Low-carbohydrate diets and men's cortisol and testosterone: Systematic review and meta-analysis

Measurement of energy availability in highly trained male endurance athletes and examination of its associations with bone health and endocrine function

PURPOSE

Despite the introduction of Relative Energy Deficiency in Sport (RED-s) in 2014, there is evidence to suggest that male endurance athletes still present with a high prevalence of low energy availability (LEA). Previous findings suggest that energy availability (EA) status is strongly correlated with impairments in endocrine function such as reduced leptin, triiodothyronine (T3), and insulin, and elevated bone loss. This study aimed to report the current EA status, endocrine function and bone health of highly trained Irish male endurance athletes.

METHODS

In this cross-sectional study, participants (n = 3 triathletes; n = 10 runners) completed a 7-day testing period during the competition season using lab-based measures, to ascertain EA status, hormone level and rates of bone metabolism. Serum blood samples were obtained to assess hormone levels and markers of bone metabolism.

RESULTS

Mean EA was < 30 kcal/kg lean body mass (LBM)/day in 76.9% of athletes. There was a strong association between LEA and low carbohydrate intake, and lower LBM. Mean levels of insulin, IGF-1 and leptin were significantly lower than their reference ranges. Elevated mean concentrations of β-CTX and a mean P1NP: β-CTX ratio < 100, indicated a state of bone resorption.

CONCLUSION

The EA level, carbohydrate intake, hormone status and bone metabolism status of highly trained male endurance athletes are a concern. Based on the findings of this study, more frequent assessment of EA across a season is recommended to monitor the status of male endurance athletes, in conjunction with nutritional education specific to EA and the associated risks.

Joint effect of testosterone and neurofilament light chain on cognitive decline in men: The Shanghai Aging Study

INTRODUCTION

The association of testosterone and cognitive decline is inconclusive, and its joint effect with neurofilaments light chain (NfL) remains largely unknown.

METHODS

A total of 581 non-demented older men in the Shanghai Aging Study were included. Blood total testosterone (TT), free testosterone (FT), and NfL were measured at baseline. The relationships between TT, FT, TT/FT-NfL, and cognitive decline were explored by Cox regression models.

RESULTS

During a median follow-up of 6.7 years, there was an inverse association between TT/FT and cognitive decline (TT, trend p = .004, Q1 vs Q4, hazard ratio [HR] = 4.39, 95% confidence interval [CI] = 1.60 to 12.04; FT, trend p = .002, Q1 vs Q4, HR = 5.29, 95% CI = 1.50 to 16.89). Compared to participants with high TT/FT-low NfL, those with low TT/FT-high NfL had significantly higher risks of cognitive decline (TT, HR = 5.10, 95% CI = 1.11 to 23.40; FT, HR = 6.14, 95% CI = 1.34 to 28.06).

DISCUSSION

Our findings suggest that the combination of testosterone and neurodegenerative markers may provide reliable predictive insights into future cognitive decline.

HIGHLIGHTS

Testosterone is inversely associated with cognitive decline in older men. There is a joint effect of testosterone and NfL on cognitive decline. Sex hormone and neurodegeneration may synergistically contribute to cognitive deterioration.

Obesity, Dietary Patterns, and Hormonal Balance Modulation: Gender-Specific Impacts

Understanding the intricate relationship between nutrition, hormonal balance, and gender-specific factors is crucial for developing targeted interventions to mitigate obesity-related endocrine disruptions and improve metabolic health. This narrative review examines the impact of various dietary patterns on hormonal regulation in both men and women, focusing on their effects on hormonal balance and metabolic health in the context of obesity. Calorie restriction, the Western diet, high-fat diets, low-CHO diets, plant-based diets, and the Mediterranean diet are analyzed in relation to their influence on obesity-related endocrine disruptions and metabolic health. Future research directions include investigating the specific mechanisms underlying dietary influences on hormonal regulation, addressing the gender-specific metabolic differences and body fat distribution, and exploring the dietary needs of individuals undergoing gender transition. Personalized dietary interventions tailored to individual metabolic and hormonal profiles are essential for optimizing health outcomes across the gender spectrum. By integrating gender-specific considerations into dietary recommendations, healthcare professionals can better support individuals in achieving optimal metabolic health and hormonal balance.

Physiologic Adaptation to Macronutrient Change Distorts Findings from Short Dietary Trials: Reanalysis of a Metabolic Ward Study

An influential 2-wk cross-over feeding trial without a washout period purported to show advantages of a low-fat diet (LFD) compared with a low-carbohydrate diet (LCD) for weight control. In contrast to several other macronutrient trials, the diet order effect was originally reported as not significant. In light of a new analysis by the original investigative group identifying an order effect, we aimed to examine, in a reanalysis of publicly available data (16 of 20 original participants; 7 female; mean BMI, 27.8 kg/m2), the validity of the original results and the claims that trial data oppose the carbohydrate-insulin model of obesity (CIM). We found that energy intake on the LCD was much lower when this diet was consumed first compared with second (a difference of -1164 kcal/d, P = 3.6 × 10-13); the opposite pattern was observed for the LFD (924 kcal/d, P = 2.0 × 10-16). This carry-over effect was significant (P interaction = 0.0004) whereas the net dietary effect was not (P = 0.4). Likewise, the between-arm difference (LCD - LFD) was -320 kcal/d in the first period and +1771 kcal/d in the second. Body fat decreased with consumption of the LCD first and increased with consumption of this diet second (-0.69 ± 0.33 compared with 0.57 ± 0.32 kg, P = 0.007). LCD-first participants had higher β-hydroxybutyrate levels while consuming the LCD and lower respiratory quotients while consuming LFD when compared with LFD-first participants on their respective diets. Change in insulin secretion as assessed by C-peptide in the first diet period predicted higher energy intake and less fat loss in the second period. These findings, which tend to support rather than oppose the CIM, suggest that differential (unequal) carry-over effects and short duration, with no washout period, preclude causal inferences regarding chronic macronutrient effects from this trial.

Sarcopenia and Diabetes: A Detrimental Liaison of Advancing Age

Sarcopenia is an age-related clinical complaint characterized by the progressive deterioration of skeletal muscle mass and strength over time. Type 2 diabetes (T2D) is associated with faster and more relevant skeletal muscle impairment. Both conditions influence each other, leading to negative consequences on glycemic control, cardiovascular risk, general health status, risk of falls, frailty, overall quality of life, and mortality. PubMed/Medline, Scopus, Web of Science, and Google Scholar were searched for research articles, scientific reports, observational studies, clinical trials, narrative and systematic reviews, and meta-analyses to review the evidence on the pathophysiology of di-abetes-induced sarcopenia, its relevance in terms of glucose control and diabetes-related outcomes, and diagnostic and therapeutic challenges. The review comprehensively addresses key elements for the clinical definition and diagnostic criteria of sarcopenia, the pathophysiological correlation be-tween T2D, sarcopenia, and related outcomes, a critical review of the role of antihyperglycemic treatment on skeletal muscle health, and perspectives on the role of specific treatment targeting myokine signaling pathways involved in glucose control and the regulation of skeletal muscle metabolism and trophism. Prompt diagnosis and adequate management, including lifestyle inter-vention, health diet programs, micronutrient supplementation, physical exercise, and pharmaco-logical treatment, are needed to prevent or delay skeletal muscle deterioration in T2D.

The Effects of Different Types of Diets on Steroid Hormone Concentrations

The great popularity of various diets in recent years has led us to reflect on their suitability for our health. The aim of this communication is to review current knowledge on the influence of the most well-known diets on the concentrations of the main steroids and to consider possible mechanisms. The influence of diet on hormone concentrations is expected, but the literature data on this topic are inconsistent and yield conflicting results. The main problem in evaluating these influences is the change in weight that a change in diet induces. This effect needs to be filtered out in order to discover interesting associations between diet and steroid hormones. This is illustrated by the example of the effects of ketogenic diets on testosterone levels in men, where the direct effect of the diet is to reduce testosterone levels, but a number of papers have described increases that are due to diet-related weight loss and the modification of obesity-induced changes. A second major driver is the change in circadian rhythm, and it is necessary to assess hormonal changes induced by changing the time of day of the diet. Such shifts within the circadian rhythm rather than due to a particular type of diet itself are documented by changes in the circadian rhythm of cortisol.

The Potential Role of Nutrition in Overtraining Syndrome: A Narrative Review

Competition between athletes and an increase in sporting knowledge have greatly influenced training methods while increasing the number of them more and more. As a result, the number of athletes who have increased the number and intensity of their workouts while decreasing recovery times is rising. Positive overtraining could be considered a natural and fundamental process when the result is adaptation and improved performance; however, in the absence of adequate recovery, negative overtraining could occur, causing fatigue, maladaptation, and inertia. One of the earliest forms of fatigue is overreaching. It is considered to be an accumulation of training that leads to reduced sports performance, requiring days or weeks to recover. Overreaching, if followed by adequate recovery, can lead to an increase in athletic performance. Nonetheless, if overreaching becomes extreme, combined with additional stressors, it could lead to overtraining syndrome (OTS). OTS, caused by systemic inflammation, leads to central nervous system (CNS) effects, including depressed mood, further inflammation, central fatigue, and ultimately neurohormonal changes. There are therefore not only physiological, biochemical, and immunological but also psychological symptoms or markers that must be considered, independently or together, being intrinsically linked with overtraining, to fully understand OTS. However, to date, there are very few published studies that have analyzed how nutrition in its specific food aspects, if compromised during OTS, can be both etiology and consequence of the syndrome. To date, OTS has not yet been fully studied, and the topic needs further research. The purpose of this narrative review is therefore to study how a correct diet and nutrition can influence OTS in all its aspects, from prevention to treatment.

Effect of Small and Large Energy Surpluses on Strength, Muscle, and Skinfold Thickness in Resistance-Trained Individuals: A Parallel Groups Design

BACKGROUND

Many perform resistance training (RT) to increase muscle mass and strength. Energy surpluses are advised to support such gains; however, if too large, could cause unnecessary fat gain. We randomized 21 trained lifters performing RT 3 d/wk for eight weeks into maintenance energy (MAIN), moderate (5% [MOD]), and high (15% [HIGH]) energy surplus groups to determine if skinfold thicknesses (ST), squat and bench one-repetition maximum (1-RM), or biceps brachii, triceps brachii, or quadriceps muscle thicknesses (MT) differed by group. COVID-19 reduced our sample, leaving 17 completers. Thus, in addition to Bayesian ANCOVA comparisons, we analyzed changes in body mass (BM) with ST, 1-RM, and MT changes via regression. We reported Bayes factors (BF10) indicating odds ratios of the relative likelihood of hypotheses (e.g., BF10 = 2 indicates the hypothesis is twice as likely as another) and coefficients of determination (R2) for regressions.

RESULTS

ANCOVAs provided no evidence supporting the group model for MT or squat 1-RM. However, moderate (BF10 = 9.9) and strong evidence (BF10 = 14.5) indicated HIGH increased bench 1-RM more than MOD and MAIN, respectively. Further, there was moderate evidence (BF10 = 4.2) HIGH increased ST more than MAIN and weak evidence (BF10 = 2.4) MOD increased ST more than MAIN. Regression provided strong evidence that BM change predicts ST change (BF10 = 14.3, R2 = 0.49) and weak evidence predicting biceps brachii MT change (BF10 = 1.4, R2 = 0.24).

CONCLUSIONS

While some group-based differences were found, our larger N regression provides the most generalizable evidence. Therefore, we conclude faster rates of BM gain (and by proxy larger surpluses) primarily increase rates of fat gain rather than augmenting 1-RM or MT. However, biceps brachii, the muscle which received the greatest stimulus in this study, may have been positively impacted by greater BM gain, albeit slightly. Our findings are limited to the confines of this study, where a group of lifters with mixed training experience performed moderate volumes 3 d/wk for 8 weeks. Thus, future work is needed to evaluate the relationship between BM gains, increases in ST and RT adaptations in other contexts.

Ketogenic Diet and Multiple Health Outcomes: An Umbrella Review of Meta-Analysis

Numerous studies have examined the effects of ketogenic diets (KD) on health-related outcomes through meta-analyses. However, the presence of biases may compromise the reliability of conclusions. Therefore, we conducted an umbrella review to collate and appraise the strength of evidence on the efficacy of KD interventions. We conducted a comprehensive search on PubMed, EMBASE, and the Cochrane Database until April 2023 to identify meta-analyses that investigated the treatment effects of KD for multiple health conditions, which yielded 23 meta-analyses for quantitative analyses. The evidence suggests that KD could increase the levels of low-density lipoprotein cholesterol (LDL-C), total cholesterol (TC) and high-density lipoprotein cholesterol (HDL-C), the respiratory exchange rate (RER), and could decrease total testosterone and testosterone levels (all p-random effects: <0.05). The combination of KD and physical activity can significantly reduce body weight and increase the levels of LDL-C and cortisol. In addition, KD was associated with seizure reduction in children, which can be explained by the ketosis state as induced by the diet. Furthermore, KD demonstrated a better alleviation effect in refractory childhood epilepsy, in terms of median effective rates for seizure reduction of ≥50%, ≥90%, and seizure freedom. However, the strength of evidence supporting the aforementioned associations was generally weak, thereby challenging their credibility. Consequently, future studies should prioritize stringent research protocols to ascertain whether KD interventions with longer intervention periods hold promise as a viable treatment option for various diseases.

Global Scientific Trends on Healthy Eating from 2002 to 2021: A Bibliometric and Visualized Analysis

Diet has been recognized as a vital risk factor for non-communicable diseases (NCDs), climate changes, and increasing population, which has been reflected by a rapidly growing body of the literature related to healthy eating. To reveal a panorama of the topics related to healthy eating, this study aimed to characterize and visualize the knowledge structure, hotspots, and trends in this field over the past two decades through bibliometric analyses. Publications related to healthy eating between 1 January 2002 and 31 December 2021 were retrieved and extracted from the Web of Science database. The characteristics of articles including publication years, journals, authors, institutions, countries/regions, references, and keywords were assessed. The analyses on co-authorship, co-occurrence, and co-citation were performed and network visualization maps were constructed by VOSviewer. Major subdomains identified by bibliometrics were further discussed and analyzed. A total of 12,442 articles on healthy eating were identified. Over the past two decades, the annual global publications increased from 71 to 1764, showing a nearly 25-fold growth. The journal Nutrients published the most articles and The American Journal of Clinical Nutrition possessed the highest citations. The United States, Harvard University, and Hu, Frank B. were identified as the most productive and influential country, institution, and author, respectively. The co-occurrence cluster analysis of the top 100 keywords formed four clusters: (1) the food insecurity environment for youths highlighting the necessity and significance of implementing healthy eating in early life; (2) sustainable advantages of the Mediterranean diet; (3) the importance of an overall healthy lifestyle optimization leveraged by eHealth; (4) the challenges during the course of healthy eating against obesity, which are prominent in reflecting the knowledge structure, hotspots, and trends. Moreover, COVID-19, orthorexia nervosa, sustainability, microbiota, food insecurity, and e-health are identified keywords that represented the latest high-frequency keywords and indicated the emerging frontiers of healthy eating. This study indicates that the number of publications on healthy eating will increase in the future and that healthy dietary patterns and clinical applications of healthy eating will be the next hotspots in this research field.

Ketogenic state improves testosterone serum levels-results from a systematic review and meta-analysis

BACKGROUND

It is widely demonstrated that obesity and hypogonadism are bi-directionally correlated, since the hypogonadism prevalence is higher in obese population, while weight loss increases testosterone serum levels. Several approaches are available to contrast weight excess, from simple dietary regimens to more complex surgical procedures. Ketogenic diets (KD) fit in this context and their application is growing year after year, aiming to improve the metabolic and weight patterns in obese patients. However, KD influence on testosterone levels is still poorly investigated.

OBJECTIVES

To systematically evaluate the potential effect of KD on testosterone levels.

METHODS

A systematic literature search was performed until April 2022 including studies investigating testosterone levels before and after KD. Secondary endpoints were body weight, estradiol and sex-hormone binding globulin serum levels. Any kind of KD was considered eligible, and no specific criteria for study populations were provided.

RESULTS

Seven studies (including eight trials) were included in the analysis for a total of 230 patients, five using normocaloric KD and three very low calories KD (VLCKD). Only three studies enrolled overweight/obese men. A significant total testosterone increase was recorded after any kind of KD considering 111 patients (2.86 [0.95, 4.77], p = 0.003). This increase was more evident considering VLCKD compared to normocaloric KD (6.75 [3.31, 10.20], p < 0.001, versus 0.98 [0.08, 1.88], p = 0.030). Meta-regression analyses highlighted significant correlations between the post-KD testosterone raise with patients' age (R-squared 36.4, p < 0.001) and weight loss (R-squared 73.6, p < 0.001).

CONCLUSIONS

Comprehensively, KD improved testosterone levels depending on both patients' age and KD-induced weight loss. However, the lack of information in included studies on hormones of the hypothalamic-pituitary-gonadal axis prevents an exhaustive comprehension about mechanisms connecting ketosis and testosterone homeostasis.

Obesity, type 2 diabetes, and testosterone in ageing men

In the absence of obesity, adverse lifestyle behaviours, and use of medication such as opioids serum testosterone concentrations decrease by only a minimal amount at least until very advanced age in most men. Obesity is heterogeneous in its phenotype, and it is the accumulation of excess adipose tissue viscerally associated with insulin resistance, dyslipidaemia, inflammation, hypothalamic leptin resistance and gliosis that underpins the functional hypogonadism of obesity. Both central (hypothalamic) and peripheral mechanisms are involved resulting in a low serum total testosterone concentration, while LH and FSH are typically in the normal range. Peripherally a decrease in serum sex hormone binding globulin (SHBG) concentration only partially explains the decrease in testosterone and there is increasing evidence for direct effects in the testis. Men with obesity associated functional hypogonadism and serum testosterone concentrations below 16 nmol/L are at increased risk of incident type 2 diabetes (T2D); high testosterone concentrations are protective. The magnitude of weight loss is linearly associated with an increase in serum testosterone concentration and with the likelihood of preventing T2D or reverting newly diagnosed disease; treatment with testosterone for 2 years increases the probability of a positive outcome from a lifestyle intervention alone by approximately 40%. Whether the additional favourable benefits of testosterone treatment on muscle mass and strength and bone density and quality in the long-term remains to be determined.