Why ‘night owls’ are more likely to put on belly fat: a new study

The study found that ‘night owls’ were more likely to have their main meals in the evening, consumed fewer foods rich in vitamins and fibre, and had more abdominal fat compared with ‘early birds’.

The findings have been published in the journal Frontiers in Nutrition.

However, the study does not prove that a late-night lifestyle in itself causes obesity. It merely identified a link between chronotype and health status.

What the researchers found

The study involved 287 women aged between 18 and 45 living in New Zealand. First, the researchers determined their chronotype — whether they were ‘early birds’, ‘night owls’ or somewhere in between. The participants then recorded everything they ate and drank over a five-day period.

In addition, the researchers assessed their body composition using DXA scans — a method that allows for the precise measurement of body fat and its distribution. Blood samples were also taken from the participants.

It turned out that women with an evening chronotype:

• were more likely to eat late in the evening;
• consumed fewer foods rich in vitamins, minerals and fibre;
• had a higher body mass index;
• were more likely to accumulate fat around the abdomen;
• exhibited less favourable metabolic indicators.

Although their total calorie intake was virtually the same as that of the other groups, the distribution of their meals throughout the day was quite different.

Why is belly fat considered more dangerous?

The researchers focused not only on overall weight, but also on exactly where fat is stored.

‘Night owls’ were more likely to accumulate fat around the waist. This type of obesity is considered more dangerous, as it is associated with an increased risk of type 2 diabetes, cardiovascular disease and metabolic disorders.

Blood tests also showed that participants with an evening chronotype had higher levels of insulin, triglycerides and leptin, whilst their levels of ‘good’ cholesterol (HDL) were lower.

Why does this happen?

Scientists believe that metabolism is influenced not only by what we eat, but also by the time at which we eat.

The body operates according to its internal biological clock, and eating also serves as a kind of signal for it. If the majority of calories are consumed late in the evening, whilst a person eats almost nothing in the morning, this can affect the functioning of the metabolism.

Furthermore, participants with an evening chronotype were more likely to choose less healthy foods and consumed fewer essential micronutrients.

Is there a reason to change your routine?

The authors emphasise that the results cannot yet be considered definitive. The study was conducted only among women, so it is not known whether the same patterns would be observed in men or people of other ages.

Furthermore, the study merely demonstrates a link between chronotype and health; it does not prove that going to bed late is the direct cause of weight gain.

Nevertheless, the study confirms that sleep patterns, mealtimes and the quality of one’s diet can play an important role in preventing obesity and metabolic disorders.

Why this is important

Modern lifestyles are increasingly causing people to go to bed later, work in the evenings and have dinner at a later hour.

New research shows that it is not only the number of calories that matters for health, but also when a person eats and how closely their routine aligns with their internal biological clock.

Background

A chronotype is an innate characteristic of a person’s biological clock that determines when they find it easiest to wake up, work and go to bed. People are usually broadly categorised as ‘early birds’, ‘night owls’ and those who fall somewhere in between.

Previous studies have already shown that an evening chronotype is more often associated with late meals, a less healthy diet and an increased risk of obesity. This new study is one of the few in which researchers have assessed not only body mass index but also the precise distribution of body fat, as well as a wide range of metabolic indicators.

Source

van der Merwe C. et al. Chronotype and associations with dietary intake, meal timing, body composition, and metabolic biomarkers. Frontiers in Nutrition (2026).