Evaluating the Keto Diet

Dr. Russell Wilder first proposed using ketogenic diets to treat epilepsy in children in 1921 (Wheless 2008). Since then, the “keto diet,” as it is known today, has attracted interest in numerous areas of health and nutrition. From weight loss to cardiovascular disease to type 2 diabetes, supporters of this low-carb diet claim it can prevent or cure many of life’s maladies. But before tossing aside all those starchy and sweet foods, it is worth delving a bit further into the evidence.

Ketosis is a physiological metabolic state induced by a lack of available glucose in the body. This can occur with prolonged fasting or, as in the keto diet, with a low intake of dietary carbohydrates. During ketosis, the body shifts its primary source of fuel from carbohydrates to fats (Zarnowska 2020). Yet while many tissues can directly use fatty acids for energy, the brain cannot. The liver oxidizes fatty acids to form ketone bodies, which can cross the blood-brain barrier, in order to provide the brain with a source of fuel (Ashtary-Larky et al. 2022). 

The keto diet thus seeks to mimic a state of fasting by limiting carbohydrate intake, usually to less than 50 g per day. These carbohydrates are replaced with fats; in general, 70% to 90% of calories on the keto diet come from fat. Adherents are encouraged to consume eggs, meat, poultry, seafood, full-fat dairy, nuts, oils and solid fats, and nonstarchy vegetables (Ashtary-Larky et al. 2022). Fruits, grains, beans, and starchy vegetables are not recommended (Firman et al. 2024).

Advantages

Evidence suggests that the keto diet is effective in preventing seizures in those with refractory epilepsy. While the precise mechanism is not known, it is believed that by shifting the brain’s main source of energy from carbohydrates to fats, various biochemical pathways are altered, allowing a state of homeostasis to return (Zarnowska 2020). Most studies on the keto diet and epilepsy have been conducted in children rather than adults, and its utility in the treatment of adult epilepsy remains uncertain (Zarnowska 2020).

Weight loss is now perhaps the most frequently cited reason for following the keto diet. Multiple studies have demonstrated that the keto diet is as effective as its higher carbohydrate counterparts for weight loss (Firman et al. 2024, Ashtary-Larky et al. 2022). There is limited evidence suggesting that keto diets may lead to greater reductions in fat mass and visceral adipose tissue than non-keto diets when combined with resistance training. However, these findings are primarily from small, short-term studies and are thus far from conclusive (Paoli et al. 2021, Vargas-Molina et al. 2020).

The keto diet may reduce insulin resistance and hyperglycemia in people with type 2 diabetes who are overweight or obese (Batch et al. 2020). Unfortunately, it is unclear whether these effects are due to the keto diet itself or the resulting weight loss (Firman et al. 2024).

Disadvantages

As previously stated, the keto diet restricts fruits, grains, and other high-carbohydrate foods and replaces them with high-fat foods, often from animal sources. This necessarily leads to an increase in saturated fat intake and a corresponding decrease in dietary fiber intake, and it can result in micronutrient deficiencies if not supplemented (Crosby et al. 2021). The increase in saturated fat intake is of particular interest, as it is a known risk factor for development of atherosclerosis and cardiovascular disease (Batch et al. 2020).

Lastly, the keto diet is, by definition, restrictive, limiting both total intake and sources of carbohydrates. Adherence to any restrictive diet is difficult, regardless of one’s motivation for following it, especially in the long term (Batch et al. 2020). Apart from the perhaps unfavorable sensory aspects, some people experience side effects such as headache, dizziness, constipation, and nausea upon initiation of the keto diet (Ashtary-Larky et al. 2022, Crosby et al. 2021).

The keto diet has its perks but carries with it significant risks. And while it certainly has a place in treatment of refractory pediatric epilepsy, it is unclear whether its use should be expanded beyond this specific population. The keto diet does appear to be safe in the short term, and it may be favored by some due to its relatively simplistic approach to weight loss. That said, it has not been shown to be superior to other diets and has not been investigated for long-term use. A balanced diet that includes whole grains, fruits, and vegetables alongside lean proteins and unsaturated fats is still the ideal. Those looking to follow a keto diet should carefully weigh the benefits against the risks.ft