Timing
meals later at night can cause weight gain and impair fat metabolism
University of Pennsylvania School of Medicine
New findings suggest eating late at night could be more
dangerous than you think. Compared to eating earlier in the day, prolonged delayed eating can increase weight, insulin and cholesterol levels, and negatively affect fat metabolism, and hormonal markers implicated in heart disease, diabetes and other health problems, according to results from researchers at the Perelman School of Medicine at the University of Pennsylvania.
The findings offer the first experimental evidence on the
metabolic consequences of consistent delayed eating compared to daytime eating.
"We know from our sleep loss studies that when you're sleep deprived, it negatively affects weight and metabolism in part due to late-night eating, but now these early findings, which control for sleep, give a more comprehensive picture of the benefits of eating earlier in the day," said Namni Goel, PhD, a research associate professor of psychology in Psychiatry in the division of Sleep and Chronobiology, and lead author of the ongoing study.
"Eating later can promote a negative profile of weight,
energy, and hormone markers -- such as higher glucose and insulin, which are
implicated in diabetes, and cholesterol and triglycerides, which are linked
with cardiovascular problems and other health conditions."
In the study, nine healthy weight adults underwent two
conditions, one of daytime eating (i.e., three meals and two snacks between 8
a.m. and 7 p.m.) for eight weeks and another of delayed eating (i.e., three
meals and two snacks eating from noon to 11 p.m.) for eight weeks.
There was a two-week washout period between conditions to make
sure there was no carry over effect. The sleep period was held constant,
between 11 p.m. to 9 a.m.
Participants visited Penn's Center for Human Phenomic Science to
get metabolic measures and blood drawn at the beginning, after the first eating
condition, after the two-week washout, and after the second eating condition.
This allowed the team to measure changes in weight, metabolism
and energy used, and made sure the two week washout allowed all measures to
return to baseline before the next condition.
The team found that when participants ate later, compared to the
daytime condition, weight increased.
Respiratory quotient, i.e. the ratio of carbon dioxide produced
by the body to oxygen consumed by the body that indicates which macronutrients
are being metabolized, also rose during the delayed eating condition,
indicating later eating led to metabolizing fewer lipids and more carbs.
The researchers also found that a series of other measures
reflecting negative metabolic profiles increased in the delayed condition,
including insulin, fasting glucose, cholesterol, and triglyceride levels.
Conducting a 24-hour hormonal profile, they also found that in
during daytime eating condition, the hormone ghrelin, which stimulates
appetite, peaked earlier in the daytime, while leptin, which keeps you
satiated, peaked later, suggesting that the participants received cues to eat
earlier, and eating earlier likely helped them to stay satiated longer.
This suggests that eating earlier may help prevent overeating in
the evening and at night. As sleep-wake cycles were constant, melatonin levels
remained constant in both groups.
"While lifestyle change is never easy, these findings
suggest that eating earlier in the day may be worth the effort to help prevent
these detrimental chronic health effects," said Kelly Allison, PhD, an
associate professor of psychology in Psychiatry and director of the Center for
Weight and Eating Disorders, and senior author on the study.
"We have an extensive knowledge of how overeating affects
health and body weight, but now we have a better understanding of how our body
processes foods at different times of day over a long period of time."
Similar yet much shorter previous studies have suggested similar
results, but this is the first long-term study looking at the timing of eating
patterns that also controlled for sleep-wake cycles, exercise, macronutrient
intake, etc. to pinpoint the effects of prolonged eating at different times of
day.