| Increased weight loss compared to isocaloric diets (lower insulin and ketogenesis would increase energy expenditure). |
There is no evidence that IF leads to higher energy expenditure: isocaloric studies performed in metabolic chambers show similar weight loss in diets with different proportions of macronutrients (27); RCTs show the same weight loss for daily caloric restriction and intermittent fasting, while maintaining similar weekly caloric intake (33,36,37) and no difference in adaptive thermogenesis (42). |
| Reduced hunger compared to traditional daily caloric restriction. |
Conflicting results in humans (4). Studies with a proper control group did not show an overall difference in hunger ratings, though individual preferences exist (30,32,38). |
| Improvement in insulin resistance, independent of weight loss. |
Data derived from animal models (2,11,16). In humans, conflicting results, but many studies without a proper control group. Overall, there is no clear evidence of improvement in IR, independent of weight loss (4). However, a post hoc analysis suggests benefits in those who had previous insulin resistance (34). Timing of food intake could also have a role (6). |
| Improvement in glucose control in type 2 diabetes. |
RCTs show similar reductions in weight and HbA1c (36,65). However, there is evidence that increased meal frequency is associated with poorer glycemic control (66,67). |
| Anti-aging and anti-inflammatory effects. |
Many animal models demonstrate increased longevity and reduction in chronic diseases with caloric restriction and IF, but data in humans are lacking (1,11). Many benefits are alleged to be associated with ketogenesis, but it is unclear whether the level of ketone bodies achieved in popular IF patterns would be enough to elicit the same responses observed in rodents (11). Fasting-mimicking diets have been developed to promote these benefits and have shown a reduction in inflammatory and oxidative stress markers, but not clinical outcomes to date (72–74). |
| Popular negative claims |
Current status of evidence |
| IF would lead to overeating on feast days and could trigger eating disorders. |
IF does not lead to overeating or bingeing on feast days and does not trigger eating disorders (43). Nonetheless, patients with previous eating disorders were excluded from main trials, and IF is not recommended for this population. |
| IF could reduce lean mass. |
Conflicting results. Several studies suggest positive effects on lean mass, including one in trained men (48). However, a recent randomized trial with TRF observed a higher appendicular lean mass loss after the intervention (47). More data are needed. |
| IF is not sustainable and leads to higher attrition rates. |
Conflicting results, but IF has a slightly higher attrition rate in larger trials (4,33). One key trial has shown that with MADF, there was a trend of increasing calories on fasting days and decreasing on feasting days, resembling the overall daily calorie restriction pattern (33). |
| IF leads to side effects, such as nutrient deficiency and lethargy. |
Trials with different IF patterns show it is generally safe and well-tolerated, with no increase in overall side effects (4). |
