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Back To Blog > Ketogenic Diets – The Good, The Bad, and The Ugly

This post is by associate Triage Practitioner, and guest blogger, Matthew Savage 

Despite major advances in medical and health sciences, obesity is still a major concern across the world. With a constant stream of different diets hitting the market and promising amazing results, it is important to consider the effects of certain diets on the body and mind and not simply examining the weight lost in the process. Ketogenic diets are high fat (60% macronutrient content), very low carbohydrates (5-10%) and moderate protein diets (30%) and are said to deprive the body of fuel from carbohydrates (glycogen). Low carbohydrate diets differ from Ketogenic diets as levels of carbohydrates are still high enough for the brain to continue utilising glucose as its main fuel source. However, Keto diets force the body to use Ketone bodies (KBs) as a source of alternative fuel and these bodies mainly include acetoacetate (AcAc) and 3-beta-hydroxybutyrate (3HB), produced by fatty acids in the liver in a process known as ketogenesis. Research suggests that these bodies can produce the equivalent, if not more, fuel per gram for the body’s organs, including the brain. This change in the way the body produces fuel is said to aid in weight loss by burning fat directly, leading to a reduction in body fat, something that “Keto diets” are praised for. However, as with all diets, there are positives and negatives of each.

Postives of Ketogenic Diets

Once the body is deprived of carbohydrates and blood concentration of ketone bodies increases, the body is said to be in a state of ketosis. This involves eating less than 50 grams of carbohydrates a day and will usually take 2-4 days for the body to make this transition. This is said to have several health benefits, including the following:

  • Rapid weight loss – Eating a high level of carbohydrates can raise blood insulin levels which tells your body to store glucose and fat. This can lead to an increase in fat levels. Reducing levels of carbohydrates has been shown to help overweight people to reduce body fat percentages quickly. It is said that this rapid weight loss can initially give a positive psychological boost to those on the diet (particularly obese people), kick starting adherence to diet (Muscogiuri et al, 2019).
  • Therapeutic benefits – Much research has shown that Ketogenic diets can have very positive effects in the treatment of epilepsy, diabetes and cardiac dysfunction (Harvey et al, 2019). Epilepsy, a condition characterised by seizures linked to periods of overexcitement in brain cells, has been traditionally very difficult to treat. Periods of starvation and increased levels of KBs have been shown to have a positive effect in reducing the frequency of seizures in drug-resistant epilepsy (Meira et al, 2019).
  • Neuroprotective qualities – Recent research has suggested that ketones can reduce inflammation and neurodegeneration associated with conditions such as Alzheimer’s and other dementias. Many researchers believe that glucose utilization in brain cells is impaired in those with Alzheimer’s disease, leading to the death of brain cells due to a lack of energy. Keto diets provide an alternative fuel source for the brain which can be utilized and reduce death of brain cells. In addition to this, KBs can reduce reactive oxidative species, a cause of inflammation in the brain and a major factor in further damage for those with dementias.

Negatives of Ketogenic Diets

Most experts agree that a healthy diet is one that can be sustained over the long term. However, much research suggests that Keto diets are not sustainable over a longer-term period, for several reasons:

  • Weight loss vs fat loss – Research suggests that keto diets can induce rapid weight loss. However, this is often in the form of water loss and due to a much-reduced energy intake, which can lead to feelings of severe fatigue. Substantial reductions in body weight can impact psychological wellbeing poorly through lack of energy and hormonal changes, as well as having an impact on bone health (Paoli et al, 2015). Results of some studies which suggest power increases due to keto diets are also often ambiguously designed and these increases are often due to a less weight contributing to
  • Reduced performance for elite athletes – It is extremely difficult to find any elite athletes who follow a keto diet for a number of reasons and a recent systematic review found mixed results, with mostly negative impacts found for keto on athletes compared to high carbohydrate diets (Bailey and Hennessy, 2020). Changing the levels of KBs in our blood leads to changes in our red blood cells, haemoglobin, and the body’s ability to transport oxygen. More oxygen is needed to metabolise fat compared to carbohydrates, and this leads to declines in performance, a rise in the rate of perceived exertion, longer recovery times and declines in general exercise performance (Fogelholm, 1994).
  • Our Brains still need glucose – Although many advocates suggest that Ketone bodies can supply the brain with all its fuel requirements, most note that this is not possible and only 75% of the brain can be supplied by KBs. Certain areas of the brain can only function properly with a supply of glucose, and this is fuelled by the small amount of carbohydrates consumed in the diet and through a process called glucogenesis, whereby the liver produces new glucose by breaking down amino acids from protein. Whilst this is not considered dangerous for healthy individuals, this can cause issues in people with damaged liver, kidneys, or other organs. Failure of gluconeogenesis is usually fatal and can lead to hypoglycaemia, causing brain dysfunction, coma, and death. This means it is important to consider how healthy your organs are before undertaking a keto diet and to take the time to understand the effects the diet can have on the brain.


It is important to remember that there is no one individual diet that suits us all. A recent study by Harvard University, presented at the American Society of Nutrition conference in June 2019, investigated how our DNA affects our diet tolerances and reactions to different foods. The study found that DNA accounts for less than 30% of these differences, even in identical twins. It also found that sleep regime, stress levels, exercise levels and gut health were more important than DNA when it came to our body’s responses to dietary inputs. This is important to consider as it means that no one diet can work for everyone, so each must be considered on an individual basis. A keto diet may work for some people, such as the clinically obese or those with epilepsy or other long-term conditions, and a very low carbohydrate diet may lead to benefits for that individual. However, it may be damaging to others, such as athletes who compete in high intensity, short-duration sports which require short bursts of anaerobic activities, such as football (Weiss, 2019). Because of this, it’s important to consider your overall health and the benefits keto may have before undertaking such a diet simply for quick weight loss.

About Matt Savage

Matthew Savage is an associate Triage Practitioner, has an MSc in Psychology, is a qualified personal trainer, and has worked within the field of cognitive rehabilitation for 5 years. He is an FA qualified football coach, with a keen interest in moral behaviour and wellbeing within team sports. 


Paoli A, et al. (2015). Ketosis, ketogenic diet and food intake control: a complex relationship. Front Psychol. 2015; 6:27.

Fogelholm M. (1994). Effects of bodyweight reduction on sports performance. Sports Med. 1994 18(4): 249–67.

Wroble, K. A., Trott, M. N., Schweitzer, G. G., Rahman, R. S., Kelly, P. V., & Weiss, E. P. (2019). Low-carbohydrate, ketogenic diet impairs anaerobic exercise performance in exercise-trained women and men: a randomized-sequence crossover trial. The Journal of sports medicine and physical fitness, 59(4), 600–607.

Meira I.D et al.  (2019). Ketogenic Diet and Epilepsy: What We Know So Far. Front Neuroscience.

Muscogiuri, G., Barrea, L., Laudisio, D. et al. The management of very low-calorie ketogenic diet in obesity outpatient clinic: a practical guide. J Transl Med 17, 356 (2019).

Keto Diets


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