A tough diet, but it has a place

One of the “most extreme” of diet interventions appears to be both safe and effective, Austrian researchers say.

Their randomised controlled trial of alternate-day fasting (ADF) – in which healthy, non-obese people switched between 36 hours of zero-calorie intake and 12 hours of unrestricted eating – proved beneficial without impairing immune function or bone health.

As such, they suggest in a paper in the journal Cell Metabolism, it is a simple alternative to calorie restriction that provokes similar improvements on cardiovascular parameters and body composition. 

They stress, however, that it is not recommended as a general nutrition scheme for everybody – at least not yet. 

“We feel that it is a good regime for some months for obese people to cut weight, or it might even be a useful clinical intervention in diseases driven by inflammation,” says Frank Madeo, from the University of Graz. 

“However, further research is needed before it can be applied in daily practice.” 

Madeo says the study was the largest of its kind, designed to explore a broad range of parameters, from physiological to molecular measures.

He and colleagues allocated 60 participants to either an ADF group or a control group and monitored them over four weeks in the home and during periodic visits to a research facility. 

They also studied 30 people who had already practised more than six months of strict ADF and compared them to normal, healthy controls who had no fasting experience. For this ADF cohort, the main focus was to examine the long-term safety of the intervention.

“We found that on average during the 12 hours when they could eat normally, the participants in the ADF group compensated for some of the calories lost from the fasting, but not all,” says co-author Harald Sourij, from the Medical University of Graz. 

“Overall, they reached a mean calorie restriction of about 35% and lost an average of 3.5 kilograms during four weeks of ADF.”

“The elegant thing about strict ADF,” adds colleague Thomas Pieber, “is that it doesn’t require participants to count their meals and calories: they just don’t eat anything for one day.”

The researchers found several biological effects in the ADF group, including less belly fat, lower cholesterol, reduced levels of a marker linked to age-associated disease and inflammation, and other changes that have been linked to health and longevity.

One notable finding was that even after six months of ADF, the participants’ immune function appeared to be stable. Previous studies have shown that calorie-restrictive diets can result in malnutrition and a decrease in immune function.

“The reason might be due to evolutionary biology,” Madeo suggest. “Our physiology is familiar with periods of starvation followed by food excesses. 

“It might also be that continuous low-calorie intake hinders the induction of the age-protective autophagy program, which is switched on during fasting breaks.”

Related reading: Fasting lowers risk of age-related diseases