Intermittent fasting
Intermittent fasting, Eng. intermittent fasting (lat. inter mittere = interrupt / suspend '), is a special form of a diet where ever, is changed in a certain rhythm, between periods of normal food intake and fasting. In various animal models, intermittent fasting in the so -fed animals leads - compared to animals with conventional diet - to a higher life expectancy and a lower rate of age-related diseases. The achieved thereby effect similar to that of calorie restriction.
Description
When intermittent fasting phases followed by periods without food intake with normal diet. The rhythm between normal food intake and fasting is constant and in most laboratory experiments, a 24 -hour exchange. That is, a 24 hours fasting period followed by a period with 24 hours of normal diet. Fasting here means the total absence of solid food, liquid is taken up only in the form of water. This type of diet is mentioned in the Anglo-Saxon literature every other day diet (EOD, " every other day diet" ) or alternate day fasting (ADF).
Effects and observations
Since the beginning of the 20th century is known from experiments with rodents and many other species that a restriction of food intake - compared to ad-libitum diet - positive effect on the life expectancy of the animals. In addition, the incidence of age-related diseases is proven to reduce.
For many years it was assumed that these positive effects are solely caused by a reduction in energy intake. A reduced energy intake, so the thesis is less stressful for the body cells. Modified studies in the 1980s showed, however, that this simplified model of explanation is obviously wrong. In these recent studies, the animals were given a day is not a food and the next day any of it (ad libitum). The animals were so "full feed " the next day by each compensate for the " day of hunger ". In comparison with the control group, which was fed every day ad libitum fed by the EOD mice had only minor deficiencies in energy intake. Some of their energy intake was even higher and the body weight was maintained.
In addition, the diätisch malnourished animals lived significantly longer and were significantly more resistant than their every day ad libitum -fed counterparts. The EOD mice were reduced in the serum levels are measured in glucose and insulin. The blood pressure was significantly reduced. The neurons in the brain of these animals were also more resistant to excitotoxic induced by kainic acid, stress.
The intermittent fasting also results in the experimental animals a significantly reduced tumor growth, both implanted and induced tumors. In addition, the survival time is increased in rats as well as in tumorous mice at intermittent fasting. In rats, the intermittent fasting also has a cardioprotective effect. These animals also showed a higher resistance to strokes. Also on renal function in rats, intermittent fasting has a positive effect. The glomerular filtration rate ( GFR) and renal plasma flow (RPF ) were maintained with increasing age. On the glomerular permselectivity fasting had little effect, however.
In a study of chronic heart failure has been produced artificially in rats by occluding the left coronary artery. Two weeks after surgery, a portion of the animals were switched to intermittent fasting, the remaining normal diet. When converted to intermittent fasting group, the survival rate after six weeks at 88.5 %, while only 23% was in the other group. The ratio of heart mass to body mass was at the compound on a diet animals was significantly lower ( 2.4 ± 0.17 to 3.9 ± 0.18, P < 0.01). Perfusionsversuche the isolated heart showed a significantly better cardiac function obtained in the diet rats. In these animals were also a number of angiogenic factors, such as Ashif - 1 - α, and BDNF, VEGF, up-regulated in the heart. According to an increased capillary density in the border area of the ischemic myocardium, as well as an increased expression of VEGF in the heart muscle cells ( cardiomyocytes ) was detected by immunohistochemistry in these animals. Anti -apoptosis factors such as Akt and Bcl -2 were also overexpressed.
In addition, causes intermittent fasting in rats that the progression of diabetic nephropathy is significantly slowed. In the model organism BB rat, the incidence of diabetes mellitus was significantly reduced by intermittent fasting.
In transgenic mice of type 3xTgAD who develop Alzheimer 's disease, cut both the animals with caloric restriction and the intermittent fasting better in terms of their cognitive abilities than their normally fed transgenic conspecifics.
The effects of life extension, however, are strongly dependent on the age at which the intermittent fasting was begun, and the genotype of the animals. In mice of a particular genotype (A / J) was reduced even the average life expectancy and maximum life, if only began at the age of ten months with the intermittent fasting. Began at the age of six months, there was no significant change, while a diet beginning six weeks after the birth of both the average life expectancy, and the maximum life span increased. When C57BL/6J genotype significantly positive effects with regard to medium life expectancy and maximum life span were recorded at six weeks and six months. Began in this strain at the age of 10 months with the intermittent fasting, so the maximum lifespan was increased, while the average life expectancy was unchanged. In rats from the Wistar genotype, however still a life extension by intermittent fasting could also be achieved at the age of 18 months. The nematode Caenorhabditis elegans can be increased by 40 to 56 percent by the intermittent fasting life expectancy.
In a study of obese asthmatics, the patients' symptoms improved by intermittent fasting. The peak flow improved within three weeks after the start of fasting from an average of 335 l / min to 382 l / min and remained during the course of the study at this level. The ASUI ( Asthma Symptom Utility Index ) patients, an increase in parallel to also. A number of biomarkers of inflammation, such as TNF- α and BDNF, and oxidative stress, such as nitrotyrosine, 8- isoprostane and Carbonylproteinen (CP ), were significantly reduced in the blood serum of intermittent fasting patients.
Intermittent fasting leads as the calorie restriction to similar physiological and metabolic changes. A major difference however, is that the intermittent fasting significantly higher plasma concentrations of ketone bodies can be detected.
Reasons for the positive effects of intermittent fasting
The causes of the life-prolonging effect in experimental animals are still largely unclear. Several models are discussed.
The resistance of the body cells - as some authors suggest - by the interplay of anabolic and catabolic processes improved. In addition, potentially damaged cells and biomolecules are increasingly being "repaired".
When food intake by the body insulin is released. Then several signaling pathways are initiated by receptor tyrosine kinases. This tissue-specific effector or processes are activated. One of the signal chain runs through protein kinases, which has proven detrimental impacts on model organisms on life expectancy. The cause of this effect is obvious by the inhibition FOXO3. This transcription factor reduces the replicative senescence. In addition, the proliferation rate is increased on the insulin signaling cascade, causing the degradation of the telomeres is accelerated at the ends of chromosomes. If the necessary for this signal chain genes switched off in the model organism Drosophila ( gene knockout ), then the life of these insects increased by a factor of two. Conversely, fasting, that more sirtuin -1 is expressed, which in turn stimulates the expression of FOXO3. FOXO3 puts the cell in a kind of idle state ( quiescence ), whereby the cell cycle slows down and the production of antioxidant enzymes, such as manganese superoxide dismutase ( MnSOD ) and iron superoxide dismutase ( FeSOD ) and the catalase is increased in the cells of. These antioxidant enzymes in turn help to better deal with the cells to oxidative stress, which is a major factor in the aging of cells.
The GTPase RHEB obviously plays an essential role in the intermittent fasting. The up-regulated by fasting genes require this enzyme for their induction.
Intermittent fasting in humans
The results obtained on model organisms are not readily transferable to humans. In many cases, the control group of animals was fed ad libitum and had limited movement options, which definitely leads to unhealthy lifestyles by being overweight. Therefore, it is still largely unclear whether intermittent fasting in people with a low or normal body mass index has any positive effect.
In human studies not statistically secured positive results could be obtained. This significant positive changes have already been found two weeks after the start of the diet. For practicing Muslims were before, during and after the fasting month of Ramadan blood samples. Food intake during Ramadan is limited to the hours of the night and is a form of Intermittent Fasting dar. In the blood samples, an increase in HDL and a decrease in LDL levels over the course of Ramadan could be measured. The aggregation tendency of platelets decreased during fasting.
In order to obtain evidence-based data, there is a need for further human studies. The dietary pattern of the intermittent fasting is that of our ancestors before the beginning of agriculture and animal husbandry closer than the Essrhythmen of modern times.
Is proven General, that a balanced and not too abundant diet, along with physical and mental activity, the best measures against premature aging are.
History
The results of the first controlled animal experiments for intermittent fasting was published in 1934. Mice served as experimental animals. The intermittent fasting was limited to two days per week. The observed prolongation of life, however, was considered by the authors as not significant. The intermittently fed males were on average 745 days of age, the females 819 In comparison, 712 or 773 days in the control group. Back in 1887 were carried out by the Russian doctor Zealand experiments on chickens. However, over the impact on the life he made no statements. Sergius Morgulis, professor of biochemistry at the University of Nebraska, introduced in 1913 experiments with intermittent fasting by in salamanders. But even here, the research interest was not on the investigation into how the measure affects the life expectancy - it came to his attention to the effects on the growth of animals. Anton J. Carlson and Frederick Hoelzel of the University of Chicago in 1945 found in rats that were fed intermittently, both an extension of the life span, as well as a reduced incidence of tumors. The optimal interval Almost certain it fast to a tag in three days. The average life of the animals thus increased by 15% in females and 20% in males.