Two hundred and twenty healthy adults, split into two groups. One group ate as usual for two years. The other was told to cut calories by 25 percent, with a high-satiety diet, behavioral coaching and vitamin and mineral supplements to head off deficiencies. As the volunteers lost body fat and muscle, the researchers lowered their calorie prescriptions three times so the cut stayed at 25 percent.
That is the design of CALERIE, formally the “Comprehensive Assessment of Long-Term Effects of Reducing Intake of Energy,” a randomized trial run at three sites: the Pennington Biomedical Research Center in Baton Rouge, Tufts University in Boston and Washington University in St. Louis. It ended in 2012 and TRT World called it the longest-running trial of its kind in humans. Funding came from the National Institutes of Health.
What the volunteers showed
The results have come out in pieces. In 2016, Tufts researchers reported in the journal Aging that the restricted group had significantly lower markers of chronic inflammation. The immune system otherwise held up, including antibody production after vaccination. “This is the first study to examine these effects over two years on healthy, normal- or slightly over- weight individuals,” said Simin Nikbin Meydani, who led that analysis.
A smaller analysis looked at 53 participants, 36 women and 17 men, aged 21 to 50 in the wider trial. Those in the restriction group, 34 of them, had cut about 15% on average. Two years on, the dieters were 8.7 kg lighter on average, and the 19 controls were 1.8 kg heavier. Spending 24 hours in a metabolic chamber, the restricted group burned 80-120 kcal a day less than their weight loss predicted. Their cells also produced fewer reactive oxygen species, the by-products of metabolism that damage tissue. The authors read both findings as support for two long-standing theories of ageing.
Another analysis, published in Science, found that people who trimmed intake by about 14 percent made more T cells. Eric Ravussin of Pennington explained why: “Calorie restriction helps prevent the thymus from shrinking so the person generates more T cells.” The same work flagged a protein, PLA2G7, whose lower levels under restriction are linked to less age-related inflammation.
Why the animal record muddies it
None of that measures how long anyone lived. The idea itself dates to the 1930s, when Cornell researchers found that rats and mice on restricted diets lived 40% longer. In 2009 the Wisconsin gerontologist Richard Weindruch reported that a moderately trimmed diet held back ageing in a rhesus monkey colony across 20 years.
Then the National Institute on Aging reported its own monkey study in Nature. Julie Mattison’s team gave rhesus monkeys 30% fewer calories than controls for 23 years and found no gain in longevity, young or old at the start, though the animals did put off diabetes, cancer and cardiovascular disease. Steven Austad wrote that the diets might explain the split. Sucrose made up 28.5% of the Wisconsin monkeys’ food and 3.9% of the NIA monkeys’ food. Diabetes struck over 40% of the Wisconsin controls; at the NIA the figure was 12.5%.
Leanne Redman, a lead author at Pennington, put the human limit plainly. “The Rolls-Royce of a human longevity study would carry on for many decades to see if people do actually live longer,” she said.
Sources
- Moderately reducing calories in non-obese people reduces inflammation (Tufts Now)
- Restricting calories could slow ageing in humans (The European Scientist)
- Eat less, live longer and healthier, a study suggests (TRT World)
- Calorie restriction doesn't slow ageing, monkey study suggests (The Guardian)
