[Intermittent fasting, used for weight loss, means fasting on
alternate days, whole days with a specific frequency per week, or
during a set time frame. Although effective in animal studies,
evidence in human studies is less convincing.] [https://portside.org/]


 PORTSIDE CULTURE 

 DIET REVIEW: INTERMITTENT FASTING FOR WEIGHT LOSS  
[https://portside.org/2020-03-09/diet-review-intermittent-fasting-weight-loss]


 

 Harvard T. H. Chan 
 February 1, 2020
Harvard T. H. Chan newsletter
[https://www.hsph.harvard.edu/nutritionsource/healthy-weight/diet-reviews/intermittent-fasting]


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 _ Intermittent fasting, used for weight loss, means fasting on
alternate days, whole days with a specific frequency per week, or
during a set time frame. Although effective in animal studies,
evidence in human studies is less convincing. _ 

 Finding yourself confused by the seemingly endless promotion of
weight-loss strategies and diet plans? , Harvard T. H. Chan 

 

WHAT IS IT?

Intermittent fasting is a diet regimen that cycles between brief
periods of fasting, with either no food or significant calorie
reduction, and periods of unrestricted eating. It is promoted to
change body composition through loss of fat mass and weight, and to
improve markers of health that are associated with disease such as
blood pressure and cholesterol levels. Its roots derive from
traditional fasting, a universal ritual used for health or spiritual
benefit as described in early texts by Socrates, Plato, and religious
groups. [1] Fasting typically entails a steady abstinence of food and
beverages, ranging from 12 hours to one month. It may require complete
abstinence, or allow a reduced amount of food and beverages.

Prolonged very low calorie diets can cause physiological changes that
may cause the body to adapt to the calorie restriction and therefore
prevent further weight loss. [2] Intermittent fasting attempts to
address this problem by cycling between a low calorie level for a
brief time followed by normal eating, which may prevent these
adaptations. However, research does not consistently show that
intermittent fasting is superior to continuous low calorie diets for
weight loss efficiency.

HOW IT WORKS

The most common methods are fasting on alternate days, for whole days
with a specific frequency per week, or during a set time frame. [3]

	* _Alternate-day fasting_—Alternating between days of no food
restriction with days that consist of one meal that provides about 25%
of daily calorie needs. Example: Mon-Wed-Fri consists of fasting,
while alternate days have no food restrictions.
 	* _Whole-day fasting_—1-2 days per week of complete fasting or up
to 25% of daily calorie needs, with no food restriction on the other
days. Example: The 5:2 diet approach advocates no food restriction
five days of the week, cycled with a 400-500 calorie diet the other
two days of the week.
 	* _Time-restricted feeding_—Following a meal plan each day with a
designated time frame for fasting. Example: Meals are eaten from
8am-3pm, with fasting during the remaining hours of the day.

THE RESEARCH SO FAR

Physiologically, calorie restriction has been shown in animals
to increase lifespan and improve tolerance to various metabolic
stresses
[https://www.hsph.harvard.edu/news/press-releases/molecular-mechanism-behind-health-benefits-of-dietary-restriction-identified/] in
the body. [4] Although the evidence for caloric restriction in animal
studies is strong, there is less convincing evidence in human studies.
Proponents of the diet believe that the stress of intermittent fasting
causes an immune response that repairs cells and produces positive
metabolic changes (reduction in triglycerides, LDL cholesterol, blood
pressure, weight, fat mass, blood glucose). [3,5] An understandable
concern of this diet is that followers will overeat on non-fasting
days to compensate for calories lost during fasting. However, studies
have not shown this to be true when compared with other weight loss
methods. [5]

A systematic review of 40 studies found that intermittent fasting was
effective for weight loss, with a typical loss of 7-11 pounds over 10
weeks. [2] There was much variability in the studies, ranging in size
from 4 to 334 subjects, and followed from 2 to 104 weeks. It is
important to note that different study designs and methods of
intermittent fasting were used, and participant characteristics
differed (lean vs. obese).  Half of the studies were controlled
trials comparing the fasting group to a comparison group and/or a
control group (either continuous calorie restriction or usual
lifestyle), with the other half examining an intermittent fasting
group alone. A brief summary of their findings:

	* Dropout rates ranged from 0-65%. When comparing dropout rates
between the fasting groups and continuous calorie restriction groups,
no significant differences were found. Overall, the review did not
find that intermittent fasting had a low dropout rate, and therefore
was not necessarily easier to follow than other weight loss
approaches.
 	* When examining the 12 clinical trials that compared the fasting
group with the continuous calorie restriction group, there was no
significant difference in weight loss amounts or body composition
changes.
 	* Ten trials that investigated changes in appetite did not show an
overall increase in appetite in the intermittent fasting groups
despite significant weight loss and decreases in leptin hormone levels
(a hormone that suppresses appetite).

A randomized controlled trial that followed 100 obese individuals for
one year did not find intermittent fasting to be more effective than
daily calorie restriction. [6] For the 6-month weight loss phase,
subjects were either placed on an alternating day fast (alternating
days of one meal of 25% of baseline calories versus 125% of baseline
calories divided over three meals) or daily calorie restriction (75%
of baseline calories divided over three meals) following the American
Heart Association guidelines. After 6 months, calorie levels were
increased by 25% in both groups with a goal of weight maintenance.
Participant characteristics of the groups were similar; mostly women
and generally healthy. The trial examined weight changes, compliance
rates, and cardiovascular risk factors. Their findings when comparing
the two groups:

	* No significant differences in weight loss, weight regain, or body
composition (e.g., fat mass, lean mass).
 	* No significant differences in blood pressure, heart rate, fasting
glucose, and fasting insulin. At 12 months, although there were no
differences in total cholesterol and triglycerides, the alternate-day
fasting group showed significantly increased LDL cholesterol levels.
The authors did not comment on a possible cause.
 	* The dropout rate was higher in the alternate-day fasting group
(38%) than in the daily calorie restriction group (29%).
Interestingly, those in the fasting group actually ate less food than
prescribed on non-fasting days though they ate more food than
prescribed on fasting days.

POTENTIAL PITFALLS

This type of dietary pattern would be difficult for someone who eats
every few hours (e.g., snacks between meals, grazes). It would also
not be appropriate for those with conditions that require food at
regular intervals due to metabolic changes caused by their
medications, such as with diabetes. Prolonged periods of food
deprivation or semi-starvation places one at risk for overeating when
food is reintroduced, and may foster unhealthy behaviors such as an
increased fixation on food. [7,8]

Individuals with the following conditions should abstain from
intermittent fasting:

	* Diabetes
[https://www.hsph.harvard.edu/nutritionsource/diabetes-full-story/]
 	* Eating disorders that involve unhealthy self-restriction (anorexia
or bulimia nervosa)
 	* Use of medications that require food intake
 	* Active growth stage, such as in adolescents
 	* Pregnancy, breastfeeding

UNANSWERED QUESTIONS

	* How often and for how long should one fast to see a therapeutic
benefit?
 	* Is this diet safe and beneficial for everyone (e.g., generally
healthy population, higher risk individuals with chronic diseases,
elderly)?
 	* What are the long-term effects of intermittent fasting?
 	* Is there a risk of negatively influencing the dietary behaviors of
other family members, especially in children who see their parents
abstaining from food and skipping meals?

BOTTOM LINE

Although certain benefits of caloric restriction have been
demonstrated in animal studies, similar benefits of intermittent
fasting in humans have not been observed. It is unclear that
intermittent fasting is superior to other weight loss methods in
regards to amount of weight loss, biological changes, compliance
rates, and decreased appetite. Certain people who typically eat one or
two meals a day or do not eat for long stretches of time may show
better compliance with this type of regimen.

More high-quality studies including randomized controlled trials with
follow-up of greater than one year are needed to show a direct effect
and the possible benefits of intermittent fasting. Strong
recommendations on intermittent fasting for weight loss cannot be made
at this time. 

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