Can changing when you eat work as well as personalised dietitian advice for improving blood sugar? A 12-month randomised trial in adults at increased risk of type 2 diabetes tested that question. The short answer is more nuanced than the usual fasting headlines.
At four months, a nine-hour daily eating window was not clinically worse than individualised dietitian guidance for HbA1c, a measure of average blood glucose. It was not better, either. At 12 months, the researchers could no longer confirm that the meal-timing approach was no worse than dietitian guidance. In both groups, the actual changes in HbA1c were small and not clinically meaningful.
This does not mean time-restricted eating is useless. It suggests that meal timing may be a practical option for some people, especially in the short term, but it is not a proven substitute for a high-quality eating pattern or ongoing professional support.
What is time-restricted eating?
Time-restricted eating, sometimes called time-restricted feeding, is a form of intermittent fasting. Instead of prescribing specific foods or a calorie target, it limits all meals and calorie-containing drinks to a consistent daily window.
In this study, participants in the time-restricted eating group were asked to:
- eat within a self-selected nine-hour window each day;
- finish their last calorie-containing food or drink by 7 pm; and
- consume only water, black coffee or herbal tea outside that window.
Most participants chose an eating window from 10 am to 7 pm. This is important: the study did not test every version of intermittent fasting, and it did not test prolonged or alternate-day fasting.
How was the trial designed?
The Australian multicentre trial included 247 adults with overweight or obesity who had a high score on an established type 2 diabetes risk assessment. Their average age was 56, about three-quarters were women, and their average HbA1c was 5.8% (40 mmol/mol).
Participants were randomly assigned to one of two groups:
- Time-restricted eating: a nine-hour daily eating window, with the final eating occasion by 7 pm. Participants did not receive advice about changing the amount or types of food they ate.
- Individualised dietitian guidance: personalised advice on diet quality, portion sizes, carbohydrates, heart-healthy eating, food labels, alcohol and weight management.
This was not a comparison between time-restricted eating and doing nothing. Both groups received five personalised telehealth consultations during the first three months, totalling about three hours of support. Participants in both groups were also encouraged to increase physical activity and received practical text messages after the active support period.
What did the trial find at four months?
The main outcome was the difference between the groups in HbA1c at four months. The researchers designed the study to test whether time-restricted eating was non-inferior to dietitian guidance. In plain language, they asked whether the meal-timing strategy performed no worse than dietitian guidance by more than a small, pre-agreed margin of 0.10 percentage points in HbA1c.
At four months:
- time-restricted eating met that non-inferiority threshold;
- it was not superior to dietitian guidance; and
- the average difference between groups was only -0.02 percentage points in HbA1c.
That difference was small, and the confidence interval crossed zero. The researchers also stressed that the absolute HbA1c changes in both groups were not clinically meaningful.
What happened at 12 months?
The longer-term result was less certain. At 12 months, the average difference between groups was 0.05 percentage points in HbA1c, with the confidence interval extending from -0.02 to 0.11.
Because the upper end of that range moved just beyond the study’s 0.10-percentage-point non-inferiority margin, the researchers could no longer conclude that time-restricted eating was no worse than dietitian guidance.
This does not prove that dietitian guidance was clearly superior. The between-group difference was not statistically significant, and HbA1c changed very little in either group. It means the trial could not provide the required statistical assurance that the two approaches remained sufficiently similar at 12 months.
What about weight, blood pressure and other measures?
Both groups lost a modest amount of weight. At four months, average weight loss was about 2.1 kg with time-restricted eating and 2.4 kg with dietitian guidance. At 12 months, the average losses were about 2.0 kg and 2.9 kg, respectively. The difference between groups was not statistically significant.
There were also no clear between-group differences in fasting glucose, nocturnal glucose, insulin resistance, blood pressure, waist size or body composition at the main follow-up points. Dietitian guidance produced larger improvements in total and LDL cholesterol at four months, but those differences were no longer clear at 12 months.
The dietitian-guidance group reported a larger reduction in energy intake and more favourable changes in fibre, saturated fat and sodium. That is a useful reminder that when you eat and what you eat are different questions.
Was time-restricted eating easier to follow?
Self-reported adherence was higher in the time-restricted eating group. Participants reported following their plan on about 5.5 days per week during the first four months and 4.9 days per week from months four to 12. Corresponding adherence in the dietitian-guidance group was about 4.8 and 4.2 days per week.
However, higher reported adherence did not translate into better blood glucose outcomes. It may simply mean that a clear rule about eating times felt easier to remember than several recommendations about food choice, portions and meal planning.
A total of 194 participants completed the 12-month visit. More people withdrew because of the assigned intervention during the later follow-up in the time-restricted eating group than in the dietitian-guidance group, so the long-term practicality of the approach will not be the same for everyone.
Was it safe?
Adverse events were mostly minor, and their frequency and type did not differ between groups. Reported events included fatigue, headache, diarrhoea, nausea or vomiting, light-headedness and other common health complaints. The trial involved adults at risk of type 2 diabetes, not a population routinely using glucose-lowering medicines that can cause hypoglycaemia.
If you already have diabetes, fasting can change the timing and amount of carbohydrate you consume. That can affect insulin and medicines such as sulfonylureas, which can cause low blood glucose. Diabetes UK advises speaking with your healthcare team before starting intermittent fasting if you use insulin or other diabetes medication.
Extra caution is also sensible during pregnancy or breastfeeding, for people with a history of an eating disorder, older adults with frailty, people with kidney or liver disease, and anyone whose work, training or medication schedule makes prolonged gaps between meals unsafe.
What the study does not prove
- It did not show that time-restricted eating prevents type 2 diabetes.
- It did not show that time-restricted eating lowers HbA1c more than dietitian guidance.
- It did not compare time-restricted eating with no support.
- It did not test people with established type 2 diabetes as the main study population.
- It did not test very short eating windows, prolonged fasting or alternate-day fasting.
Fewer than one-third of participants had HbA1c in the prediabetes range at baseline, which may have limited how much their HbA1c could improve. Around 75% of participants were women, most were white, and socioeconomic status was not collected, so the findings may not apply equally to all communities.
What does this mean for people at risk of type 2 diabetes?
The most reasonable interpretation is that a consistent daytime eating window can be one optional structure for some adults. It may appeal to people who prefer a simple timing rule or who have limited access to a dietitian. But it should not be presented as a shortcut that makes food quality irrelevant.
For reducing type 2 diabetes risk, stronger long-term evidence supports a broader lifestyle approach: nutritious food choices, regular physical activity, adequate sleep, weight management where appropriate, and structured support that can be maintained. The US National Institute of Diabetes and Digestive and Kidney Diseases notes that modest weight loss, a reduced-calorie eating plan and regular activity can help prevent or delay type 2 diabetes in people at high risk.
If you want to try an eating window
Discuss it with a qualified healthcare professional if you take glucose-lowering medication or have another health condition. If it is considered suitable, focus on a plan that is realistic rather than extreme:
- Choose a window that fits work, sleep, family meals and cultural routines.
- Avoid compensating with very large meals at the end of the fasting period.
- Build meals around vegetables, fibre-rich carbohydrates, protein and healthy fats.
- Keep hydrated and pay attention to dizziness, weakness, headaches or low-glucose symptoms.
- Review progress using meaningful measures, not only whether you kept to the clock.
The bottom line
In this randomised trial, a nine-hour daily eating window performed no worse than individualised dietitian guidance for HbA1c at four months, but that conclusion could not be confirmed at 12 months. Neither approach produced a clinically meaningful change in HbA1c, although both were associated with modest weight loss.
Time-restricted eating may be a practical short-term choice for some people, not a universal answer. A sustainable eating pattern, good food quality and support that fits the individual still matter.
Sources
- Parr EB, Charrouf R, Hutchison AT, et al. Time-restricted eating versus dietetic guidance on glycaemic outcomes in adults at risk of type 2 diabetes: a non-inferiority randomised clinical trial. Diabetologia. 2026;69(9):2458-2471. doi:10.1007/s00125-026-06762-x.
- National Institute of Diabetes and Digestive and Kidney Diseases. Preventing Type 2 Diabetes.
- Diabetes UK. Intermittent fasting diets for type 2 diabetes remission.
This article is for general education and does not replace individual medical advice. Do not change diabetes medication or begin a fasting plan without discussing it with your healthcare team.