Which of the following is a side effect of the keto diet?

The side effect of kidney stones is closely associated with the keto diet due to the high levels of dietary fat and low levels of carbohydrates. When following a ketogenic diet, the body shifts into a state of ketosis, which can alter the body's acid-base balance and lead to an increase in the excretion of certain substances, such as calcium and oxalate, both of which are components of kidney stones. This dietary change can promote conditions that favor the formation of stones in susceptible individuals.

In contrast, while diarrhea can occur during dietary changes, it is less specific and not universally experienced on the keto diet. Blurry vision is not a commonly recognized side effect directly linked to the keto diet, and hypertension is generally more associated with excessive sodium intake, rather than the structure of the keto diet itself. Thus, the connection between the keto diet and the formation of kidney stones is well-established, making it the most appropriate choice in this context.