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Eating a late dinner may slow nighttime burning of fat — and lead to weight gain

In the study, individuals who ate their last meal of the day at 10 p.m. rather than 6 p.m. burned less fat overnight. They also had higher blood sugar levels.

late dinner
Blood tests revealed that the participants’ blood glucose (sugar) levels were higher after the late dinner than after the earlier one. In addition, the participants’ bodies burned less fat while they slept.
Photo by Wiktor Karkocha on Unsplash

When people eat their dinner late in the evening, they may be at greater risk of gaining excess weight, according to a small study published recently in the Journal of Clinical Endocrinology & Metabolism.

In the study, individuals who ate their last meal of the day at 10 p.m. rather than 6 p.m. burned less fat overnight. They also had higher blood sugar levels.

“If the metabolic effects we observed with a single meal keep occurring chronically, then late eating could lead to consequences such as diabetes or obesity,” says Dr. Jonathan Jun, the study’s senior author and an associate professor of medicine at Johns Hopkins University, in a released statement.

These findings add to growing evidence that the timing of our meals contributes to obesity and metabolic syndrome (a cluster of syndromes, including high blood sugar, high blood pressure and excess body fat around the waist, that increases the risk of heart disease, stroke and type 2 diabetes). One previous study found, for example, that women who ate their largest meal in the morning experienced greater weight loss over a 12-week period than those who ate their largest meal in the evening.

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Most studies of meal timing have not taken into account sleep schedules, however. Nor have they looked in any detail at how the body responses metabolically to when food is consumed. Jun and his colleagues decided to conduct a more rigorous study to help fill that research gap.

Study details

For the study, the researchers recruited 20 volunteers (10 men and 10 women). All were healthy and in their 20s or 30s. The volunteers were brought to a clinical research lab on two different occasions for three-day visits. For a week before each visit, they wore an actigraph (a wrist-worn device that keeps track of when someone is awake and asleep, as well as when they are physically active).

On the second night in the lab (the test day — the first night was simply to acclimate them to sleeping in a lab), the participants were given four meals with a total of 2,100 calories. They received 25 percent of the calories at breakfast, 30 percent at lunch, 35 percent a dinner and 10 percent in a snack. Each meal consisted of 50 percent carbohydrates, 35 percent fat, and 15 percent protein. The food also contained non-radioactive tracers than enabled the researchers to measure the speed at which the participants burned off the fat.

Breakfast was served at 8 a.m. and lunch at 1 p.m. during both visits. The timing of the dinner and the snack, however, were switched. During one visit, dinner was at 6 p.m. and the snack at 10 p.m. During the other, those meals were reversed, and dinner was served late, at 10 p.m.

In the lab, the participants went to bed at 11 p.m. and were awoken at 7 a.m.

Key findings

Blood tests revealed that the participants’ blood glucose (sugar) levels were higher after the late dinner than after the earlier one. In addition, the participants’ bodies burned less fat while they slept.

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“On average, the peak glucose level after the late dinner was about 18 percent higher, and the amount of fat burned overnight decreased by about 10 percent compared to eating an earlier dinner,” says Dr. Chenjuan Gu, the study’s first author and a postdoctoral researcher at Johnson Hopkins University, in a released statement.

“The effects we have seen in healthy volunteers might be more pronounced in people with obesity or diabetes, who already have a compromised metabolism,” she adds.

Interestingly, the meal-timing-related metabolic differences observed in the study were more pronounced in the volunteers whose at-home actigraph readings showed them to be earlier sleepers.

A matter of timing

This was a small study involving young, healthy adults. And the participants were observed in the lab for very brief periods. Its findings may not be generalizable.

“We still need to do more experiments to see if these effects continue over time, and if they are caused more by behavior (such as sleeping soon after a meal) or by the body’s circadian rhythms,” says Jun.

Still, for people attempting to drop excess pounds, this study — along with other research — suggests that not consuming food late at night may help.

In other words, when we eat, as well as what and how much we eat, may be important for our health.

FMI:  You’ll find an abstract on the Journal of clinical Endocrinology & Metabolism’s website.