A newly published review article in The New England Journal Of Medicine has examined an array of current research on intermittent fasting, from animal studies to human clinical trials. The review clarifies different fasting regimes while also outlining a variety of health benefits the eating strategies can confer in humans.

Although intermittent fasting is currently a bit of a dietary trend, scientists have been investigating the effects of irregular caloric intakes in animals for several decades. Mark Mattson, an author on the new review and neuroscientist from Johns Hopkins University, explains one of the key processes triggered by intermittent fasting is called metabolic switching.

When an organism is starved of food it shifts how it produces energy, switching from readily accessible glucose in consumed food to a process called ketogenesis, whereby molecules called ketone bodies are produced though the conversion of fat stores. This energy production shift is dubbed metabolic switching, and Mattson’s review article suggests frequent shifts between the two metabolic states can result in an array of health benefits.

“Periodic flipping of the metabolic switch not only provides the ketones that are necessary to fuel cells during the fasting period but also elicits highly orchestrated systemic and cellular responses that carry over into the fed state to bolster mental and physical performance, as well as disease resistance,” write Mattson and co-author Rafael de Cabo.

John Hopkins University

The review breaks intermittent fasting into two general categories: alternate day fasting and time-restricted feeding. Alternate day fasting involves significant caloric restriction on one day or more each week – the modern 5:2 eating regime is a variation on alternate day fasting. Time restricted feeding, on the other hand, involves fasting for a period within the 24-hour cycle – this category would include the common 16:8 regime, which restricts all caloric intake to a period of no more than eight hours in a given 24-hour period.

What is the ideal intermittent fasting regime? That is still unclear. The article notes that ketone bodies have been found to begin rising in humans within eight to 12 hours of fasting, suggesting time-restricted feeding methods could be effective in harnessing the health benefits of metabolic switching. So 16 hours of fasting every day may be an easy way to implement a form of intermittent fasting. A recent study has even suggested dropping that fasting period down to 14 hours a day confers health benefits.

Mattson and de Cabo suggest in the review article that physicians incorporate intermittent fasting dietary strategies into treatment regimes for patients at risk of everything from dementia to cardiovascular disease. And, understanding the challenges patients have in maintaining these kinds of dietary interventions, the article describes gradually increasing fasting periods over a number of months as the most effective way to deploy such dietary changes.

So, for example, the article suggests for the first month’s intervention a patient only drop to either 10-hour feeding a day for five days a week, or 1,000 calories in total one day per week. Gradually over several months this intervention would transition, so by month four the patient reaches either a complete time restricted feeding regime eating only six hours a day every day, or a 5:2 regime of no more than 500 calories for two days every week.

“Patients should be advised that feeling hungry and irritable is common initially and usually passes after two weeks to a month as the body and brain become accustomed to the new habit,” Mattson explains.

The review article does stress there is much still to be explored in terms of the long-term effects of intermittent fasting and in understanding the biological mechanisms that may be at play. However, it does seem increasingly clear that our current culture of always available food, and near constant snacking, is not necessarily the best way to feed. And, while there is still more research needed before broad conclusions and recommendations can be made, Mattson is confident we are close to a point where intermittent fasting regimes could be incorporated into popular health advice.

“We are at a transition point where we could soon consider adding information about intermittent fasting to medical school curricula alongside standard advice about healthy diets and exercise,” Mattson concludes.

The new review article was published in The New England Journal of Medicine.

Source: Johns Hopkins Medicine