8-Hour Time-Restricted Eating and Liver Enzymes in Adults With Obesity: What the Research Shows

8-Hour Time-Restricted Eating and Liver Enzymes in Adults With Obesity: What the Research Shows

Medical disclaimer: This article summarises published research for informational purposes only. It is not medical advice and is not a substitute for guidance from a qualified health professional. Always consult your doctor before starting any fasting protocol, especially if you have an existing health condition or take medication.

Study at a Glance

What This Study Looked At

Researchers wanted to know whether a simple 8-hour daily eating window — with no calorie counting and no food restrictions beyond timing — could produce meaningful weight loss and metabolic improvements in adults with obesity, and whether this restrictive eating pattern was safe to sustain over 12 weeks. As part of a broader safety evaluation, the research team also tracked routine liver chemistry, including ALT and AST, in a population that did not have a prior diagnosis of fatty liver disease. This makes it a useful reference point alongside our coverage of time-restricted eating and fatty liver disease, which focuses on people already diagnosed with the condition.

Who Was Studied

Participant profile: Adults with obesity (BMI approximately 30–45), generally healthy, without diagnosed diabetes or fatty liver disease at baseline.

How the protocol worked in this study: Participants ate freely — no calorie targets, no macronutrient rules — but only within an 8-hour window from 10 a.m. to 6 p.m. Outside that window, only water and non-caloric beverages were permitted, for the full 12-week study period.

What the Researchers Found

Body weight and energy intake

• Weight loss occurred purely from the natural drop in intake that came from compressing the eating window — participants were never told to eat less.

Safety panel, including liver enzymes

• As part of a companion safety analysis, routine blood chemistry — including ALT and AST — was tracked alongside complete blood count, self-reported adverse events, and measures of disordered eating and body image.
• Liver enzymes showed no meaningful change from baseline to week 12, consistent with a population that did not have elevated liver enzymes to begin with.
• No significant adverse events, and no worsening of disordered eating patterns or body image, were reported over the study period.

What Did Not Change

• Complete blood count values remained stable throughout the study.
• Self-reported body image and disordered eating measures showed no worsening.
• Liver enzymes (ALT, AST) did not shift meaningfully, reinforcing that an 8-hour eating window did not stress liver function in this population.

What the Researchers Concluded

The authors concluded that an 8-hour time-restricted eating window is a feasible, low-burden strategy that produces modest but meaningful weight loss in adults with obesity through a natural reduction in energy intake, without evidence of adverse effects on routine safety markers, including liver enzymes, over 12 weeks.

What This Means If You Fast

• A basic 8-hour window can work without calorie counting. Participants ate freely within their window and still cut roughly 341 kcal/day on average — see our guide on 16:8 vs 18:6 fasting if you want to compare window lengths.
• Liver enzymes likely won't move much if they're already normal. This study's stable ALT/AST results suggest people without elevated liver enzymes at baseline shouldn't expect big changes there — the bigger wins tend to show up in weight and intake. For people who do have elevated liver enzymes or diagnosed fatty liver, see our coverage of fasting and fatty liver disease.
• Safety data supports starting simple. The absence of adverse changes in blood counts or disordered eating measures over 12 weeks is reassuring for people considering a straightforward 8-hour window as a starting point.
• Weight loss here was modest, not dramatic. A 2.6% reduction over 12 weeks is a realistic expectation for time-restricted eating alone, without added calorie restriction or exercise.
• This wasn't a fully randomized trial. The comparison data came from a historical/matched group rather than people randomized alongside the TRF participants, so treat the specific numbers as suggestive rather than definitive.

Study Limitations

• Small sample size (23 participants), limiting statistical power, especially for secondary safety outcomes like liver enzymes.
• Comparison group was historical/matched rather than concurrently randomized, which is a weaker design than a true RCT.
• Short duration (12 weeks) — longer-term effects on liver markers remain unclear.
• Energy intake was self-reported via food logs, introducing potential reporting bias.
• Participants did not have confirmed liver disease at baseline, so results may not generalize to people with existing NAFLD or elevated liver enzymes.
• This summary was written from model training knowledge due to network access restrictions (403 errors) on PubMed and publisher sites at generation time; readers should verify exact figures against the original publication.

Source

Gabel, K., Hoddy, K. K., Haggerty, N., Song, J., Kroeger, C. M., Trepanowski, J. F., Panda, S., & Varady, K. A. (2018). Effects of 8-hour time restricted feeding on body weight and metabolic disease risk factors in obese adults: A pilot study. Nutrition and Healthy Aging, 4(4), 345–353. PMID: 29951594

Frequently Asked Questions

Does 8-hour time-restricted eating change liver enzymes like ALT and AST?

In this trial, ALT and AST did not change meaningfully over 12 weeks, likely because participants did not have elevated liver enzymes at baseline. Bigger liver enzyme changes tend to appear in studies that specifically enroll people already diagnosed with fatty liver disease.

How much weight did participants lose with 8-hour time-restricted eating?

Participants lost approximately 2.6% of body weight over 12 weeks, driven by a natural reduction in daily energy intake of roughly 341 kcal, without deliberately counting calories.

Is this study as strong as a randomized controlled trial?

Not quite — the comparison data came from a historical or matched group rather than participants randomized at the same time, which is a weaker study design than a true RCT. The findings are best treated as an early, suggestive pilot result.

Did 8-hour time-restricted eating cause any safety concerns?

No. The safety analysis found no significant adverse events and no negative changes in blood counts, body image, or disordered eating measures over the 12-week study period.

Do you need to count calories for an 8-hour eating window to work?

No. Participants in this study ate freely within their 8-hour window and still reduced their daily intake by roughly 341 calories on average without any deliberate calorie tracking.

Related Research and Articles

• Can Intermittent Fasting Reverse Fatty Liver?
• Does Fasting Help Fatty Liver Disease?
• Alternate-Day Fasting and Fatty Liver: What a 2023 Study Found
• Time-Restricted Eating and Liver Steatosis: A 2023 Nutrients Study
• 16:8 vs 18:6 Intermittent Fasting: Which Should You Choose?
• How to Reverse Insulin Resistance

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