An emerging scientific field known as chrononutrition suggests that healthy eating depends not only on what is eaten, but also on when. Researchers say the body's internal clock, or circadian rhythm, plays a significant role in how food is metabolised, with implications for weight, blood sugar and cardiovascular health.
Breakfast: earlier eating linked to heart health
A study of more than 100,000 people in France found that those who ate breakfast later had a higher risk of cardiovascular disease. The same research found that a longer overnight fast, achieved by eating earlier in the evening rather than delaying breakfast, was associated with better heart health. Researchers noted this may be particularly relevant for shift workers and others vulnerable to circadian disruption, who are advised, where possible, to limit food intake to daytime hours.
Lunch: earlier meals linked to greater weight loss
Marta Garaulet, from the University of Murcia in Spain, led a study following 420 adults on the same weight-loss programme over 20 weeks. Those who ate an earlier lunch lost more weight, and lost it more quickly, than those who ate lunch later in the day. A separate small randomised controlled trial of 32 healthy women, who ate identical meals for two weeks, found that those who ate a later lunch showed poorer blood sugar control and burned fewer carbohydrates.
Dinner: later eating linked to poorer blood sugar control
Frank Scheer, professor of medicine and neuroscientist at Brigham and Women's Hospital in Boston, said the body responds differently to food depending on the time of day, since the internal clock regulates most aspects of physiology. Eating when the body's clock signals it is time for sleep can create what researchers call "circadian misalignment."
In a 2022 study of more than 800 adults, participants who drank a glucose drink one hour before bedtime processed it less efficiently than those who drank it four hours earlier, showing higher blood sugar levels and lower insulin production. Researchers believe melatonin, which rises as the body prepares for sleep, plays a key role in this effect. The impact was greater in people carrying a variant of the MTNR1B gene, which is associated with increased risk of type 2 diabetes.
Later eating has also been linked to increased hunger the following day, with research showing it disrupts hormones that regulate appetite, including reduced production of leptin, the hormone that signals fullness. At the same time, later eating has been associated with the body storing fat rather than breaking it down.
In a study of nearly 1,200 adults, an international team of researchers, including Scheer, found that later eating was linked to a higher body mass index specifically among individuals genetically predisposed to obesity, while eating earlier reduced this risk.
Chronotype also plays a role
Giovanna Muscogiuri, assistant professor at the University of Naples Federico II in Italy, said a person's chronotype, whether they are a morning "lark" or an evening "owl", also influences eating patterns. Morning types are more likely to follow a Mediterranean diet, while evening types tend to delay meals and eat more energy-dense foods later in the day.
Chronotype also affects how the body responds to food. Morning types tend to have earlier peaks in insulin sensitivity and an earlier release of melatonin than evening types, who as a result of later eating are more vulnerable to poorer glucose control and weight gain. Muscogiuri noted that sleep duration and quality also affect hunger and cravings, with sleep-deprived individuals more likely to overeat and choose energy-dense foods.
Practical guidance
Based on the research, experts recommend eating at regular times each day. Fibre-rich carbohydrates, such as whole grains, legumes and fruit, are best consumed earlier in the day, when the body is better able to process them. In the evening, a lighter, protein-rich meal is recommended. Muscogiuri's review also suggests including foods that support sleep in the evening, such as nuts, seeds and tryptophan-rich proteins including chicken, salmon and tuna, as tryptophan has been shown to improve sleep quality.
Researchers conclude there is no single universal "best" time to eat, but recommend consuming the largest meal earlier in the day and eating the evening meal at least three hours before bedtime.
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