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Intermittent Fasting: Basics, Advantages, and Disadvantages
Unbeknownst to many, there are various forms of intermittent fasting. The three most common and widely accepted fasting schedules are whole-day fasting, time-restricted feeding, and alternate-day fasting. Whole-day fasting usually entails one or two days of complete fasting per week; the other days, dieters are encouraged to eat as they wish or “ad libitum.” Some whole-day fasting permits dieters to eat 25% of total daily energy on fasting days. Time-restricted fasting allots a certain number of hours eat day to eating. Beyond this feeding window, dieters typically completely refrain from caloric intake; however, some programs allow up to 25% of daily caloric need during the fasting periods. Finally, alternate-day fasting entails fasting every second day and ad libitum feeding on alternate days. Fasting days may allow for one meal that consists of 25% of daily caloric needs.

Continuous energy restriction can reduce free fat mass and body fat. Usually, 10-60% of weight reduction using continuous energy restriction is free fat mass. Intermittent fasting is effective because it affects the size of adipocytes of white adipose tissue. Hypertrophic obesity (increased fat cell size) is a bigger determinant of metabolic diseases than hyperplastic obesity (increased number of fat cells). Further, other studies show a decrease in inguinal (subcutaneous depot) and epididymal (visceral depot) fat cells in those that participate in intermittent fasting. A decrease in the size of these depots is related to an increase in insulin sensitivity, most likely because of an increase in the number of insulin receptors. As well, by decreasing the secretion of pro-inflammatory mediators and pro-inflammatory phenotype in white adipose tissue, intermittent fasting can regulate the secretions of adipocyte cytokines. Studies have shown that hepatic and visceral fat stores may be more sensitive to lipolytic effects of catecholamines during energy restriction than subcutaneous fat. Thus, the abdominal and intramuscular fat would be lost first under an energy restriction diet.

But intermittent fasting is not without its risks. Intermittent fasting may have adverse effects on normal-weight individuals in the short term. Periods of intermittent energy restriction every week will cause lipolysis and fluctuations in free fatty acids. Whole-day fasting will result in fluctuations of free fatty acids that are three to four times greater than a normal overnight fast. These fluctuations can lead to skeletal muscle insulin resistance. Single instances of t24-48 hour fasts in individuals of normal weight have also resulted in an increase in hepatic and intramyocellular triglyceride content, unlike after a regular 12-hour fast. This one-off fast did not result in an increase in hepatic fat in non-obese premenopausal women; although it did result in an increase in intramyocellular triglycerides by 2.4%-3.6%. Men, however, saw an increase in hepatic fat (0.42%-0.74%) and no increase in intramyocellular triglycerides. This is likely because of altered mitochondrial function and fat oxidation from augmented oxidative stress or a decrease in apolipoprotein B-100 production and hepatic lipid export.

Health Benefits of Fasting and Caloric Restriction
This study suggests there are many potentially psychologic benefits of fasting or intermittent calorie restriction. However, some behavioral modifications, specifically not binge eating following a fasting period are essential in maintaining the beneficial results of intermittent fasting.

Potential Benefits and Harms of Intermittent Energy Restriction and Intermittent Fasting Amongst Obese, Overweight and Normal Weight Subjects—A Narrative Review of Human and Animal Evidence
Intermittent energy restriction has become popular as a means of weight control amongst people who are overweight and obese, and is also undertaken by normal weight people. This article summarises randomized comparisons of intermittent and isoenergetic continuous energy restriction for weight loss to manage overweight and obesity. It also summarises the potential beneficial or adverse effects of IER on body composition, adipose stores and metabolic effects from human studies, including studies amongst normal weight subjects and relevant animal experimentation.

Popular Weight Loss Strategies: a Review of Four Weight Loss Techniques
Despite the growing popularity of fad diets and exercise plans for weight loss, there are limited studies that actually identify long-term weight loss solutions. Consuming extremely low caloric intake for short periods of time tends to be effective; however, such diets lead to weight gain once a normal diet is resumed. Both intermittent fasting and the paleo diet lead to weight loss because of overall decreased caloric intake.

Effects of intermittent fasting on body composition and clinical health markers in humans
"Intermittent fasting" can be used to describe a variety of programs that alter the timing of eating by utilizing short-term fasts in order to improve body fat percentage and overall health. This article examines studies conducted on intermittent fasting programs to determine if they are effective at improving body composition and instances of disease. Intermittent fasting can be alternate-day fasting, whole-day fasting, and time-restricted feeding. Research on time-restricted feeding is limited, and clear conclusions cannot be made at present. Future studies should examine long-term effects of intermittent fasting and the potential synergistic effects of combining intermittent fasting with exercise.

Distraction, Not Hunger, is Associated with Lower Mood and Lower Perceived Work Performance on Fast Compared to Non-Fast Days During Intermittent Fasting
This article describes how dieting and fasting have been found to result in poor mood, increased anxiety, nervousness, irritability, anger, frustration, depression, poor concentration, slower reaction times, and poorer memory. The article defines intermittent fasting as the consumption of 500-800 kcal/day on some days and others during which dieters can consume as much as they want. The study suggests that reduced blood sugar impacts mood and perceived work performance, because of an increased cognitive load resulting from an increased attention towards food and eating. The study, however, only used a limited number of participants and did not compare results to individuals on a traditional diet. The use only of lean young females is also a limitation. This group was used because they were likely to agree. Overall, this study is in accordance with the proposition that intermittent fasting has a negative impact on mood.

Effect of Ramadan Fasting on Fatigue, Mood, Sleepiness, and Health-Related Quality of Life of Healthy Young Men in Summer Time in Germany: A Prospective Controlled Study
The purpose of the study was to determine the effect of Ramadan fasting on fatigue, mood and health-related quality of life in healthy males during the summer in Germany. This study showed that Ramadan fasting did not significantly influence mood, fatigue and quality of life. The article states fasting provides advantages to dieters; however, there is not sufficient evidence to verify this claim. This study had some limitations: the participants were not random because of religious reasons. Additionally, they did not control and record the calorie intake of all participants in order to determine the natural effect of fasting during Ramadan. Further, the fact that the cause of starvation was religious could also have psychological impacts on the individuals of the study and cause their moods to differ than a fasted control group.

Physiological and Behavioral Responses to Intermittent Starvation in C57BL/6J Mice
This study showed that mice displayed an increased body mass and fatness in a 13-day intermittent fast. However, body mass returned to normal when the diet was continued up to 42 days. This study is in conversation with the dual intervention point model, which postulates there is an upper and lower boundary for weight and adiposity. Between these two boundaries, there is no physiological regulation of weight. Over the first 13 days of treatment, the data was consistent with the dual intervention point model as the mice increased body mass and adiposity. In the short term, an increase in food intake, decreased physical activity and reduced body temperature, which contributed to the increase in body mass and fatness. However, the body mass of mice who participated in intermittent fasting for 42 days was fairly regular. This is inconsistent with the dual intervention point model. Intermittent starvation resulted in a decreased physical activity level, suggesting rather than overcompensating by eating more, rats decreased energy expenditure. However, this study observed rats, who may possess significant differences when compared to human subjects.

Massive Obesity Treated by Intermittent Fasting: A Metabolic and Clinical Study
Famine is typically accompanied by by depression, apathy and occasional paradoxical irritability. However, the data in this article does not support this conception. Although there were outbursts of disagreement during the second half of the study. These outbursts were concerning trivial matters. The author stated that overall, the good humor and cooperation throughout the long study were exceptional. This study suggests that gross obesity is not necessarily more difficult to treat than obesity of lesser degrees, and also that emotional obstacles can be overcome. While this article does provide citations, to support it’ claim; it provides no evidence to verify these claims.