Intermittent Fasting and the Ketogenic Diet

| September 1, 2018 | 0 Comments

Christopher Still, DO, FACN, FACP, Co-Clinical Editor, Bariatric Times; Medical Director for the Center for Nutrition and Weight Management, and Director for Geisinger Obesity Research Institute, Geisinger Medical Center, Danville, Pennsylvania.

Dear Colleagues,

Though we have multiple safe and effective surgical and non-surgical options for treating obesity and its comorbid conditions, no one therapy acts as a magic bullet. Diet and exercise need to be incorporated into the long-term plan for optimal health and success. Back in 2015, I discussed the following diets that were popular at that time: 1) low-calorie diet, 2) low-fat diet 3) low-carbohydrate diet 4) the Mediterranean diet, and 5) commercial diets. Since then, there has been a lot of buzz about other types of diet plans, particularly intermittent fasting and the ketogenic diet.

Intermittent fasting. According to the Obesity Medicine Association (OMA), intermittent fasting describes dietary approaches that focus on cycling between prolonged periods of fasting and eating during defined periods of time. The periods of fasting involve intentionally fasting for longer than the traditional 8 to 12 hours of overnight fasting that naturally occurs during sleep after the evening meal until breakfast the next morning. Despite the recent popularity of intermittent energy restriction and associated weight loss claims, the supporting evidence base is limited.

A recent study by Gabel et al[1] investigated the effects of time restricted feeding on body weight and metabolic disease risk factors in adults with obesity (body mass index [BMI] 30–45 kg/m2) between 25- and 65-years old. Subjects participated in an eight-hour time restricted feeding intervention, feeding ad libitum (as desired) between 10:00 to 18:00h and water fasting between 18:00 to 10:00 h for 12 weeks. The researchers found that body weight, energy intake, and systolic blood pressure decreased in the time restricted group compared to a matched historical control group.

Of note, subjects in the study were encouraged to drink plenty of water and were permitted to consume “energy-free” beverages, such black tea, coffee, and diet sodas. They were also required to “measure” their adherence to the fasting regimen each day. Both of these details are important because 1) consumption of sugar-sweetened beverages adds to a sometimes already high caloric intake and is linked to obesity, weight gain, and metabolic syndrome,[2] and 2) adherence is crucial to any diet plan.

Ketogenic diet. The ketogenic diet is a low-carbohydrate, high-fat diet that shares many similarities with the Atkins and other low-carb diets. It involves drastically reducing carbohydrate intake and replacing it with fat to put the body into a metabolic state called “ketosis, which helps to increase feelings of satiety.” When this happens, your body becomes efficient at burning fat for energy and turns fat into ketones in the liver, which are then expelled through urine.

Recent research has shown that in patients with obesity (BMIs 35.9±1.2kg/m2–39.4±1.0kg/m2), adherence to the ketogenic diet for 24 weeks resulted in a 1) significant decreases in the level of triglycerides, total cholesterol, low-density lipoprotein (LDL) cholesterol, and glucose; and 2) a significant increase in the level of high-density lipoprotein (HDL) cholesterol.[3] Blood glucose levels were also significantly decreased.

In my experience, the big three most popular diets are intermittent fasting, ketogenic, and paleo, which is another low-carb diet that focuses on consuming foods presumed to have been eaten by early humans. As with any weight loss regimen, these diets should be implemented under provider supervision. One problem with the changing popularity of diets is that some physicians might not be educated on their specific instructions or available evidence, and therefore, might be hesitant to recommend them to patients.

This is another area where the obesity medicine specialist’s role has increased. Certified obesity medicine specialists are trained in all aspects of obesity care, including diet. This background allows them to assist in a multidisciplinary setting with matching a patient with a particular diet.

The jury is still out on which diet is the best for weight loss and comorbid condition improvement as no one plan has proven superior among others. I believe that the best diet is the one in which the patient can adhere.


Christopher Still, DO, FACN, FACP


  1. Gabel K, Hoddy KK, Haggerty N, et al. Effects of 8-hour time restricted feeding on body weight and metabolic disease risk factors in obese adults: A pilot study. Nutr Healthy Aging. 2018;4(4):345–353.
  2. Ruff RR, Akhund A, Adjoian T, Kansagra SM. Calorie intake, sugar-sweetened beverage consumption, and obesity among New York City adults: findings from a 2013 population study using dietary recalls. J Community Health. 2014;39(6):1117–1123.
  3. Dashti HM, Mathew TC, Hussein T, et al. Long-term effects of a ketogenic diet in obese patients. Exp Clin Cardiol. 2004;9(3):200–205.
  4. Gomez-Arbelaez D, Bellido D, Castro AI, et al. Body composition Changes after very-low-calorie ketogenic diet in obesity evaluated by 3 standardized methods. J Clin Endocrinol Metab. 2017;102(2):488–498.

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