Why do ketone levels vary throughout the day?

Individuals vary in their blood ketone levels (i.e., beta-hydroxybutyrate – aka BOHB) over the course of a day and from day to day. This can be due to variations in dietary carbohydrate and protein from meal to meal and from day to day.

However, different individuals tend to vary in the levels and pattern of their blood ketones. Some people are highest in the morning and tend to have reduced levels after meals (perhaps due to the dietary protein and carbs they consume). Others of us tend to be low in the morning and then rise during the day.

Additional factors that increase blood BOHB are endurance exercise and also after consuming fats containing medium chain triglycerides (MCT) such as butter, coconut oil, or purified MCT oil. In contrast, there is often a steep drop in BOHB after high intensity exercise, the mechanism for which has yet to be proven. This post-sprint drop in BOHB tends to be temporary (lasting for an hour or two), which means that it’s cause is very different from the days-long drop in blood BOHB that one sees after a large carb meal.