Low-Carbohydrate Diet for Obesity. The New England Journal of Medicine,348(21), 2082-2090.
  6. Gardner, C. D., Trepanowski, J. F., Del Gobbo, L. D. & al, e. (2018). Effect of Low-Fat vs Low-Carbohydrate Diet on 12-Month Weight Loss in Overweight Adults and the Association With Genotype Pattern or Insulin Secretion. JAMA,319(7), 667-679.
  7. Nordmann, A., Nordmann, A., Briel, M., Keller, U., Yancy, W. J., Brehm, B. & Bucher, H. (2006). Effects of low-carbohydrate vs low-fat diets on weight loss and cardiovascular risk factors: a meta-analysis of randomized controlled trials. Clinical Governance: An International Journal,11(4).
  8. Johnston, B. C., Kanters, S., Bandayrel, K., Wu, P., Naji, F., Siemieniuk, R. A., Ball, G. D., Busse, J. W., Thorlund, K., Guyatt, G., Jansen, J. P. & Mills, E. J. (2014). Comparison of weight loss among named diet programs in overweight and obese adults: a meta-analysis.JAMA,312(9), 923-33.

Lily Soutter, Nutritionist BSc (Hons) Human Nutrition, Dip ION

Lily graduated from Newcastle University with a BSc (Hons) degree in Food and Human Nutrition (AfN accredited) where she was awarded the Sage Faculty for Excellence Scholarship. She then went on to gain a Nutritional Therapy Diploma from the Institute of Optimum Nutrition. Lily’s extensive knowledge of the science of food and health, enables her to regularly write for The Times, The Telegraph, The Daily Mail, The Independent, Women’s Health and Cosmopolitan. Her frequent TV appearances include ITV’s primetime series Save Money: Lose Weight with Dr. Ranj Singh. Lily sees clients from her clinic in Chelsea and from the Portobello Clinic, a private medical practice based in Notting Hill.