Weight loss efficacy of alternate day fasting versus daily calorie restriction in subjects with subclinical hypothyroidism: a secondary analysis

Intermittent Fasting on Neurologic Diseases: Potential Role of Gut Microbiota

As the global population ages, the prevalence of neurodegenerative diseases is surging. These disorders have a multifaceted pathogenesis, entwined with genetic and environmental factors. Emerging research underscores the profound influence of diet on the development and progression of health conditions. Intermittent fasting (IF), a dietary pattern that is increasingly embraced and recommended, has demonstrated potential in improving neurophysiological functions and mitigating pathological injuries with few adverse effects. Although the precise mechanisms of IF's beneficial impact are not yet completely understood, gut microbiota and their metabolites are believed to be pivotal in mediating these effects. This review endeavors to thoroughly examine current studies on the shifts in gut microbiota and metabolite profiles prompted by IF, and their possible consequences for neural health. It also highlights the significance of dietary strategies as a clinical consideration for those with neurological conditions.

Clinical application of intermittent fasting for weight loss: progress and future directions

Intermittent fasting diets have become very popular in the past few years, as they can produce clinically significant weight loss. These diets can be defined, in the simplest of terms, as periods of fasting alternating with periods of eating. The most studied forms of intermittent fasting include: alternate day fasting (0-500 kcal per 'fast day' alternating with ad libitum intake on 'feast days'); the 5:2 diet (two fast days and five feast days per week) and time-restricted eating (only eating within a prescribed window of time each day). Despite the recent surge in the popularity of fasting, only a few studies have examined the health benefits of these diets in humans. The goal of this Review is to summarize these preliminary findings and give insights into the effects of intermittent fasting on body weight and risk factors for cardiometabolic diseases in humans. This Review also assesses the safety of these regimens, and offers some practical advice for how to incorporate intermittent fasting diets into everyday life. Recommendations for future research are also presented.

Cardiometabolic Benefits of Intermittent Fasting

This review aims to summarize the effects of intermittent fasting on markers of cardiometabolic health in humans. All forms of fasting reviewed here-alternate-day fasting (ADF), the 5:2 diet, and time-restricted eating (TRE)-produced mild to moderate weight loss (1-8% from baseline) and consistent reductions in energy intake (10-30% from baseline). These regimens may benefit cardiometabolic health by decreasing blood pressure, insulin resistance, and oxidative stress. Low-density lipoprotein cholesterol and triglyceride levels are also lowered, but findings are variable. Other health benefits, such as improved appetite regulation and favorable changes in the diversity of the gut microbiome, have also been demonstrated, but evidence for these effects is limited. Intermittent fasting is generally safe and does not result in energy level disturbances or increased disordered eating behaviors. In summary, intermittent fasting is a safe diet therapy that can produce clinically significant weight loss (>5%) and improve several markers of metabolic health in individuals with obesity.

Causal Association Between Serum Thyrotropin and Obesity: A Bidirectional, Mendelian Randomization Study

CONTEXT

The association between serum thyrotropin (TSH) and obesity traits has been investigated previously in several epidemiological studies. However, the underlying causal association has not been established.

OBJECTIVE

This work aimed to determine and analyze the causal association between serum TSH level and obesity-related traits (body mass index [BMI] and obesity).

METHODS

The latest genome-wide association studies (GWASs) on TSH, BMI, and obesity were searched to obtain full statistics. Bidirectional 2-sample mendelian randomization (MR) was performed to explore the causal relationship between serum TSH and BMI and obesity. The inverse variance-weighted (IVW) and MR-Egger methods were used to combine the estimation for each single-nucleotide variation (formerly single-nucleotide polymorphism). Based on the preliminary MR results, free thyroxine (fT4) and free 3,5,3'-triiodothyronine (fT3) levels were also set as outcomes to further analyze the impact of BMI on them. BMI and obesity were treated as the outcomes to evaluate the effect of serum TSH on them, and TSH was set as the outcome to estimate the effect of BMI and obesity on it.

RESULTS

IVW and MR-Egger results both indicated that genetically driven serum TSH did not causally lead to changes in BMI or obesity. Moreover, the IVW method showed that the TSH level could be significantly elevated by genetically predicted high BMI (β = .038, SE = 0.013, P = .004). In further MR analysis, the IVW method indicated that BMI could causally increase the fT3 (β = 10.123, SE = 2.523, P < .001) while not significantly affecting the fT4 level.

CONCLUSION

Together with fT3, TSH can be significantly elevated by an increase in genetically driven BMI.

Effects of Intermittent Fasting on the Circulating Levels and Circadian Rhythms of Hormones

Intermittent fasting has become an increasingly popular strategy in losing weight and associated reduction in obesity-related medical complications. Overwhelming studies support metabolic improvements from intermittent fasting in blood glucose levels, cardiac and brain function, and other health benefits, in addition to weight loss. However, concerns have also been raised on side effects including muscle loss, ketosis, and electrolyte imbalance. Of particular concern, the effect of intermittent fasting on hormonal circadian rhythms has received little attention. Given the known importance of circadian hormonal changes to normal physiology, potential detrimental effects by dysregulation of hormonal changes deserve careful discussions. In this review, we describe the changes in circadian rhythms of hormones caused by intermittent fasting. We covered major hormones commonly pathophysiologically involved in clinical endocrinology, including insulin, thyroid hormones, and glucocorticoids. Given that intermittent fasting could alter both the level and frequency of hormone secretion, decisions on practicing intermittent fasting should take more considerations on potential detrimental consequences versus beneficial effects pertaining to individual health conditions.

Correlation between Thyroid Homeostasis and Obesity in Subclinical Hypothyroidism: Community-Based Cross-Sectional Research

OBJECTIVE

It remains unknown whether obesity has an effect on the pituitary-thyroid feedback control axis in subclinical hypothyroidism (SCH). We aimed to investigate the association of thyroid homeostasis with obesity in a SCH population.

METHODS

Our study consisted of a community-based and cross-sectional study from the Epidemiological Survey of Thyroid Diseases in Fujian Province, China. A total of 193 subjects with SCH (90 males and 103 females) without a history of treatment of thyroid disease, such as surgery, radiation, and thyroid hormone or antithyroid medication, were included in the present study. Indices of obesity, including body mass index (BMI), waist circumference (WC), and waist-height ratio (WHtR) were measured.

RESULTS

Our results showed that the secretory capacity of the thyroid gland (SPINA-GT) and Jostel's thyrotropin index (TSHI) were negatively correlated with BMI, WC, and WHtR, whereas the reciprocal of the thyrotroph thyroid hormone resistance index (TTSI-1) was positively correlated with BMI (all p < 0.05). After adjustment for age, sex, smoking, iodine status, and glucolipid metabolism, the associations between TSHI, TTSI (reciprocal transformation), and BMI still persisted (all p < 0.05).

CONCLUSIONS

These results suggest that low levels of thyroid homeostasis indexes may be associated with overall obesity in SCH, rather than central adiposity.

Prolonged fasting induces long-lasting metabolic consequences in mice

To endure prolonged fasting, animals undergo important acute physiological adjustments. However, whether severe fasting also leads to long-term metabolic adaptations is largely unknown. Forty-eight-hour fasting caused a pronounced weight loss in adult C57BL/6 male mice. Seven days of refeeding increased body adiposity to levels above baseline, whereas fasting-induced reductions in lean body mass and energy expenditure were not fully recovered. Respiratory exchange ratio and locomotor activity also remained altered. A fasting/refeeding cycle led to persistent suppression of Pomc mRNA levels and significant changes in the expression of histone deacetylases and DNA methyltransferases in the hypothalamus. Additionally, histone acetylation in the ventromedial nucleus of the hypothalamus was reduced by prolonged fasting and remained suppressed after refeeding. Mice subjected to 48-h fasting 30 days earlier exhibited higher body weight and fat mass compared to aged-matched animals that were never food-deprived. Furthermore, a previous fasting experience altered the changes in body weight, lean mass, energy expenditure and locomotor activity induced by a second cycle of fasting and refeeding. Notably, when acutely exposed to high-palatable/high-fat diet, mice that went through cumulative fasting episodes presented higher calorie intake and reduced energy expenditure and fat oxidation, compared to mice that had never been subjected to fasting. When chronically exposed to high-fat diet, mice that experienced cumulative fasting episodes showed higher gain of body and fat mass and reduced energy expenditure and calorie intake. In summary, cumulative episodes of prolonged fasting lead to hypothalamic epigenetic changes and long-lasting metabolic adaptations in mice.