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June 04, 2017

Penn study warns of harmful metabolic effects for late night eaters

A new study on the metabolic consequences of consistent delayed eating compared to daytime eating offers up the first experimental evidence of physiological changes that occur as a result of these contrasting dietary habits.

Researchers involved in the study examined the timing of food consumption as a lifestyle decision closely linked to sleep health and behavior, noting that those who eat late are often experience disrupted sleep patterns.

“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, a Penn research associate professor of psychology 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.”

To complete the study, the research team recruited nine healthy weight adults who followed two dietary conditions for equal lengths of time. The first condition was an eight-week daytime eating regimen of three meals and two snacks between the hours of 8 a.m. and 7 p.m. The second condition was an eight-week delayed eating regimen consisting of three meals and two snacks from noon to 11 p.m.

To prevent a carryover effect, all participants were given a two-week washout period and sleep conditions were held constant between the hours of 11 p.m. and 9 a.m.

Throughout the study, participants attended Penn's Center for Human Phenomic Science to undergo metabolic measurements and blood drawings during each condition of the experiment. Tests include measurements in weight change, metabolism and energy used compared to baseline results during the washout period.

When the participants ate later in the, the researchers found, their weight increased compared to the daytime eating condition. Their respiratory quotient — the ratio of carbon dioxide produced by the body to oxygen consumed — showed that their bodies metabolized fewer fats and more carbs.

Hormonally, study participants in the daytime eating condition demonstrated a more beneficial hunger response. Ghrelin, the hormone that stimulates appetite, spiked early in the day. Leptin, the hormone that keeps us feeling full, peaked later in the day. Eating earlier could ultimately help prevent us from consuming more later at night.

“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, 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.”

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