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.
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