By: Raphael Gabiazon
Fasting is an eating pattern in which caloric intake is restricted to a time window of 8–12 hours or less per day (1). This method is especially utilized in intermittent fasting diets for weight loss that incorporates regular time periods allocated to fasting which commonly consists of a daily fast for 16 hours, a 24-hour fast on alternate days, or a fast 2 days per week on non-consecutive days (2, 3). A popular approach to this diet was first pioneered by Martin Berkhan called the “16/8” intermittent fasting style which involves 16 hours of fasting and an 8-hour window for eating one’s daily calories (4). While considered a fad diet by some – a type of diet that becomes popular for a short time and makes unreasonable claims for rapid weight loss and improving health – there is scientific evidence to support the supposed claims that intermittent fasting can produce. Specifically, intermittent fasting can help with weight loss, has anti-aging benefits, and improves cognitive performance. This article will examine the science-based evidence regarding these benefits.
Like most diets, intermittent fasting diets are designed to promote fat loss through caloric restriction which is a consistent pattern of reducing average daily caloric intake (5). It does this by primarily reducing one’s frequency of eating during the day with the intention that it will result in a caloric deficit. This caloric deficit is typically required in diets for weight loss and refers to consuming fewer calories than your body needs to maintain its current weight. A meta-analysis – a research process that statistically analyzes studies examining the same question (6) – found that intermittent fasting was beneficial for weight loss without affecting lean mass (muscle tissue) compared to normal eating patterns (7). Reductions in lean mass accounting for 8–10% of total weight loss tend to occur with diets (8). Maintaining lean mass is particularly important because this tissue is integral to metabolic processes for physical functioning (9). Its role in metabolism is a contributing factor to the expensive metabolic rate of muscle which is approximately 4.5 to 7.0 kcal/lb of lean mass per day (10). With regards to intermittent fasting, it may preserve lean mass which can mitigate the reductions in metabolism associated with muscle loss in diets (11), and therefore expend more calories to be in a caloric deficit. Support for this diet-induced weight loss with intermittent fasting has been shown in a systematic review – which summarizes academic literature pertaining to a topic under investigation (12) – reviewed 40 studies and found a typical loss of 7-11 pounds over 10 weeks (13). Contrary to this finding, a systematic review and meta-analysis of intermittent fasting compared to an alternative continuous caloric restriction diet found no differences in measures of body fat (14). It is important to note that this lack of finding does not mean that intermittent fasting cannot elicit reductions in body fat. Rather, it suggests the necessity of a caloric deficit that must be present in intermittent fasting. Alternatively, combining methods to produce a caloric deficit with intermittent fasting is also a protocol that has been found to significantly enhance weight loss in obese populations (15). Regardless of the diet used, a caloric deficit is required, and intermittent fasting offers to be an effective method to facilitate this process.
Although there is a benefit of weight loss with intermittent fasting for body composition – which describes the relative proportion of lean mass to fat tissue in the body (16) – this can also influence factors that are associated with anti-aging benefits. Caloric restriction has been well established to induce mechanistic changes in the body that are reportedly responsible for delaying the aging process such as lowering body size; maintaining a low body temperature; decreasing the volume of adipose tissue (body fat), hyperglycemia (high blood sugar) and hyperinsulinemia (high insulin); and modifying metabolic systems (17). While some age-related changes are benign, others can reduce functions that are essential for daily functioning and increase the risk of disease, frailty, or disability (18). This is a reason why there is much research interest to identify interventions for attenuating or delaying the aging process. Intermittent fasting has been proposed to be an intervention for slowing aging. A study of fruit flies – a species with a lifespan of 2 to 3 months that is extensively used in aging research (19) – were able to live longer when put into fasting diets (20). As for humans, intermittent fasting may have beneficial effects on measures of oxidative stress. It is thought that aging is characterized by the progressive loss of cellular tissue and organ function which are reportedly due to oxidative stress – a process defined as an accumulation of reactive oxygen and nitrogen species which are chemically reactive molecules containing oxygen and nitrogen (21-23). Intermittent fasting in overweight males has been shown to reduce malondialdehyde which is a marker for oxidative stress (24). These findings suggest that intermittent fasting can mitigate outcomes associated with oxidative stress which may underlie its anti-aging benefits. However, it is likely that these benefits are driven by the caloric deficit normally produced by intermittent fasting. Taken together, intermittent fasting can produce a caloric deficit that may be essential for delaying the aging process.
In addition to the benefits of weight loss and health promotion that can be derived from intermittent fasting, it also potentiates to enhance cognitive performance. Typically, cognitive performance is a measure of functions like attention; memory; knowledge; decision making; planning; reasoning; judgment; perception; comprehension; language; and visuospatial function which are all integral for any tasks that require an individual to acquire and understand knowledge (25). Research examining intermittent fasting has advocated it as a potential intervention to improve cognitive functioning. A study on adolescents found they improved performance in tests of working memory after only 4 weeks of intermittent fasting (26). This improvement in working memory may be a function of attentional processes that is likely enhanced due to Norepinephrine (also known as Noradrenaline) – a neurotransmitter and a hormone that increases attention – which is shown to be greater with intermittent fasting in obese male mice (27-29). Additional research also shows that intermittent fasting may improve cognitive performance by inducing Brain-Derived Neurotrophic Factor – a protein responsible for reorganizing neurons (the fundamental cells in the brain) that is related to learning and memory (30, 31). Unlike the caloric deficit that is essential for the weight loss and health benefits associated with intermittent fasting, it is still unclear whether decreasing calories alone translates into improving cognitive performance. Generally, self-reports indicate that cognitive performance is impaired with weight-loss dieting (32). Although, weight loss can reportedly increase cognitive performance (33), which suggests that a caloric deficit may play a role in cognitive-related benefits linked to intermittent fasting.
Based on the evidence provided, the findings support the claims that intermittent fasting can help with weight loss, mitigate age-related changes, and improve cognitive performance. Underlying these benefits is a caloric deficit that may be derived from various intermittent fasting protocols as mentioned previously. Intermittent fasting is only one method of producing a caloric deficit and may be combined with others to accurately ensure one is consuming fewer calories. Tracking calories is a popular approach for caloric deficit strategies with the use of smartphone applications, like MyFitnessPal or MyNetDiary, that can be integrated into intermittent fasting protocols. While intermittent fasting may be great for dieting, it is not a one-size-fits-all. As with any successful diet, the best diet is the one that you can sustain for the long term.
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