07-18-2026
Night owls have poorer metabolic health even when they eat the same calories
Women who are natural night owls have been found to carry more body fat and show less favorable blood sugar and cholesterol levels than women who prefer earlier schedules
A study of nearly 300 New Zealand women found this held even though both groups ate about the same amount of food each day. What separated them was timing
The night owls ate little in the morning and pushed their biggest meals into the late evening, and that late-night eating tracked closely with higher body fat and poorer metabolic health
Whether someone is an early bird or a night owl comes down to chronotype, the body’s built-in preference for when to sleep, wake, and feel alert
To classify participants, the researchers used a questionnaire that pinpoints the midpoint of a person’s sleep on work-free days
The team then divided them into evening types, morning types, and an intermediate group between the two
Rozanne Kruger, a professor of nutrition and dietetics at Griffith University, led the analysis, which drew on a larger women’s health study run at Massey University in Auckland, New Zealand
These were healthy women, not patients. All 287 were aged 18 to 45 and free of the chronic conditions that usually complicate this kind of work
The evening types stood apart. They carried a higher body mass index, 31.4 compared with 26.1 among earlier risers, a larger proportion of body fat, and more fat packed around the abdomen
Their blood told a similar story, with higher fasting insulin, triglycerides, and long-term blood sugar
Across a full day, morning and evening types took in almost identical amounts of energy, with the evening group edging ahead by roughly 50 calories, a rounding error against everything else they ate
Where the two groups split was the clock. Morning and intermediate types front-loaded their eating, taking in about 15% of the day’s energy before ten in the morning
The evening types managed only about nine percent that early, then made up for it after dark. After eight in the evening, the pattern flipped
Evening types ate close to a quarter of their daily energy in the late-night window, roughly 2.5 times their morning share, while the earlier group took in about eleven percent
The night-time food also leaned toward carbohydrate and fat. This reversal did the real work in the study
“Both morning-types and evening-types consumed similar amounts of food or energy across the day, but it was the timing of eating that was crucial,” said Kruger
To see where that late eating landed on the body, the team measured the ratio of fat stored around the abdomen to fat on the hips and thighs
This is a gauge of belly fat that flags heart and metabolic risk more sharply than weight alone. No previous study had tracked this measure across chronotypes
The contrast was sharpest here. Among the women with the most abdominal fat, the evening types’ late eating stood out most clearly
They had significantly more energy, carbohydrate and fat taken in after eight in the evening than the earlier risers managed, and significantly less in the early morning
The blood work aligned with the pattern. Evening types ran higher on insulin, triglycerides, and glycated hemoglobin, a marker of average blood sugar, and lower on protective HDL cholesterol
A larger review pooling dozens of studies has reached the same conclusion, finding that evening types carry worse markers of heart and metabolic health even when they eat no more than early risers
The body handles food differently depending on the hour. In the morning the body is primed to burn energy with insulin working efficiently and blood sugar remaining under control
As night falls, that machinery winds down in preparation for the overnight fast
Eat a large meal close to bedtime and the food arrives when the body has already turned toward storage rather than use
Over months and years, the authors argue, that mismatch can push energy into fat instead of fueling activity, especially around the middle
A trial has shown the effect directly. When volunteers ate later in the day, they burned fewer calories, felt hungrier, and their fat tissue tilted toward storing energy rather than releasing it
Skipping breakfast may set the trap. Going without an early meal tends to leave people hungrier by evening
This can lead to overeating or heavy snacking at night, exactly the pattern the evening types showed
Most of the evening types were younger Pacific women from more deprived areas, so chronotype cannot be considered in isolation from diet, culture, and socioeconomic factors
The researchers adjusted for those factors, but they could not fully separate them, and the findings need testing in more varied groups
The study also captured a single moment in time, so it cannot prove that late eating caused the extra fat rather than the reverse
Diet was self-reported, and the team measured clock time rather than each woman’s internal biological night. Even so, the work adds something concrete
It is among the first to show, in healthy young women, that meal timing rather than total intake lines up with body fat, central fat and metabolic markers across chronotypes
Nudging the biggest meals earlier, and easing off late-night eating, could give night owls a way to lower their risk without eating less overall
“The research highlights that when people eat may be just as important as what they eat,” said Kruger
The study is published in the journal Frontiers in Nutrition
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