The Safety Limits Of An Extended Fast: Lessons from a Non-Model Organism

Fieldwork on animals living in extreme conditions as a source of biomedical innovation

Most biomedical research on animals is based on the handful of the so-called standard model organisms, i.e. laboratory mice, rats or Drosophila, but the keys to some important biomedical questions may simply not be found in these. However, compared with the high number of molecules originating from plants in clinical use, and with the countless unique adaption mechanisms that animals have developed over the course of evolution to cope with environmental constrains, there is still few investigations on wild animals with biomedical objectives, and field studies are far fewer. A major limitation is insufficient funding, the main causes of which we analyze. We argue, however, that fieldwork is a key driver in generating new scientific knowledge as part of a One Health approach, by observing/documenting and understanding the diverse and largely unexplored biological processes evolved by animals adapted to unusual environmental conditions, which would be extreme conditions for humans. These conditions do not only refer to extreme temperatures, since lack of food or water, high pressures or lack of oxygen, are clearly extreme constraints. To conduct this research, there are serious limitations we propose to address. Specific techniques and methods are requested, not only to work in extreme environments, but also to minimize the ecological footprint of field work. The erosion of biodiversity is a major threat. The reduction of animal disturbance, a key issue, requires specific technologies and expertise. An ethical approach is requested, for the sake of transparency and to comply with the Nagoya Protocol on genetic resources. An interdisciplinary expertise and a meticulous planning are requested to overcome the field constraints and interface the associated laboratory work. We recommend focusing on the major threats to global human health today, which wild animals appear to resist particularly well, such as antibioresistance and diseases associated with lifestyle and senescence.

Diversifying the concept of model organisms in the age of -omics

In today's post-genomic era, it is crucial to rethink the concept of model organisms. While a few historically well-established organisms, e.g. laboratory rodents, have enabled significant scientific breakthroughs, there is now a pressing need for broader inclusion. Indeed, new organisms and models, from complex microbial communities to holobionts, are essential to fully grasp the complexity of biological principles across the breadth of biodiversity. By fostering collaboration between biology, advanced molecular science and omics communities, we can collectively adopt new models, unraveling their molecular functioning, and uncovering fundamental mechanisms. This concerted effort will undoubtedly enhance human health, environmental quality, and biodiversity conservation.

The impact of nutrition and lifestyle modification on health

The main recommendations from public health entities include healthy diets and physical activity as the main lifestyle factors impacting the development of chronic diseases such as cardiovascular and metabolic diseases, cancer, and even neurological diseases. Randomized clinical trials have been designed to demonstrate those lifestyle modifications can change the pattern of chronic diseases development and progression. Among these, nutrition is one of the most impacting factors. Therefore, nutrition and diets were also included in different randomized clinical trials, and most of them showed a favorable impact of nutrition modification on the participant's health. Nevertheless, study designs were considerably different, and future studies are needed to support nutrition modifications further. The choice of a healthy considered diet, like the Mediterranean diet, was shown to impact chronic diseases, cardiovascular risk, and adult life expectancy mainly due to its anti-inflammatory and antioxidant properties. Furthermore, a high intake of fibers, fruits, and vegetables together with a low intake of fat and energy-dense, processed foods contribute to an inflammation reduction and a more robust immune system leading. Besides these well-known properties, all lifestyle modifications must be personalized according to the availability of foods, geographic localizations, and the healthy status of the patient.

Fasting increases microbiome-based colonization resistance and reduces host inflammatory responses during an enteric bacterial infection

Reducing food intake is a common host response to infection, yet it remains unclear whether fasting is detrimental or beneficial to an infected host. Despite the gastrointestinal tract being the primary site of nutrient uptake and a common route for infection, studies have yet to examine how fasting alters the host's response to an enteric infection. To test this, mice were fasted before and during oral infection with the invasive bacterium Salmonella enterica serovar Typhimurium. Fasting dramatically interrupted infection and subsequent gastroenteritis by suppressing Salmonella's SPI-1 virulence program, preventing invasion of the gut epithelium. Virulence suppression depended on the gut microbiota, as Salmonella's invasion of the epithelium proceeded in fasting gnotobiotic mice. Despite Salmonella's restored virulence within the intestines of gnotobiotic mice, fasting downregulated pro-inflammatory signaling, greatly reducing intestinal pathology. Our study highlights how food intake controls the complex relationship between host, pathogen and gut microbiota during an enteric infection.

Alterations in rat adipose tissue transcriptome and proteome in response to prolonged fasting

Various pathophysiological situations of negative energy balance involve the intense depletion of the body's energy reserves. White adipose tissue is a central place to store energy and a major endocrine organ. As a model of choice to better understand how the white adipose tissue dynamically responds to changes in substrate availability, we used the prolonged fasting paradigm, which is characterized by successive periods of stimulated (phase 2) and then reduced (phase 3) lipid mobilization/utilization. Using omics analyses, we report a regulatory transcriptional program in rat epididymal (EPI) adipose tissue favoring lipolysis during phase 2 and repressing it during phase 3. Changes in gene expression levels of lipases, lipid droplet-associated factors, and the proteins involved in cAMP-dependent and cAMP-independent regulation of lipolysis are highlighted. The mRNA and circulating levels of adipose-secreted factors were consistent with the repression of insulin signaling during prolonged fasting. Other molecular responses are discussed, including the regulation of leptin and adiponectin levels, the specific changes reflecting an increased fibrinolysis and a possible protein catabolism-related energy saving mechanism in late fasting. Finally, some differences between internal and subcutaneous (SC) adipose tissues are also reported. These data provide a comprehensive molecular basis of adipose tissue responses when facing a major energetic challenge.

Transcriptional Changes Involved in Atrophying Muscles during Prolonged Fasting in Rats

Food deprivation resulting in muscle atrophy may be detrimental to health. To better understand how muscle mass is regulated during such a nutritional challenge, the current study deciphered muscle responses during phase 2 (P2, protein sparing) and phase 3 (P3, protein mobilization) of prolonged fasting in rats. This was done using transcriptomics analysis and a series of biochemistry measurements. The main findings highlight changes for plasma catabolic and anabolic stimuli, as well as for muscle transcriptome, energy metabolism, and oxidative stress. Changes were generally consistent with the intense use of lipids as fuels during P2. They also reflected increased muscle protein degradation and repressed synthesis, in a more marked manner during P3 than P2 compared to the fed state. Nevertheless, several unexpected changes appeared to be in favor of muscle protein synthesis during fasting, notably at the level of the phosphatidylinositol-3-kinase (PI3K)/protein kinase B (AKT)/mammalian target of rapamycin (mTOR) signaling pathway, transcription and translation processes, and the response to oxidative stress. Such mechanisms might promote protein sparing during P2 and prepare the restoration of the protein compartment during P3 in anticipation of food intake for optimizing the effects of an upcoming refeeding, thereby promoting body maintenance and survival. Future studies should examine relevance of such targets for improving nitrogen balance during catabolic diseases.

Unravelling the health effects of fasting: a long road from obesity treatment to healthy life span increase and improved cognition

In recent years a revival of interest has emerged in the health benefits of intermittent fasting and long-term fasting, as well as of other related nutritional strategies. In addition to meal size and composition a new focus on time and frequency of meals has gained attention. The present review will investigate the effects of the main forms of fasting, activating the metabolic switch from glucose to fat and ketones (G-to-K), starting 12-16 h after cessation or strong reduction of food intake. During fasting the deactivation of mTOR regulated nutrient signalling pathways and activation of the AMP protein kinase trigger cell repair and inhibit anabolic processes. Clinical and animal studies have clearly indicated that modulating diet and meal frequency, as well as application of fasting patterns, e.g. intermittent fasting, periodic fasting, or long-term fasting are part of a new lifestyle approach leading to increased life and health span, enhanced intrinsic defences against oxidative and metabolic stresses, improved cognition, as well as a decrease in cardiovascular risk in both obese and non-obese subjects. Finally, in order to better understand the mechanisms beyond fasting-related changes, human studies as well as non-human models closer to human physiology may offer useful clues.KEY-MESSAGESBiochemical changes during fasting are characterised by a glucose to ketone switch, leading to a rise of ketones, advantageously used for brain energy, with consequent improved cognition.Ketones reduce appetite and help maintain effective fasting.Application of fasting patterns increases healthy life span and defences against oxidative and metabolic stresses.Today's strategies for the use of therapeutic fasting are based on different protocols, generally relying on intermittent fasting, of different duration and calorie intake.Long-term fasting, with durations between 5 and 21 days can be successfully repeated in the course of a year.

Chronic Inflammation in the Context of Everyday Life: Dietary Changes as Mitigating Factors

The lifestyle adopted by most people in Western societies has an important impact on the propensity to metabolic disorders (e.g., diabetes, cancer, cardiovascular disease, neurodegenerative diseases). This is often accompanied by chronic low-grade inflammation, driven by the activation of various molecular pathways such as STAT3 (signal transducer and activator of transcription 3), IKK (IκB kinase), MMP9 (matrix metallopeptidase 9), MAPK (mitogen-activated protein kinases), COX2 (cyclooxigenase 2), and NF-Kβ (nuclear factor kappa-light-chain-enhancer of activated B cells). Multiple intervention studies have demonstrated that lifestyle changes can lead to reduced inflammation and improved health. This can be linked to the concept of real-life risk simulation, since humans are continuously exposed to dietary factors in small doses and complex combinations (e.g., polyphenols, fibers, polyunsaturated fatty acids, etc.). Inflammation biomarkers improve in patients who consume a certain amount of fiber per day; some even losing weight. Fasting in combination with calorie restriction modulates molecular mechanisms such as m-TOR, FOXO, NRF2, AMPK, and sirtuins, ultimately leads to significantly reduced inflammatory marker levels, as well as improved metabolic markers. Moving toward healthier dietary habits at the individual level and in publicly-funded institutions, such as schools or hospitals, could help improving public health, reducing healthcare costs and improving community resilience to epidemics (such as COVID-19), which predominantly affects individuals with metabolic diseases.

Safety, health improvement and well-being during a 4 to 21-day fasting period in an observational study including 1422 subjects

Only few studies document longer periods of fasting in large cohorts including non-obese participants. The aim of this study was to document prospectively the safety and any changes in basic health and well-being indicators during Buchinger periodic fasting within a specialised clinic. In a one-year observational study 1422 subjects participated in a fasting program consisting of fasting periods of between 4 and 21 days. Subjects were grouped in fasting period lengths of 5, 10, 15 and 20±2 days. The participants fasted according to the Buchinger guidelines with a daily caloric intake of 200-250 kcal accompanied by a moderate-intensity lifestyle program. Clinical parameters as well as adverse effects and well-being were documented daily. Blood examinations before and at the end of the fasting period complemented the pre-post analysis using mixed-effects linear models. Significant reductions in weight, abdominal circumference and blood pressure were observed in the whole group (each p<0.001). A beneficial modulating effect of fasting on blood lipids, glucoregulation and further general health-related blood parameters was shown. In all groups, fasting led to a decrease in blood glucose levels to low norm range and to an increase in ketone bodies levels (each p<0.001), documenting the metabolic switch. An increase in physical and emotional well-being (each p<0.001) and an absence of hunger feeling in 93.2% of the subjects supported the feasibility of prolonged fasting. Among the 404 subjects with pre-existing health-complaints, 341 (84.4%) reported an improvement. Adverse effects were reported in less than 1% of the participants. The results from 1422 subjects showed for the first time that Buchinger periodic fasting lasting from 4 to 21 days is safe and well tolerated. It led to enhancement of emotional and physical well-being and improvements in relevant cardiovascular and general risk factors, as well as subjective health complaints.