Does Intermittent Fasting Really Work?

A concept that has been around for many years, but that is now getting significant attention in the health and fitness world, is Intermittent Fasting (“IF”). If you haven’t heard about it, IF is the practice of cycling between periods of eating and fasting. The theory is that IF leads to the consumption of fewer calories, as well as the lowering of insulin levels, which reduces cellular absorption of glucose and increases the burning of fat for energy. The lowering of caloric intake and insulin levels has a variety of potential health benefits, including weight loss and the prevention of various diseases (e.g., heart disease, diabetes, Alzheimer’s, cancer). To give you a sense of how IF is employed, one of the most common IF structures is restricting eating to eight hours daily (e.g., between 10am and 6pm).

While there are big potential benefit claims for IF, a key question is whether science backs up the claims. A significant amount of animal studies have been completed, and while the results are generally positive, there remain caveats:

·       An animal study completed in 2018 concluded that IF has the ability to reduce caloric intake and weight. However, the study also indicated that IF may actually increase the risk of Type 2 diabetes given an increase in abdominal fat and indications on improper bodily use of insulin.

·       The results of an animal study published in 2013 indicated that IF was associated with learning and memory improvements relative to a control group.

·       Another animal study published in 2015 found that IF triggered a response in the brain that reduced inflammation associated with neurogenerative disorders (e.g., Alzheimer's disease, Parkinson's disease, stroke).

So, animal studies have generally been positive, though much less human trial data is available. What human trial data is available appears to be mixed. For example, researchers from the University of Illinois-Chicago, Indiana University, and the Salk Institute for Biological Studies published a report in 2018 of their findings from a twenty-three patient study that restricted eating (without restricting caloric intake) to an eight hour daily period for twelve weeks produced a modest reduction in body weight (~2.6%) relative to a control group. There was little change in other health measures, including fat mass, lean mass, visceral fat mass, diastolic blood pressure, LDL cholesterol, HDL cholesterol, and triglycerides relative to the control group. However, the patients’ Systolic blood pressure decreased.

In summary, IF appears to have the potential to contribute to weight loss, though it’s not clear that it offers a significant benefit relative to alternative forms of caloric restriction (i.e., dieting). As for other physiological benefits, the limited existing human trial data does not show potential benefits, though more human trials are needed to confirm.

So, if you’re looking to lose some weight, IF appears to be a legitimate option, though you shouldn’t expect a major transformation. If you’re hoping to use IF as a means to achieve broader physiological and neurological benefits, the jury is still out.