According to the senior study author
Wendy L. Bennett, M.D., M.P.H., an associate professor of medicine at Johns
Hopkins University School of Medicine in Baltimore, although ‘time-restricted
eating patterns’ — known as intermittent fasting — are popular, rigorously
designed studies have not yet determined whether limiting the total eating
window during the day helps to control weight.
This study evaluated the association
between time from the first meal to last meal with weight change. Nearly 550
adults (18 years old or older) from three health systems in Maryland and
Pennsylvania with electronic health records were enrolled in the study.
Participants had at least one weight and height measurement registered in the
two years prior to the study’s enrollment period (Feb.-July 2019).
Overall, most participants (80%)
reported they were white adults; 12% self-reported as Black adults; and about
3% self-identified as Asian adults. Most participants reported having a college
education or higher; the average age was 51 years; and the average body mass
index was 30.8, which is considered obese. The average follow-up time for
weight recorded in the electronic health record was 6.3 years.
Participants with a higher body mass
index at enrollment were more likely to be Black adults, older, have Type 2
diabetes or high blood pressure, have a lower education level, exercise less,
eat fewer fruits and vegetables, have a longer duration from last mealtime to
sleep and a shorter duration from first to last meal, compared to the adults
who had a lower body mass index.
The research team created a mobile
application, Daily24, for participants to catalog sleeping, eating and wake up
time for each 24-hour window in real time. Emails, text messages and in-app
notifications encouraged participants to use the app as much as possible during
the first month and again during “power weeks” — one week per month for the
six-month intervention portion of the study.
Based on the timing of sleeping and
eating each day recorded in the mobile app, researchers were able to measure:
·
the
time from the first meal to the last meal each day;
·
the
time lapse from waking to first meal; and
·
the
interval from the last meal to sleep.
They calculated an average for all data
from completed days for each participant.
The data analysis found:
·
Meal
timing was not associated with weight change during the six-year follow-up
period. This includes the interval from first to last meal, from waking up to
eating a first meal, from eating the last meal to going to sleep and total
sleep duration.
·
Total
daily number of large meals (estimated at more than 1,000 calories) and medium
meals (estimated at 500-1,000 calories) were each associated with increased
weight over the six-year follow up, while fewer small meals (estimated at less
than 500 calories) was associated with decreasing weight.
·
The
average time from first to last meal was 11.5 hours; average time from wake up
to first meal measured 1.6 hours; average time from last meal to sleep was 4
hours; and average sleep duration was calculated at 7.5 hours.
·
The
study did not detect an association meal timing and weight change in a
population with a wide range of body weight.
As reported by Bennett, even though
prior studies have suggested intermittent fasting may improve the body’s
rhythms and regulate metabolism, this study in a large group with a wide range
of body weights did not detect this link. Large-scale, rigorous clinical trials
of intermittent fasting on long-term weight change are extremely difficult to
conduct; however, even short-term intervention studies may be valuable to help
guide future recommendations.
Although the study found that meal
frequency and total calorie intake were stronger risk factors for weight change
than meal timing, the findings could not prove direct cause and effect,
according to lead study author Di Zhao, Ph.D., an associate scientist in the
division of cardiovascular and clinical epidemiology at Johns Hopkins Bloomberg
School of Public Health.
Researchers note there are limitations
to the study since they did not evaluate the complex interactions of timing and
frequency of eating. Additionally, since the study is observational in nature,
the authors were unable to conclude cause and effect. Future studies should
work toward including a more diverse population, since the majority of the
study’s participants were well-educated white women in the mid-Atlantic region
of the U.S., the authors noted author.
Researchers also were not able to
determine the intentionality of weight loss among study participants prior to
their enrollment and could not rule out the additional variable of any
preexisting health conditions.
According to the American Heart
Association’s 2022 statistics, 40% of adults in the U.S. are obese; and the
Association’s current diet and lifestyle recommendations to reduce
cardiovascular disease risk include limiting overall calorie intake, eating
healthy foods and increasing physical activity.
The 2017 American Heart Association scientific statement: Meal Timing and Frequency: Implications for Cardiovascular Disease Prevention did not offer clear preference for frequent small meals or intermittent fasting. It noted that irregular patterns of total caloric intake appear to be less favorable for the maintenance of body weight and optimal cardiovascular health. And, altering meal frequency may not be useful for decreasing body weight or improving traditional cardiometabolic risk factors.
Journal article: https://www.ahajournals.org/doi/10.1161/JAHA.122.026484
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