5.1. LF – a general overview
Whereas the metabolic switch and the changes in signalling pathways above described also apply at the beginning of LF, the question is whether these effects persist, decrease or increase in the course of LF. Evidently, it will depend on the duration of fasting, the individual profile including age, nutritional and health status, as well as personal inclination for the procedure [
89]. One of the first detailed scientific observations of a non-obese voluntary subject on total fasting ended safely after 31 days [
16]. Other case reports of persons fasting during several weeks were published and brought stupefaction in the medical community and the public. Many Authors have stressed the well-being, the absence of hunger and lifted mood reported by fasting obese and non-obese subjects [
90]. The human capacity to live without energy intake for periods of almost 40 days has been often reported in non-obese subjects during hunger strikes [
91].
A medically supervised practice of LF has a long tradition in Europe and in particular in Germany. The safety of this programme has been recently documented in large cohort studies [
15,
24]. This type of LF, generally lasting from 4 to 21 days, has been studied in various clinical conditions: chronic inflammatory disorders [
92,
93] and rheumatoid arthritis [
59,
94], hypertension [
95], irritable bowel syndrome [
96], insulin resistance, type 2 diabetes and metabolic syndrome [
97,
98], fibromyalgia [
99], breast and ovarian cancer [
100], osteoarthritis [
101], obesity [
102], and fatty liver [
103]. Furthermore, MRI evaluation documented significant changes in body composition after 14 days of fasting [
104].