- Animal studies have shown significant metabolic benefits of time-restricted feeding.
- Preliminary human studies suggest these findings may be applicable to humans.
- A recent review looks at the evidence from both animal and human studies.
- The authors suggest more research is necessary into what patterns of restricted eating are both feasible and beneficial for humans.
Researchers have reviewed the evidence for the health benefits of time-restricted eating — a type of intermittent fasting in which people only eat during a window of time each day.
In the review, which appears in the Endocrine Society’s journal Endocrine Reviews, the researchers looked at animal studies and initial human studies. They found evidence that time-restricted eating can help prevent and manage various chronic metabolic diseases.
However, the researchers also call for more substantive studies to further demonstrate the positive effects time-restricted eating might have in humans and to determine what underlying mechanisms may account for these effects.
Time-restricted eating has received significant attention from researchers in recent years. In time-restricted eating, people typically eat their normal diet but only within a specified time period each day. This can range from 6 to 12 hours.
Scientists have demonstrated the benefits of time-restricted eating mainly in mouse studies. However, there are an increasing number of pilot studies involving human participants that have shown promising results.
Corresponding author Prof. Satchidananda Panda from the Regulatory Biology Laboratory at the Salk Institute for Biological Studies in San Diego, CA, spoke with Medical News Today. He said that time-restricted feeding studies in animals suggest potential health benefits of time-restricted eating in humans.
“Animal studies so far have shown that time-restricted eating affects many organs and even the gut microbiome in a beneficial way. Several pathways and molecules that are associated with metabolic diseases, such as prediabetes, diabetes, adiposity […], fatty liver disease, and certain cancers are modulated in a desirable way by time-restricted feeding,” said Prof. Panda.
For the authors of the recent review, a key benefit of time-restricted eating is its potential to help correct a person’s disrupted circadian rhythm.
Circadian rhythms are a series of processes in the body that operate over a 24-hour cycle. Prof. Panda and his colleagues note that circadian rhythms evolved in response to changes in light, temperature, humidity, and access to nutrients that occur as a consequence of the Earth’s day and night cycle.
If someone has a disrupted circadian rhythm, they are at risk of different health issues, including metabolic diseases, cancers, immune system problems, mood changes, and reproductive issues.
Modern forms of living can disrupt the circadian rhythm in various ways. According to Prof. Panda and his colleagues, 40% of the population work, care, or socialize late into the night, which results in circadian rhythm disruption.
One underlying cause of this disruption could be increased food intake outside of what the body anticipates according to its circadian rhythm — that is, at night time rather than during the day.
Prof. Panda and his colleagues point out that the circadian rhythms associated with the peripheral organs and the majority of the brain are primarily affected by the timing of nutrition intake.
As a consequence, time-restricted eating that involves an overnight fasting period has the potential to support circadian rhythms and reduce the risk of the negative health effects to which a disrupted circadian rhythm can lead.
Prof. Panda and his colleagues also highlight how mouse studies demonstrate that time-restricted feeding can reduce adipose tissue and is likely to improve gut health.
The researchers note that there have been relatively few human studies looking at the benefits of time-restricted eating. However, the initial findings of those studies back up the benefits seen in animal models, including reductions in body weight, body fat, waist circumference, and body mass index.
Prof. Dorothy Sears from the Division of Endocrinology and Metabolism at the University of California San Diego School of Medicine also spoke with MNT.
Prof. Sears is an expert on time-restricted eating and the circadian rhythm. She said that Prof. Panda and his colleagues’ study “is a thorough review article that summarizes the accumulating evidence that alignment of food intake with the body’s biological rhythms promotes health.”
The current research also gives an indication of the ideal time window in which to limit food intake.
Speaking with MNT, Prof. Panda said, “The human studies have tested 4-, 6-, 8-, 10-, and 12-hour time-restricted eating, and these studies show some dose responses.”
“Four- and 6-hour time-restricted eating can have many benefits among [people with overweight and obesity], but it also reduces quality of life due to its adverse effects on feeling excessive hunger, dizziness, headache, and nausea, etc.”
“Eight- and 10-hour time-restricted eating windows are well tolerated, yield several benefits, and people voluntarily adopt such practices long term.”
“Twelve-hour time-restricted eating may not produce immediate benefits within a few months, but we do not know in the long term if it could impart some benefits.”
According to Prof. Sears, “There is insufficient research evidence that supports any particular regimen, e.g., best time of day to start/stop eating or how many ‘eating’ hours per day.”
“Accumulating evidence suggests that the general ideal regimen is to consume calories during the morning and afternoon, consuming a small percentage of daily calories in the evening — 30% or less of the total calories — and completely avoiding calorie intake at night.”
– Prof. Dorothy Sears
“Promising evidence from Dr. Panda’s lab in mice supports that an occasional ‘day off’ from time-restricted eating, or eating at night may still confer benefit in humans,” said Prof. Sears.
However, Prof. Panda said to MNT that some people should consult a medical professional before starting time-restricted eating.
“Most people and caregivers feel it is safe for anyone from teenagers to older adults to practice 12-hour time-restricted eating on most days. Ten-hour time-restricted eating is also feasible for many people who have no chronic disease,” said Prof. Panda.
“For people with type 1 diabetes, type 2 diabetes, and related chronic conditions, time-restricted eating of 10 hours or shorter […] may need medical supervision for potential hypoglycemia and medication adjustments. Similarly, people with other chronic conditions may also consult their physician before starting 8- or 10-hour time-restricted eating.”
“Time-restricted eating of 6 or 4 hours may not be advisable for most people. Such a short eating window may also inadvertently substantially reduce daily calorie intake or reduce the intake of certain macro- or micronutrients. Such short time-restricted eating may also not be sustainable in the long term,” advised Prof. Panda.
Prof. Sears supported this, saying to MNT that, “overall, time-restricted eating seems to have low risk for most individuals, including those with type 2 diabetes.”
“Some individuals report modest, transient side effects, such as nausea or lightheadedness. Because of the small study sizes, self-reported compliance, and diverse regimen specifics, more research is needed to fully evaluate these.”
“People with conditions that impact metabolism — for example, thyroid disorders, diabetes, and pregnancy — should consult their healthcare provider before starting a regimen that includes fasting for longer than overnight,” suggested Prof. Sears.
Prof. Panda told MNT that scientists need to carry out much more research to further understand the benefits of time-restricted eating in animals and humans.
“Most time-restricted eating studies have been on young male mice. We have to expand these studies to both sexes and in older mice.”
“Many time-restricted eating benefits point to molecular changes in multiple organs, but we don’t know what those changes are. So, in-depth molecular studies in multiple organs are needed for better mechanistic understanding of time-restricted eating.”
“Although time-restricted eating may appear easy to adopt, many find it difficult […] So implementation research on finding personal, interpersonal, cultural, work-related, and societal barriers to adopting time-restricted eating [is] needed,” said Prof. Panda.
For Prof. Sears, larger, more powerful studies are necessary to better understand how exactly to implement time-restricted eating.
Prof. Sears said that “randomized controlled trials sufficiently large in sample size are sorely needed to properly assess various food intake timings and their associated health changes. All published randomized controlled studies to date include small numbers of individuals, [and] thus, results from these are unreliable.”
“Nonetheless, these studies are highly suggestive of diverse health benefits that warrant additional research. Key areas of interest include cardiometabolic disease, cancer, cognition, and mental health.”
– Prof. Dorothy Sears
“There are several large trials now funded by the National Institutes of Health and the Department of Defense to test benefits of circadian-aligned food intake timing,” explained Prof. Sears. “Results from these should be illuminating and provide more statistically robust interpretations to guide public health recommendations.”