Time-restricted eating is a fasting diet where the food intake is restricted to a short, typically eight-hour, window each day. It is associated with health benefits such as weight loss, improved sleep, protection against cognitive disorders, and improved cognitive function. The cognitive effects of time-restricted eating have primarily been explained by the production of ketogenesis – an alternative energy source produced when calories are restricted – and anti-inflammatory cytokines. The gut microbiota is the trillions of microorganisms inhabiting the intestinal tract and has also been associated with improved mental health through communication via the gut-brain axis. This review aims to investigate whether changes in the microbiota may mediate the effect of time-restricted eating on cognitive function. Studies investigating the effect of time-restricted eating on the microbiota were systematically reviewed. The results indicate that time-restricted eating may alter the microbiome composition and increase butyrate-producing bacteria. Butyrate is a short-chain fatty acid associated with the expression of genes involved in neural development and the reduction of neuroinflammation. Limited by the few studies reviewed, the results may indicate a possible link between time-restricted eating and cognitive function via the microbiota, although more research is needed.

The intermittent fasting diet has a historical past, but recently, it has regained popularity as a weight loss strategy for the general public. Athletes have also picked up this specialized diet in search of a competitive edge. There are ample studies testing athletes of all levels, but most do not include females or report sex-specific results. This systematic review aimed to identify current research on the effects of intermittent fasting in the understudied population of female athletes. Following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, a comprehensive search was conducted in three databases, including PubMed, Cochrane, and SPORTDiscus, and a total of six studies with experimental or observational designs testing the various effects of intermittent fasting on physical, physiological, and psychological parameters were included. This systematic review shows that studies found significant changes in calorie and fluid intake, body composition, nutrient utilization, well-being, and athletic performances with no changes in muscle strength, ratings of perceived exertion, blood lactate levels, and cognitive function. Multiple studies in this review found mixed results on changes in heart rate and athletic performance (vertical jump height), and no studies found negative effects on athletic performance except in the survey of athletes’ perceptions. Due to conflicting results of current research, more studies are needed to determine the effects of intermittent fasting combined with continuous exercise on athletic women.

Inledning: Övervikt och fetma är förknippat med flera ämnesomsättningssjukdomar. Kostens betydelse har blivit central i det förebyggande arbetet av övervikt och fetma. Periodisk fasta har under de senaste åren blivit ett populärt verktyg för viktnedgång och förbättring av den allmänna hälsan. Tidsbegränsat ätande (TRF) är en form av periodisk fasta där fastandet sker mellan 14–16 timmar per dygn och resterande timmarna är s.k ätfönster. Preliminära data från studier antyder att TRF som kosthållning för med sig en rad hälsofördelar såsom att förbättra den metabola hälsan och kan därmed förebygga en rad ämnesomsättningssjukdomar. Syfte: Syfte med detta litteraturarbete var att analysera ifall tidsbegränsat ätande (TRF) kan främja viktminskning och förbättra de metabola parametrarna hos människor som har övervikt eller lider av fetma. Metod: Sex experimentella studier analyserades. Studierna söktes i databasen PubMed med sökorden: ”time restricted feeding” OR ”time restricted eating”. De inkluderade studierna valdes på basis av fastställda inklusions- och exklusionskriterier. Resultat: Största delen av de inkluderade studierna visade att TRF har en positiv påverkan på viktminskning. De flesta studierna förbättrade inte fasteglukos hos TRF-gruppen i jämförelse med kontrollgruppen. Två studier visade en signifikant förbättring av några av glukosparametrarna. Två av studierna visade att fasteinsulin och HOMA-IR minskade signifikant. Endast en studie visade att faste-triglyceridvärdet minskade.  Diskussion: Sammanfattningsvis visar de flesta studierna att TRF ger viktminskning utan kaloribegränsning och därmed skulle TRF kunna fungera som ett bra verktyg för viktnedgång. Vidare verkar längden på ätfönstret (4-12 timmar) och tiden på dagen (morgon och förmiddag) när matintaget sker viktigt både för att ge viktminskning och för att förändra de metabola parametrarna. TRF skulle därför kunna användas som ett möjligt redskap för att förebygga fetma och därmed förbättra olika metabola parametrar som i sin tur kanske kan förhindra/skjuta upp insjuknande i metabola syndromet, diabetes typ 2 samt hjärt- och kärlsjukdomar. / Introduction: Overweight and obesity are associated with several metabolic diseases. The importance of diet has become central in the preventive work of overweight and obesity. Periodic fasting has in recent years become a popular tool for weight loss and improvement of general health. Time-restricted eating (TRF) is a form of periodic fasting where the fasting window is between 14–16 hours per day and the remaining hours are so-called eating windows. Preliminary data from studies suggest that TRF contributes to a number of health benefits, improves metabolic health, and thus can prevent a number of metabolic diseases. Aim: The aim of this review was to analyze whether time-restricted eating (TRF) can promote weight loss and improve the metabolic parameters of overweight and obese people. Method: Six experimental studies were analyzed. The studies were searched in the PubMed database; the keywords were: "time restricted feeding" OR "time restricted eating". The included studies were selected on the basis of established inclusion and exclusion criteria. Results: Most of the included studies showed that TRF has a positive effect on weight loss. Most studies showed no significant improvement in fasting glucose in the TRF group compared to the control group. Two studies showed a significant improvement in some of the glucose parameters. Two of the studies showed a significant reduction in fasting insulin and HOMA-IR. Only one study showed a significant reduction in the fasting triglyceride value. Discussion: In summary, most studies showed that TRF provides weight loss without calorie restriction, and thereby TRF could work as a good tool for weight loss. Furthermore, the length of the eating window (4-8 hours) and the time of day (morning and before noon) when food intake takes place are important both to provide weight loss and to change the metabolic parameters. TRF could therefore be used as a possible tool to prevent obesity and thereby improve various metabolic parameters that may prevent / delay the onset of metabolic syndrome, type 2 diabetes, and cardiovascular disease.