Does eating a low-protein diet extend your life, or does that only apply to mice?
Eating less animal protein appears beneficial in middle age, but after the age of 65 getting enough protein is actually important. Replace animal protein with plant protein where possible, and discuss major dietary changes with your doctor.
Eating less animal protein appears to be beneficial for middle-aged people, but the source of the protein matters more than the total amount. In a large British study involving more than 56,000 participants, a low animal protein pattern was associated with less biological ageing and an average of 1.5 extra years of life. People who ate little plant protein, on the other hand, aged faster and lived shorter lives. A generally low-protein diet, without any distinction by source, made no difference.
Research among Americans shows a similar pattern. People between the ages of 50 and 65 who ate a lot of protein had a 75% higher all-cause mortality and a four times higher risk of dying from cancer than people who ate little protein. This association hardly applied to plant proteins. A particularly striking finding: across all age groups, eating a lot of protein was associated with a fivefold higher risk of dying from diabetes.
After the age of 65, the picture reverses. In older adults, eating more protein is associated with lower mortality; those who consume too little risk muscle loss. That is dangerous: muscle loss in later life increases mortality. Protein restriction as a life-extension strategy therefore does not work for everyone.
What holds true in animal experiments does not automatically apply to humans. Restricting certain amino acids that occur in high concentrations in red meat extended lifespan in animal research, but the optimal levels for humans have not yet been established. Eating little meat (less than weekly) was associated with lower mortality in four of the six populations followed; among people who maintained this for more than twenty years, life expectancy was on average 3.6 years higher. After the age of ninety, that advantage appears to fade.
The common thread: replace animal protein with plant protein as much as possible, especially if you are between 50 and 65. If you are older, getting enough protein is probably more important than restricting it. Always discuss major dietary changes with your doctor, especially if you use medication or already have difficulty maintaining muscle mass.
The evidence rests largely on large studies in which people were followed for many years, including the NHANES study in the United States and a British study with more than 56,000 participants. None of these studies can prove cause and effect: people who eat little animal protein differ from those who eat a lot of it in more ways than one. Animal research into specific amino acids suggests biological mechanisms, but the translation to humans has not yet been made. The findings regarding 50-to-65-year-olds and those over 65 are internally consistent and confirmed by multiple data sources, which increases confidence, but does not provide certainty.