Nutrients 2019, 11, 1192; doi:10.3390/nu11051192 www.mdpi.com/journal/nutrients
Energy Metabolism and Intermittent Fasting:
The Ramadan Perspective
Nader Lessan * and Tomader Ali
Imperial College London Diabetes Center (ICLDC), Abu Dhabi, UAE; firstname.lastname@example.org
* Correspondence: email@example.com; 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
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 hours and 3 weeks i.e., in a short
term, long term/prolonged or an intermittent pattern . 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 . 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  and to prolong life in more primitive species
including Escherichia coli and yeast . 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 . 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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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 . 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 . 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 .
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 1,2) 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) . 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 . 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 .
Thermic effect of food is the rise in energy expenditure that occurs with food intake . 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 a greater rise in EE than fat or carbohydrates. Although TEF is
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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 .
Table 1. Energy Expenditure in Ramadan.
Ref. Year Study Cohort
Healthy adults 1-week
(BL) as well as first and
second week of
Ramadan (R1) and (R2);
n = 7).
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.
Healthy adults during
RMR (n = 29, 16 female)
Activity (total steps per
day) (n = 11, 5 female);
TEE (n = 10, 5 female).
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.
Healthy adults, 2 days
pre-Ramadan (T1); the
2nd day (T2), and the
28th day (T3) of fasting;
& 1 month after, (n =
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.
Healthy fasting (FAST,
n = 9) and non-fasting
(CNT, n = 8) adults pre
additionally assessed at
days 10, 20 & 30 of
Ramadan (am) & (pm).
32 ± 8
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.
Table 2. Energy intake and weight changes during Ramadan.
Ref Year Study Cohort Gender &
Age (years) Reported Observations
adults with normal
body weight; n =
1476; 553 female and
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).
adults, two days
second (T2) and 28th
day (T3) of Ramadan;
and 1 month
post-Ramadan (T4); n
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.
(FAST, n = 9) and
non-fasting (CNT, n =
8) adults pre and
assessed at days 10,
20 & 30 of Ramadan
both (am) and (pm).
FAST: 32 ±
8, CNT: 35
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
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adults, n = 46; 24
female and 22 male.
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.
 2011 173 families fasting
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.
adults at one-week
first week (T2), end of
second week (T3),
and end of last week
(T4) of Ramadan; n =
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 hours 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
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
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].
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’ . Early
studies also indicated a progressive decrease in daily urinary nitrogen excretion suggestive of an
increase in conservation of body protein  and that urine output gradually decreased throughout
the fasting period .
In 2006, a study on prolonged absolute fast (44-days) on a healthy non-obese man shed light on
changes in various metabolic parameters . 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
Nutrients 2019, 11, 1192 5 of 15
(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 .
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 −12.4kg. R2 = 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).
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) .
y = -0.3724x + 58.582
R² = 0.9798
1 2 3 4 5 6 7 8 9 10111213141516171819202122232425262728293031
Day of Fast (Day)
1 2 3 4 5 6 7 8 910111213141516171819202122232425262728293031
Relative Rate of Weight Change
Day of Fast (Day)
Max = 0.67
Max = 0.64
Max = 0.47
Max = 0.42
Nutrients 2019, 11, 1192 6 of 15
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
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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 . 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.
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 . 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 2,000 and male 2,500 kcal/day) in the UK , (2) 2300 kcal/day (female 2,000 and
male 2,600 kcal/day) in the USA  and 2255 kcal/day (female 2,010 and male 2,600 kcal/day) in
Australia . Collectively, an average adult consumes ~2268 kcal/day (female 2,003 and male 2,533
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).
Ramadan nutrition planning (RNP) is encouraged as per DaR guidelines, which take into
consideration variations in cultural food choice and calorie consumption (range of 1200kcal/day for
weight reduction for females to maximum of 2000 kcal/day weight maintenance for males) . 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-hour 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 hours (Figure 2A (III) and 2B (III)).
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
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
Nutrients 2019, 11, 1192 8 of 15
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.
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 2,000 and male 2,500 kcal/day), (2) the USA 2300
kcal/day (female 2,000 and male 2,600 kcal/day) and (3) for Australia 2225 kcal/day (female 2,010 and
male 2,600 kcal/day). Collectively, an average adult consumes ~2270 kcal/day (female 2,003 and male
2,533 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 15
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 . 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 . 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 . 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 . It has also been shown that weight loss is greater among Asian populations
compared with Africans and Europeans  and that there does not appear to be any gender
difference in the absolute magnitude of weight loss with Ramadan fasting.
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) . Studies into
RMR changes in Ramadan are however few in number. A study by El Ati and colleagues (1995) is
the earliest reported . 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 . 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  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  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 . Differences in daily
activity patterns between Ramadan and non-Ramadan periods were observed (Figure 4). Activity in
Nutrients 2019, 11, 1192 10 of 15
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.
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
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 .
AlSubheen and colleagues have also shown that carbohydrate oxidation drops and lipid oxidation
gradually increases through the Ramadan fasting day .
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 .
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 . The insulin
resistance observed  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
Nutrients 2019, 11, 1192 11 of 15
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 15
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 . Similar to
calorie-restricting diets targeting calorie reduction at ~500–800 kcal/day , 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].
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) . Along with protein loss, weight loss also
occurs; initially at a higher rate (~1kg/day) which then decreases (~0.7 kg/day by 24 hrs, 0.5 kg/day
by day 6 and 0.3 kg/day from day 21 onwards) . Importantly, the few small studies of energy
expenditure in the context of Ramadan fast have found no evidence of a metabolic adaptation .
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 . Although the increased appetite at the end of the fasting day  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 ; also reported with high inter-individual
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 . Fluid homeostasis during Ramadan fast has been investigated in several
studies and has been reviewed elsewhere . 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 . Furthermore, hypohydration has
been shown to have no significant effect on RMR and blood glucose in healthy subjects .
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 . 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
Nutrients 2019, 11, 1192 13 of 15
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).
Conflicts of Interest: The authors declare no conflict of interest.
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