What is a ketogenic diet?
The ultimate aim of the ketogenic diet is to switch your body’s energy system to a state of ketosis, and so typically, you’ll restrict your carbohydrate intake and increase your fat intake, whilst keeping your protein intake moderate. But what exactly is ketosis?
When you eat carbohydrates, like rice or bread, your body uses the glucose from those foods as its main source of fuel. But when there’s not enough carbohydrate to use as fuel, the body creates an energy source from fat, known as ketones. When ketones become the main source of energy for your body, you go into a state of ketosis.1
To achieve ketosis, then, you need to keep your carbohydrate intake very low. Most people who follow a ketogenic diet will track their carbohydrate intake — specifically, their net carbohydrate intake, which is the total carbohydrate minus the fibre content. This means that on the diet, you should aim for around 50g grams or less of net carbohydrates per day, though some do aim for around 30 grams or less, depending on their needs and goals.2
What foods are included?
In order to keep your carbohydrate intake low, and your fats and proteins high, your diet should include a variety of the following foods:
- Lean meats, poultry, fish and seafood
- Low carbohydrate vegetables, like broccoli, cauliflower, zucchini, and spinach
- Low carbohydrate fruits like strawberries and blueberries
- Nuts and seeds
- Oils, such as olive oil, coconut oil, and avocado oil
- Low carbohydrate dairy products, like cream, cheese, and high-fat yoghurts
- Low-carbohydrate foods, like protein bars and shakes
- Low or no-calorie sweeteners, such as stevia
What foods are avoided?
Generally, any food that has a significant amount of net carbohydrates is often eliminated from a ketogenic diet. Some of these foods include:
- Grains like wheat, barley, rice, oats, and corn
- Legumes, like chickpeas, lentils, and beans
- Pseudograins, such as quinoa and buckwheat
- High carbohydrate vegetables, like sweet potato and potato
- High carbohydrate fruits, like bananas, mangos, dates, and watermelon
- Full-sugar soft drinks
- Processed foods with a high carbohydrate content, like chips and crisps
Why would you cut out carbohydrates?
The main reason for adopting the ketogenic diet, and thus heavily lowering your carbohydrate intake, is to enter a state of ketosis. The ketones that are used as energy will replace the carbohydrates, which can commonly come from higher sugar sources, like bread and pasta. This can result in the regulation of blood sugar levels, because when you do consume carbohydrates, the levels tend to rise quickly — particularly if those carbohydrates are low in fibre. The body responds by producing insulin, which stores the sugar away in fat cells, thus dropping the blood sugar levels. By eliminating the majority of sugar-heavy carbs, you can potentially reduce these sporadic spikes and drops in blood sugar.3 Some studies have also suggested that the release of ketones rather than sugar can affect other parts of the body, like the nervous system.4
Are carbohydrates essential?
One of the major arguments against the ketogenic diet is that we ‘need’ carbohydrates. The truth is, however, carbohydrates are not ‘essential’ as such. The human body can create glucose using protein in a process called gluconeogenesis, or it can create ketones from fat to supply energy.5, 6
But while they’re not essential, some carbohydrate-containing foods can have many other beneficial nutrients, and some of those are considered essential.7 It’s worth noting, though, that this can be the case with most diets, and that they all have their pros and cons.
Can the ketogenic diet help you lose weight?
In terms of using the ketogenic diet for weight loss, there are a number of studies that support it as an effective method.8 If you adopt the diet, then you’ll probably experience an initial drop in weight. But, because carbohydrates typically help your body to retain water, this will likely be due to loss of water weight, as a result of your lower-carb intake, rather than actual fat loss.
That being said, because the ketogenic diet is generally lower in processed and high-sugar foods, which are often calorie-dense and nutrient-empty, you may well experience some weight loss due to the calorie loss. This might also be aided by the suppression of your appetite, as on the ketogenic diet, you may feel less hungry, and so you could be likely to consume fewer calories overall. With this, you may also see a reduction in cravings and binge-eating.9
The diet also has the potential to increase your metabolism, which means that you could burn more calories whilst at rest — not exercising. The higher your metabolism, the easier it is to lose weight.10 And, though some researchers suggest that weight loss experienced during ketosis is because of an intentional reduction in energy intake, some studies have found that people can lose weight even when their intake isn’t even restricted — they eat normally.11
With all this in mind, it’s important to remember that not everyone has success with a ketogenic diet. Some find it too restrictive for their preferences and lifestyles, and are unable to maintain it. Others could see an increase in appetite and cravings, particularly during the initial stages. As with any diet, it has to work with you and your lifestyle in order to have a meaningful impact on your weight loss.
Other benefits of a ketogenic diet
Studies have shown that the benefits of the ketogenic diet aren’t just limited to weight loss, however. The nervous system, for instance, experiences multiple benefits whilst the body is in the state of ketosis, including improvement in symptoms of nervous system disorders such as epilepsy, in addition to increased levels of GABA, which is the main ‘calming’ brain chemical.12
There are also some significant reductions in disease risk factors, such as improvements in insulin sensitivity, reduction in blood sugar levels, and reduction in triglyceride levels, in addition to steady energy levels, reduced cravings and appetite, and improved focus and concentration.13, 14
The downsides of a ketogenic diet
As with any style of eating, the ketogenic diet does have some potential downsides. When you begin the diet, for example, you may experience something known as ‘keto flu’. This is a period where your body switches over to a state of ketosis, and begins using ketones as its main energy source. This change can give rise to a number of symptoms, including lethargy, cravings, brain fog, and a general feeling of being unwell.
Along with above, nutritional deficiencies can also occur if the diet is not balanced. The two most common deficiencies are electrolytes, like sodium, potassium, magnesium, and calcium, and fibre.15, 16 Low electrolyte levels can cause low energy and muscle cramps, whilst a low fibre intake can lead to various digestive symptoms such as constipation and bloating.
Some people also experience a drop in athletic performance. This can be temporary, as part of the ‘keto flu’, and some research suggests that it’s only anaerobic exercise such as weight-lifting or sprinting that is limited during ketosis.17, 18
There’s little to no research as of yet to show whether the ketogenic diet is safe during pregnancy and breastfeeding, so it’s advised not to follow it if you are either. And, though it is doable, it can also be difficult to follow if you’re vegetarian or vegan.
The bottom line: is a ketogenic diet healthy?
As is the case with any diet or eating style, not everyone’s bodies will react the same. Some might experience beneficial results, and some won’t. So whilst the ketogenic diet can offer a number of benefits, including potential weight loss, it can also be unhealthy if not adhered to properly, and if you don’t consume enough of a well-rounded diet. If you do try the diet, then make sure to keep the amount of processed meats and junk food to a minimum, and include a variety of fresh vegetables and fruits, and high-quality lean meats and fish. Ultimately, though, if you’re unsure whether the ketogenic diet is right for you, it’s important that you consult your local GP for further advice. If you’re interested in finding more about how to get the most out of your diet, head over to our advice page for more information.
If you'd like to read more about the effect of various diets on your health, as well as find more information on how you can promote good gut health, then head over to our Gut Health advice centre.
1Paoli, A., Rubini, A., Volek, J. S., and 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(08)
2Paoli, A., Rubini, A., Volek, J. S., and 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(08)
3Hu, F. B., Van Dam, R. M., and Liu, S. (2001). Diet and risk of type II diabetes: the role of types of fat and carbohydrate, Diabetologia, 44(07)
4Kimura, I., Inoue, D., Maeda, T., et al. (2011). Short-chain fatty acids and ketones directly regulate sympathetic nervous system via G protein-coupled receptor 41 (GPR41), Proceedings of the National Academy of Sciences, 108(19)
5Westman, E. C., Mavropoulos, J., Yancy, W. S., and Volek, J. S. (2003). A review of low-carbohydrate ketogenic diets, Current Atherosclerosis Reports, 05(06)
6Westman, E. C. (2002). Is dietary carbohydrate essential for human nutrition? The American Journal of Clinical Nutrition, 75(05)
7Westman, E. C. (2002). Is dietary carbohydrate essential for human nutrition? The American Journal of Clinical Nutrition, 75(05)
8Bueno, N. B., de Melo, I. S. V., de Oliveira, S. L., 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(7)
9Gibson, A. A., Seimon, R. V., Lee, C. M., et al. (2015). Do ketogenic diets really suppress appetite? A systematic review and meta-analysis, Obesity Reviews, 16(01)
10Paoli, A., Grimaldi, K., Bianco, A., Lodi, et al. (2012). Medium term effects of a ketogenic diet and a Mediterranean diet on resting energy expenditure and respiratory ratio, BMC Proceedings, 06(03)
11Johnstone, A. M., Horgan, G. W., Murison, S. D., et al. (2008). Effects of a high-protein ketogenic diet on hunger, appetite, and weight loss in obese men feeding ad libitum, The American Journal of Clinical Nutrition, 87(01)
12Hartman, A. L., Gasior, M., Vining, E. P. and Rogawski, M. A. (2007). The neuropharmacology of the ketogenic diet, Pediatric Neurology, 36(05)
13Boden, G., Sargrad, K., Homko, C., et al. (2005). Effect of a low-carbohydrate diet on appetite, blood glucose levels, and insulin resistance in obese patients with type 2 diabetes, Annals of Internal Medicine, 142(06)
14Phinney, S. D., Bistrian, B. R., Wolfe, R. R., and Blackburn, G. L. (1983). The human metabolic response to chronic ketosis without caloric restriction: physical and biochemical adaptation, Metabolism, 32(09)
15Westman, E. C., Mavropoulos, J., Yancy, W. S., and Volek, J. S. (2003). A review of low-carbohydrate ketogenic diets, Current Atherosclerosis Reports, 05(06)
16Phinney, S. D., Bistrian, B. R., Wolfe, R. R., and Blackburn, G. L. (1983). The human metabolic response to chronic ketosis without caloric restriction: physical and biochemical adaptation, Metabolism, 32(09)
17Bilsborough, S. A., and Crowe, T. (2003). Low carbohydrate diets: what are the potential short and long term health implications? Asia Pacific Journal of Clinical Nutrition, 12(04)
18Phinney, S. D. (2004). Ketogenic diets and physical performance, Nutrition & Metabolism, 01(01)