Intermittent Fasting and Metabolic Health

Abstract

Given the ongoing strain that the obesity epidemic has placed on public health outcomes, new and effective approaches to weight control are needed. One approach to improving weight and metabolic outcomes is intermittent fasting, which consists of multiple different timing schedules for temporary food avoidance, including alternate-day fasting, other similar full-day fasting patterns, and time-restricted feeding (where the day's food is consumed over a 6-h period, allowing for 18 h of fasting). These feeding schedules have favorable metabolic effects by intermittently inducing the metabolism of fatty acids to ketones. The regimens overall lead to a decrease in weight and have been linked to improvements in dyslipidemia and blood pressure. While more research is needed on longer-term outcomes and this approach should be avoided in particular health conditions, intermittent fasting should be considered as an option for individuals who have a pattern of unhealthy weight gain using standard eating patterns.

Keywords: intermittent fasting; ketones; metabolic syndrome; obesity; type 2 diabetes.

Figure 1

Glucose and ketone levels over the course of three meal eating patterns. (A) The standard meal pattern of three meals daily does not result in an appreciable rise in ketone levels. (B) The 5:2 or alternate-day fasting pattern allows ketones to rise during prolonged fasting, followed by suppressed ketones during the typical feeding day. (C) When meals are compressed to a 6-h period each day, ketones are able to rise during the time between feeding periods. From Anton et al., Obesity 2018: 26(2): 254–268; used by permission [16].

Figure 2

Glucose infusion rate (GIR) and glucose level during hyperinsulinemic clamp before and after 20 days of intermittent fasting. Participants were eight healthy males who had a hyperinsulinemic clamp performed before and after 20 days of alternating-day fasting for 20 h. Left axis (bars) shows the glucose infusion rate (GIR) necessary to maintain euglycemia during both clamps. Right axis (dots) shows the plasma glucose concentrations. Black bars and dots represent data from the clamp before the fasting intervention; gray bars and dots are data from after the fasting intervention. Following fasting, the insulin-mediated glucose update increased from 6.3 ± 0.6 to 7.3 ± 0.3 mg/kg/min. * p < 0.05 for comparing after fasting values to before fasting values. From Halberg et al. J Appl Phys 2005: 99(6):2128–2136; used by permission [35].