What is the keto diet?
Ketogenic diets restrict carbohydrate intake to less than 50 grams a day (as opposed to a low carb diet which is 50-100grams of carbs a day). There are many variations of the keto diet, they are best grouped according to overall calorie intake:
- Very low calorie ketogenic diet- less than 800 calories/day
- Low calorie ketogenic diet- more than 800 calories/day
- Isocaloric ketogenic diet- for management of epilepsy
Low calorie ketogenic diets are by definition high fat diets because if protein was used to increase calories then the liver would start taking the amino acids from the protein and turn them into glucose, a process called gluconeogenesis, when glucose is present ketosis will stop. The keto diet is not the only way to achieve ketosis, it can also be done with prolonged fasting or using a shakes based Very Low Calorie Diet (VLCD). The advantage of ketosis over other diets is that it reduces hunger and cravings helping individuals adhere to lower calories.
How do keto diets work?
Ketosis is a backup mechanism for the body to survive in periods of food shortage. Keto diets cause an initial rapid water weight loss as glycogen stores in the liver and muscles become depleted. When there are no glycogen stores left and no further carbs from the diet almost all the body’s energy needs come from fat.
One of the main roles of carbohydrates is to bind fat within fat cells so it remains stored and can’t be released to be burned for energy, when there are no carbs it causes the fatty acids to become free within the cell so they can be actively transported into the blood stream.
A lack of carbs also effects 3 major hormones to cause fatty acids to be transported out of fat cells: there is less insulin from the pancreas, more glucagon from the pancreas and increased glucocorticoids from the adrenal glands.
When large quantities of fatty acids become available from fat stores they travel to the liver and are converted to chemicals called ketone bodies which pour out of the liver and travel to organs to be used as an alternative fuel source. These ketone bodies are what reduce hunger and craving and this helps adherence to the diet.
Are keto diets effective?
Evidence for keto diets as a treatment for weight loss is still accumulating, guidelines from well recognised medical societies do not yet include it in their protocols. This lack of data means the debate around keto is often opinionated and spiteful. To date studies comparing the keto diet to other diets with the same daily calorie intake have shown a similar degree of weight loss.
A meta-analysis for the Very Low Calorie Keto Diet (VLCKD) has recently been published, 12 studies including 801 patients with ketogenic phases of at least 4 weeks were included. Data showed an average of 15.6kg lost and waist circumference reduction of 12.6cm1. The study found it was associated with a weight loss lower than bariatric surgery but greater than weight loss medications. VLCKD has a well described 3 phase protocol and should be performed under the supervision of a weight loss clinician.
Many studies have shown the value of low carbohydrate diets in type 2 diabetes mellitus with improvements in glucose, HbA1c and insulin levels, logically the same would be true for ketogenic diets however randomized trials are needed comparing keto to other diets with the same daily caloric intake to ascertain if the keto approach has any advantage in improving these markers.
Are keto diets healthy?
It is a worry that every study involving keto shows an increase in LDL cholesterol. It has been clearly demonstrated in clinical trials that LDL cholesterol is the cause of atherosclerosis which leads to heart attack, stroke and kidney disease. While a short period of raised LDL is not likely to impact the overall life-time risk of these problems there is no data available to say long-term keto is safe in this regard.
The long-term approach for most patients is to avoid the extremes and reduce carbohydrates but not down the level ketogenic diets require. Refined sugar, rice, bread, pasta, potato and processed foods should be avoided in routine use. The carbohydrates that can be consumed are fruit and vegetables- they have a low caloric density, are high in fibre and rich in vitamins that the body needs to function.
- 1. Castellana et al. 2020. Efficacy and safety of very low calorie ketogenic diet (VLCKD)
in patients with overweight and obesity: A systematic review and meta-analysis. Journal of Reviews in Endocrine and Metabolic Disorders.