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What Intermittent Fasting Does for Your Muscles

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One of the biggest health trends to shake up the nutrition and fitness world in the past few years has been intermittent fasting (IF), also called time-restricted feeding.  It’s helped many people achieve rapid weight loss and other metabolic health benefits, and we’re just now learning how something so simple as regulated eating can even benefit your muscles.

There are many versions of IF, but all of them stem from a basic concept of constructing a schedule in which food is only eaten within specified windows of time.  Some variations of IF are choosing only to eat for an 8-hr time period and fasting for the remaining 16 hours per day, or eating during a 10-hr time period and fasting for the remaining 14 hrs. 

In the September edition of the journal Nature Communications, researchers carried out a study on IF and its effect on muscle health.  Specifically, they wondered if changing the pattern of eating had any downstream effects to the rhythms which muscle gene expression uses.  Within the muscles, gene expression has its own rhythms in addition to the body’s overall circadian rhythms.  We know that people who eat on a set schedule have better whole-body metabolism, so are the benefits related to IF caused by changing other rhythms in the body?

When humans engage in time-restricted feeding patterns, body mass decreases, but insulin sensitivity improves and pancreatic beta cells become more responsive regardless of the amount of calories eaten during the feeding period.  The exact mechanisms behind this are still unknown.  Combining earlier research about time-restricted feeding and mice, the researchers turned to studying metabolites in the skeletal muscle of eleven overweight men on an IF protocol.

Our Muscles Have Clocks of Their Own

Muscles function on an internal clock and have specific times for carrying out their cellular activities.  The gene clock expression within skeletal muscle and peripheral tissue affects cellular metabolism and is directly tied to taking in energy (i.e. eating)  with our diurnal clock. 

Skipping meals, especially breakfast, wreaks havoc on these peripheral tissue genes and their timed cycles.  It disrupts the clock-controlled gene in white blood cells, while also causing blood sugar to overreact and spike undesirably after meals in both healthy people and diabetics—meaning when you finally do get around to eating, the response of your blood sugar is much more exaggerated than if you had eaten before.

Paying close attention to the fluctuation of the expression of core clock genes in skeletal muscle, the researchers noted the oscillations between certain genes and the absence of oscillations in others.

What the Results Show

The study participants ate a diet consisting of 32% carbohydrates, 19% protein, and 49% fat for five days, and samples of their blood serum and muscle biopsies were taken.  They followed either a standard, unrestricted feeding pattern or ate for 8-hrs a day and fasted the remaining 16 hrs.

The men who ate in the time-restricted feeding pattern had changes occur in their metabolites (substances that are byproducts of processes and activities in the body) in both their blood and their muscles.  This type of IF also changed the rhythmic daily fluctuation of these metabolites, but it did not change the actual clock of the muscles themselves.

Notably, the daily rhythm of the expression of genes related to amino acid transport and protein synthesis were changed by the time-restricted feeding.  By changing the hours during which the men in the study ate, they were effectively able to stimulate their muscles into periodically expressing a gene which assists the transport of amino acids.

These immediate results demonstrate that some of the benefits associated from changing your body’s clock for eating can subtly and positively help your muscles function better, while not disrupting any of the cellular schedules already in progress.

References

Lundell, L.S., Parr, E.B., Devlin, B.L. et al. Time-restricted feeding alters lipid and amino acid metabolite rhythmicity without perturbing clock gene expressionNat Commun 11, 4643 (2020). https://doi.org/10.1038/s41467-020-18412-w

2 COMMENTS

  1. “skeletal muscle of eleven overweight men on an IF protocol.”

    MEN. MEN. MEN.

    Women reading AND writing these pieces about IF REALLY need to understand this massively important distinction that's usually sitting right there in the research (subjects' biological sex). Do NOT generalize what you're reading out to women. We do NOT have the same experience with IF for well-understood evolutionary reasons. And, the older an adult woman is, the more iffy those men's results are for us.

    Why is it IF is going around and nobody brings up the term anorexia? Because that's what it is for women **especially when they are already at a medically healthy body weight and aren't satisfied with their body image**.

    • Alison, thank you for your thoughtful input. I am aware that there are definitely differences in how men and women respond to IF, mostly due to hormonal interactions. This is a great topic I'd like to cover in the future! However, please remember that this is an inclusive site and we have both men and women who read our content. This is not a site only written for and by women. If readers chose to find out more information about how IF may work for them, they are welcome to read the linked study in the references section and perform their own research.

      I disagree with you regarding IF being akin to anorexia. IF is going around because it has improved the health of many, many people of all genders.

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