Many health trends come and go, but one dietary trend that has seemed to endure the craze is intermittent fasting. The primary reason intermittent fasting (IF) has remained so popular is because it offers flexibility to fit a busy schedule, and (while I don't typically advise mindlessly eat as long as your fasting) it doesn't ultimately demand restricted eating.

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A THOROUGH LOOK AT
INTERMITTENT FASTING AND
CALORIE RESTRICTION AS A
BENEFIT TO HEALTH

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Many health trends come and go, but one dietary trend that has
seemed to endure the craze is intermittent fasting.
The primary reason intermittent fasting (IF) has remained so
popular is because it offers flexibility to fit a busy schedule, and
(while I don't typically advise mindlessly eat as long as your
fasting) it doesn't ultimately demand restricted eating.
What is intermittent fasting, and how is it done?
Intermittent fasting is defined as diet regimen that cycles
through a period of time in which the body is driven into a
catabolic state through fasting, where no significant calorie
intake occurs, met with periods of fed states where no calorie
restriction occurs. The windows for fasting are typically around
16 hours, met with an 8 hour fed state.

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Intermittent fasting can be used in a few different ways:
 Time restricted feeding: You restrict the time you are
allowed to eat to set hours of the day. For example, you eat
all of your meals in an 8 hour window, from 9-5 pm.
During the window, no calories are restricted, and outside
of this window, no calories are consumed.
 Alternative day fasting: You alternate the days on which
you restrict your caloric intake with ones where there are
no restrictions. For example, Mon-Wed-Fri you fast for 24
hours/limit calories to 25% of daily intake, while
alternative days have no restrictions
 Full Day Fast: You only consume water and other liquids
for 24 hours1-2 days per week.
The most common approach is time restricted feeding. Now,
most guidelines state that timing of these fed/fasted windows
won’t matter – ie a fed state from 9 am – 5 pm will produce the
same results as a fed window from 1 pm – 9 pm. We’ll talk
about why that’s not always true in a moment. But first, lets look
at the research that demonstrates the health benefits to in
fasting.
Are There Benefits to Intermittent Fasting?
 Weight Loss: A systematic review of over 40 studies on
intermittent fasting have shown it to have benefits on
weight loss in the short term, with average weight loss
around 9-11 lbs at 10 wks (1). This occurs for two reasons.
#1 – during fasting, the body goes into catabolic state to
continually feed the brain. This means that when we run

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out of bioavailable sugar and glycogen stores, the body will
start breaking down our fat as fuel, hence, fat loss. This
mechanism typically peaks at about 12-14 hours, with some
evidence suggesting the benefit is lost after the 16 hour
mark (hence the common 16 hours fasted/8 hours fed
approach).
#2 - during fasted states, the body increases production of
human growth hormone (HGH), which helps maintain lean
muscle mass. Therefore, in catabolic states in the presence
of HGH, the body preferences fat breakdown instead of
lean muscle mass (again, favouring fat loss). To further
avoid muscle loss and promote fat mass loss, I typically
recommend to incorporate some form daily exercise and to
maintain a high fat/high lean protein diet while using
intermittent fasting.
 Reduced Cancer Risks: The risks for certain types of
cancer development and reoccurrence can be lowered
through the use of intermittent fasting. Studies have shown
higher leptin level in the body do contribute towards the
development of certain cancers. Through intermittent
fasting, leptin levels can not only be lowered, adiponectin
levels can be increased, which is a hormone that has been
shown to be protective metaplastic cell development.A trial
published in JAMA Oncology in 2016 demonstrated that
fasting 13 hours or more per night resulted in a statistically
significant improvement in glucoregulation and reduction
in the reoccurrence rates of breast cancer (2), making is a

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simple non-pharmaceutical approach to minimizing breast
cancer reoccurrence.
 Improved Cardiovascular Health: Intermittent fasting
helps reduce low-density lipoprotein (LDL) or “bad”
cholesterol and triglyceride levels. Having high levels of
both LDL cholesterol and triglycerides increase risks of
heart disease, heart attacks, and strokes. Using a
combination of intermittent fasting methods and eating a
healthy diet can naturally reduce these risks.
 Better Regulation of Insulin Levels:The amount of sugar
people consume in their diets has become a major cause of
insulin resistance, which in one of the contributing factors
of diabetes. By incorporating fasting methods just a few
days each week,Intermittent fasting helps us become more
sensitive to insulin, the fat storage hormone, and leptin, our
satiety hormone, ultimately improving sugar metabolism,
while reducing insulin resistance.
 Improved Mental Stability: People who practice
intermittent fasting report energy, as well as lower levels of
anger, confusion, tension, and stress. Additionally, they
found they were less prone to mood swings with longer
periods of mood stability throughout their days. This likely
has correlation to better blood sugar stability, as well as
improved mitochondrial function. Fasting has been shown
to boost the quality of mitochondria (the energy producers
of every cell) by speeding the rate in which old and
damaged mitochondria are cleared.

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Where the research falls short:
The first shortcoming to intermittent fasting is that when you
compare apples to apples, research to date shows that
intermittent fasting provides no further long term benefit over
calorie restriction, and calorie restriction provides no long term
benefits in weight loss. In fact, most long term evidence
shows calorie restriction has negative impacts to long loss.
Now let me be clear here – daily calorie deficits are a good
thing. Eating the same/slightly less and exercising more could
never be a bad thing. However, when we examine some of the
major clinical studies conducted on weight loss (the TODAY
study, the Women’s Health Initiative study, the Diabetes
Prevention program), data shows that despite initial weight loss
compared to control groups, continuous calorie restriction did
not amount to long term changes in weight, or body
composition. In fact, the members of these trails not only gained
back all their weight, but also now have to follow a calorie
restricted diet to maintain it. (4,5,6)
With this being said, the long term data for intermittent fasting
benefits just simply doesn’t exist yet. Understanding that calorie
restriction and intermittent fasting both have underlying
catabolic actions call for the need for more long term studies
with follow ups greater than 1 year would be needed before
drawing conclusions to the long term safety of intermittent
metabolism.
The second biggest pitfall to intermittent fasting research is that

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majority of it is done in men. No large scale, long term follow
up trials have yet to be conducted on female subjects, which
is a problem. Numerous trials to date show higher negative
sequelae to dietary restrictions in women, such as carbohydrate
deprivation inducing under functioning thyroid in as little as 6
wks, and ketosis caused menstrual dysfunction in 45% of
women after 6 months (7). And while we don't have great
human trials for intermittent fasting for women, rat trials show
significant impacts to reproductive hormones in as little as two
weeks following IF.8This information should be extrapolated
with caution when deciding if intermittent fasting is right for
you.
When should intermittent fasting be avoided?
While health benefits from IF exist for many people, the
following people should not engage in restrictive dieting without
the counsel of a medical professional:
 Type I Diabetes – while I do use IF in some of my insulin
dependent patients, it is recommended on a case by case
basis, and with close supervision. Uneducated users can
risk hypoglycemic events and severe health risks.
 Eating disorders that involve unhealthy self-restriction
(anorexia, bulimia nervosa, orthorexia)
 Use of medications that require food intake or result in
hypoglycemia
 Active growth stage, such as infants or adolescents
 Pregnancy, breastfeeding – there’s just not enough research
to confirm its safety in pregnancy, and restrictive dieting
during breast feeding usually leads to decreased milk
supply.

8. Website- https://www.courtneyholmbergnd.ca/ Phone No- (647) 351-7282
My general advise remains to assess things on a case by
case basis to determine if intermittent fasting is right for
you, and for how long. Until more research confirms more
long term benefits and conclusive benefits in women, I
usually advice sticking to IF 2-3 days a week, and
maintaining a whole foods, plant time.
To find out if intermittent fasting and which methods are
right for you, please feel free to contact Dr. Courtney
Holmberg, ND at 647-351-7282 to schedule an
appointment today!
References:
Seimon RV, Roekenes JA, Zibellini J, Zhu B, Gibson AA,
Hills AP, Wood RE, King NA, Byrne NM, Sainsbury A.
Do intermittent diets provide physiological benefits over
continuous diets for weight loss? A systematic review of
clinical trials. Mol Cell Endocrinol. 2015 Dec 15;418:153-
72
Catherine R. Marinac, BA; Sandahl H. Nelson, MS; Caitlin
I. Breen, BS, BA; Sheri J. Hartman, PhD; Loki Natarajan,
PhD; John P. Pierce, PhD; Shirley W. Flatt, MS; Dorothy
D. Sears, PhD; Ruth E. Patterson, PhD. Prolonged Nightly
Fasting and Breast Cancer Prognosis. JAMA Oncol.
2016;2(8):1049-1055. doi:10.1001/jamaoncol.2016.0164
Seimon RV, Roekenes JA, Zibellini J, Zhu B, Gibson AA,
Hills AP, Wood RE, King NA, Byrne NM, Sainsbury A.
Do intermittent diets provide physiological benefits over

9. Website- https://www.courtneyholmbergnd.ca/ Phone No- (647) 351-7282
continuous diets for weight loss? A systematic review of
clinical trials. Mol Cell Endocrinol. 2015 Dec 15;418:153-
72
Trepanowski JF, Kroeger CM, Barnosky A, Klempel MC,
Bhutani S, Hoddy KK, Gabel K, Freels S, Rigdon J, Rood
J, Ravussin E. Effect of Alternate-Day Fasting on Weight
Loss, Weight Maintenance, and Cardioprotection Among
Metabolically Healthy Obese Adults: A Randomized
Clinical Trial. JAMA Internal Medicine. 2017 May 1.
Johnstone AM. Fasting–the ultimate diet?. Obesity
Reviews. 2007 May 1;8(3):211-22.
Harvie M, Howell A. 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. Behavioral Sciences. 2017 Jan 19;7(1):4.
Mady MA1, Kossoff EH, McGregor AL, Wheless
JW, Pyzik PL, Freeman JM. The ketogenic diet:
adolescents can do it, too. Epilepsia. 2003 Jun;44(6):847-
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