Fasting and starvation — a way to good health or a dangerous trend?

Aim of the study: To assess the effects of intermittent fasting diets, diets with continuous energy restriction, and unrestricted (ad libitum) diets on intermediate cardiometabolic outcomes in randomized clinical trials.

Results: The review identified 99 randomized clinical trials involving 6,582 adults with varying health conditions (720 healthy participants and 5,862 with existing health conditions). All intermittent fasting and continuous energy restriction diet strategies reduced body weight compared with an ad libitum diet. Compared with continuous energy restriction, alternate-day fasting was the only intermittent fasting strategy that showed a benefit in body weight reduction (mean difference: -1.29 kg (95% CI -1.99 to -0.59), moderate certainty of evidence). In addition, alternate-day fasting led to a small reduction in body weight compared with both time-restricted eating and whole-day fasting (mean differences: -1.69 kg (-2.49 to -0.88) and -1.05 kg (-1.90 to -0.19), respectively; both with moderate certainty of evidence).

Aim of the study: To examine the evidence for intermittent fasting (IF), an alternative to calorie-restricted diets, as a treatment for obesity, an important health concern in Canada where few effective office-based treatment strategies are available.

Results: Intermittent fasting shows promise for treating obesity. So far, studies have been small and short. Longer-term research is needed to understand the sustainable role IF can play in weight loss.

Aim of the study: The objective of this meta-analysis was to compare the effectiveness of different intermittent fasting (IF) regimens for weight loss in the general population and compare them with traditional caloric energy restriction (CER).

Results: The exploratory random-effects network analysis of 24 RCTs (n = 1,768) ranked ADF as the most effective, followed by CER and TRE. The meta-analysis showed that IF regimens resulted in weight loss similar to CER (mean difference 0.26 kg, 95% CI: -0.31 to 0.84; p = 0.37). Compliance was generally high (>80%) in trials lasting less than 3 months. This meta-analysis concludes that IF is comparable to CER and is a promising alternative for weight loss. Of the three regimens, ADF was the most effective for weight loss, followed by CER and TRE. Further well-powered RCTs with longer interventions are needed to draw firm conclusions.

Aim of the study: Recent observations have shown that extending the daily eating period may contribute to the onset of chronic diseases. Time-restricted eating (TRE) is a diet that specifically limits this daily eating window. It may be a dietary approach that improves health markers. The aim of this study was to review how time-restricted eating affects human health.

Results: Of the 494 articles collected, 23 were included in the analysis. Overall adherence to TRE was 80%, with an unintended 20% reduction in calorie intake. TRE led to an average weight loss of 3% and a loss of fat mass. This fat loss was also seen without any calorie restriction. Interestingly, TRE produced beneficial metabolic effects independently of weight loss, suggesting an intrinsic effect based on aligning eating patterns with the circadian clock. TRE is a simple, well-tolerated diet that produces many beneficial health effects based on the principles of chrononutrition. However, more rigorous studies are needed to confirm these effects, understand their mechanisms, and assess their relevance to human health.

Aim of the study: Intermittent fasting is a broad term for a range of programs that change when people eat by using short-term fasts to improve body composition and overall health. This review examines studies of intermittent fasting programs to determine whether they improve body composition and clinical health markers associated with disease.

Results: Alternate-day fasting trials lasting 3 to 12 weeks appear to effectively reduce body weight (≈3%-7%), body fat (≈3-5.5 kg), total cholesterol (≈10%-21%), and triglycerides (≈14%-42%) in people who are normal-weight, overweight, or obese. Whole-day fasting trials lasting 12 to 24 weeks also reduce body weight (≈3%-9%) and body fat, and improve blood lipids (≈5%-20% reduction in total cholesterol and ≈17%-50% reduction in triglycerides). Research on time-restricted feeding is limited, so no clear conclusions can be drawn at present. Future studies should examine the long-term effects of intermittent fasting and the possible combined effects of intermittent fasting and exercise.