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Cons of Intermittent Fasting

Intermittent fasting is a relatively new dieting trend that is being practiced with greater frequency. Intermittent fasting consists of many strategies like alternate day fasting, a dieter eats approximately 25% of the recommended caloric intake 2 days of the week and maintains normal caloric input 5 days of the week, or time restricted feeding, where a dieter abstains from eating for 16 hours a day and eats normally throughout the remaining 8 hours (Stockman, Thomas, Burke, & Apovian, 2018). The basic premise of the diet is a dieter takes extended breaks from caloric consumption. Diets following an intermittent fasting protocol are effective in weight loss, have a higher rate of adherence than a typical caloric restriction protocol, and have been shown to reduce the rate of several chronic diseases (Harvie & Howell, 2016). However, intermittent fasting has some drawbacks. Intermittent fasting may not be a viable diet strategy for individuals with medical conditions, it may hinder athletic performance, and may be difficult to start or maintain due minor physical ailments (Headland, Clifton, Carter, & Keogh, 2016).

Diet modification is a big part of treating metabolic disorders like diabetes and high cholesterol. One of the goals of diabetes nutritional treatments is to improve glucose homeostasis and reduce episodes of hypoglycemia. Corey et al. (2018) found that people with Type II diabetes who embarked on an intermittent fasting protocol were twice as likely to have a hypoglycemic incident during a fasting period when compared to diabetics following a typical caloric restriction diet. A study of mice with genetic history of high cholesterol found when mice followed an intermittent fasting protocol, it aggravated the development of obesity, had higher levels of cholesterol, greater glucose intolerance, and a greater incidence of atherosclerosis, than mice who were fed normally or mice without the genetic predisposition (Dorighello et al., 2013). Intermittent fasting should not be considered as a viable dieting strategy for individuals with Type II diabetes or a family history of high cholesterol.

Intermittent fasting protocols may be harmful to athletic performance. In a study of anaerobic power as measured by the Wingate cycling test, Naharudin and Yusof (2018) found athletes following an intermittent fasting diet had a quicker time to exhaustion than those following a normal eating pattern. The athletes on the intermittent fasting diet had decreased utilization of glycogen stores and higher rates of dehydration compared to other athletes. In weight restricted sports like judo, intermittent fasting negatively influences fatigue and decreases jump power. During a study of Judokas following a Ramadan intermittent fasting protocol, Aloui et al. (2016) discovered athletes at the end of the month had higher self-reported episodes of fatigue and a decreased average power output during a 30 second jump test. This decrease in power is likely associated with a decrease in lean body mass and neural recruitment. Following an intermittent fasting diet seems likely to be a hindrance on athletic performance.

Intermittent fasting may cause minor to severe discomfort for some adherents. In a 6-month intervention comparing intermittent fasting and caloric restrictions among overweight, pre-menopausal women, around 15% of the participants following the intermittent fasting protocol experienced minor physical discomforts such as constipation, headaches, chills, and low energy, as well as minor behavior changes such as an increased temper, lack of concentration, and a preoccupation about food (Harvie et al.,2011). This may be due to the abnormal eating pattern of intermittent fasting depriving the patient of energy for extended periods, and over filling the gut during feedings. There is also risk of a client going into a starvation state during a prolonged fast, which can cause severe health problems. In a study of rats undergoing alternate day fasting, Ahmet, Wan, Mattson, Lakatta, and Talan ( 2010) found an increase in left atrial diameter, thickening of the heart valves , and reduced cardiac reserve. These changes greatly reduce heart function.

Intermittent fasting has been shown to effective weight loss strategy, may have positive affects on health. However, there are possible weaknesses with following an intermittent fasting protocol. It may cause more harm if the person has Type II diabetes or a genetic predisposition to high cholesterol, may decrease athletic performance, and may lead to minor or severe physical ailments. Intermittent fasting may work for some people, but if a client is diabetic, an athlete, or prone to discomfort, caloric restriction may be a better strategy.


Ahmet, I., Wan, R., Mattson, M. P., Lakatta, E. G., & Talan, M. I. (2010). Chronic alternate-day fasting results in reduced diastolic compliance and diminished systolic reserve in rats. Journal of Cardiac Failure, 16(10), 843-853.

Aloui, A., Chtourou, H., Briki, W., Tabben, M., Souissi, N., Shephard, R., & Chamari, K. (2016). Rapid weight loss in the context of Ramadan observance: Recommendations for judokas. Biology of Sport, 33(4), 407-413.

Corley, B. T., Carroll, R. W., Hall, R. M., Weatherall, M., Parry-Strong, A., & Krebs, J. D. (2018). Intermittent fasting in Type 2 diabetes mellitus and the risk of hypoglycaemia: A randomized controlled trial. Diabetic Medicine, 35(5), 588-594.

Dorighello, G. G., Rovani, J. C., Luhman, C. J., Paim, B. A., Raposo, H. F., Vercesi, A. E., & Oliveira, H. C. (2013). Food restriction by intermittent fasting induces diabetes and obesity and aggravates spontaneous atherosclerosis development in hypercholesterolaemic mice. British Journal of Nutrition, 111(06), 979-986.

Harvie, M. N., & Howell, T. (2016). Could intermittent energy restriction and intermittent fasting reduce rates of cancer in obese, overweight, and normal-weight subjects? A summary of evidence. Advances in Nutrition: An International Review Journal, 7(4), 690-705.

Harvie, M. N., Pegington, M., Mattson, M. P., Frystyk, J., Dillon, B., Evans, G., . . . Howell, A. (2011). The effects of intermittent or continuous energy restriction on weight loss and metabolic disease risk markers: A randomized trial in young overweight women. International Journal of Obesity, 35(5), 714-727.

Headland, M., Clifton, P., Carter, S., & Keogh, J. (2016). Weight-loss outcomes: A systematic review and meta-analysis of intermittent energy restriction trials lasting a minimum of 6 Months. Nutrients, 8(6), 354.

Naharudin, M. N., & Yusof, A. (2018). The effect of 10 days of intermittent fasting on Wingate anaerobic power and prolonged high-intensity time-to-exhaustion cycling performance. European Journal of Sport Science, 18(5), 667-676.

Stockman, M., Thomas, D., Burke, J., & Apovian, C. M. (2018). Intermittent fasting: Is the wait worth the weight? Current Obesity Reports, 7(2), 172-185.

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