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Effect of Intermittent Fasting on Reproductive Hormone Levels in Females and Males: A Review of Human Trials.
Cienfuegos, S, Corapi, S, Gabel, K, Ezpeleta, M, Kalam, F, Lin, S, Pavlou, V, Varady, KA
Nutrients. 2022;14(11)
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Intermittent fasting is a term for three different diet regimes. Alternate day fasting involves a feast day where individuals can eat what they want followed by a water only day. The 5:2 diet involves 5 feast days and 2 fast days per week. Time-restricted eating (TRE) involves a short eating window of a specific number of hours per day. Although these are all popular diet regimes for weight loss, animal studies have highlighted concerns with regards to reproductive health. This review paper aimed to summarise the human research on the effects of intermittent fasting on reproductive hormone levels in both men and women. It was found that overall, there were very few studies, however evidence was found on the effect of intermittent fasting on some of the sex hormones. For women, moving calorie intake to earlier in the day may be of benefit to oestrogen, sex hormone binding globulin, and androgen levels in those with polycystic ovary syndrome (PCOS). In addition, a fasting diet may be of benefit to androgen and SHBG levels in women with PCOS. However even though weight loss may be achieved with intermittent fasting, this is insufficient to improve the gonadotrophins. Intermittent fasting was found to be safe in women who were breastfeeding, with no significant change to milk production. In men, TRE was found to negatively affect testosterone levels, but had no effect on SHBG. The effect of intermittent fasting on sex hormones may involve changes in the gut microbiome and circadian rhythms as a direct result of intermittent fasting. It was concluded that the sex hormone levels of women with PCOS may benefit from intermittent fasting, however in men it may be detrimental to sex hormone production. This study could be used by healthcare professionals to understand that recommending an intermittent fasting diet may be of benefit to hormone levels and fertility in women with PCOS, however this may not be the case for men.
Abstract
Intermittent fasting is a popular diet for weight loss, but concerns have been raised regarding the effects of fasting on the reproductive health of women and men. Accordingly, we conducted this literature review to clarify the effects of fasting on reproductive hormone levels in humans. Our results suggest that intermittent fasting decreases androgen markers (i.e., testosterone and the free androgen index (FAI)) while increasing sex hormone-binding globulin (SHBG) levels in premenopausal females with obesity. This effect was more likely to occur when food consumption was confined to earlier in the day (eating all food before 4 pm). In contrast, fasting did not have any effect on estrogen, gonadotropins, or prolactin levels in women. As for men, intermittent fasting reduced testosterone levels in lean, physically active, young males, but it did not affect SHBG concentrations. Interestingly, muscle mass and muscular strength were not negatively affected by these reductions in testosterone. In interpreting these findings, it is important to note that very few studies have been conducted on this topic. Thus, it is difficult to draw solid conclusions at present. From the limited data presented here, it is possible that intermittent fasting may decrease androgen markers in both genders. If this is the case, these results would have varied health implications. On the one hand, fasting may prove to be a valuable tool for treating hyperandrogenism in females with polycystic ovarian syndrome (PCOS) by improving menstruation and fertility. On the other hand, fasting may be shown to decrease androgens among males, which could negatively affect metabolic health and libido. More research is warranted to confirm these preliminary findings.
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Food Timing, Circadian Rhythm and Chrononutrition: A Systematic Review of Time-Restricted Eating's Effects on Human Health.
Adafer, R, Messaadi, W, Meddahi, M, Patey, A, Haderbache, A, Bayen, S, Messaadi, N
Nutrients. 2020;12(12)
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Time restricted eating (TRE) is a type of intermittent fasting that limits food intake to a window lasting between 4 and 12 hours each day. Animal studies have found that TRE has beneficial effects on chronic diseases such as obesity, diabetes, and heart disease, and there are early indications of benefits to human health too. This systematic review examined previous studies exploring the effects of TRE on human health. The study authors analysed data from 22 clinical trials. The eating window in the trials varied from 4 to 12 hours, with the most common pattern being an 8-hour eating window, followed by a 16-hour fasting period. The overall adherence to TRE was 80%, with a 20% unintentional reduction in energy intake. TRE resulted in an average weight loss of 3% as well as a reduction in fat mass. This fat loss was also observed without any energy restriction. Interestingly, TRE produced metabolic benefits such as improvements in blood sugar and blood pressure even when there was no weight loss. This suggests that the beneficial effects of TRE are due to the realignment of eating with the circadian clock. More rigorous studies are needed, however, to confirm those effects, understand their mechanisms and assess their applicability to human health.
Abstract
INTRODUCTION Recent observations have shown that lengthening the daily eating period may contribute to the onset of chronic diseases. Time-restricted eating (TRE) is a diet that especially limits this daily food window. It could represent a dietary approach that is likely to improve health markers. The aim of this study was to review how time-restricted eating affects human health. METHOD Five general databases and six nutrition journals were screened to identify all studies published between January 2014 and September 2020 evaluating the effects of TRE on human populations. RESULTS Among 494 articles collected, 23 were finally included for analysis. The overall adherence rate to TRE was 80%, with a 20% unintentional reduction in caloric intake. TRE induced an average weight loss of 3% and a loss of fat mass. This fat loss was also observed without any caloric restriction. Interestingly, TRE produced beneficial metabolic effects independently of weight loss, suggesting an intrinsic effect based on the realignment of feeding and the circadian clock. CONCLUSIONS TRE is a simple and well-tolerated diet that generates many beneficial health effects based on chrononutrition principles. More rigorous studies are needed, however, to confirm those effects, to understand their mechanisms and to assess their applicability to human health.
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The Effectiveness of Intermittent Fasting to Reduce Body Mass Index and Glucose Metabolism: A Systematic Review and Meta-Analysis.
Cho, Y, Hong, N, Kim, KW, Cho, SJ, Lee, M, Lee, YH, Lee, YH, Kang, ES, Cha, BS, Lee, BW
Journal of clinical medicine. 2019;8(10)
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Calorie restriction (CR) is known to reduce body weight and to improve various cardiovascular risk factors. Due to the many difficulties in sustaining daily CR, intermittent fasting (IF) has been proposed as an alternative strategy for achieving and maintaining weight reduction. The aim of this study was to investigate the effectiveness of IF on weight loss and glucose metabolism by analysing the effect size of previous studies among the general population without diabetes mellitus. A total of 12 studies were included in this study. The total number of participants was 545 (261 in the intervention group and 284 in the control group). Study analysis indicates an improvement in glycaemic control and insulin resistance through IF diet as compared with a non-fasting control group. Lean mass was relatively conserved in the IF diet group however, no significant weight reduction was identified. Authors conclude that IF diet may improve fat distribution in the general population without chronic metabolic disease.
Abstract
The effects of an intermittent fasting diet (IFD) in the general population are still controversial. In this study, we aimed to systematically evaluate the effectiveness of an IFD to reduce body mass index and glucose metabolism in the general population without diabetes mellitus. Cochrane, PubMed, and Embase databases were searched to identify randomized controlled trials and controlled clinical trials that compared an IFD with a regular diet or a continuous calorie restriction diet. The effectiveness of an IFD was estimated by the weighted mean difference (WMD) for several variables associated with glucometabolic parameters including body mass index (BMI) and fasting glucose. The pooled mean differences of outcomes were calculated using a random effects model. From 2814 studies identified through a literature search, we finally selected 12 articles (545 participants). Compared with a control diet, an IFD was associated with a significant decline in BMI (WMD, -0.75 kg/m2; 95% CI, -1.44 to -0.06), fasting glucose level (WMD, -4.16 mg/dL; 95% CI, -6.92 to -1.40), and homeostatic model assessment of insulin resistance (WMD, -0.54; 95% CI, -1.05 to -0.03). Fat mass (WMD, -0.98 kg; 95% CI, -2.32 to 0.36) tended to decrease in the IFD group with a significant increase in adiponectin (WMD, 1008.9 ng/mL; 95% CI, 140.5 to 1877.3) and a decrease in leptin (WMD, -0.51 ng/mL; 95% CI, -0.77 to -0.24) levels. An IFD may provide a significant metabolic benefit by improving glycemic control, insulin resistance, and adipokine concentration with a reduction of BMI in adults.
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Intermittent Fasting in Cardiovascular Disorders-An Overview.
Malinowski, B, Zalewska, K, Węsierska, A, Sokołowska, MM, Socha, M, Liczner, G, Pawlak-Osińska, K, Wiciński, M
Nutrients. 2019;11(3)
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Intermittent fasting (IF) is an eating pattern that cycles between periods of fasting and eating. IF has gained popularity in recent years with people wanting to lose weight, and it may have many long-term health benefits. In this review, the authors looked at human and animal studies using variations of IF including time restricted eating (TRE), where eating is confined within a specific window during the day (for example 8 hours eating and 16 hours fasting), and alternate day fasting (ADF), where a day of eating normally is alternated with a day of either fasting entirely, or significant calorie restriction. The authors found that IF is related to many beneficial effects on the cardiovascular system, involving atherosclerosis progression, benefits for diabetes mellitus type 2 such as improved glucose metabolism and insulin sensitivity, lowering of blood pressure, and other cardiovascular risk factors (such as lipid profile and inflammation). It is currently unclear whether the benefits of IF are solely due to weight loss or other mechanisms. The success of every type of diet depends on compliance, and IF seems to be as easy or easier to follow than more traditional diets for many people. Fasting is not recommended for people with hormonal imbalances, pregnant and breastfeeding women, and diabetics. People with eating disorders and underweight people are also not recommended to use the intermittent fasting diet. In recent years, the IF diet and its varieties have become increasingly popular. This diet not only serves to reduce body weight but seems to have other long-term health benefits. However, individuals’ current health and situation should be considered before commencing the IF diet.
Abstract
Intermittent fasting is a form of time restricted eating (typically 16 h fasting and 8 h eating), which has gained popularity in recent years and shows promise as a possible new paradigm in the approach to weight loss and the reduction of inflammation, and has many potential long term health benefits. In this review, the authors will incorporate many aspects of fasting, mainly focusing on its effects on the cardiovascular system, involving atherosclerosis progression, benefits for diabetes mellitus type 2, lowering of blood pressure, and exploring other cardiovascular risk factors (such as lipid profile and inflammation).
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Calories, carbohydrates, and cancer therapy with radiation: exploiting the five R's through dietary manipulation.
Klement, RJ, Champ, CE
Cancer metastasis reviews. 2014;33(1):217-29
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Radiation therapy is standard care for cancer patients alongside surgery and chemotherapy. However, there are still some cancers which seem to withstand this treatment. This study looks at whether calorie reduction (CR) and carbohydrate restriction can have any impact on treatment outcomes. The reason for exploring this idea comes from data showing a high level of ‘glycolysis’ (a need for sugar) in cancer cells. Calorie reduction is defined as 30-50% less calories per day achieved either by intermittent fasting or a fixed calorie regime. Carbohydrate restriction is defined as a ketogenic diet (KD); a diet which removes carbohydrate foods and sugars and focuses on high fat foods and limited protein. Both nutritional protocols have been shown to have similar metabolic effects of reducing blood sugar levels and insulin activity, and thus reducing the ability of cancer cells to communicate. The 5R principle of radiotherapy tries to exploit the differences between cancer cells and healthy tissue. The 5Rs are Repair to DNA damage, Repopulation of the tumour, Redistribution of cells, Reoxygenation of the tumour area and Radio resistance in cells which do not respond to treatment. The concern with restricting calories and carbohydrates is triggering detrimental weight loss in cancer patients, although some fat loss may be beneficial in overweight patients with hormonal cancers. Intermittent fasting seems to fit well with typical radiation treatment schedules over 2-3-month periods. Trials of ketogenic diets on healthy volunteers have shown it encourages muscle mass which is a strong predictor of survival in cancer patients. Of the two, a carbohydrate-restricted, ketogenic diet appears the most viable adjunct to radiation therapy.
Abstract
Aggressive tumors typically demonstrate a high glycolytic rate, which results in resistance to radiation therapy and cancer progression via several molecular and physiologic mechanisms. Intriguingly, many of these mechanisms utilize the same molecular pathways that are altered through calorie and/or carbohydrate restriction. Furthermore, poorer prognosis in cancer patients who display a glycolytic phenotype characterized by metabolic alterations, such as obesity and diabetes, is now well established, providing another link between metabolic pathways and cancer progression. We review the possible roles for calorie restriction (CR) and very low carbohydrate ketogenic diets (KDs) in modulating the five R's of radiotherapy to improve the therapeutic window between tumor control and normal tissue complication probability. Important mechanisms we discuss include (1) improved DNA repair in normal, but not tumor cells; (2) inhibition of tumor cell repopulation through modulation of the PI3K-Akt-mTORC1 pathway downstream of insulin and IGF1; (3) redistribution of normal cells into more radioresistant phases of the cell cycle; (4) normalization of the tumor vasculature by targeting hypoxia-inducible factor-1α downstream of the PI3K-Akt-mTOR pathway; (5) increasing the intrinsic radioresistance of normal cells through ketone bodies but decreasing that of tumor cells by targeting glycolysis. These mechanisms are discussed in the framework of animal and human studies, taking into account the commonalities and differences between CR and KDs. We conclude that CR and KDs may act synergistically with radiation therapy for the treatment of cancer patients and provide some guidelines for implementing these dietary interventions into clinical practice.