Ketosis is a metabolic state in which the body burns fat for energy instead of carbohydrates. It occurs when the body's glycogen stores are depleted and the liver starts producing ketone bodies from fatty acids as an alternative fuel source for the brain and other organs .
In the state of ketosis, the body relies on ketones as its primary source of energy, and the production of ketones in the liver increases. This results in several positive benefits [1,2]:
- Weight loss
- Improved insulin sensitivity
- Reduce risk of heart disease
- Reduce symptoms of Alzheimer’s Disease & Epilepsy
Additionally, when ketones are used by the brain, improvements in cognitive function and alertness can be observed. There is also some potential that ketones can improve the outcomes of brain injuries .
This may be because ketones provide a more stable and consistent source of energy than glucose, which as fluctuate depending on the timing of food consumption .
There are several ways to reach ketosis, such as fasting, prolonged exercise, or perhaps the most effective is following a ketogenic diet.
The Ketogenic Diet
The ketogenic diet, which involves restricting carbohydrate intake to very low levels and increasing protein and fat intake to induce ketosis. Typically, carbohydrates are restricted to less than 50 g per day but there are several versions of the diet :
Standard Ketogenic Diet
Very low carbohydrates, moderate protein, high fat. Typically, 70% fat, 20% protein, 10% carbohydrates.
Cyclical Ketogenic Diet
Involves cycling carbohydrate refeeding days, e.g., 5 ketogenic days and 2 high carbohydrate days.
Targeted Ketogenic Diet
Carbohydrates are allowed around workouts.
High Protein Ketogenic Diet
Similar to the standard ketogenic diet, but with more protein. Typically, 60% fat, 35% protein, and 5% carbohydrates.
Note: Only the standard and high protein versions of the ketogenic diet have been well researched to date.
There is a large amount of information available online to help with the practicalities of a ketogenic diet. Here is a quick summary:
The ‘Good’ – Ketogenic foods to eat 
- Fatty fish (Salmon, trout, tuna, mackerel)
- Butter and cream
- Nuts and seeds
- Healthy Oils (Olive oil)
- Low carbohydrate vegetables (Greens, tomatoes, onions)
- Salt, pepper and spices
The ‘Bad’ – Ketogenic foods to avoid 
- Sugary foods
- Beans or legumes
- Root vegetables
- ‘Low fat’ marketed products (Low fat condiments)
- Some condiments and sauces (Barbecue sauce, ketchup)
- Unhealthy oils (processed vegetable oils)
- ‘Sugar free’ diet foods (Sugar free candies)
Some Things To Be Aware Of
Being in ketosis can have side effects, especially during the initial phase of adaptation to a low-carbohydrate or ketogenic diet – often referred to as ‘keto flu’ [5,6,7].
Some other less common side effects:
- Low energy
- Increased appetite
- Trouble sleeping
- Reduced exercise performance
- Digestive discomfort
Potential long term negative effects of a ketogenic diet
- Low blood protein
- Extra fat in liver
- Kidney stones
- Micronutrient deficiencies
Dieting to achieve ketosis may not suit everyone, and it is recommended that you listen to your body and not push the boundaries of it. Remember, there is more than one way to achieve ketosis, and starting with a gentler method such as 12:12 or 16:8 intermittent fasting may be a good place to start.
Daniel Glassbrook, PhD
Daniel is a sports scientist and researcher, currently working as the first team sports scientist for the Newcastle Falcons Rugby Club, and a postdoctoral researcher in sports related concussion at Durham University.
1. Paoli, A., Rubini, A., Volek, J. S., & Grimaldi, K. A. (2013). Beyond weight loss: a review of the therapeutic uses of very-low-carbohydrate (ketogenic) diets. European journal of clinical nutrition, 67(8), 789-796.
2. Veech, R. L. (2004). The therapeutic implications of ketone bodies: the effects of ketone bodies in pathological conditions: ketosis, ketogenic diet, redox states, insulin resistance, and mitochondrial metabolism. Prostaglandins, leukotrienes and essential fatty acids, 70(3), 309-319.
3. Prins, M. L., & Matsumoto, J. H. (2014). The collective therapeutic potential of cerebral ketone metabolism in traumatic brain injury. Journal of lipid research, 55(12), 2450-2457.
4. Longo, V. D., & Mattson, M. P. (2014). Fasting: molecular mechanisms and clinical applications. Cell metabolism, 19(2), 181-192
5. Healthline (N.d). The Ketogenic Diet: A Detailed Beginner’s Guide to Keto. https://www.healthline.com/nutrition/ketogenic-diet-101
6. Masood W, Annamaraju P, Uppaluri KR. Ketogenic Diet. [Updated 2022 Jun 11]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK499830/
7. Martin-McGill, K. J., Bresnahan, R., Levy, R. G., & Cooper, P. N. (2020). Ketogenic diets for drug‐resistant epilepsy. Cochrane Database of Systematic Reviews, (6).