Caloric restriction has lengthened the lifespans in fruit flies, roundworms, monkeys, lemurs, bats, spiders, and many, many rodents in lab studies. But an important question remains: Does caloric restriction have the same effect on humans?
What’s new — Scientists think consuming fewer calories may have health benefits beyond weight maintenance, potentially tweaking metabolic and immune system functioning. A new paper, published in Science this month, found that participants who reduced their caloric intake by 14 percent over two years had increased the size of their thymus glands, an organ with an important role in immune system response.
The Comprehensive Assessment of Long-term Effects of Reducing Intake of Energy — or CALERIE — trial is, according to its principal researchers, the first controlled study of calorie restriction in healthy humans.
More than 200 people participated. Researchers established their usual calorie intake at the start of the experiment and then asked some to reduce it by 14 percent. The others, a control group, made no dietary changes.
The thymus glands of the calorie-restricted group “significantly” increased in mass and volume
The researchers zeroed in on the thymus gland, an organ that helps develop T cells, a soldier of the immune system that fights foreign invaders in the body. It doesn’t produce T cells (those 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 saw that the thymus glands of the calorie-restricted group “significantly” increased in mass and volume. Meanwhile, the control group “showed no significant change.” The thymus gland shrinks with age, so an increase in its mass and volume would make the gland resemble more what it looked like when the person was younger.
The researchers also looked for clues of the biological mechanisms in play through the gene expressions of body fat. Changes in the body can cause different genes to be upregulated or downregulated, which can spark reactions at the biomolecular level. Specifically, a protein called PLA2G7 was less active in the calorie-restricted group. PLA2G7 negatively impacts one of a group of inflammasomes, the part of the immune system that regulates inflammation.
They ran a side research project, artificially reducing the expression of PLA2G7 in lab mice. They found that this produced a similar effect, increasing the mass and volume of the mice’s thymus glands. The mice also had lower rates of age-related types of inflammation (which manifest earlier in mice because of their short lifespans).
Why it’s a hack — For decades, as animal studies piled up, scientists have looked for evidence that caloric restriction could extend the human lifespan. So have a few book-hawking, self-appointed biohackers and promoters of diet fads. Recently, “anti-aging” has been a popular label for diet products. Some scientists have contended that caloric restriction only helps extend longevity (for humans and animals) by helping them maintain a healthy body weight.
However, the CALERIE study has outlined mechanisms by which caloric restriction could go beyond that. People who reduced their caloric intake by 14 percent seemed to have effectively increased the size of their thymus glands, a major player in the immune system.
The study concludes:
Collectively, our findings demonstrate that sustained [caloric restriction] in humans activates a core 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 This Affects Longevity — The thymus, located behind the sternum and between the lungs, grows and wears out faster than most organs. It reaches its largest size during puberty. As one ages, the gland is replaced by fatty issue and is a non-functional lump by age 75. This is one reason older people are at greater risk of infection, inflammation, and cancer. If caloric restriction can revive the thymus, it would help the immune system stay primed for longer.
Hack Score — Six out of ten skipped desserts 🍽🍽🍽🍽🍽🍽