Dear Colleagues. Thank you for stopping by this site. I hope it can be a resource that helps you understand and approach fasting in a thoughtful and helpful way in your practice whether you personally counsel patients about it or not. On this page I aim to outline the research base that supports this practice at a higher level than the more patient focused articles on this site.
I am very pleased to present to you my own grant funded fasting study: Feasibility Study of a Low-Carbohydrate/ Time-Restricted Eating Protocol for Insulin-Using Type 2 Diabetic Patients
This study outlines all the methods I use to help patients with Type 2 Diabetes safely transition off insulin using fasting. I will note the caveat that the main thing I learned from this study that changed my practice is that I take a week and have people focus on low-carb eating first before starting the fasting to ease into things. This makes for a smoother transition than the study protocol where we start both at the same time. The references section is full of interesting fasting studies if you want to dive deeper.
Other Research:
If you are looking for a great place to start reviewing the physiology and application of fasting regimens I can recommend this review article that was published in the December 2019 New England Journal of Medicine.
Effects of Intermittent Fasting on Health, Aging, and Disease. Rafael de Cabo, Ph.D., and Mark P. Mattson, Ph.D. N Engl J Med 2019;381:2541-51.
This article provides a great overview of the cellular physiology of fasting in the body. I find it amazing how hard wired this process is in every cell and system of the body. The body is designed to function in the fasted state and take care of all kinds of metabolic processes. This is where I got the idea for the cellular switch that I have featured on the “Three Step Weight Loss Plan” page.
The article also reviews interesting research related to longevity, obesity, DM2, heart disease, neurologic disease, inflammatory conditions and cancer.
At the conclusion of this article they make suggestions about the incorporation of intermittent fasting into current health care practice and lifestyles. They envision a future state where instruction begins in medical school. They suggest entire facilities and programs that train people to eat in this manner for various metabolic effects.
My perspective is that while I love the education idea, we do not need to wait to train the next generation of doctors to implement this. We don’t need lots of money for new programs or centers. These interventions are simple and free. They can be completed quickly in clinic by knowledgeable medical providers. I do it every day with amazing results. I feel this will be the standard of care in the future.
I started approaching fasting regimens from the standpoint of treatment of Type 2 diabetes because I noticed we were always cutting insulin prior to colonoscopy. Pretty much every physician I have talked to recognizes this phenomenon as an obvious observable truth. Fasting lowers blood sugar. What is nice is that this is readily observable in objective clinical studies also.
Early Time-Restricted Feeding Improves Insulin Sensitivity, Blood Pressure, and Oxidative Stress Even without Weight Loss in Men with Prediabetes. Sutton, E. Cell Metabolism 2018;27:1212–1221.
This study is an interesting study in which 12 pre-diabetic men were studied on a 10-week crossover study. It was an iso-caloric feeding study which was specifically designed to make sure the individuals did not change their weight during the study. The two groups were control of 12 hours eating vs an IF feeding regimen (early time restricted eating, breakfast and lunch consumed between 6:30am and 3pm). Amazingly insulin sensitivity was significantly increased in the IF group independent of any weight loss. I have often heard people say that fasting helps only because of weight loss. This study would suggest otherwise. The fasted interval itself appears to be giving space to the insulin receptor complex to reset.
Eating two larger meals a day (breakfast and lunch) is more effective than six smaller meals in a reduced-energy regimen for patients with type 2 diabetes: A Randomized crossover study. Kahleova, H., Diabetologia. 2014;57:1552-1560.
This study gets to the very heart of the debate over diabetic and weight loss diets. In this randomized controlled trial researchers compared the effects of eating 6 small meals throughout the day compared to two time restricted meals (16:8) in a 12 week crossover study of 54 patients.
From their conclusion section: “Eating only breakfast and lunch reduced body weight, hepatic fat content, fasting plasma glucose, C-peptide and glucagon, and increased insulin sensitivity more than the same caloric restriction split into six meals. These results suggest that, for type 2 diabetic patients on a hypoenergetic diet, eating larger breakfasts and lunches may be more beneficial than six smaller meals during the day.”
The additional commentary I would like to make on this study is that again this was an isocaloric study with the six meal and the 2 meal groups getting the same calories. I will say this is great from comparing the efficacy of the fasted interval itself, but I am so curious to have this study repeated without specific calorie restrictions and targets.
As a point of practical counseling people are far less likely to consume the same amount of food on these two regimens. It is also highly unlikely that regular people outside of a controlled clinical study can count calories and control meals to the degree required in this trial. Six-meal-a-day eating leads to far greater calorie intake in general than a 16:8 regimen and I highly anticipate an ad-lidum study in this regard would show even greater support for the IF regimen.
I also note that neither of the arms were following low-carbohydrate regimens which can have substantial additional benefit in diabetic treatment.
There are many studies that are supportive of fasting practices but I would like to review one study which, on the surface, does not seem so supportive. The article is:
This study randomized 116 patients to 3 months of either 3 normal meals throughout the day or a time restricted window of eating all food from 12pm to 8pm daily. Although the TRF group did lose about 2 pounds over this study the result was not statistically different from the control group.
I want to highlight that the only intervention in this study was to obtain all food in the 12-8 window. There was specifically no advice given about macronutrient composition or healthy food choices. Also no advice given about number of meals or snacking. The authors state that there was no difference in energy intake between the groups. Another isocaloric study.
Now it would be nice if the time-restricted effect worked all by itself in this study. However, I think this is a great study and gives us a very helpful piece of information. You unfortunately can’t tell someone “Just eat whatever you want between noon and 8 and it’s guaranteed to work.” It’s more complex than that.
To explain my perspective I will note that I think there is an important distinction to make between what this research studied: time restricted eating, and some form of fasting. Popular press picked up on this article and opined that this basically proves that intermittent fasting doesn’t work and could even be counterproductive.
Fasting by its definition is to go without food. It follows logically that someone following a fasting practice would get in fewer calories in a day in which they are practicing fasting. I really have a hard time getting my mind around all the isocaloric studies because it goes against the very idea of fasting.
The most common objection I receive when talking to physicians about fasting regimens is “Well that only works because of calorie restriction.” The implication being why bother with the difficulty of fasting regimens when you can just portion control and not go to all the trouble.
I never really argue against this perspective, at least when focusing only on weight effects. I don’t think it is a logical refutation. Yes, you get less calories by fasting and less calories can lead one to lose weight. That is not a bad thing. It turns out that cutting calories is not easy for many people. You do not often find people who are successful in the long term with portion control practices. For many people it is easier to eat nothing for a period of time and then eat normal meals than always eating less than they want.
This study, however, did not have a calorie restriction. It was time restricted, but the spirit of the intervention is not “fasting.” So if you are going to dismiss fasting regimens as a waste of time for weight loss please do not use a study that did not calorie restrict participants to support your position.
My observation is in ordered to have significant success with a time restricted paradigm there should be counseling to eliminate a typical meal and not replace it. People should continue with the other two meals as planned and specifically avoid snacking. This is a discipline. It is not taking it easy on anyone. I usually tell people “two normal meals within 6-8 hours and that’s it.” I also give people detailed advice on choosing healthy foods. All this stuff matters as I think this study demonstrates. When combining time restriction with calorie restriction and healthy food choices I routinely see significant progress.
I will hopefully be adding and reviewing additional studies as time allows but this is a good place to start. Are you aware of interesting research that you would like included on this page? Have questions or comments on this research? Send me a note on the contact page.