For type 2 diabetes, focusing on when you eat – not what – can help control blood sugar

Type 2 diabetes affects 1.2 million Australians and accounts for 85-90% of all diabetes cases. This chronic condition is characterised by high blood glucose (sugar) levels, which carry serious health risks. Complications include heart disease, kidney failure and vision problems.

Diet is an important way people living with type 2 diabetes manage blood glucose, alongside exercise and medication. But while we know individualised, professional dietary advice improves blood glucose, it can be complex and is not always accessible.

Our new study looked at the impact of time-restricted eating – focusing on when you eat, rather than what or how much – on blood glucose levels.

We found it had similar results to individualised advice from an accredited practising dietitian. But there were added benefits, because it was simple, achievable, easy to stick to – and motivated people to make other positive changes.

What is time-restricted eating?

Time-restricted eating, also known as the 16:8 diet, became popular for weight loss around 2015. Studies have since shown it is also an effective way for people with type 2 diabetes to manage blood glucose.

Time-restricted eating involves limiting when you eat each day, rather than focusing on what you eat. You restrict eating to a window during daylight hours, for example between 11am and 7pm, and then fast for the remaining hours. This can sometimes naturally lead to also eating less.

Giving your body a break from constantly digesting food in this way helps align eating with natural circadian rhythms. This can help regulate metabolism and improve overall health.

For people with type 2 diabetes, there may be specific benefits. They often have their highest blood glucose reading in the morning. Delaying breakfast to mid-morning means there is time for physical activity to occur to help reduce glucose levels and prepare the body for the first meal.

How we got here

We ran an initial study in 2018 to see whether following time-restricted eating was achievable for people with type 2 diabetes. We found participants could easily stick to this eating pattern over four weeks, for an average of five days a week.

Importantly, they also had improvements in blood glucose, spending less time with high levels. Our previous research suggests the reduced time between meals may play a role in how the hormone insulin is able to reduce glucose concentrations.

Other studies have confirmed these findings, which have also shown notable improvements in HbA1c. This is a marker in the blood that represents concentrations of blood glucose over an average of three months. It is the primary clinical tool used for diabetes.

However, these studies provided intensive support to participants through weekly or fortnightly meetings with researchers.

While we know this level of support increases how likely people are to stick to the plan and improves outcomes, it is not readily available to everyday Australians living with type 2 diabetes.

What we did

In our new study, we compared time-restricted eating directly with advice from an accredited practising dietitian, to test whether results were similar across six months.

We recruited 52 people with type 2 diabetes who were currently managing their diabetes with up to two oral medications. There were 22 women and 30 men, aged between 35 and 65.

Participants were randomly divided into two groups: diet and time-restricted eating. In both groups, participants received four consultations across the first four months. During the next two months they managed diet alone, without consultation, and we continued to measure the impact on blood glucose.

In the diet group, consultations focused on changing their diet to control blood glucose, including improving diet quality (for example, eating more vegetables and limiting alcohol).

In the time-restricted eating group, advice focused on how to limit eating to a nine-hour window between 10am and 7pm.

Over six months, we measured each participant’s blood glucose levels every two months using the HbA1c test. Each fortnight, we also asked participants about their experience of making dietary changes (to what or when they ate).

What we found

We found time-restricted eating was as effective as the diet intervention.

Both groups had reduced blood glucose levels, with the greatest improvements occurring after the first two months. Although it wasn’t an objective of the study, some participants in each group also lost weight (5-10kg).

When surveyed, participants in the time-restricted eating group said they had adjusted well and were able to follow the restricted eating window. Many told us they had family support and enjoyed earlier mealtimes together. Some also found they slept better.

After two months, people in the time-restricted group were looking for more dietary advice to further improve their health.

Those in the diet group were less likely to stick to their plan. Despite similar health outcomes, time-restricted eating seems to be a simpler initial approach than making complex dietary changes.

Is time-restricted eating achievable?

The main barriers to following time-restricted eating are social occasions, caring for others and work schedules. These factors may prevent people eating within the window.

However, there are many benefits. The message is simple, focusing on when to eat as the main diet change. This may make time-restricted eating more translatable to people from a wider variety of socio-cultural backgrounds, as the types of foods they eat don’t need to change, just the timing.

Many people don’t have access to more individualised support from a dietitian, and receive nutrition advice from their GP. This makes time-restricted eating an alternative – and equally effective – strategy for people with type 2 diabetes.

People should still try to stick to dietary guidelines and prioritise vegetables, fruit, wholegrains, lean meat and healthy fats.

But our study showed time-restricted eating may also serve as stepping stone for people with type 2 diabetes to take control of their health, as people became more interested in making diet and other positive changes.

Time-restricted eating might not be appropriate for everyone, especially people on medications which don’t recommend fasting. Before trying this dietary change, it’s best speak to the healthcare professional who helps you manage diabetes.