A review of salivary composition changes induced by fasting and its impact on health

Nurul Fadhilah Kamalul Aripin; N. Idayu Zahid; Mohd Aizat Abdul Rahim; Hashim Yaacob; Parvez I. Haris; Zubaidah Haji Abd. Rahim; Rauzah Hashim

doi:10.26599/FSHW.2022.9250004

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Review Article | Open Access

A review of salivary composition changes induced by fasting and its impact on health

Nurul Fadhilah Kamalul Aripin^{^a^,^b}, N. Idayu Zahid^{^b}, Mohd Aizat Abdul Rahim^{^c}, Hashim Yaacob^{^d}, Parvez I. Haris^{^e}, Zubaidah Haji Abd. Rahim^{^f}(), Rauzah Hashim^{^b^,^f}()

School of Chemical Engineering, College of Engineering, Universiti Teknologi MARA, Shah Alam 40450, Malaysia

Centre for Fundamental and Frontier Sciences in Nanostructure Self-Assembly, Department of Chemistry, Faculty of Science, Universiti Malaya, Kuala Lumpur 50603, Malaysia

Department of Oral and Craniofacial Sciences, Faculty of Dentistry, Universiti Malaya, Kuala Lumpur 50603, Malaysia

UMSC Dental Specialist Clinic, UM Dentistry Tower, Universiti Malaya, Medical Centre, Kuala Lumpur 50603, Malaysia

Leicester School of Allied Health Sciences, De Montfort University, Leicester LE1 9BH, United Kingdom

Chancellery (Research and Innovation), Universiti Malaya, Kuala Lumpur 50603, Malaysia

Peer review under responsibility of Tsinghua University Press.

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Abstract

Human saliva is an indispensable fluid that maintains a healthy oral cavity which otherwise can lead to oral diseases (dental caries and periodontitis). In addition, salivary metabolites and microbiome profile provide early detection of systemic diseases such as cancer and obesity. Salivary diagnostic has gained popularity due to its non-invasive sampling technique. Fasting (abstinence from food or drink or both) research for weight loss and improve health is common, but studies using fasting saliva are scarce. Some metabolites in fasting saliva have been reported with interesting results, which can be enhanced by considering different confounding factors. For example, fasting saliva contains higher salivary nitrite, which is related to nitric oxide (NO). NO is a vasodilator supporting the healthy function of endothelial cells and its deficiency is connected to many diseases. The timely supply of NO through exogenous and endogenous means is highlighted and the potential advantage of fasting salivary composition changes in relation to COVID-19 infection is speculated. This review aims to provide a general discussion on the salivary composition, properties, and functions of the whole saliva, including the health benefits of fasting.

Keywords

Saliva Fasting Nitrate Nitrite Nitric oxide

References

[1]

F. Gonzalez Crussi, The body fantastic, MIT Press, 2021.

Crossref

[2]

R. Toprani, D. Patel, Betel leaf: revisiting the benefits of an ancient Indian herb, South Asian J. Cancer. 2(3) (2013) 140-141. https://doi.org/10.4103/2278-330X.114120.

Condition		Rate (mL/min)	Ref
Unstimulated whole saliva (UWS)	sleep time	0	[11]
	average	0.12–0.16	[19]
	salivary gland hypofunction	< 0.1	[19]
	normal 16-hour waking	0.3	[19]
Stimulated whole saliva (SWS)	minimum	0.7–1.0	[11]
	maximum	1-3	[11]
	hypofunction	< 0.7	[17]
Fasting whole saliva	6 hours (without food and water)	0.10±0.02	[23]
	Ramadan	0.11±0.04	[39]
	Ramadan	0.08-1.40	[40]

Inorganic/Organic Component	Non-fasting Concentration			Fasting Concentration
Inorganic/Organic Component	UWS	SWS	Ref	UWS	Ref
Abbreviations: UWS, SWS, NA (not available). ^* Average value measured for the first ten days of Ramadan. ^**Average value measured at 12 am during the first week of Ramadan.
pH	5.7–6.2	up to 8	[13]	7.7 ± 0.2	[50]
Bicarbonate (mmol/L)	6 ± 3	16 ± 5	[51]	NA
Phosphate (mmol/L)	6 ± 2	3 ± 1	[51]	9 ± 3	[23]
Urea (mmol/L)	3.6 ± 1.3	2.7 ± 0.9	[52]	NA
Potassium (mmol/L)	20 ± 2	14 ± 3	[51]	12 ± 4	[53]
Magnesium (mmol/L)	0.20 ± 0.08	0.15 ± 0.05	[54]	0.10 ± 0.05	[53]
Calcium (mmol/L)	1.3 ± 0.2	1.5 ± 0.4	[51]	2.6 ± 0.6	[23]
Calcium (mmol/L)	2.6 ± 0.6	1.5 ± 0.4	[23]	2.6 ± 0.6	[23]
Sodium (mmol/L)	6 ± 3	21 ± 12	[51]	7 ± 3	[53]
Chloride (mmol/L)	16 ± 2	18 ± 7	[51]	NA
Fluoride (μmol/L)	1.4 ± 0.8	1.2 ± 0.6	[55]	NA
Thiocyanate (mmol/L)	0.7 ± 0.4	0.3 ± 0.2	[56,57]	NA
Nitrite (μmol/L)	110 ± 90	NA	[23]	162 ± 100	[23]
Total Protein (mg/L)	1630 ± 720	1350 ± 290	[58]	1140 ± 650	[23]
Statherin (μmol/L)	4.9 ± 0.6	NA	[59]
sIgA (mg/L)	76 ± 40	38 ± 22	[57,60]	90 ± 69	[60]
sIgA (mg/L)	110 ±70	38 ± 22	[57,60]	90 ± 69	[60]
Amylase (U = mg maltose/mL/min)	317 ± 290	453 ± 390	[61]
Peroxidase (mg/L)		5−6	[13]
Lysozyme (mg/L)	29 ± 13	23 ± 11	[56]
Lactoferrin (mg/L)	8 ± 10	6 ± 5	[56]
MUC5B (mg/L)	830 ± 480	460 ± 200	[62]
MUC7 (mg/L)	440 ± 520	320 ± 330	[62]
Glucose (mg/100 mL)	68 ± 1	NA	[40]	^*55 ± 1	[40]
Melatonin (pg/mL)	18 ± 5	NA	[63]	^**6 ± 8	[63]

Fasting Regimes Definition	Characteristic and Objective	Comment
Time restricted feeding (TRF): limited food intake to a time window of 8–12 h or less every day.	No caloric restriction but limiting the eating duration as an effective strategy to reduce the overall caloric intake.	Intake of water is possible/allowed^[82]. TRF is known to improve health^[79,82-85].
Prolonged fasting (PF): fasting over extended period, more than 2 days.	No food is allowed, but water intake is possible/allowed. PF is usually not practiced for health reason.	PF may be done for religious or other social reasons (e.g., in protest, hunger strike). More than 24 h fasting could cause bodily harm due to protein depletion^[81,86].
Intermittent Fasting (IF)
Alternate day fasting (ADF): fasting every other day or on certain days of the week.	Starving one day, feasting the next. Ad libitum caloric intake is followed on non-fasting days^[87]. ADF is practiced for health reason.	Most common example of ADF. Calories are severely restricted for 2 days (preferably non-consecutive), and then normal eating for the other 5 days in the week^[88].
Modified alternate day fasting (MADF): like ADF but a specific caloric restriction (15%‒25% dietary needs) applies on fasting days.	Controlled calorie intake is practised alternately during fasting period e.g. a three-day of very low calorie diet (~20% dietary requirement) followed by a three-day of full calorie diet^[89]. MADF is practiced for health reason.	During fasting, calorie-free food, non-starchy vegetables and water are allowed. Ad libitum diet is followed on non-fasting days^[89].
Types of religious fasting
Ramadan fasting (RF), an obligatory fasting for every practising Muslims. It is like TRF but practise during the Ramadan month for 30 days.	No intake of food or water are allowed from sunrise to sunset. The number of hours depends on the geographical location.	Known to improve health/reported to have health benefits^[90]. However, over- indulgence in food after the RF may occur and reduce the health advantage^[91].
Non-obligatory Monday and Thursday fasting for Muslims: this is like ADF fasting.	No intake of food or water are allowed from sunrise to sunset on Monday and Thursday. The number of hours depends on the geographical location.	on Monday and Thursday. The number of hours depends on the geographical location. No significant loss to body weight and body fat percentage was observed^[92].
Daniel fasting: like MADF observed by the Christians. The common fasting period is for 21 days.	Ad libitum calorie intake on restricted diet of fruits, vegetables, grains, legumes, nuts, seeds and oil are allowed^[93].	Study found it can reduce the risk of cardiovascular and metabolic disease^[94].
Ekadashi fasting: like prolonged fasting (PF), it is a periodic fasting observed by the Hindus for 36 h period.	No intake of food or water are allowed from sunset of the first day to the morning of the final day.	During the breaking fast, meal usually consists of rice, greens (“agathi keerai”), gooseberry (amla) and turkey berry (sundaikai)^[95].
Yom Kippur fasting: like prolonged fasting (PF), it is observed by Jews for 25 h to celebrate the tenth day of the seventh month of the Hebrew calendar.	No intake of food or water is allowed for 25 h starting from before sunset and the fast ends after nightfall.	No metabolic changes that show significant health impacts due to the short fasting period^[96].
Fasting observed by Buddhists, is like MADF but is practiced all year around.	Typical vegetarian diet. Consumption of meat, dairy products, pungent vegetables (i.e. garlic, welsh, onion, garlic chives, asant, and leeks), alcohol, and processed foods are prohibited.	The dietary restriction is aimed to improved longevity. No significant deficiencies in micronutrients (calcium, vitamin E, vitamin B12) were observed despite no intake of meat and dairy products^[97,98].