A new trial investigating the health and weight loss effects of alternate-day fasting (ADF) in healthy adults has found the extreme dietary strategy provokes several beneficial health effects while causing significant weight loss. The research suggests the diet is at least as effect as general caloric restriction, and potentially easier for individuals to tolerate.
“Strict ADF is one of the most extreme diet interventions, and it has not been sufficiently investigated within randomized controlled trials,” says Frank Madeo, one of the researchers working on the study from the University of Graz in Austria. “In this study, we aimed to explore a broad range of parameters, from physiological to molecular measures. If ADF and other dietary interventions differ in their physiological and molecular effects, complex studies are needed in humans that compare different diets.”
The ADF model examined in this study required subjects to eat only on every other day, leading to 36-hour periods of fasting followed by 12-hour periods of unregulated eating. The strategy has often been referred to as the “fast and feast” diet, as individuals are allowed to eat whatever they want during the feasting phase in a given 48-hour period.
The new research recruited 60 healthy, non-obese adults. All the subjects were randomly divided into ADF or control groups. The control group could eat whatever they wanted for four weeks, while the ADF group could eat whatever they wanted but only during the 12-hour feast phase after 36 hours of fasting. The primary goal of the four-week study was to closely examine the biological effects of such an extreme eating strategy.
“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 Harald Sourij, another researcher working on the project. “Overall, they reached a mean calorie restriction of about 35 percent and lost an average of 3.5 kg (7.7 lb) during four weeks of ADF.”
Alongside lower overall caloric intakes and weight loss, a number of other biomarkers pointing to beneficial health effects were identified in the ADF cohort. Longevity biomarkers such as lowered levels of triiodothyronine and sICAM-1 were identified, as well as reductions in cholesterol levels. These observations are relevant since both the ADF and control subjects were non-obese and healthy at the beginning of the study, it is hypothesized that this form of fasting can confer beneficial effects on individuals regardless of their baseline health.
A second arm to the study looked at the effects of ADF across a longer period of time, examining 30 subjects following the eating strategy for six months. There has been some debate over whether long-term dietary interventions can result in negative health effects, and some research has suggested extreme caloric restriction for six to 12 months can result in declines in bone mineral density and white blood cell counts.
Interestingly, the six-month arm of the study revealed none of these negative effects in the ADF cohort, leading the researchers to hypothesize this eating strategy may be more sustainable and beneficial over the long term compared to caloric restriction. But before you go jumping into a long-term fasting regime, the researchers do note some caveats.
“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 Madeo. “However, further research is needed before it can be applied in daily practice. Additionally, we advise people not to fast if they have a viral infection, because the immune system probably requires immediate energy to fight viruses. Hence, it is important to consult a doctor before any harsh dietary regime is undertaken.”
Madeo’s point regarding the effect of fasting on the immune system is particularly important in light of several recent rodent studies finding fasting had detrimental effects on the animals’ immune system, exacerbating metabolic dysfunction and promoting allergic responses. Another divisive animal study revealed last year that alternate day fasting could damage the pancreas and increase risk for type 2 diabetes.
So, while this new research is certainly a promising tick in the column promoting ADF-style eating patterns, there are still lots of unanswered questions for scientists to resolve before we conclusively can say fasting strategies are beneficial or even wholly safe. Thomas Pieber, an endocrinologist working on the study from the Medical University of Graz, says at the very least this new research suggests ADF may be a better short-term weight loss option for some people who struggle with the continuous restrictions involved in calorie-controlled dieting.
“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 one day,” says Pieber.