Intermittent fasting for obesity and related disorders: unveiling myths, facts, and presumptions

Abstract

Intermittent fasting (IF) is an increasingly popular method of weight loss, as an alternative to daily caloric restriction (DCR). Several forms of IF exist, such as alternate-day fasting or time-restricted feeding regimens. Some of its proponents claim several health benefits unrelated to caloric restriction or weight loss, which rely mainly on animal models. Although several studies published in the last few years confirm that IF can be a useful and safe therapeutical option for obesity and related disorders, no superiority to conventional caloric restriction diets have emerged. There are still several questions left answered. In this Review, we discuss some of the claims, unveiling myths, facts, and presumptions about several models of IF. The focus of this article is obesity, but there is a brief discussion of the potential benefits of IF on overall human health.

Using Intermittent Fasting as a Non-pharmacological Strategy to Alleviate Obesity-Induced Hypothalamic Molecular Pathway Disruption

“…Thus, the presence of ad libitum feeding windows in IF protocols emerged as an alternative protocol for dietary restriction interventions. The stress promoted by the low caloric intake is replaced by the metabolic stress induced by intermittent windows of prolonged fasting or alternate days of deficient caloric intake ( 78 , 80 ). However, it is essential to highlight that both interventions must be carried out with professional supervision.…”

“…Despite its high popularity, there is no standardization of IF protocols ( 80 ). It is established that protocols do not impose water restrictions.…”

“…All include periods of food restriction, which may refer to total deprivation from food consumption during some hours of the day (fasting window) or a full day containing no-energy food. Recently, some papers ( 80 , 83 ) have been considering IF in three specific categories: (a) Complete Alternate Day Fasting (ADF) – consists of days with ad libitum feeding intercalated by whole days of food restriction, (b) Modified alternate-day fasting (MADF) or alternate-day modified fasting (ADMF) – with two non-consecutive days of total food restriction within the week, or two days of food intake of about 20% of the total caloric necessity with meals distributed throughout the day (c) Time-restricted feeding (TRF) – consisting of a protocol with a fasting window (usually 16 h) followed by a food intake window of approximately 8 h, with the meals distributed within this period, according to individual needs. The main point of the protocols is not to change the average weekly caloric intake but to change the frequency of food consumption ( 78 , 80 ).…”

The Effects of Caloric Restriction and/or Intermittent Fasting on Bone Health

“…Rehabilitation and lifestyle modifications that preserve and/ or promote gains in bone mass include regular physical activity, resistance training and dietary modification such as increased protein intake, adequate intake of calcium and vitamin D, and supplementation with magnesium and, possibly, vitamin K [1][2][3][4][5] . In contrast, numerous studies indicate that caloric restriction (CR) and/ or intermittent fasting (IF), which have been proposed to augment rehabilitation for such conditions as stroke, cardiomyopathy, and heart failure [6][7][8][9] , may negatively impact bone health [10][11][12] . Thus, it is important to clarify the impact of these diets on bone metabolism so that fracture risk is mitigated in the context of rehabilitative healthcare.…”

“…The fasting period can be practiced in different ways such as fasting every other day, fasting for two to three days at a time, or even fasting during particular hours of each day (also referred to as time-restricted feeding). The effects of CR and/or IF on weight loss and other outcomes have been extensively summarized elsewhere [10][11][12] . However, not all of these effects are beneficial, as evidenced in the somewhat conflicting literature reporting on the impact that these diets have on bone metabolism.…”