Energy Metabolism and Intermittent Fasting: The Ramadan Perspective

Abstract

Intermittent fasting (IF) has been gaining popularity as a means of losing weight. The Ramadan fast (RF) is a form of IF practiced by millions of adult Muslims globally for a whole lunar month every year. It entails a major shift from normal eating patterns to exclusive nocturnal eating. RF is a state of intermittent liver glycogen depletion and repletion. The earlier (morning) part of the fasting day is marked by dominance of carbohydrate as the main fuel, but lipid becomes more important towards the afternoon and as the time for breaking the fast at sunset (iftar) gets closer. The practice of observing Ramadan fasting is accompanied by changes in sleeping and activity patterns, as well as circadian rhythms of hormones including cortisol, insulin, leptin, ghrelin, growth hormone, prolactin, sex hormones, and adiponectin. Few studies have investigated energy expenditure in the context of RF including resting metabolic rate (RMR) and total energy expenditure (TEE) and found no significant changes with RF. Changes in activity and sleeping patterns however do occur and are different from non-Ramadan days. Weight changes in the context of Ramadan fast are variable and typically modest with wise inter-individual variation. As well as its direct relevance to many religious observers, understanding intermittent fasting may have implications on weight loss strategies with even broader potential implications. This review examines current knowledge on different aspects of energy balance in RF, as a common model to learn from and also map out strategies for healthier outcomes in such settings.

Full text

nutrients
Review
Energy Metabolism and Intermittent Fasting: The
Ramadan Perspective
Nader Lessan * and Tomader Ali
Imperial College London Diabetes Center (ICLDC), Abu Dhabi 48338, UAE; tfali@icldc.ae
*Correspondence: nlessan@icldc.ae; Tel.: +971-2-4040-519
Received: 18 April 2019; Accepted: 9 May 2019; Published: 27 May 2019


Abstract:
Intermittent fasting (IF) has been gaining popularity as a means of losing weight. The
Ramadan fast (RF) is a form of IF practiced by millions of adult Muslims globally for a whole lunar
month every year. It entails a major shift from normal eating patterns to exclusive nocturnal eating.
RF is a state of intermittent liver glycogen depletion and repletion. The earlier (morning) part of
the fasting day is marked by dominance of carbohydrate as the main fuel, but lipid becomes more
important towards the afternoon and as the time for breaking the fast at sunset (iftar) gets closer. The
practice of observing Ramadan fasting is accompanied by changes in sleeping and activity patterns,
as well as circadian rhythms of hormones including cortisol, insulin, leptin, ghrelin, growth hormone,
prolactin, sex hormones, and adiponectin. Few studies have investigated energy expenditure in the
context of RF including resting metabolic rate (RMR) and total energy expenditure (TEE) and found
no significant changes with RF. Changes in activity and sleeping patterns however do occur and are
different from non-Ramadan days. Weight changes in the context of Ramadan fast are variable and
typically modest with wise inter-individual variation. As well as its direct relevance to many religious
observers, understanding intermittent fasting may have implications on weight loss strategies with
even broader potential implications. This review examines current knowledge on different aspects of
energy balance in RF, as a common model to learn from and also map out strategies for healthier
outcomes in such settings.
Keywords: fast; intermittent; Ramadan; energy expenditure; weight
1. Introduction
Fasting can be defined as the voluntary abstinence from or reduction of some or all food, drink,
or both (absolute) for a period of time lasting typically between 12 h and 3 weeks i.e., in a short
term, long term/prolonged or an intermittent pattern [
1
]. Fasting is a common practice in different
religious disciplines, including Islam, Christianity, Judaism and Hinduism. In Islam, the practice
entails abstinence from eating and drinking between dawn and sunset [
2
]. Fasting is distinct from
starvation, which is a chronic and severe deficiency in caloric energy intake below the level needed to
maintain life.
Health benefits of intermittent fasting have been demonstrated in both randomized controlled
trials and observational studies [
3
,
4
]. Caloric restriction (CR) has also been shown to prevent several
chronic degenerative and inflammatory diseases [
5
] and to prolong life in more primitive species
including Escherichia coli and yeast [
6
]. In humans, the evidence on the positive effects of CR on
longevity is indirect; for example the increased life expectancy in the Okinawan population, from the
Kyushu Island in Japan, has been attributed at least in part to low calorie intake [
7
]. Mechanistically,
the effect of CR on longevity has been attributed to fasting-induced modulation of neuroendocrine
systems, hormetic stress responses, increased systemic production of neurotrophic factors, reduced
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Nutrients 2019,11, 1192 2 of 16
mitochondrial oxidative stress, decreased pro-inflammatory cytokine production and insulin resistance,
as well as decreased aging-associated signals and autophagy promotion [5,8,9].
Prolonged fasting has also been associated with positive effects on mood due to the alteration in
physiology at a cellular level via increases in availability of central endogenous neurotransmitters,
endogenous opioids and endocannabinoids [
10
]. Cancer studies demonstrated that fasting and
fasting-mimicking diets (FMDs) positively promote differential effects in both normal and malignant
cells via reduction in insulin-like growth factor (IGF-1), insulin and glucose with paralleled increases
in ketone bodies [
11
]. In contrast, negative effects of fasting have been reported for instance on
non-communicable diseases [
8
,
11
,
12
], on changes to sleep patterns, cognitive function, [
13
,
14
] and
have also been associated with fluctuations in mood, weight and a plethora of other changes [15,16].
Fasting is a state of negative energy balance, and as such different fasting regimens have been
used to achieve weight loss, as well as other health benefits. In the context of Muslim Ramadan-type
fasting, changes in energy intake depend on social, cultural and individual factors and can range
from a reduction to an increase in weight [
17
–
19
]. Whether this is accompanied by changes in energy
expenditure is not well-known and merits further exploration for its possible implications in weight
loss management strategies in general [20].
This review will be examining current knowledge about different aspects of energy balance in the
context of the Ramadan fast as a commonly practiced model of intermittent fasting. In the broader
context, potential positive implications include the use of for such strategies to help with weight
maintenance, is not weight loss, and thus a multitude of other consequential positive health benefits.
Relevant literature (Tables 1and 2) directly and indirectly related to the Ramadan fast, including short-
and long-term fasting and also prolonged and intermittent type fasting will be explored. In the context
of Ramadan, changes in energy dynamics (intake versus expenditure) have been extrapolated based
on our previous quantitative studies, knowledge of physiology and alterations in energy utilization
during feeding and non-feeding periods. The aim of this review is firstly, to discuss the various aspects
influencing energy modulations during Ramadan fasting; secondly, to shed light on key knowledge
gaps in our understanding of energy balance in relation to changes in both body composition and
physiological adaptation in various models of fasting to include key periods such as the Ramadan
fasting period and; lastly, to contribute to the focused directionality of future studies in key aspects
that warrant further detailed investigations.
2. Energy Expenditure (EE)
When body weight is in a relatively stable state, there is equilibrium between energy intake (EI)
and energy expenditure (EE). High EI levels in combination with low EE results in a positive energy
balance and storage of energy, primarily as body fat. Total (daily) Energy Expenditure (TEE) consists
of Resting Metabolic Rate (RMR), Thermic Effects of Food (TEF) and Activity Energy Expenditure
(AEE) [
20
]. Different components of EE have been reviewed elsewhere [
21
–
24
] and will only be
discussed briefly here.
Resting Metabolic Rate (RMR) is the quantity of energy at rest needed to maintain body temperature,
repair internal organs, support cardiac function, maintain ionic gradients across cells, and support
respiration. In most people, this constitutes approximately two-thirds of total energy expenditure [
25
].
RMR is influenced by age, sex, body weight, pregnancy, and hormonal status. The highest rates of
energy expenditure per unit of body weight occur during infancy and decline through childhood. In
adult life, the decline continues at approximately 2% per decade because of a decline in lean body
mass. Females have a lower energy expenditure per unit of weight than do males, probably because
of the higher proportion of body fat and less lean body mass in women [
26
]. Thermic effect of food
is the rise in energy expenditure that occurs with food intake [
26
]. This rise is in part due to the
‘obligatory’ energy cost of ingestion, digestion, and metabolic processing of nutrients, and in part
due to a ‘facultative’ component arising from the sensory aspects of food and meal stimulation of the
sympathetic nervous system. Different macronutrients have different thermic effects; protein causes

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a greater rise in EE than fat or carbohydrates. Although TEF is normally a small component of TEE
(~10%) it is nonetheless an important component in energy imbalance states as it is influenced by meal
size and composition, the nature of the previous diet, insulin resistance, physical activity, and ageing
influence TEF [27].
Table 1. Energy Expenditure in Ramadan.
Ref. Year Study Cohort Gender & Age
(Years) Reported Observations
[14] 2010
Healthy adults
1-week
pre-Ramadan
baseline (BL) as
well as first and
second week of
Ramadan (R1) and
(R2); n=7).
Males; 21 ±3
SenseWear Pro Armband
measurements indicated EE and
METs significantly lower during
Ramadan and a shift in circadian
patterns (of body temperature, a delay
in bedtime and an increase in total
sleep time and nap time) during
Ramadan. No significant difference in
the number of meals.
[24] 2018
Healthy adults
during Ramadan
and non-Ramadan
periods. RMR (n=
29, 16 female)
Activity (total steps
per day) (n=11, 5
female); TEE (n=
10, 5 female).
Female and male;
33 ±9
Indirect calorimetry; (a) activity
during and post- Ramadan; no
significant difference, (b) activity
pattern: morning & afternoon
significantly lower during Ramadan.
Nocturnal activity was higher during
Ramadan, (c) TEE & RMR during and
post-Ramadan: no significant
difference; main factor influencing
TEE was body weight.
[28] 1995
Healthy adults, 2
days pre-Ramadan
(T1); the 2nd day
(T2), and the 28th
day (T3) of fasting;
& 1 month after, (n
=16).
Female; 25–39
Indirect calorimetry; calculations from
metabolic chamber; REE unchanged
during and post-Ramadan, compared
with pre- Ramadan. EE throughout
the circadian cycle was dramatically
affected during fasting with a
significant decrease observed from
11am to 5pm during Ramadan.
Nightly EE values did not change
significantly.
[29] 2017
Healthy fasting
(FAST, n=9) and
non-fasting (CNT,
n=8) adults pre
and post-Ramadan.
FAST group
additionally
assessed at days 10,
20 & 30 of
Ramadan (am) &
(pm).
Male; FAST: 32 ±8
and CNT: 35 ±9
Indirect calorimetry; significant group
×time interaction, reduced body
mass and adiposity in FAST, without
changing lean mass; for CNT subjects,
remained unchanged. Ramadan
fasting induces diurnal metabolic
adjustments (morning v. evening)
with no carryover effect observed
throughout Ramadan fasting despite
the extended daily fasting period and
changes in body composition.

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Table 2. Energy intake and weight changes during Ramadan.
Ref Year Study Cohort Gender & Age
(Years) Reported Observations
[18] 2014
Healthy fasting
adults with normal
body weight; n=
1476; 553 female
and 923 male)
Female and male;
≥18
In the female subgroup, body weight
(SMD =−0.04, 95% CI =−0.20, 0.12)
remained unchanged, while in males,
Ramadan fasting resulted in weight
loss (SMD =−0.24, 95% CI =−0.36,
−0.12, p=0.001).
[28] 1995
Healthy fasting
adults, two days
pre-Ramadan (T1);
second (T2) and
28th day (T3) of
Ramadan; and 1
month
post-Ramadan (T4);
n=16
Female; 25–39
Total daily energy intake, body
weight, fat mass and fat free mass
remain unchanged. REE pattern
change; lower during the fasting day
versus night but no significant change
overall.
[29] 2017
Healthy fasting
(FAST, n=9) and
non-fasting (CNT,
n=8) adults pre
and post-Ramadan.
FAST group
additionally
assessed at days 10,
20 & 30 of
Ramadan both (am)
and (pm).
Male; FAST: 32 ±8,
CNT: 35 ±9
Significant group ×time interaction
revealed reduced body mass and
adiposity in FAST, without changing
lean mass, whereas CNT subjects
remained unchanged. Although RF
induces diurnal metabolic
adjustments (morning v. evening), no
carryover effect was observed
throughout Ramadan fasting despite
the extended daily fasting period and
changes in body composition.
[30] 2009
Healthy fasting
adults, n=46; 24
female and 22
male.
Female and male;
24 ±3
Total energy intake was higher during
Ramadan (13 and 11 MJ/day) than
before and after Ramadan (11 and 9
MJ/day) in men and women,
respectively.
[31] 2011 173 families fasting
Ramadan
Female and male;
age unspecified
59.5% reported weight gain
post-Ramadan; 40% attributed food
types, 31.2% attributed to relative lack
of physical exercise and 14.5%
referred that to increase in food
consumption. 65.2% of those with
increased expenditure reported
weight gain.
[32] 2007
Healthy fasting
adults at one-week
pre-Ramadan (T1),
first week (T2), end
of second week
(T3), and end of
last week (T4) of
Ramadan; n=57
Female; 22 ±4
Body weight and BMI decreased
significantly during Ramadan fasting.
The mean physical activity level was
not significantly different. The overall
activity patterns remained similar;
1.54 pre-and 1.51 during Ramadan
2.1. Short-Term Fasting
Metabolically, fasting can be divided into three distinct key stages: Stage 1: a post-absorptive
phase ~6–24 h after beginning fasting where the central nervous system (CNS) and many other
issues preferentially use glucose produced from glycogen breakdown. Lipolysis and ketogenesis and
gluconeogenesis increase, but the latter to a lower extent. Glycogenolysis decreases. Stage 2: the

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gluconeogenic phase occurs ~1–10 days after beginning fasting. Here, protein catabolism is used to
feed glucose to the CNS while other tissues feed on ketones and fat. Lipolysis and ketogenesis increase
and then plateau, gluconeogenesis on the other hand begins to decrease and no glycogenolysis occurs.
Stage 3: is a protein conservation phase that occurs when fasting extends beyond 10 days. Protein
catabolism is decreased to a minimum, fatty acids are used ubiquitously and ketones are utilized as
fuel in the CNS. Lipolysis and ketogenesis plateaus while gluconeogenesis decreases and then plateaus
but to a much lower extent when compared to ketogenesis [33,34].
2.2. Prolonged Fasting-Some Historic Examples
Early studies in 1915 by Francis Benedict looking into chemical and physiological alterations in
a lean man fasting thirty-one days demonstrated significant declines in body weight (
−
12.4 kg with
a rate of
−
0.84 kg/day at Day 1 declining to 0.32 kg/day by Day 31), (Figure 1). Levels of various
biological markers such as body temperature and blood pressure were maintained [35,36].
Figure 1.
Time-dependent Changes in Weight during Prolonged Fasting (31 Days). Adapted from:
Francis Gano Benedict: A study of Prolonged Fasting. (
a
), Daily Net Weight Loss: calculation of daily
weight reduction in 31 days (D) of fasting. Initial weight was 59.86 kg at D1, final weight was 47.47 kg at
D31, total weight loss
−
12.4 kg. R
2
=9798 indicated a linear relationship between time and net weight
loss. (
b
) Changes in Rate of Daily Weight Loss: relative to starting rate of weight loss, rate of weight
loss per day indicates various changes whereby a steep rate of weight loss we observed in the first five
days of fasting (D1–5; Maximum Rate 0.67), followed by a slower rate of weight loss in the following 10
days (D5–15; Maximum Rate 0.64), which decreased further in the next 10 days (D15–25; Maximum
Rate 0.47) before reaching a plateau in the last five days of the fasting month (D25–30; Maximum Rate
0.42).

Nutrients 2019,11, 1192 6 of 16
In 1916, Spriggs reported various cases of fasting used as a method to treat diabetes whereby
fasting was ‘continued in bed until the urine has been sugar-free for twenty-four hours, unless there is
some definite contraindication, such as nausea, vomiting, insomnia, or faintness’ [
37
]. Early studies
also indicated a progressive decrease in daily urinary nitrogen excretion suggestive of an increase in
conservation of body protein [
38
] and that urine output gradually decreased throughout the fasting
period [39].
In 2006, a study on prolonged absolute fast (44-days) on a healthy non-obese man shed light on
changes in various metabolic parameters [
40
]. The TEE was not measured, but was estimated to be
1638–2155 kcal/day of which 13.0–17.1% was from protein oxidation. Total weight loss was 24.5 kg and
body mass decreased by 25.5%; a quarter to a third was fat mass and the remainder to fat-free mass
which was predominantly muscle and approximately 20% was total body protein.
More recently, in 2015, Müller and colleagues investigated effects of caloric restriction (CR) and
weight loss on 32 subjects aged between 20–37 years old in a controlled environment. Patterns of
habitual food intake, resting energy expenditure and physical activity were assessed. The 10 week
(week) dietary intervention period duration included 1 week of overfeeding (at +50% of daily energy
requirements; 4059
±
52 kcal/day) followed by 3 weeks of CR (at
−
50% of energy requirements; 1353
±
154 kcal/day) and a subsequent 2 weeks of re-feeding (at +50% of energy requirements; 4059
±
452
kcal/day). Protein intake was 97
±
11 g/day (baseline); 146
±
17 g/day (overfeeding), 49
±
6 g/day (CR),
and 146
±
17 g/day (re-feeding), respectively. The study reports a +1.8 kg weight gain (overfeeding),
−
6.0 kg (CR), and +3.5 kg (re-feeding). CR reduced fat mass and fat-free mass from skeletal muscle
(
−
5%), liver (
−
13%), and kidneys (
−
8%) by a total of 114 and 159 g/day, respectively. CR also led to
reductions in resting energy expenditure (
−
266 kcal/d) and respiratory quotient (
−
15%). The study
concluded that during early weight loss, adaptive thermogenesis is associated with a fall in insulin
secretion and body fluid balance [41].
3. The Ramadan Fast: A Shift from Normal Eating Patterns
A typical eating pattern in most cultures includes three main meals, often accompanied by snacks
in between (Figure 2). Alterations in this ‘normal’ pattern can have important implications to energy
balance. Some of the more common fasting regimens include intermittent fasting (IF), periodic fasting
(PF) and time restricted fasting (TRF) [8].
Ramadan fasting and Ramadan-type fasting are somewhat different from other forms of fasting
mentioned above. Ramadan, the ninth month in the Islamic Calendar, requires Muslims to fast daily
from dawn to dusk and the criteria are clearly defined in the Holy Quran [
2
]. No food or drink is
allowed after suhoor until iftar. The fast is traditionally broken with something sweet such as dates.
This is followed by the main meal which tends to be heavy and carbohydrate-rich. Between iftar and
suhoor, food can be taken without any restriction. Ramadan is a lunar month and as such lasts 29–30
days. The fast is a religious obligation for all adult Muslims. Exempt groups include the sick and also
women during their menstrual period. Many people who are religiously exempt opt to fast, often for
social and cultural reasons.
In addition to Ramadan fasting, many Muslims practice the same dawn-to-sunset type of fast on
other days of the year and this may include Mondays and Thursdays. Fasting some days may have
some physiological differences from fasting an entire month as some physiological adaptations which
may happen later during Ramadan may not occur in the short term.

Nutrients 2019,11, 1192 7 of 16
Figure 2.
Changes in Feeding Patterns and Energy Intake during Various Fasting Periods. The five
feeding and fasting patterns are: (I) normal feeding, (II), calorie restriction, (III) intermittent fasting (e.g.,
5:2), (IV) Ramadan fast and (V) prolonged fasting and starvation. (
a
) Hourly Differences in Feeding
Patterns between Various Fasting Models: hourly timings of feeding and energy intake (meals) are
indicated per day in relation to fasting periods (arrows) and reflected in glycaemic control (traces).
(
b
), Daily and Weekly Differences in Feeding Patterns Between Various Fasting Models: daily and
weekly feeding patterns are mapped against calorie intake which can be regular such as in in normal
feeding (I), indicated by single colour arrows or a combination of low, normal or high calorie intake
as in intermittent fasting (III), indicated by mixed colour arrows. Ramadan fast (IV) is unique as it
combined low and high calorie intake as indicated by the two single colour arrows. The first week is
broken down into seven individual days. Weekly indications follow thereafter.

Nutrients 2019,11, 1192 8 of 16
4. The Ramadan Diet
Management of a healthy balanced diet is necessary not only for the maintenance of a healthy
weight, but for the maintenance of the overall nutritional health of individuals too. Energy intake
plays a central role [42]. Nonetheless, multiple factors influencing energy intake such as cultural and
lifestyle differences, make it difficult to maintain healthy balanced diet long-term. During non-fasting
periods, recent statistics indicate that average daily adult energy intake is: (1) 2250 kcal/day (female
2000 and male 2500 kcal/day) in the UK [
43
], (2) 2300 kcal/day (female 2000 and male 2600 kcal/day) in
the USA [
44
] and 2255 kcal/day (female 2010 and male 2600 kcal/day) in Australia [
45
]. Collectively, an
average adult consumes ~2268 kcal/day (female 2003 and male 2533 kcal/day) (Figure 3A) with an
additional margin for genetic (e.g., predisposition to overweight/obesity) and environmental influences
(e.g., daily activity and feeding habits).
Figure 3.
Energy intake (EI) recommendations and resultant weight changes in Ramadan and
non-Ramadan periods. Energy intake recommended guidelines for female and male adults. (
a
)
indicates values for the (1) UK 2250 kcal/day (female 2000 and male 2500 kcal/day), (2) the USA 2300
kcal/day (female 2000 and male 2600 kcal/day) and (3) for Australia 2225 kcal/day (female 2010 and
male 2600 kcal/day). Collectively, an average adult consumes ~2270 kcal/day (female 2003 and male
2533 kcal/day). (
b
), Energy intake recommendations during Ramadan in comparison to standard and
low calorie diets. in order of left to right: based on the calculated average of 2270 kcal/day as a standard
adult EI (Figure 3A), a healthy Ramadan diet matched calorie intake is achievable. In reality, a higher
EI is experienced in Ramadan (~3000 calories). However, weight maintenance (at 1800 kcals/day) is
achievable during Ramadan as suggested by Diabetes and Ramadan (DaR) Alliance Ramadan Nutrition
Plans (RNP) recommendations. This holds true for weight loss at the 1500 and 1200 kcals/day calorie EI
for both non-Ramadan and Ramadan periods.

Nutrients 2019,11, 1192 9 of 16
Ramadan nutrition planning (RNP) is encouraged as per DaR guidelines, which take into
consideration variations in cultural food choice and calorie consumption (range of 1200 kcal/day for
weight reduction for females to maximum of 2000 kcal/day weight maintenance for males) [
46
]. Due to
the inevitable changes in feeding patterns and associated physiological shifts in circadian rhythms,
hormone levels fluctuations and overall daily lifestyle, Ramadan meal planning becomes an essential
component for healthy Ramadan fasting. This is of particular importance for patients with chronic
conditions, such as diabetes. A ‘Ramadan Plate’ is recommended to contain a balanced selection of
carbohydrates (40–50% of total daily calorie intake (TDCI) of low glycaemic index and high-fibre
containing foods), protein (20–30% of TDCI of non-red meat sources and legumes) and reduced fat
intake (35% of TDCI of mostly mono- and poly-saturated fatty acids). Suhoor, the pre-dawn meal,
is recommended to constitute 30–40% energy intake for the day, iftar 40–50% and snacks 10–20%
as necessary.
In theory, in terms of energy intake, skipping one main meal in a 24-h period should be associated
with a major reduction in food content and energy intake. This is the principle in the intermittent
5:2 fasting diet where fasting can be up to 18 h (Figure 2(AIII,BIII)). Therefore, during Ramadan, in
addition to eating healthily, this reduction in energy intake could lead to weight loss but in practice
this does not occur in most cultures (Figure 3B). Many studies indicate a great variability in Ramadan
diets [
30
,
47
] in different cultures, age groups, geographical locations and duration of fasting hours as
well as the impact of physiological and pathological conditions (e.g., diabetes) and associated with
modest reduction of energy intake in most but not all groups studied.
El Ati and colleagues investigated a group of 16 healthy female volunteers fasting during Ramadan
and reported 84% of total daily energy intake was taken at the evening meal, and the remaining 16%
was taken between 8 p.m and midnight. This is in contrast to periods before Ramadan where breakfast,
lunch and dinner constituted 9.4, 41.6 and 21.8% of total daily energy intake. Although the findings of
this small study cannot be generalized to the larger population of fasting Muslims, the observation of
a disproportionately large meal at iftar time is a common finding [
31
,
48
]; often reflected in feeding
patterns (Figure 2) and in glycaemic profiles.
5. Weight and Body Composition Changes During Ramadan Fasting
There seems to be much inter-individual variability in weight trends with Ramadan fasting and
as with other modalities of weight change; one would expect these to be determined by individual,
cultural and social factors as well as genetic, epigenetic and other factors such as gut microbiome.
Several small studies (with participants between 16–81 years old in most) have examined the effect(s)
of Ramadan on body weight and reported a modest weight loss of 1–2 kg by the end of Ramadan,
with some other studies reporting weight gain [
18
,
19
]. A meta-analysis of the older studies (by Kul et
al., 2014) showed a small weight loss of around 0.7 kg in fasting men, but no significant change in
fasting women [
18
]. The largest study of 202 participants (Hajek et al., 2012) recruited at mosques
in East London showed a net weight loss of around 0.8 kg by the end of Ramadan [
49
]. As in some
other studies that had post-Ramadan weight recorded, this study showed that all the lost weight was
regained 4–5 weeks after Ramadan [
18
]. In terms of satiety and hunger, the levels remained the same
for males during Ramadan while for females more hunger was experienced earlier in the month and
then decreased as the Ramadan month progressed [30,50].
In a more recent excellent meta-analysis, Fernando and colleagues showed that the mean weight
loss with Ramadan fasting was 1.34 kg and that most of the weight was regained a few weeks
post-Ramadan [
51
]. It has also been shown that weight loss is greater among Asian populations
compared with Africans and Europeans [
19
] and that there does not appear to be any gender difference
in the absolute magnitude of weight loss with Ramadan fasting.

Nutrients 2019,11, 1192 10 of 16
6. Energy Expenditure During Ramadan Fasting
6.1. Resting Metabolic Rate (RMR) During Ramadan Fasting
RMR is known to decrease with prolonged fasting and this may be a counter-regulatory way
to decrease energy loss (Benedict, 1915; Forbes, 1987; Garrow, 1978; Woo et al., 1985) [
26
]. Studies
into RMR changes in Ramadan are however few in number. A study by El Ati and colleagues (1995)
is the earliest reported [
28
]. Different aspects of EE in the context of the Ramadan fast in 16 female
participants were explored. RMR at four different time points around Ramadan (before Ramadan, the
first week of Ramadan, the last week of Ramadan, and the month after Ramadan) were investigated
along with daily EE trends. The study reported a reduction in RMR during Ramadan and metabolic
rate patterns were found to be different between Ramadan and non-Ramadan days; lower during
the fasting day versus night, with a rise around iftar, but no significant change overall. Total daily
energy intake, body weight, fat mass and fat free mass remained unchanged. Similarly, a study by
Bahammam and colleagues found a reduction in EE and metabolic equivalents (METs) measured by
accelerometry during Ramadan fasting [
14
]. In our own study of 45 male and female subjects we found
no overall difference in RMR between Ramadan and non-Ramadan periods (mean
±
SD: 1365
±
230
compared with 1363
±
274 kcal/day for Ramadan and post-Ramadan respectively, p=0.713, n=29).
However, multiple linear regressions and controlling for the effects of age, sex, and body weight, RMR
was higher in the first week of Ramadan and showed a significant downward trend in subsequent
weeks [
24
] potentially due to metabolic adaptation medicated both centrally and locally (e.g., via gut
hormones). Thorough investigations, particularly in the context of Ramadan, need to be conducted
to more accurately and precisely assess the contribution of these individual factors in fasting-related
energy regulation.
6.2. Activity Energy Expenditure (AEE) During Ramadan Fasting
As well as changes in meal times and content, Ramadan period is associated with major changes
in activity patterns throughout the fasting day. Much of the daily activity and AEE tends to occur
nocturnally after iftar [
52
] with inter-individual variability reported in various other studies [
32
,
52
,
53
].
A recent study by our group (Lessan et al., 2018) investigated daily activity patterns using accelerometers
an overall reduction in daily activity energy expenditure [
24
]. Differences in daily activity patterns
between Ramadan and non-Ramadan periods were observed (Figure 4). Activity in the morning (1974
±
583 compared with 3606
±
715, p=0.001) and afternoon (3193
±
783 compared with 4164
±
670, p=
0.002) were significantly lower during Ramadan compared with post-Ramadan. Nocturnal activity
was higher during Ramadan (1261
±
629 compared with 416
±
279, p=0.001). No significant difference
in evening activity levels between during and post-Ramadan periods was seen however the study
found a reduction in activity during fasting hours and a rise after iftar. Furthermore, major change in
sleeping patterns and times was reported.

Nutrients 2019,11, 1192 11 of 16
Figure 4.
Energy expenditure and physical activity pre-, during and post-Ramadan. (
a
) Box plot of
daily total number of steps during and post-Ramadan. The effect of Ramadan fasting on activity in
11 participants. (
b
) Box plot of total number of steps at different periods within one day (per night,
morning, afternoon, and evening) during and post-Ramadan in 11 participants. Comparisons made
with the Wilcoxon signed-rank test. Total mean
±
SD number of steps per day (9950
±
1152 compared
with 11,353
±
2053, p=0.001), activity in the morning (1974
±
583 compared with 3606
±
715, p=
0.001) and afternoon (3193
±
783 compared with 4164
±
670, p=0.002) were significantly lower during
Ramadan compared with post-Ramadan. Nocturnal activity was higher during Ramadan (1261
±
629 compared with 416
±
279, p=0.001). No significant difference in evening activity levels between
during and post-Ramadan periods was observed. (
c
) TEE and RMR during and post-Ramadan: the
correlation between TEE and weight during and post-Ramadan in 10 participants. No significant
difference between Ramadan and post-Ramadan regression lines (ANCOVA; t=0.35, p=0.727); the
main factor influencing TEE was body weight (t=2.72, p=0.015).

Nutrients 2019,11, 1192 12 of 16
6.3. Thermic Effect Of Food (TEF) During Ramadan Fasting
There have been no studies specifically investigating TEF in the context of Ramadan fasting and it
is difficult to speculate how TEF would change with the Ramadan fast. However, there are a number
of considerations in speculating what changes to TEF might be expected with the Ramadan fast. Firstly,
TEF is related to serum insulin and insulin resistance. Insulin resistance and plasma insulin level
are known to be higher during the Ramadan fast, especially in the evening and around iftar period.
This may lead to a reduction in TEF. Secondly, dietary fat has a lower thermic effect than protein.
Several studies of diet during Ramadan have indeed, reported a higher fat content; this can also cause
a reduction in TEF during Ramadan. Finally, a major meal is skipped during Ramadan, and although
this can in part be compensated by over-snacking at nights, a net reduction in TEF may be expected.
Well-conducted studies of TEF during Ramadan can provide a better insight into energy dynamics
during Ramadan and help with weight management around the Ramadan period.
6.4. Fuel Utilization During Ramadan Fasting
Few studies have investigated fuel utilization in the context of the Ramadan fast. Using indirect
calorimetry, El Ati has shown that during Ramadan fat oxidation increases through the fasting day.
Carbohydrate oxidation decreases gradually from morning to iftar time. The differences in fuel
oxidation at different time points in Ramadan and non-Ramadan days were significant [
51
]. AlSubheen
and colleagues have also shown that carbohydrate oxidation drops and lipid oxidation gradually
increases through the Ramadan fasting day [29].
6.5. Total Energy Expenditure (TEE) During Ramadan Fasting
El Ati and colleagues reported measurements of energy expenditure by indirect calorimetry at
several time points through Ramadan and non-Ramadan days reportedly in a metabolic chamber. No
total energy expenditure values were however reported. Substrate oxidation and biochemical assays
were also carried out over the four-day test period between 8 a.m. and 11 p.m. at three hourly intervals.
The study reports that resting energy expenditure measured at 8 a.m. remained unchanged during and
after Ramadan, compared to pre- Ramadan durations. However, the EE throughout the circadian cycle
was dramatically affected during Ramadan fasting periods whereby, and unlike the nightly energy
expenditure values, a significant decrease in energy expenditure was observed from 11 a.m. to 5 p.m.
hours during Ramadan fasting periods [13].
Our study in healthy non-obese volunteers investigated changes in RMR and TEE in free-living
conditions. The study of TEE utilizing doubly-labelled water and accelerometer aided techniques by
our group reported no differences in TEE between Ramadan and Post-Ramadan periods (mean
±
SD:
2224
±
434 compared with 2121
±
719 kcal/day for Ramadan and Post-Ramadan, p=0.7695, n=10)
(Figure 4). TEE did not differ significantly between Ramadan and Post-Ramadan [
24
]. The insulin
resistance observed [
24
] was a result of the compounding factors of reduction in circulating leptin, a
gradual shift from carbohydrate to lipid as dominant fuel as the fasting day progresses and the variable
weight change determined by individual, social and cultural factors, rather than physiological changes.
7. Discussion and Concluding Remarks
Calorie restriction and different forms of fasting have been shown to have major physiological
effects; from health benefits to longevity [
6
,
54
]. Ramadan fasting has also been shown to have beneficial
effects including positive changes in body composition with reported reduction in body fat as well as
weight loss which is a common although not universal consequence [
50
]. Similar to calorie-restricting
diets targeting calorie reduction at ~500–800 kcal/day [
55
], skipping a meal during fasting, such as
in the context of Ramadan, can theoretically lead to weight loss. However, dietary changes during
Ramadan vary and often include an increase in carbohydrate intake [56,57].

Nutrients 2019,11, 1192 13 of 16
Weight loss strategies including many dietary interventions are often unsuccessful in the medium
and the long term. One explanation for this is the phenomenon of adaptive thermogenesis. This occurs
by promoting optimization of energy reserves while preserving protein pools via reduction in basal
metabolism, decrease in secretion of anabolic factors (e.g., insulin) and increase in catabolic hormones
(e.g., adrenaline and glucagon) [
3
]. Along with protein loss, weight loss also occurs; initially at a higher
rate (~1 kg/day) which then decreases (~0.7 kg/day by 24 h, 0.5 kg/day by day 6 and 0.3 kg/day from day
21 onwards) [
33
]. Importantly, the few small studies of energy expenditure in the context of Ramadan
fast have found no evidence of a metabolic adaptation [
24
]. This finding needs to be investigated in
larger studies and if confirmed, may have important implications on Ramadan and IF as potential
weight loss strategies. Admittedly, overcompensation with an increase in energy intake at the evening
meal is common practice in observers of the Ramadan fast [
31
]. Although the increased appetite at
the end of the fasting day [
49
] is the main drive for this phenomenon, this is in many ways voluntary.
With appropriate education and a shift in food choices it may be possible to limit this increase in intake
of energy dense food and make the prospect of weight loss with the Ramadan fast more realistic.
Aside from weight changes, Ramadan fasting induces a plethora of physiological and metabolic
alterations. The impact of Ramadan on sleep alone includes decreased total sleep time, delayed sleep,
decreased sleep period time (decreased REM sleep duration, decreased proportion of REM sleep) and
increased proportion of non-REM sleep [13]; also reported with high inter-individual variation.
An important issue on interpretation of Ramadan studies is the potential hypohydration that
would be expected towards the end of the Ramadan fasting day. A study investigating the effects of
prolonged fasting and fluid deprivation reported a loss of body weight of around 1.5 kg in individuals
fasting between 10 pm and 4 pm the next day; the weight loss was presumed to be due to loss of
body water [
39
]. Fluid homeostasis during Ramadan fast has been investigated in several studies and
has been reviewed elsewhere [
58
]. Water turnover has been shown to increase during Ramadan fast
with concomitant increases in indicators of body hydration including haematocrit, serum urea and
creatinine and urine osmolality. However, total body water appears to be conserved and aside from
potentially contributing to weight loss that might be observed in Ramadan, no detrimental effects
on health have been directly attributed to negative water balance and hypohydration at the levels
experienced during Ramadan [
58
]. Furthermore, hypohydration has been shown to have no significant
effect on RMR and blood glucose in healthy subjects [59].
Studies of Ramadan fasting in general need to be interpreted carefully and with consideration for
certain factors such as the timing of previous meal, methodological differences and also hydration status.
An important and relevant factor in studies of Ramadan fasting is the duration of the fast, and hence
geographical location; the impact tends to be most marked in countries at higher altitudes and with
more daylight hours [
60
]. Fasting hours also include the seasonal changes whereby fasting Ramadan
during winter months for instance would have physiologically different effects when compared to
fasting Ramadan during summer months. Although the literature specifically pertaining to energy
expenditure changes during Ramadan is steadily mounting, it is currently small in number. Therefore,
future studies need to address these variables to tackle the inter-variability issues that continually
arises in the current literature.
In conclusion, although the metabolic consequences of Ramadan fast are complex, there is
potential for using this month as a weight reduction model provided the fasting is carried out
mindfully; balancing food type, quantity and levels of physical activity. Pre-Ramadan planning
(nutrition plans, medication and health checks) is necessary; more so for individuals with chronic
conditions such as diabetes who need specialist advice should Ramadan fast be deemed suitable in the
first place. The long-term effects are thus of interest and studies are necessary for elucidation.
Author Contributions: The authors have contributed equally to the writing and editing of the manuscript.
Funding: This research received no external funding.
Acknowledgments: This work has been supported by Imperial College London Diabetes Centre (ICLDC).

Nutrients 2019,11, 1192 14 of 16
Conflicts of Interest: The authors declare no conflict of interest.
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