Fasting may have benefits for healthy people, new research suggests, although there are some caveats.
People often alter their diets — in order to lose weight, improve their cardiovascular health, and become healthier overall. There are many different ways to do so.
A recent study looked into alternate-day fasting (ADF) to see whether it is a viable alternative to other methods, such as intermittent fasting or caloric restriction.
The researchers found that a number of health benefits accompanied weight loss in participants who practiced ADF.
The results of their investigation appear in the journal Cell Metabolism.
ADF as an option
Researchers — many from the Medical University of Graz, in Austria — conducted a randomized controlled trial. They enrolled 60 participants in a 4-week trial and randomly assigned them to either an ADF group or a control group.
The control group participants could eat whatever they wanted whenever they wanted, and the ADF group alternated between a 36-hour, no-calorie fast and 12 hours of unlimited eating.
The researchers followed the ADF group with continuous glucose monitoring to ensure that they did not consume any calories during their fasting periods. The participants also kept diaries during their fasting days.
The team also worked with 30 people who had been on a strict ADF diet for the last 6 months or more, in order to asses the long term safety of the practice.
All of the participants had a healthy weight and good overall health.
Unexpected biological benefits
While those in the ADF group often compensated for some of their lost calories when they were allowed to eat, they did not compensate for them all. Overall, they experienced a mean caloric restriction of around 35% and lost an average of 7.7 pounds during the 4-week trial.
There were health benefits, as well. The participants in the ADF group had reduced levels of soluble intercellular adhesion molecule-1, a marker linked to inflammation and age-related disease.
They also had lower levels of the thyroid hormone triiodothyronine, without experiencing any problems with thyroid function. Previous research has associated lowered levels of this hormone with longevity.
Additionally, the ADF group had lower levels of cholesterol and reduced trunk, or belly, fat. They also had some restriction in amino acids, which research in rodents suggests may extend the lifespan.
Furthermore, the ADF group experienced an upregulation in ketone bodies, which researchers consider a health benefit, on both the fasting days and non-fasting days.
"Why, exactly, calorie restriction and fasting induce so many beneficial effects is not fully clear, yet," says Dr. Thomas Pieber, the Director of Endocrinology at the Medical University of Graz.
"The elegant thing about strict ADF is that it doesn't require participants to count their meals and calories: They just don't eat anything for 1 day."
Dr. Thomas Pieber
Prior studies have indicated that long term adherents of ADF could experience malnutrition and an impaired immune function. However, the researchers found no immune function problems in the present cohort who had practiced ADF for 6 months or more.
Future applications of ADF
While this study uncovered benefits of ADF, the authors do not recommend it as something everybody should practice. They caution of other caveats, as well.
"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 Prof. Frank Madeo, of the Institute of Molecular Biosciences at the University of Graz.
"However, further research is needed before it can be applied in daily practice."
The researchers also warn against fasting while experiencing a viral infection. They recommend consulting a physician before undertaking a new diet, particularly one that is as strict as ADF.