Ketogenic Diet vs Intermittent Fasting
The ketogenic diet involves the consumption of very low amounts of carbohydrate and high amounts of fat,1 whereas intermittent fasting prescribes caloric restriction over various intervals of time.2 In essence, one approach specifies what to eat (ie, ketogenic diet), whereas the other specifies when to eat (ie, intermittent fasting).3
The Mechanism Behind the Diets
Both the ketogenic diet and intermittent fasting are currently well-known and popular dietary methods aimed to promote weight loss.4,5 They both work by promoting ketogenesis, the process of utilizing ketone bodies rather than glucose as energy source,2,6,7 and various studies have found each diet to be effective in facilitating weight loss and improving metabolic profiles including insulin sensitivity, fasting blood glucose, hemoglobin (Hb) A1c, and lipid levels.8,9 As the two diets share similar biological mechanisms, combining them can – in theory – promote ketogenesis, facilitate weight loss, and improve metabolic profiles more effectively than using one dietary approach alone.
Studies on the Combined Diet
Although not many studies have been conducted on the efficacy and safety of ketogenic diet combined with intermittent fasting among individuals with type 2 diabetes mellitus (T2DM), some trials seem to suggest that the combination may be effective in combating obesity and insulin resistance.3,10,11 One case study on a normal weight woman with T2DM found a 2.9% drop in HbA1c levels (from 9.3% to 6.4%) during 4 months of dietary intervention.3 The favorable change was found despite minimal reduction in weight, and the authors concluded that the combination may be more effective than using only one dietary approach. Another case report studied the effects of intermittent fasting with a low-carbohydrate diet on three men with T2DM using diabetic pharmacotherapy.11 The study highlighted that all three participants experienced 10-18% weight loss, reductions in HbA1c levels, and discontinuation of insulin therapy after several months of intervention.
Despite some preliminary evidence suggesting that the combined diet may be effective in improving glycemic control and weight in individuals with T2DM, more studies are needed to determine its efficacy and safety.
Potential Risks of Combining the Diets
Individuals with T2DM should speak with their health care team and nutritionist before starting on a ketogenic diet combined with intermittent fasting. It is important to consider the risks and side effects of each diet. Although intermittent fasting is generally safe in individuals with controlled T2DM, they should be aware of the risk of developing hypoglycemia, which is especially high in those on insulin and/or sulfonylurea.2 Additionally, individuals may experience the “keto flu” during the initial period of adjustment, also known as the keto induction.3 Symptoms may include headache, fatigue, dizziness, gastrointestinal discomfort, nausea, and decreased energy, which normally resolve within the first month.12