Can Fasting and Early Eating Help Prevent Type 2 Diabetes? What a Major New Study Found
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- Meta description (155 characters): A major randomized trial tested intermittent fasting plus early eating against calorie restriction for diabetes risk. Here’s what it found.
A note on scope: This article covers a study in adults at increased risk of developing type 2 diabetes, not people already diagnosed with it. The research looked at whether a specific fasting approach could help prevent diabetes and improve glucose metabolism, not whether it can reverse existing diabetes. If you have diabetes and are considering fasting, talk to your doctor first, since fasting can affect blood sugar and medication needs in ways that require medical supervision.
Intermittent fasting and time-restricted eating have both grown in popularity as approaches to metabolic health. A large, well-designed randomized controlled trial from the University of Adelaide, published in Nature Medicine in 2023, set out to test a specific combination of the two, “intermittent fasting plus early time-restricted eating”, against standard calorie restriction in adults at increased risk of type 2 diabetes. The results offer a genuinely useful look at both the benefits and the real-world challenges of this approach.
How the Study Was Designed
The trial, known as the DIRECT study (Daily vs. Intermittent Restriction of Energy to reduce Diabetes risk), enrolled 209 adults with an average age of around 58 who were at increased risk of type 2 diabetes but not yet diagnosed. To qualify, participants scored at least 12 on the Australian Type 2 Diabetes Risk Assessment Tool and had maintained a stable weight for six months beforehand.
Participants were randomly assigned to one of three groups:
1. Intermittent fasting plus early time-restricted eating (iTRE): Ate about 30% of their daily energy needs between 8:00 a.m. and noon, followed by a 20-hour fast, on three non-consecutive days a week. They ate normally (ad libitum) on the other days.
2. Calorie restriction (CR): Consumed about 70% of their daily energy needs every day, with no specific meal timing, guided by provided meal plans.
3. Standard care: Received a general weight-loss information booklet, without personalized counseling.
The study ran for 18 months, with frequent clinic visits (every two weeks for the first six months, then monthly) and individual nutritional counseling for the two intervention groups during the first six months.
What the Study Found
At six months, the intermittent fasting group showed meaningfully better post-meal (postprandial) glucose control than the calorie restriction group, measured by a lab test called postprandial glucose area under the curve. This matters because how the body handles blood sugar after a meal is considered a better predictor of future diabetes risk than a fasting glucose test alone.
The fasting group also showed:
- Greater improvements in postprandial insulin levels, suggesting better insulin sensitivity
- Greater reductions in BMI, body fat, and waist circumference than the calorie restriction group
Both the fasting and calorie restriction groups improved more than the standard-care group on A1c (a marker of average blood sugar over time), blood pressure, and triglycerides.
By 18 months, the picture changed. The gap between the fasting and calorie-restriction groups had narrowed substantially, and adherence had dropped off considerably in the fasting group. Only about 42% of participants in the fasting group were still following the plan at 18 months, compared with nearly 80% in the calorie-restriction group. Around half of the fasting group had already reduced their fasting days from three to two per week after the six-month mark, when the study allowed adjustments.
Participants in the fasting group also reported more side effects, including fatigue, headaches, and constipation, than the calorie-restriction group, which may help explain the drop-off in adherence.
Why Compliance Was a Challenge
Commenting on the findings, intermittent fasting researcher Dr. Krista Varady noted that combining early eating with multi-day fasting can be difficult to sustain socially, since skipping dinner several days a week can interfere with eating alongside family or friends and lead to feelings of deprivation over time.
Varady has suggested that more flexible approaches, such as a later eating window (for example, noon to 8:00 p.m.), might be easier for people to maintain while still supporting weight management and blood sugar control. She has also pointed out that time-restricted eating in general tends to naturally reduce calorie intake by roughly 300-500 calories a day, which is part of why it can be effective, even without a strict counting approach.
What This Means If You’re Considering Fasting for Metabolic Health
The short-term benefits were real. Over six months, intermittent fasting plus early eating outperformed calorie restriction alone on several important markers of diabetes risk, particularly post-meal glucose and insulin response.
The long-term sustainability is a genuine concern. The approach tested in this study, three non-consecutive 20-hour fasting days a week with a tight morning eating window, was difficult for many participants to maintain for 18 months. Calorie restriction, while producing less dramatic short-term results, was followed more consistently over time.
A less restrictive approach might work better for more people. Based on this and related research, a later or more flexible eating window, and less frequent fasting, may offer a better balance between effectiveness and real-world sustainability, though more research is needed to confirm this directly.
This is about prevention, not treatment. This study looked at people at risk of developing type 2 diabetes, not people who already have it. If you have diabetes, especially if you take insulin or other glucose-lowering medication, fasting needs to be approached under medical supervision, since it can increase the risk of dangerously low blood sugar (hypoglycemia).
Frequently Asked Questions
Can intermittent fasting reverse type 2 diabetes?
This study didn’t test that question. It looked at diabetes prevention in people at risk, not reversal in people already diagnosed. Some separate research has explored fasting and very-low-calorie diets in people with existing type 2 diabetes with promising but more limited results, and this remains an active area of research. Anyone with diabetes considering fasting should do so under medical guidance.
Is intermittent fasting better than calorie restriction for diabetes risk?
In this study, intermittent fasting plus early eating showed greater short-term benefits for post-meal glucose control, but the advantage narrowed by 18 months, partly because fewer people stuck with the more restrictive plan. Calorie restriction was easier to sustain long-term for most participants.
What eating window did the study actually test?
Participants ate 30% of their daily calories between 8:00 a.m. and noon, then fasted for 20 hours, on three non-consecutive days a week, eating normally on the other days.
Is a later eating window just as effective?
This specific study didn’t test a later window directly, but researchers in the field, including Dr. Varady, have suggested later windows may be easier to maintain. More direct research comparing timing approaches is still needed.
Should I try this if I don’t have diabetes but want to reduce my risk?
This approach showed real benefits for metabolic risk markers, but it’s worth being honest about adherence difficulty based on this trial. Starting with a schedule you can realistically sustain, and discussing significant dietary changes with a doctor or dietitian, especially if you have other health conditions, is a sensible approach.
The Bottom Line
A major randomized trial found that combining intermittent fasting with early time-restricted eating produced meaningfully better short-term improvements in glucose control than standard calorie restriction, in adults at increased risk of type 2 diabetes. But the approach proved difficult to sustain, with adherence dropping sharply by 18 months. The honest takeaway is that this specific fasting protocol works, but may not be realistic for everyone long-term, and researchers are now exploring more flexible versions that might be easier to stick with.
This article summarizes findings from a specific clinical trial for informational purposes and is not medical advice. If you have diabetes or are considering a significant change to your eating pattern, consult a doctor or registered dietitian first, especially if you take any glucose-lowering medication.
Related reading: Smoking and Diabetes: A Bad Combination for Your Health
Sources:
- Teong, X.T., et al.: Intermittent fasting plus early time-restricted eating versus calorie restriction and standard care in adults at risk of type 2 diabetes: a randomized controlled trial, Nature Medicine, 2023
- Medical News Today: Intermittent Fasting and Type 2 Diabetes
- University of Adelaide press release on the DIRECT study findings.https://www.nestlehealthconnect.com.au/sites/default/files/2023-10/NESBD3321%20Optifast%20Study%20Summary_FA_EMAIL.pdf
Note: Drafted with AI, edited by our team.
Disclaimer: This article is for informational purposes only.
