Water-only fasting boosts human growth hormone without weight loss

By Priyanjana Pramanik, MSc.Reviewed by Susha Cheriyedath, M.Sc.Feb 25 2025

Could skipping meals for just one day supercharge your body's HGH production? New research reveals how a simple 24-hour water fast dramatically boosts HGH levels—especially for those who need it most.

Study: Weight loss-independent changes in human growth hormone during water-only fasting: a secondary evaluation of a randomized controlled trial. Image Credit: SewCreamStudio / Shutterstock

In a recent study published in the journal Frontiers in Endocrinology, researchers explored the impact of fasting for 24 hours while drinking only water on their weight, human growth hormone (HGH) secretion, and other physiological parameters.

Their findings indicate that fasting increased the secretion of HGH by the pituitary gland independently of weight loss. However, while fasting-induced HGH changes were inversely correlated with some cardiometabolic risk factors, the study did not establish a direct reduction in these risks. As growth hormone deficiency can increase the risk of cardiovascular and metabolic morbidity and mortality, this study’s results have potential implications for lowering these risks.

Background

Intermittent fasting, the practice of alternating between fasting and eating, has demonstrated several health benefits, of which weight loss is the most commonly studied. Other advantages include improving risk factors such as cholesterol levels, glucose concentrations, and blood pressure and reducing the chances of developing chronic metabolic and cardiovascular conditions.

While these benefits could be due to weight loss, they could also result from independent mechanisms, particularly when fasts last for more than 20 hours. One of these pathways is the metabolic transition that takes place during fasting so that energy is drawn from ketones derived from fatty acids instead of glucose.

Others involve enhancing immune pathways, reducing inflammation, and strengthening the microbiome. Longer fasts could also trigger natriuresis, in which sodium is excreted through urine, and higher hemoglobin levels without hemoconcentration, which suggests an improvement in oxygen-carrying capacity and may help reduce the risk of heart failure. Animal models suggest that fasting may reduce stress on the heart and strengthen cardiac muscles.

The HGH/insulin-like growth factor-1 (IGF-1) axis and HGH deficiencies are implicated in the development of heart failure, but HGH production increases during fasting, which could ameliorate these risks. However, the study confirmed that fasting-induced increases in HGH did not significantly alter IGF-1 levels.

About the Study

Researchers evaluated whether HGH changes triggered while fasting for 24 hours while drinking only water were correlated with weight changes. Subsequent analysis assessed whether fasting-related changes and basal HGH levels were associated with metabolic and cardiovascular risk factors at baseline or during the fast.

The analysis utilized data collected from a previously conducted randomized controlled trial in which 30 individuals participated for two 24-hour periods. To be included in the trial, participants could not have fasted for more than 12 hours at a time in the past year and did not deliberately restrict their caloric intake to less than 80% of the daily intake recommended by the U.S. Food and Drug Administration (FDA) in the past two years.

Exclusion criteria included having a history of stroke, myocardial infarction, peripheral vascular disease, or recent solid organ transplant. Current or former smokers, those currently receiving insulin, cancer therapies, or immunosuppressive agents, and people with immunodeficiencies or immune system disorders were also excluded.

Following a Latin square randomization design, 16 of the participants fasted on the first day and ate normally on the second, while the other 14 followed their usual diets on the first day and fasted on the second. The study intentionally did not record dietary intake during non-fasting periods to reflect real-world eating patterns rather than impose strict dietary control. Trial participants provided consent not only for the trial but also for the long-term storage of their blood samples and subsequent secondary analyses.

Blood samples were taken at baseline within 30 minutes of a typical meal, after 24 hours, and after 48 hours. For the group fasting on a given day, blood was drawn before they broke their fast. Complete blood counts, metabolic profiles, high-sensitivity C-reactive protein (hsCRP), insulin, and lipid panels were assessed, as were IGF-1 and HGH levels. Other data collected included height, weight, waist circumference, and demographics. Correlational analysis, measures of central tendency and dispersion, and statistical testing were used to analyze the data.

Findings

Two-thirds of the 30 participants were female, and they ranged in age from 18 to 70, with an average age of 44. The primary analysis results showed that fasting increased hemoglobin and HGH levels and decreased sodium, triglycerides, weight, and circulating parameters associated with insulin resistance. However, waist circumference, hsCRP, and blood pressure did not change. Another analysis showed that circulating fatty acid concentrations increased during the fasting period.

Female participants had a median baseline HGH of 0.5 ng/mL, while males had a median HGH of 0.04 ng/mL. The average weight at baseline was 72.5 kg for females and 99.3 kg for males. Baseline IGF-1 showed no differences between those with higher versus lower baselines.

HGH at baseline showed a weak inverse correlation with insulin, glucose, waist circumference, insulin resistance, and weight. It also showed a weak but positive correlation with high-density lipoprotein cholesterol (HDL-C) and changes in insulin resistance during fasting. Notably, changes in HGH during fasting were not correlated with weight loss induced by fasting or with baseline weight or HGH but were correlated with fasting-related changes in IGF-1, glucose, and hemoglobin.

The study also found that individuals with lower baseline HGH exhibited significantly larger relative increases in HGH during fasting than those with higher baseline HGH. The median HGH increase was 720% in females with low baseline HGH, compared to 38% in those with higher baseline HGH, a difference that was statistically significant. However, this effect was not significant in males.

High HGH and low HGH groups did not show significant differences in baseline weight or glucose levels while fasting. However, people with lower baseline HGH exhibited a slight tendency to show greater improvements in insulin sensitivity, primarily due to greater reductions in insulin while fasting, although this trend was not statistically significant.

The relative change in HGH while fasting was not significantly different when subjects were grouped based on their baseline weight (i.e., above or below median weight in their sex category). This suggests that fasting-induced HGH elevations were driven by baseline HGH status rather than body weight. IGF-1 showed no significant changes after a 24-hour fast, and there were no differences in IGF-1 changes between females and males or based on baseline HGH level groups.

Conclusions

While fasting can prevent or treat coronary heart disease and diabetes, the onset and advancement of heart failure involve multiple cardiovascular and metabolic pathways, which may slow the effects of water-only fasts. A 24-hour fast may trigger meaningful changes in proteins and HGH independent of weight loss while not being an onerously long period to restrict eating.

The study suggests that individuals with lower baseline HGH may experience a greater relative increase in HGH during fasting, which could have metabolic benefits. Future studies can explore the metabolic benefits of low-dose but repeated intermittent fasts over months or years while including larger sample sizes of different ages, sexes, and racial or ethnic groups.