Researchers at a large U.S. university conducted a review of water fasting and found that short-term fasting can lead to weight loss and improvements in several metabolic markers, including blood pressure and cholesterol levels. Yet these gains tended to vanish once normal eating resumed. The work, summarized from studies in the Nutrition Reviews domain, cautions readers that sustained results are unlikely without ongoing lifestyle changes.
The analysis drew on eight water fasting studies. In this approach, participants limit intake to small amounts of liquids such as juice or broth while avoiding solid foods. The researchers observed meaningful weight reductions over short periods. For example, weight loss tended to be about 4% to 6% after a five-day fast, climbed to roughly 2% to 10% between days seven and ten, and reached about 7% to 10% by days 15 to 20. These shifts show the potential for rapid early loss, but they also highlight the volatility of outcomes across different individuals and protocols.
Three of the included studies also tracked whether participants kept the weight off after the fast ended. In one trial, the entire weight loss from the five-day fast was regained within three months. In the other two studies, some of the weight returned, but participants who maintained a calorie deficit after fasting tended to fare better in keeping extra pounds at bay. This pattern suggests that the sustainability of any fasting-induced change hinges on post-fast dietary choices and ongoing energy balance.
However, the improvements seen during fasting—lower blood pressure, triglycerides, and blood sugar—were not consistently durable after people resumed their usual meals. In several cases, these markers rebounded quickly, erasing the early health benefits. Additionally, the studies reported that around three-quarters of the weight lost during fasting came from lean body mass rather than fat, underscoring a potential downside of short, aggressive fasts when muscle mass is a priority for health or physical performance.
Common adverse effects linked to water fasting included headaches, sleep disruptions, and persistent hunger. No severe complications such as metabolic acidosis or death were documented within these studies, but the researchers emphasized that fasting should not exceed five days without medical supervision. This boundary helps reduce risk and ensures monitoring for any signs of dehydration, electrolyte imbalance, or other complications that could arise during extended periods without solid food.
As a practical takeaway, the researchers noted that more conservative strategies—such as intermittent fasting schedules or calorie-controlled plans—may offer safer, more reliable paths to weight loss and metabolic health for many individuals. Intermittent approaches, which cycle periods of eating with periods of reduced caloric intake, can provide a balance between appetite control, energy levels, and long-term adherence. In addition, careful nutrition during non-fasting days helps preserve muscle and supports sustainable health gains over time.
Overall, while water fasting can produce rapid short-term weight loss and some favorable shifts in metabolic markers, these effects are typically short-lived without ongoing dietary and physical activity adjustments. The evidence suggests that safer alternatives focused on consistency, balanced nutrition, and gradual progress tend to deliver more durable results for adults seeking weight management and improved health markers.