Review warns against excessive protein intake in later life

A review of scientific research reported by ERR suggests that a high-protein diet may cause more long-term harm than benefit for older people, despite recommendations encouraging increased protein intake as populations age.

US official dietary guidelines recommend that people over 65 consume 1.2 to 1.6 grams of protein per kilogram of body weight each day. The aim is to prevent the loss of muscle mass, known as sarcopenia, and reduce the risk of falls and frailty.

The recommendation to eat more protein has also increased demand among the wider population. More than half of people in the United States increased the protein content of their diets last year, while food manufacturers responded by filling store shelves with products containing added protein. The protein-product boom has also reached Europe, including Estonia.

According to researchers, the trend carries serious risks. The authors of the new review, University of Wisconsin Madison scientists Bailey Knopf and Dudley Lamming, warn that high protein intake is associated with higher mortality. They say large population studies have found that people who consume large amounts of protein are more likely to develop type 2 diabetes and cardiovascular disease. High levels of animal protein in particular appear to accelerate ageing at the cellular level.

A recent British study of twins also challenged established assumptions. It found that high protein consumption may actually increase the risk of sarcopenia among older people. Lamming and Knopf said the finding disproves the widespread belief that eating plenty of meat ensures strong muscles in old age.

What protein restriction does in the body

Short-term clinical trials support the findings of observational studies. In one study, men who followed a low-protein diet for 43 days lost body mass and fat mass, while their fasting blood sugar levels fell. Their metabolism improved even though they consumed more calories than before.

The low-protein diet triggered what could be described as a defensive response in the body. Tissue sensitivity to insulin improved, meaning the ability to absorb glucose from the blood for energy increased, while overall energy expenditure also rose.

Animal studies suggest that these beneficial changes are linked to FGF21, a so-called hunger hormone that responds to diet-related stress. A lack of protein prompts the body to release large amounts of the hormone. According to the researchers, FGF21 stimulates white fat tissue to produce heat and burn excess calories. Once circulating in the bloodstream, it also helps lower levels of triglycerides, a type of fat in the blood, and removes ageing and inflammatory cells from tissues.

According to the researchers, restricting protein changes how cells sense the availability of nutrients. The activity of mTOR, a protein complex that accelerates cell growth and ageing, decreases in the body. This biochemical shift directs cells towards autophagy, a kind of cellular cleanup process in which they break down damaged proteins and worn-out cell organelles.