Human molecular adaptations to fasting: Insights from proteomic analysis

By Pooja Toshniwal PahariaReviewed by Benedette Cuffari, M.Sc.Mar 6 2024

In a recent study published in Nature Metabolism, researchers investigate systemic proteome adaptations to one week of fasting in humans.

Study: Systemic proteome adaptions to 7-day complete caloric restriction in humans. Image Credit: Elenyska / Shutterstock.com

Is fasting healthy?

Fasting is practiced by billions of individuals globally for religious purposes, to cure ailments such as epilepsy, and as a weight reduction aid. Despite this widespread practice, the systemic responses of humans to high-calorie restriction remain unclear.

Intermittent fasting plans can prevent and cure obesity, cardiometabolic diseases, and neurodegenerative diseases. Understanding the systemic adaptations to extended fasting in humans may lead to the identification of novel metabolic regulators and the advantages of fasting-like diets, such as ketogenic diets, as adjuncts to traditional therapies for certain diseases.

About the study

The current study included 12 healthy non-smokers, seven of whom were male and five female, before, during, and after a one week fast with absolute calorie restriction and ad libitum water intake. Individuals with comorbidities and body fat percentages of less than 12% for males and 15% for females were excluded from the study.

Study participants provided fasting blood and urine samples two days before, every day throughout, and three days after the intervention. Proximity extension assays and next-generation sequencing were utilized to quantify blood levels of 2,923 protein targets across 117 samples. Blood insulin, free fatty acids, glucose, lipids, liver enzymes, thyroid hormones, and urine nitrogen levels were also measured.

Dual-energy X-ray absorptiometry (DXA) was used to evaluate body composition before, after, and three days after a fasting period, with the mean of the two DXA measures taken before the fasting period serving as the baseline body composition. The REACTOME and Kyoto Encyclopedia of Genes and Genomes (KEGG) databases were used for pathway enrichment analysis. Mixed-effect linear regressions and genome-wide association data were used for blood protein levels to perform Bayesian mapping in protein-encoding regions.

Study findings

One week of water-only fasting caused a mean weight reduction of 5.7 kilograms among 12 participants, with a multi-organ reaction to full caloric restriction exhibiting diverse impacts of starvation duration on weight loss. The multi-organ response across individuals impacted one-third of the plasma proteome, with no severe systemic alterations observed until three days following fasting.

Extracellular matrix protein (ECM) enrichment in multiple regions characterized fasting changes, thus indicating deep-seated and non-metabolic adaptations, including significant alterations in tenascin-R, a brain-specific ECM protein.

Using proteogenomic techniques, the researchers evaluated the health effects of 212 protein molecules that change due to fasting. This analysis revealed the potential benefits of the switch-associated protein 70 (SWAP70) against rheumatoid arthritis and hypoxia-upregulated-1 gene (HYOU1) against cardiovascular disease.

At study initiation, the study participants had an average body mass index (BMI) of 25 kg/m2. During the seven-day fast, an average of 5.7 kg of weight loss was reported, which is comparable to 1.9 units of BMI.

In the initial two to three days, the predicted shift to lipid from glucose consumption was observed, with serum glucose concentrations decreasing, whereas fatty acid levels rose and plateaued. A sustained increase in serum 3-hydroxybutyrate levels during fasting indicated enhanced ketogenesis to satisfy energy requirements.

During the daily interviews, participants reported no significant adverse effects. Urinary nitrogen declined late in the fasting trial period, which is most likely due to enhanced renal urea reabsorption to save protein pools.

Starvation significantly altered 36% of protein targets, with 144 targets rising or decreasing throughout the trial period. A generalized serum proteome response was observed after three days of starvation, with few proteins altered after 24 or 48 hours.

Fasting was found to alter insulin-like growth factor (IGF) signaling, cytokine signaling, lipoprotein metabolism, and protein metabolism. Plasma proteome profiles of weight changes during fasting were slightly associated with changes in plasma 3-hydroxybutyrate levels, thus indicating that prolonged fasting had different consequences than short-term weight loss. However, dramatic effects occur after three or more days of fasting, which is longer than any regularly utilized fasting strategy.

The most highly connected proteins with weight trajectories while fasting include pulmonary surfactant-associated protein D (SFTPD) and interleukin-7 receptor (IL7R). Both of these proteins have essential roles in immunity and are associated with severe illness due to coronavirus disease 2019 (COVID-19).

Conclusions

Prolonged fasting is associated with certain health benefits, including those for rheumatoid arthritis and cardiovascular disease, thus demonstrating that the systemic reaction to fasting can guide focused treatment approaches.

The current study reported different patterns in the plasma proteome, including increased loss of the endoplasmic reticulum, which might explain lean mass loss. Potential causative mediators of fasting health benefits were also identified, of which included SWAP70 for rheumatoid arthritis and HYOU1 for cardiovascular disease.