THE TRUTHS AND ILLUSIONS SURROUNDING INTERMITTENT FASTING

By Miles Kaufman and Riley Hurr

As with every fad diet that quickly gains popularity, the science behind intermittent fasting is shrouded in myths. Despite much scientific research, most people do not have an accurate perception of both the merits and downfalls of this diet. Many people believe that intermittent fasting is the key to easy weight loss or that it will prevent them from developing diabetes, but as with most health advice, nothing is that straight forward. Intermittent fasting takes many forms. Some people only eat within an 8 hour window during the day, while others only eat on certain days of the week. Regardless of these specifics, the main principle behind intermittent fasting is to increase the amount of time your body spends in a postabsorptive state — a state during which your body is not absorbing nutrients and relying on its energy reserves instead. Many nutritionists have argued that intermittent fasting promotes weight loss and lowers one’s risk of developing heart disease and diabetes, but how effective is this method compared to other eating patterns?

When it comes to intermittent fasting, some of the most promising results are seen with regards to diabetes prevention. Type 2 diabetes is caused by insulin resistance, which, simply put, is caused by elevated blood sugar over a long period of time. Therefore, many scientists have theorized that instilling a fasting period could lower a patient’s exposure to elevated blood sugar and prevent insulin resistance from developing. In mice, intermittent fasting has been shown to both prevent and cure type 2 diabetes, but in humans the data is less straightforward. It appears that intermittent fasting can be effective at preventing type 2 diabetes, but it is unclear whether intermittent fasting is better at preventing type 2 diabetes compared to other low calorie diets. These mixed results could suggest poor study designs or they could suggest that the metabolic benefits of fasting are related to reducing caloric consumption instead of reducing exposure to high blood sugar.

There is also some data that suggests that intermittent fasting may be more effective than other weight loss methods because it adjusts an individual’s eating window to a more ideal time-period. Our circadian rhythm is designed such that hunger suppressing hormones are secreted at night, allowing us to get a full night’s sleep. Since hormones that boost your metabolism tend to be secreted during the day, some theories suggest that eating during daylight hours improves metabolic health and promotes weight loss. Studies conducted in rodents suggest that synching the feeding window to the circadian rhythm improves metabolic health, but the data that has been collected in humans is inconsistent at best.

In addition to diabetes prevention and circadian realignment, many studies have examined the relationship between intermittent fasting and cardiac health. The metabolic factors associated with fasting are also associated with low cholesterol and inflammation. Therefore, some scientists have theorized that intermittent fasting reduces cholesterol and plaque build-up which prevents heart attacks and other cardiac issues. But yet again, it seems unclear whether the driver of these health benefits is weight loss or fasting. It seems that many of the metabolic benefits of intermittent fasting are due to weight loss, but how effective is intermittent fasting at promoting weight loss? The human body was designed to store energy very effectively, because humans evolved under conditions of nutritional scarcity. Therefore, there are many biological mechanisms devoted to ensuring we do not lose weight. As fad diets come and go, people have come to realize that when it comes to weight loss, there are no proven short-cuts and no easy fixes. Most data suggests that the only way for a metabolically healthy individual to lose weight is by expending more energy than they consume, which is a difficult task considering that our bodies are hardwired to prevent energy deficits at all costs. The question remains of whether intermittent fasting is an effective weight loss strategy, and most data suggests that intermittent fasting results in weight loss because people eat less when they do not eat all day long. Most reviews of the scientific literature agree that intermittent fasting is not a more effective weight loss strategy than caloric restriction. It is also important to note that weight loss is not ideal for many people, and there are many people for whom intermittent fasting is not recommended. Athletic performance is often impaired by intermittent fasting due to the reduced energy intake. Additionally many people’s energetic needs would not be met through fasting, so it is not recommended for pregnant and breastfeeding patients, diabetic individuals or those with existing eating disorders.

Not only is intermittent fasting not ideal for everyone, in some ways fasting has been shown to promote weight gain. Fasts have been known to promote binging. During the month of Ramadan, many muslims fast from sunrise to sunset. Surprisingly, many Ramadan observers report gaining weight during the holiday, which is likely due to changes in energy expenditure and eating excess calories after sunset as overcompensation for the caloric deficit they experienced during the day.

On the other hand, many people report that they are able to restrict their caloric intake more effectively through intermittent fasting than they are through other diets. For these individuals, the current research suggests that intermittent fasting may be a valid alternative to caloric restriction. One of the main barriers to weight loss is the difficulty individuals have maintaining a caloric deficit, so any method that could possibly make that easier is worth looking into.

Credits:

Mattson, Mark P., Valter D. Longo, and Michelle Harvie. “Impact of intermittent fasting on health and disease processes.” Ageing research reviews 39 (2017): 46-58.

2. Antoni, R., Johnston, K., Collins, A., & Robertson, M. (2017). Effects of intermittent fasting on glucose and lipid metabolism. Proceedings of the Nutrition Society, 76(3), 361-368. doi:10.1017/S0029665116002986

3. Hatori, Megumi, et al. “Time-restricted feeding without reducing caloric intake prevents metabolic diseases in mice fed a high-fat diet.”