Intermittent fasting plans are usually built on alternating days of eating and fasting, or fasting two non-consecutive days of the week (known as the 5:2 diet), or some other variation. These diets have been shown in the scientific literature to produce favorable outcomes for weight loss and metabolic health, with little risk to health.
However, the main problem with this eating pattern is the inability to apply it to a modern lifestyle. For many, it is impossible to maintain regular 24 hour intervals of fasting for a significant amount of time . Life is demanding, and it is hard to perform when you’re really hungry.
That being said, there is an alternative to this aggressive approach which seems to provide many of the benefits of intermittent fasting, and in some instances even exceeds the IF regime. It’s more practical to apply to our busy lifestyles, and it’s something that is done by many children and adults alike. It’s what is referred to in the scientific literature as Time Restricted Feeding (TRF).
This type of dietary pattern focuses on limiting food intake to set intervals throughout the day. Eating windows vary between 4 and 12 hours, which means that the non-eating hours of the day are between 20 and 12 hours. However, non-caloric drinks like water, coffee and tea are consumed without restriction at all times.
When comparing the results of numerous studies looking at the weight loss and metabolic benefits of various TRF diets, the results from studies with 12 hour eating windows reported the greatest weight loss and improvements in cholesterol profiles . Amazing! We’re saying that consistently limiting your normal food intake to 12 hours of the day has tremendous beneficial health impacts!
Yet, before we jump on this bandwagon, we must consider another well-known phenomenon; the fact the obesity and metabolic disease (i.e. metabolic syndrome & type 2 diabetes) is very common among shift workers compared to the rest of the working population. This means that people who work very late and cannot establish consistent eating and sleeping patterns are at a much higher risk for developing obesity and other related health issues.
While the health risks of shift work are well documented, understanding the reason for this is less clear. Nevertheless, current evidence suggests that a mismatching between the body’s internal clock known as the “circadian clock” and external behaviors such as eating and sleeping, stresses the body to a point that can exceed the body’s ability to compensate .
If we imagine the “circadian clock” as a sophisticated computer motherboard which is controlling all the traffic lights of a city, it would make sense that this motherboard has a 24-hour cycle which operates the timing of the city’s traffic lights, adjusting for the different traffic flows throughout the day. Any event that causes traffic at the time of day which is not programmed for it, will surpass the light’s ability to control the traffic.
Similarly, but infinitely more sophisticated is our own internal motherboard, which conducts operational tasks supremely important to metabolic health on a 24-hour cycle. Some tasks like increased cortisol are scheduled in the morning when we wake up, and our ability to digest and utilize our food is optimal in the day, but poor at night.
When our behavior and our clock are not in-synch, our system is overwhelmed to a point that it must rely on less-efficient contingency plans. You probably experienced a mismatch between your behavior and circadian clock the last time you had jet-lag, or had multiple late nights with little sleep and twice the food, like 2-day Yom-Tov.
Supporting the idea of circadian/behavior synchronicity, is the results of an Israeli study that placed two groups of overweight women on the exact same diet. The only difference in the two groups was that one group ate a large breakfast, medium lunch, and small dinner while the other group consumed a small breakfast, medium lunch, and large dinner .
The results; the large-breakfast group had superior weight loss and improvements in multiple metabolic health parameters compared to the large-dinner group. Furthermore, the large-breakfast group reported less overall hunger than the large-dinner group. From these findings, we learn that it is likely beneficial to consume the majority of our food in the daytime hours, and taper off by evening. Furthermore, synchronization between our behavior and our circadian clocks likely contributes to these benefits.
Taking all of this into consideration, it is recommended to limit food intake to 12 hours throughout the day, consuming most of our food in the morning and afternoon, with a small amount in the evening. For many, this will create an eating window somewhere around 7 or 8am until 7 or 8pm. Obviously there are exceptions such as Shabbos and Yom Tov. Yet establishing a regular eating schedule outside of our holy festivals, is critical to healthy living.
For more on nutrition and functional medicine, contact Mordechai at; Functionalmedicine.co.il & firstname.lastname@example.org
 Jakubowicz, D., Barnea, M., Wainstein, J., & Froy, O. (2013). High caloric intake at breakfast vs. dinner differentially influences weight loss of overweight and obese women. Obesity, 21(12), 2504-2512.
 Patterson, R. E., Laughlin, G. A., LaCroix, A. Z., Hartman, S. J., Natarajan, L., Senger, C. M., … & Gallo, L. C. (2015). Intermittent fasting and human metabolic health. Journal of the Academy of Nutrition and Dietetics, 115(8), 1203-1212.
 Rothschild, J., Hoddy, K. K., Jambazian, P., & Varady, K. A. (2014). Time‐restricted feeding and risk of metabolic disease: a review of human and animal studies. Nutrition reviews, 72(5), 308-318.
 Scheer, F. A., Hilton, M. F., Mantzoros, C. S., & Shea, S. A. (2009). Adverse metabolic and cardiovascular consequences of circadian misalignment. Proceedings of the National Academy of Sciences, 106(11), 4453-4458.