Study: 8-Hour Fast More Effective for Weight Loss, But Inconsistent in Lowering Blood Pressure

A new study published in the journal Nutrition & Diabetes reveals that intermittent fasting with an 8-hour eating window (16:8) leads to greater weight loss compared to a 12-hour window, but is not consistently followed by improvements in cardiometabolic health indicators such as blood pressure, blood sugar, and cholesterol. This finding serves as an important signal for individuals who use fasting as a primary strategy to lose weight and reduce the risk of heart disease.

The research analyzed data from five time-restricted eating (TRE) trials involving 124 participants. A total of 95 individuals underwent TRE with varying eating window durations—11 people for 8 hours, 59 for 10 hours, and 25 for 12 hours—while the remaining 29 formed the control group. Before the intervention, all participants typically ate for at least 14 hours per day. Over 3–6 months, they reported their intake via a mobile app with timestamped photos and text descriptions.

As a result, the TRE group on average shortened their eating window by about 4 hours and lost approximately 4.8 pounds. The 8-hour window group recorded about 3.7 pounds more weight loss than the 12-hour group, and significantly more than the control group. Nevertheless, unadjusted analyses found no significant difference between the 8-hour and 10-hour groups. When researchers observed the eating windows actually achieved, shorter windows were indeed associated with greater weight loss, but this association weakened after adjusting for age, sex, and body mass index.

Regarding cardiometabolic outcomes, researchers could not establish a consistent relationship between eating window duration and improvements in most measures, including fasting glucose, HDL cholesterol, LDL cholesterol, and triglycerides. The only significant difference was a greater reduction in systolic blood pressure in the 10-hour group compared to the 12-hour group. This finding underscores that the benefits of TRE may not be uniform across all health indicators.

“We are still in the early stages of understanding the potential health effects of time-restricted eating,” said Cheng-Han Chen, MD, an interventional cardiologist and medical director of the Structural Heart Program at MemorialCare Saddleback Medical Center, who was not involved in the study. He added that the small sample size, differences between trials, and short follow-up periods might explain the limited cardiometabolic findings.

Similarly, Mir Ali, MD, a bariatric surgeon and medical director of the MemorialCare Surgical Weight Loss Center at Orange Coast Medical Center, noted that the weight loss difference between the 8-hour and 12-hour groups was not entirely conclusive due to the moderate difference and small number of participants. “Time-restricted eating can be beneficial, but there’s considerable individual variability regarding effectiveness and optimal fasting duration,” Ali said. He also warned that conditions like diabetes could make TRE less feasible or even contraindicated.

The study's limitations also came under scrutiny. This analysis lacked participant calorie intake data, had a limited sample size, and a relatively short follow-up period. Furthermore, the five trials analyzed were not all randomized controlled trials, and participants were not directly randomized into different eating window groups. Chen and Ali recommend that individuals with type 1 diabetes, hypoglycemia, a history of eating disorders, as well as pregnant women or those planning pregnancy, consult with a healthcare professional before undertaking TRE.

For readers in Indonesia, these findings are relevant amidst the growing popularity of intermittent fasting as a weight loss method, including among office workers seeking a practical approach without calorie counting. However, the study results indicate that claims of comprehensive benefits—especially for blood pressure and lipid profiles—are not yet supported by strong evidence. The public is advised not to use TRE as a substitute for hypertension or dyslipidemia treatment, but rather as a complement to a healthy lifestyle, always in consultation with a doctor.

Moving forward, the big question is not just how long the ideal eating window should be, but who benefits most and whether cardiometabolic improvements require greater weight loss or a longer intervention duration. Studies with larger samples and longer monitoring periods will be key to answering these questions.