Time restricted eating –Aligning food timing with circadian rhythms
Written by: The Institute for Functional Medicine
Chrononutrition: Food Timing, Circadian Fasting, and Resetting the Body’s Internal Clock
Circadian cycles are part of the body’s internal clock, and disruption to these biological rhythms may result in adverse health outcomes. Aligning meal timing with the body’s circadian cycle for optimal glucose and insulin responsiveness may be effective for improving metabolic health. In the field of chrononutrition, time-restricted feeding has been prominent in research, studied for its benefits on metabolic health and as a means for realigning and supporting the body’s internal clock. How do circadian considerations potentially benefit personalized health interventions for chronic disease treatment or prevention?
Timing influences human physiology. Circadian cycles are a property of the body’s internal clock, and disruption to these biological rhythms may result in adverse health outcomes. The field of chronobiology is dynamic and continues to elucidate the associations between circadian rhythms and health implications, from neurodegenerative risks to metabolic dysfunctions.1,2 Chrononutrition is the focused study of the relationship between food, metabolism, meal timing, and the circadian system. Is there metabolic benefit when aligning lifestyle behaviors such as food timing with the body’s internal clock? How do circadian considerations influence personalized health interventions for chronic disease prevention or treatment?
Aligning Food Timing With Circadian Rhythms
Most cells and tissues of the body show molecular clock activity and express cellular clock genes that contribute to tissue and system function. In metabolic processes, circadian-related components modulate the activation and expression of hormones, enzymes, and signaling pathways.3,4 Aligning meal timing with the body’s circadian cycle for optimal glucose and insulin responsiveness, as well as with hormones such as cortisol and leptin that are also affected by circadian oscillations,3 may be effective for improving metabolic health. A 2023 meta-analysis of nine RCTs (n=485 total participants) compared higher energy consumption earlier in the day with higher consumption later in the day on weight loss and metabolic parameters.5 Researchers reported a significantly greater weight loss in groups with higher energy intakes earlier compared to groups with high energy intake later in the day. In addition, significantly greater reductions in LDL cholesterol, fasting glucose, and insulin resistance (measured by HOMA-IR) were reported in groups with earlier energy intakes compared with later intakes.5
Both glucose tolerance and insulin sensitivity have been shown to be lower in the evening than in the morning,6which may contribute to an increased risk of metabolic dysfunctions for those who habitually eat meals during the evening hours. A 2020 meta-analysis (n=10 acute postprandial studies) investigated whether acute glucose and insulin responses after night-time meals (8 pm–4 am) differed from the responses after day-time meals (7 am–4 pm) in healthy adults.7 Results indicated that after an identical meal, the postprandial glucose and insulin responses were both significantly lower in the day compared to the night.7 Interestingly, specific to carbohydrate intake, a 2022 systematic review of eight randomized clinical trials (n=116 healthy adults) indicated that consumption of carbohydrates at night also led to higher postprandial glycemic values than morning consumption; however, no significant difference between morning and night carbohydrate consumption was found for postprandial insulin values.8
TIME-RESTRICTED FEEDING & CIRCADIAN REALIGNMENT
As the field of chrononutrition continues to expand and develop, time-restricted feeding (TRF) has been prominent in research, studied for its benefits on metabolic health and as a means for realigning and supporting the body’s circadian clock.9,10 As a form of circadian fasting, TRF is a dietary pattern that optimizes circadian elements by consuming food and beverage within a shortened window of time during the day, extending a person’s nightly fast to 12 hours or more. A 2022 systematic review of 22 TRF-related randomized controlled trials suggested that among adults with overweight/obesity, TRF may lead to improved insulin resistance and glycemic responsiveness throughout the day.11 Of note, most of the reviewed studies assessed the effects of a 16-hour fast/8-hour feeding regimen (day-time feeding window variable), with only one included study comparing the early TRF (eating between 6 am and 3 pm) with the mid-day TRF (eating between 11 am and 8 pm).11
Synchronizing lifestyle habits such as food timing with circadian biological rhythms has been studied in a range of health areas, including the management of non-alcoholic fatty liver disease,12,13 the reduction of blood pressure,14inflammation,15 reduced cognitive decline,16 and cancer risk.17 Evaluating the feasibility of this therapeutic nutritional approach continues to evolve. A recent pilot study tested the feasibility of implementing TRF in adults with overweight and obesity through a smartphone intervention.18 Fifty participants with a normal eating duration of 14 hours or more were enrolled. After the 90-day TRF trial, the average adherence to logging meal activities and to reducing eating windows was 64% and 47% respectively.18 Of note, 16 of the TRF participants reduced their eating window from an average of 16 hours to approximately 12 hours. In addition, decreases in body weight, waist circumference, and systolic blood pressure were reported.18
Chronotype & Personalized Nutrition
It is important to note that some patients may not be suitable candidates for therapeutic fasting treatments due to preexisting conditions. However, for some patients, TRF interventions that optimize circadian elements by encouraging energy intake earlier in the day and increasing the fasting window have the potential to improve metabolic outcomes.
As research develops, determining the optimal time period for TRF interventions (early TRF versus mid-day TRF) may be clarified. Ultimately, ideal eating times and habits could be associated with a patient’s chronotype. Genetic variations in clock genes contribute to varied circadian inclinations among individuals and may impact best sleep and meal schedules for any given person. Specific chronotypes, for example, an “early-bird” or “night-owl,” describes not only at what time a person is naturally inclined to sleep and to be awake but may also influence appetite and physical activity.19,20 Studies continue to investigate the impact of chronotype on disease development,21 and chrononutrition trials are beginning to explore chronotype influences on interventions for improved metabolic health.22
As part of a personalized, lifestyle-based approach, nutritional therapies tailored to the individual patient are crucial for effectiveness and sustainability. Circadian rhythms are just one component to consider when creating and implementing dietary interventions. A variety of factors such as potential underlying nutrient deficiencies, presentation of disease symptoms, food sensitivities, accessibility, and personal preferences may all shape personalized treatments. IFM’s suite of therapeutic food plans are all available for modification based on an individual’s health needs. Learn more about food plan personalization within the IFM framework and creating effective and sustainable nutrition-based strategies to promote health through the online course Therapeutic Food Plans: A Component of Personalized Nutrition.