Cutting so many calories can rejuvenate part of your immune system

Calorie restriction has extended life in fruit fliesroundworms, monkeys, lemursbats, spidersand many, many rodents in laboratory studies. But an important question remains: does calorie restriction have the same effect on humans?

What’s new – Scientists believe that consuming fewer calories may have health benefits beyond weight maintenance, by potentially altering the functioning of the metabolic and immune system. A new paperPosted in Science this month found that participants who reduced their calorie intake by 14% over two years increased the size of their thymus glands, an organ that plays an important role in immune system response.

The full assessment of the long-term effects of reduced energy intake – or CALERIE – is, according to its main researchersthe first controlled study of calorie restriction in healthy humans.

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Over 200 people participated. The researchers established their usual calorie intake at the start of the experiment, then asked some to reduce it by 14%. The others, a control group, made no dietary changes.

Thymus glands in the calorie-restricted group “significantly” increased in mass and volume

The researchers focused on the thymus gland, an organ that helps develop T cells, a soldier of the immune system that fights off foreign invaders in the body. It does not produce T lymphocytes (those that come from the bone marrow), but it does produce and secrete thymosin, a hormone necessary for their development and production.

Using magnetic resonance imaging, the researchers found that the thymus glands in the calorie-restricted group increased “significantly” in mass and volume. Meanwhile, the control group “showed no significant changes.” The thymus gland shrinks with age, so an increase in its mass and volume would make the gland look like it did when the person was younger.

The researchers also looked for clues about the biological mechanisms at play through body fat gene expressions. Changes in the body can cause different genes to be up-regulated or down-regulated, which can trigger reactions at the biomolecular level. Specifically, a protein called PLA2G7 was less active in the calorie-restricted group. PLA2G7 has a negative impact on one of a group of inflammasomesthe part of the immune system that regulates inflammation.

The location of the thymusShutterstock

They conducted a parallel research project, artificially reducing the expression of PLA2G7 in laboratory mice. They found that it produced a similar effect, increasing the mass and volume of the mice’s thymus glands. The mice also had lower rates of age-related inflammation (which shows up earlier in mice due to their short lifespan).

Why it’s a hack — For decades, as animal studies piled up, scientists searched for evidence that calorie restriction could extend human lifespan. So do a few book peddlers, self-proclaimed biohackers, and fad diet promoters. Recently, “anti-aging” has been a popular label for diet products. Some scientists supported this calorie restriction only extends longevity (for humans and animals) by helping them maintain a healthy body weight.

However, the CALERIE study highlighted mechanisms by which calorie restriction could go beyond this. People who reduced their calorie intake by 14% seemed to have actually increased the size of their thymus glands, a major player in the immune system.

The study concludes:

Collectively, our results demonstrate that a [caloric restriction] in humans activates a basic transcriptional program that promotes immune function, reduces inflammation, and reveals PLA2G7 as one of the potential mechanisms to mimic the beneficial effects of CR.

How it affects longevity — The thymus, located behind the sternum and between the lungs, grows and wears out faster than most organs. It reaches its greatest size during puberty. As one ages, the gland is replaced by a fatty problem and is a non-functional mass before age 75. This is one of the reasons older people are at higher risk for infection, inflammation and cancer. If calorie restriction can revive the thymus, it would help the immune system stay primed for longer.

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