Intermittent Fasting Ketosis

In a first-of-its-kind study, researchers from Münster University of Applied Sciences in Münster Germany looked to determine the effects of intermittent fasting on ketone body production and ketosis.

Intermittent fasting is an umbrella term that includes a variety of dietary strategies, including restricting eating to a specified time period each day — also known as “Time Restricted Feeding” — as well as complete abstinence of caloric intake for 24 hours, or longer.

While intermittent fasting is growing in popularity, there have been few studies documenting its specific health benefits. To date, there has been even less research activity into how intermittent fasting interplays with ketosis and ketone body production. This new study is the first to look into this area.

How the Study Was Done

The researchers recruited females between the ages of 18 years old to 30 years old. They excluded anyone who was following a “special diet” — which they specified as vegan, low-carb or ketogenic — as well as anyone with a serious illness.

They began their study with 19 volunteers and ended with 13 after six subjects dropped out of the study.

The study lasted for one week and the participants were required to follow a “5:2” intermittent fasting routine, with unrestricted feeding allowed during five of the days and complete abstinence from food for two days of that week. Further, the two fasting days were non-consecutive, with, at least, one feeding day separating the two fasting days.

The researchers were looking for the effects of this fasting strategy on the production of ketone bodies, specifically beta-hydroxybutyrate. The volunteer’s beta-hydroxybutyrate and blood glucose levels were measured each morning and evening during the study’s duration.

What the Study Found

The study results were somewhat mixed:

  • Blood glucose levels were reduced and beta-hydroxybutyrate levels were increased during the first fasting day of the study.
  • However, glucose levels increased and beta-hydroxybutyrate levels decreased during the second fasting day.

On the first day of fasting, beta-hydroxybutyrate levels reached an average high of 2.5 mmol/L, which is well into the range of being considered in ketosis. On the second fasting day, the average highest beta-hydroxybutyrate level was 1.14 mmol/L, which was significantly reduced from the first fasting day, but still much higher than the average level of .01 beta-hydroxybutyrate measured on non-fasting days.

The researchers summarized their findings as this, “Based on the data, it can be concluded that even short-term intermittent fasting can lead to an increase in ketogenesis, and even to the attainment of ketosis.”


First, we need to recognize the limitations of this study:

  • The study group was fairly small at 13 participants. The researchers initially calculated they would need 14 subjects to achieve statistical validity, so they are just short of that goal. That doesn’t necessarily render these findings invalid — just worth noting.
  • This was a “self reporting” study, meaning the participants reported their own food intake and also measured their own beta-hydroxybutyrate and glucose levels. It’s entirely possible that there were errors in the reporting.

Despite these shortcomings, it is still significant that study participants clearly experienced ketosis within relatively short time periods of abstaining from food — especially on the first day of fasting.

We look forward to more research in this area.

Learn More

You can review the full study here.

(Please review our important Medical Disclaimer here.)

Photo by Adrien Robert on Unsplash