Intermittent fasting is a dietary approach characterized by restricting caloric intake over various intervals of time.1,2 Emerging evidence seems to suggest that intermittent fasting can have beneficial effects on metabolic health by improving weight, glycemic control, and insulin resistance especially among those who are overweight or obese.3
Does Intermittent Fasting Improve Metabolic Health?
After an extended period of fasting (>8-12 hours), the body begins using fatty acids to produce ketone bodies as an alternative source of energy.2 Scientists hypothesize that this activates various cellular pathways that decrease metabolic and oxidative stress, lower inflammation, and improve glucose regulation, ultimately leading to weight loss and improved cardiometabolic health.2,4
Intermittent Fasting & Weight – An umbrella review of 11 meta-analyses of 130 randomized controlled trials (RCTs) showed that intermittent fasting is an effective weight loss approach for individuals who are overweight or obese.3 The review found that the modified alternate-day fasting and the 5:2 dietary approach were the only types of intermittent fasting shown to be associated with a >5% weight loss in overweight or obese adults. Another meta-analysis of 11 RCTs comparing intermittent fasting to continuous energy restriction reported similar weight loss benefits with intermittent fasting.5 When compared to continuous energy restriction, more weight loss was experienced with intermittent fasting, and the average weight loss in most studies was greater than 5% with intermittent fasting.
Intermittent Fasting & Insulin Resistance – The aforementioned umbrella review also reported that intermittent fasting had significant beneficial associations with numerous metabolic outcomes such as fasting plasma glucose, fasting insulin, and insulin resistance.3 Likewise, the above meta-analysis of 11 RCTs demonstrated that intermittent fasting improved insulin sensitivity significantly more than continuous energy restriction among overweight or obese individuals.5 Another meta-analysis of nine RCTs found that when compared to usual eating or other forms of time-restricted feeding, early time-restricted feeding significantly improved fasting glucose and insulin resistance measured by the homeostatic model assessment for insulin resistance, but not insulin.6
Intermittent Fasting & Heart Health – The umbrella review of 11 meta-analyses also found that intermittent fasting had significant beneficial associations with various cardiometabolic outcomes such as low-density lipoprotein (LDL) and total cholesterol, triglycerides, and blood pressure.3 One meta-analysis comparing the effects of alternate-day fasting to maintaining current lifestyle found that alternate-day fasting was associated with statistically significant reductions in both systolic and diastolic blood pressures, total cholesterol, triglycerides, and LDL-cholesterol.7 However, another meta-analysis comparing various types of intermittent fasting to continuous energy restriction did not find significant improvements in cardiometabolic measures.5 The discrepancy may be explained by the fact that the latter meta-analysis compared intermittent fasting to continuous energy restriction rather than to maintaining regular lifestyle.
How Can I Get Started on Intermittent Fasting?
Emerging evidence suggests that intermittent fasting may lead to improvements in overall metabolic health, but each individual should weigh the potential pros and cons before starting intermittent fasting. Individuals with diabetes or other medical conditions should consult with their health care team prior to fasting.2 Certain populations (eg, pregnant/lactating women, young children, older adults, individuals with immunosuppression, etc.) should be discouraged from intermittent fasting.
When you and your health care team are ready for you to start intermittent fasting, there are numerous types to choose from.1,2 Here are a few examples of some popular schedules you can follow:
- Time-Restricted Feeding: Eat during a 6- or 8-hour window and fast during the remaining 18- or 16-hour window daily
- Alternate-Day Fasting: Alternate between an eating and a fasting day; modified versions allow limited caloric intake (eg, 500-kcal meal) on a fasting day
- “5:2 Diet”: Eat for 5 days and fast for the following 2 days; eat a 500-kcal meal on a fasting day
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