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

Abstract

Intermittent energy restriction (IER) has become popular as a means of weight control amongst people who are overweight and obese, and is also undertaken by normal weight people hoping spells of marked energy restriction will optimise their health. This review summarises randomised 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. Six small short term (<6 month) studies amongst overweight or obese individuals indicate that intermittent energy restriction is equal to continuous restriction for weight loss, with one study reporting greater reductions in body fat, and two studies reporting greater reductions in HOMA insulin resistance in response to IER, with no obvious evidence of harm. Studies amongst normal weight subjects and different animal models highlight the potential beneficial and adverse effects of intermittent compared to continuous energy restriction on ectopic and visceral fat stores, adipocyte size, insulin resistance, and metabolic flexibility. The longer term benefits or harms of IER amongst people who are overweight or obese, and particularly amongst normal weight subjects, is not known and is a priority for further investigation.

Rationale for novel intermittent dieting strategies to attenuate adaptive responses to energy restriction

“…Intermittent fasting appears to produce similar results to CER in terms of weight loss and the associated changes in body composition and risk factors for metabolic disease. Several reviews , including some systematic reviews with or without meta‐analysis, concur that intermittent fasting in adults with overweight or obesity produces losses in body weight, fat mass and fat‐free mass, as well as improvements in risk factors for cardio metabolic disease (such as circulating levels of insulin, glucose or lipids) that are equivalent – albeit not superior – to those induced by CER. One caveat with this conclusion is that most of the reviewed publications were not sufficiently powered to fully assess all of these outcomes, and most outcomes were measured at less than 6 months after commencement of the intervention.…”

Energy Restriction and Colorectal Cancer: A Call for Additional Research

“…Despite these benefits, few comparative studies between CER and IER have been performed to date. In obese or overweight humans, these studies evidence similar effectiveness for body weight loss [15][16][17][18][19][20][21][22][23][24][25], with slightly better outcomes for IER regimens with regards to fat-free mass retention [16], fat mass loss, insulin sensitivity [24,25], postprandial lipemia [15], adherence, blood glucose, and anthropometric and lipid parameters [23]. It should be noted that these studies were performed with relatively small groups and for short periods of time, mostly ≤26 weeks.…”

Intermittent Fasting and Adding More days to Life

“…With over 50% of the adult population in the UK currently classified as overweight or obese, accompanied by an increased risk of type 2 diabetes and cardiovascular disease, finding more effective strategies to manage these conditions remains imperative [1] . In 2016, World Health Organization (WHO) reported that more than 1.9 billion people in the world were overweight and over 650 million people were obese which has tripled in number since 1975 [2] . To date, the most robust intervention efficient in warding off the aforementioned cellular markers of aging is calorie restriction (CR) that involves the administration of a well-balanced, nutrient-dense diet that reduces calorie intake by 20%-40% without malnutrition [3] .…”

“…There are two possible systems, 5:2 or 4:3. In the 5:2 system, in which caloric restriction is used for two days a week, and a regular diet for 5 days [35,36] . However, IF should not be used by children, pregnant women, and people performing heavy physical work [37] .…”