Intermittent Fasting: Another Diet Fad, or Yo-Yo Dieting With Benefits?

                                                                                                        
Intermittent fasting (IF), also known as alternate day fasting (ADF), has been touted as a weight loss method by celebrities and the media. It is a means of reducing calories by restricting one’s intake for several days each week, and then eating regularly the rest of the days, rather than focusing on permanent caloric restriction. Proponents of IF claim that adherence and flexibility are greater, compared with traditional calorie restricted diets.

Although fasting and severe calorie restriction for weight loss have traditionally been frowned upon by registered dietitian nutritionists because of a negative impact on metabolic rate, some newer research suggests that intermittent fasting may have benefits not only for weight loss, but also for health and aging. As a result, books and diets such as The Fast Diet, The Every-Other-Day-Diet, the 5:2 Diet, and The Alternate-Day Diet  have popped up to give consumers some guidance on this new method of dieting for weight loss and health. 

Are there rules for alternate day fasting? 

There are no official recommendations for alternate or intermittent fasting. Research on voluntary abstinence of food and drink stems from studies on the effects of religious fasting, as in Ramadan, as well as laboratory studies on animals, and some observational studies on smaller groups of individuals, all of which use different methods of fasting. Of the intervention studies that have been conducted, the following methods of fasting were used:

 

•Alternate day fasting – fasting days, with no calorie foods and beverages, are alternated with ad libitum food and beverage days.

•Modified fasting – subjects consume 20-25% of caloric needs on 2 scheduled, nonconsecutive fasting days each week, and alternate with regular eating the remaining 5 days of the week.

•Time-restricted feeding – fasting intervals lasting between 12-20 hours, alternate with regular eating. There is often one late afternoon meal. 

 

In most of the research studies, subjects could eat ad libitum, or up to their recommended calorie level on the non-fast days, but the types of foods consumed were not restricted.  

Weight loss and metabolic findings 

Although research is scant, it does suggest that all forms of IF contribute to weight loss. In a recent review of 6 studies, researchers determined that IF resulted in an almost 9% mean weight loss in overweight or obese subjects, after 6 months of the program. Further weight loss of 8.2% was seen in the following month on maintenance. Of interest, researchers noted that compared with traditional calorie restriction for weight loss, the attrition rates for the IF studies were significantly lower, at only 20% (Hankey et al., 2015).  

The effect of ADF on weight loss does not appear to be associated with the macronutrient distribution of the diet. In a study on 32 obese individuals who were fed a diet of either 25% or 45% of calories from fat, and alternated with fasting days, both groups had similar results for weight loss and reduced waist circumference (Klempel et al., 2013).  

Periodic fasting is usually associated with weight loss diets; however, the research has turned up other potential benefits as well. These include improvements in metabolic markers such as insulin, glucose, and triglyceride levels, as well as a reduction in low-density lipoprotein (LDL)-cholesterol particle size. In addition, there have been reductions in visceral fat and inflammatory markers, including C-reactive protein, tumor necrosis factor-alpha (TNF-α), adiponectin, leptin, and brain-derived neutrotophic factor. The improvements in these markers suggest that IF or ADF may be helpful in reducing the risk for metabolic syndrome, cardiovascular disease, diabetes, or even cancer.  

While IF or ADF can help individuals achieve weight loss and improve their metabolic markers, the same can be said for traditional calorie-restriction that promotes weight loss. It is important to note that studies that compared traditional continuous energy restriction against intermittent fasting found similar results for both groups. Based on current evidence, it does not appear that any form of fasting is superior to continuous calorie restriction for weight loss or metabolic improvements.  

Additional reported health benefits 

In addition to the above studies on weight loss and metabolic benefits, IF is being explored for potential benefits on brain aging, and even as a method of expanding healthy life, although most of this research is on lab animals. Human intervention studies have found that IF improves pulmonary function and reduces inflammation in subjects with asthma. In children with epilepsy, IF combined with the traditional ketogenic diet reduces seizures. These studies suggest that IF or ADF may offer an alternative or synergistic method of treatment for these and possibly other conditions.  

The bottom line 

The exact mechanism for some of the benefits of IF is uncertain, but it may be that IF helps to synchronize circadian rhythms, which affect hormones and other metabolic regulators. Evidence from studies on shift workers shows that disruptions in circadian rhythms can impact weight gain, and increase risk of diabetes, cardiovascular disease, and certain types of cancer. Whether this is the case, or simply, that the structure of an IF program limits late night eating, without an “all or nothing” or calorie counting approach, IF and ADF may be beneficial to those individuals who have struggled unsuccessfully with traditional calorie restricted diets. Certainly, more long-term research is needed, but it appears that there is no harm or negative consequences to IF, and potentially much benefit if it can be sustained.