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What's that fasting diet doing to your immune system?

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Three studies have examined the effects of fasting diets on the immune system, and found lengths and types of fasting had different, and sometimes opposite, effects. The first study, which included an Australian researcher, compared a switch from eating on day one to consuming only water on day two in both mice and in humans, and found the number of inflammation-causing cells called monocytes in the blood dropped when fasting. The second cut calorie consumption by half in mice, and found that resulted in increased protection against infections or tumours. The third study looked at the effects on the gut of multiple rounds of water-only fasting in mice, and found it weakened their immune response. The researchers say their work highlights the need to precisely define types of fasting to be able to test the effects more accurately.

Journal/conference: Cell

DOI: 10.1016/j.cell.2019.07.050

Organisation/s: The University of Sydney, Icahn School of Medicine at Mount Sinai, USA, National Institutes of Health, USA, Keio University, Japan

Funder: See individual papers for funding details.

Media Release

From: Cell Press

Peer-reviewed            Observational & Experimental Studies            People & Animals/Mice

Three studies show caloric restriction’s varying effects on the immune system

Three studies about caloric restriction appearing in the journal Cell on August 22 show that more specificity is needed when discussing the effects of fasting and fasting-like diets. The diets studied in the three papers used different lengths and types of fasting and resulted in distinct and sometimes opposite effects on the immune system.

Jordan et al. studied the effect of one round of short-term fasting on circulating monocytes.

  • By comparing blood drawn in an “eating state” from day 1 to a “fasting state” on day 2, Jordan et al. found that the short water-only fast reduced the number of pro-inflammatory monocytes in the blood.
  • This study was conducted in humans and mice.

Collins et al. studied the effect of dietary restriction on memory T cells.

  • Collins et al. cut calorie consumption in mice by 50 percent, instead of absolute water-only fasting used in the other two studies.
  • In contrast to the findings of Jordan et al., dietary restriction resulted in increased protection against infections or tumors.

Nagai et al. studied how multiple rounds of water-only fasting affect the gut immune response.

  • Researchers found that mice experienced attenuated immune response after oral immunization.

Because each paper tests the effects of a different kind of fasting, a Preview by Roberta Buono and Valter Longo in the same issue argues that it is time to establish a more specific vocabulary than ‘fasting’ or ‘intermittent fasting,’ for example, 24-hour alternate day fasting (24H ADF) or 12-hour time restricted feeding (12H TRF). They write, “Without these more precise definitions, it will be difficult to generate sufficient data to enhance our understanding of the biology of fasting responses and begin to translate this knowledge into randomized clinical trials.”

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    'Preview' article

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