The Ketogenic Diet: Fact or Fad?

ketogenic diet

The ketogenic diet has become increasingly popular over the last few years. Celebrities have claimed it useful for fat loss journeys on social media, and when you google search ‘ketogenic diet’, you are overloaded with information, so it can be difficult to tell fact from fiction. The keto diet is an eating pattern suggested for various uses, from fat loss journeys to epilepsy management. So, the question I want to answer is: Is there science behind its usefulness, or is it the latest fad diet?

Understanding the Basics of the Ketogenic Diet

A ketogenic diet is a diet which is high in fat and very low in carbohydrates. This means that the body’s main energy source comes from fat rather than the preferred sugar or carbohydrate source. In the body, this fat source is broken down into ketone bodies to be used as a fuel source, and this is where the name ketogenic diet comes from. 

The Science of Weight & Fat Loss on the Keto Diet

Weight loss comes from the net result of a calorie deficit or expending more energy than you are taking in. Therefore, the energy balance model outlined below is the cornerstone of weight loss.

ketogenic diet - Inside out nutrition

Studies have shown that weight loss from high-fat diets may be due to the use of protein as an energy source, which increases metabolism. It should be noted that when carbohydrates are broken down in the body, they attract a lot of water and are therefore known as a ‘bulky molecule’. Therefore, when individuals reduce their carbohydrate intake significantly when following a ketogenic diet, the initial weight loss experienced is water weight, not actual fat loss.

The Safety and Health Risks of the Keto Diet

Short-and long-term health consequences are associated with the keto diet, and these should be weighed before embarking on this way of eating. Due to the nature of this high-fat diet, fruits and vegetables are limited. This can result in constipation due to the low-fibre quality of the diet. Brain fog can also be a common side effect of the diet because the brain uses glucose (carbs) as its primary energy source.

Ketogenic diets are also higher in fat than most other diets, which can negatively affect blood lipid profiles. A diet high in fat is not recommended under national dietary guidelines, particularly saturated or animal fat sources such as meat, butter and cheese. However, the keto diet is high in saturated fat due to the nature of the diet. Therefore, further research is needed in this area to deduce the effects of the diet on overall cardiovascular risk factors.

The Potential Benefits of the Keto Diet for Diabetes Management

Regarding diabetes management, research has shown that low-carb/high-fat diets might help improve blood glucose control. Other health benefits have also been reported in the use of ketogenic diet therapies in individuals with both type 1 and 2 diabetes and obesity, such as weight loss and reduced cardiovascular disease risk factors. However, further research is needed in this area to reflect the complex nature of diabetes management.

Weighing Up The Ketogenic Diet

Pros Of The Keto Diet

  1. Can be used to achieve short-term weight loss goals.
  2. Can be effectively used in the management of drug-resistant epilepsy.
  3. Can be useful in individuals with type 1 and type 2 diabetes for increased glucose control.

Cons Of The Keto Diet

  1. Requires careful consideration and planning of meals.
  2. Very high in animal products which is unsustainable.
  3. Long term use can lead to vitamin and mineral deficiencies if not implemented with correct planning and guidance.
  4. Can lead to constipation due to a lack of dietary fibre.
  5. Can result in symptoms like tiredness, headache and ‘brain fog’.

Take Home Messages About The Ketogenic Diet

All in all, the ketogenic diet can be a very restrictive way of eating. The research has shown that it is a low-fibre diet; however, 90% of Irish adults already struggle to meet the recommended daily fibre intake. Wholegrains offer many benefits for heart and gut health and play a role in weight management, so you should be aiming to increase these foods in your diet, not reduce them. Regarding weight loss, I would recommend finding a dietary pattern best suits your lifestyle best. To meet your individual needs working with a registered dietitian may be beneficial to meet your individual needs.


Handjieva-Darlenska T, Handjiev S, Larsen TM, van Baak MA, Jebb S, Papadaki A, Pfeiffer AF, Martinez JA, Kunesova M, Holst C, et al. Initial weight loss on an 800-kcal diet as a predictor of weight loss success after 8 weeks: the Diogenes study. Eur J Clin Nutr 2010;64(9):994-9. doi: 10.1038/ejcn.2010.110. 

Hall KD, Chen KY, Guo J, Lam YY, Leibel RL, Mayer LE, Reitman ML, Rosenbaum M, Smith SR, Walsh BT, et al. Energy expenditure and body composition changes after an isocaloric ketogenic diet in overweight and obese men. Am J Clin Nutr 2016;104(2):324-33. doi: 10.3945/ajcn.116.133561.

Nielsen JV, Joensson EA. Low-carbohydrate diet in type 2 diabetes: stable improvement of bodyweight and glycemic control during 44 months follow-up. Nutr Metab (Lond) 2008;5:14. doi: 10.1186/1743-7075-5-14.

Tay J, Luscombe-Marsh ND, Thompson CH, Noakes M, Buckley JD, Wittert GA, Yancy WS, Jr., Brinkworth GD. A very low-carbohydrate, low-saturated fat diet for type 2 diabetes management: a randomised trial. Diabetes Care 2014;37(11):2909-18. doi: 10.2337/dc14-0845.

Moreno B, Crujeiras AB, Bellido D, Sajoux I, Casanueva FF. Obesity treatment by very low-calorie-ketogenic diet at two years: reduction in visceral fat and on the disease burden. Endocrine 2016;54(3):681-90. doi: 10.1007/s12020-016-1050-2.

Bueno NB, de Melo IS, de Oliveira SL, da Rocha Ataide T. Very-low-carbohydrate ketogenic diet v. low-fat diet for long-term weight loss: a meta-analysis of randomised controlled trials. Br J Nutr 2013;110(7):1178-87. doi: 10.1017/s0007114513000548.

National Adult Nutrition Survey. Irish Universities Nutrition Alliance. Summary report March 2011.