Breakfast may affect how the liver processes sugar after lunch — a study on dogs

The way the body reacts to breakfast can affect blood sugar levels after the next meal. In an experiment on dogs, scientists replicated the hormonal response to breakfast and found that if glucagon levels were elevated, the liver absorbed 41 per cent less glucose a few hours later.

This does not mean that the researchers have identified a ‘right’ or ‘wrong’ breakfast. The experiment did not involve humans, nor did it use ordinary food — the scientists separately controlled hormone and blood sugar levels to understand how the liver functions.

Details

After a meal, insulin is released into the blood. It helps the liver take glucose from the blood and store it for later use. Another hormone, glucagon, sends the liver the opposite signal — to release glucose back into the blood.

The body usually manages blood sugar better after a second meal if breakfast has already been eaten. This phenomenon is known as the second-meal effect. The study authors set out to investigate the role played by the insulin-to-glucagon ratio after breakfast.

The experiment involved 29 adult dogs. Sixteen animals – eight in each group – completed the full eight-hour protocol. Liver tissue from a further 13 dogs was used for additional molecular analyses.

To isolate the effects of the hormones from the influence of the meal itself, the researchers temporarily blocked the natural production of insulin and glucagon, and then administered them in precisely calculated quantities. In one group, glucagon levels remained normal after a simulated breakfast; in the other, they were elevated. Both groups received the same amount of insulin.

An hour and a half later, the 16 animals that had completed the full protocol were placed under identical conditions, simulating the body’s response after lunch. This allowed the researchers to determine whether the hormonal state following the simulated breakfast had affected liver function later that same day.

After the simulated lunch, the livers of the dogs in the group with elevated glucagon absorbed 41 per cent less glucose: 3.6 versus 6.1 milligrams per kilogram of body weight per minute. It also stored 44 per cent less glucose as glycogen. Meanwhile, the muscles and other tissues in both groups absorbed glucose at the same rate.

A likely explanation involves glucokinase – an enzyme that helps the liver capture and store glucose. Insulin, following the conditioned breakfast, increased the levels of this enzyme. Elevated glucagon interfered with this process, and a few hours later the liver was less effective at handling sugar. The authors refer to this delayed effect as the liver’s ‘metabolic memory’.

The study has significant limitations. The experiment was carried out on dogs, and breakfast and lunch were replaced by controlled administration of hormones and glucose. Glucagon levels were kept elevated for four hours, although after a normal meal they typically rise for one to two hours. It is also unknown whether the effect would persist with breakfasts and lunches of different compositions.

The study was funded by the US National Institutes of Health. One of the authors, Alan Cherrington, disclosed contracts with Alnylam and Abvance and consultancy work for Novo Nordisk, Fractyl, Sensulin and Thetis. The other authors did not declare any commercial relationships that could be considered a potential conflict of interest.

Why this is important

The results show that, for the body, breakfast and lunch are not two separate events. The hormonal response following the first meal can alter, for several hours, how the liver processes sugar after the second.

In future, this mechanism may help explain why, in some people with type 2 diabetes, blood sugar levels deteriorate over the course of the day, even if they were normal in the morning. However, neither healthy people nor patients with diabetes took part in the study. For now, this is a possible explanation rather than a proven mechanism in humans.

The study also shows that insulin and glucagon need to be studied together. However, it did not examine specific foods, breakfast times, skipping breakfast or medication. Before drawing practical conclusions, the results need to be replicated with a normal meal and then tested in humans.

Source

• Hannah L. Waterman et al., ‘Morning glucagon disrupts insulin-induced hepatic metabolic memory and subsequent afternoon glucose metabolism in canines’, *Frontiers in Endocrinology*, 29 April 2026. DOI: 10.3389/fendo.2026.1832065.
• Lorena Infante Lara, ‘Eating breakfast affects how your body responds to lunch — and a hormone is to blame’, Vanderbilt University School of Medicine, 9 June 2026: interview with the study authors.
• ‘How breakfast primes the response to the hormones that manage blood sugar’, Medical Xpress, 1 September 2026.