Metabolism & drugs Preprint

Adults who ate more protein per kilo of body weight looked biologically younger in a US survey

In 6,249 US adults, those who ate the most protein relative to their body weight were less likely to show signs of faster biological aging, measured with telomeres and three blood-and-body scores, and were less likely to die during follow-up. The data are a single snapshot of diet from two decades ago, so reverse causation cannot be ruled out, and the study is a not yet peer-reviewed preprint.

Two people born in the same year can age at different speeds. Researchers try to capture this with measures of biological age: scores built from blood tests, body measurements or the length of telomeres, the protective caps on the ends of chromosomes that shorten as cells divide. Diet is one of the things that might push these scores up or down, and protein, which the body needs for muscle, immune defence and metabolism, is an obvious candidate.

This preprint, not yet peer-reviewed, asks whether people who eat more protein look biologically younger, and whether that could help explain why they also tend to live longer.

What they did

The team used the US National Health and Nutrition Examination Survey (NHANES), which samples the population so that results can stand for the country as a whole. They analysed 6,249 adults from the 1999–2000 and 2001–2002 rounds who had diet data, blood tests and a telomere measurement. Their median age was 45.

Protein intake came from one 24-hour recall, an interview about everything eaten the day before. It was divided by body weight, giving grams of protein per kilogram per day. The usual recommended amount for adults is 0.8 g/kg. The median participant ate 0.95 g/kg, and 62% met the recommendation. People were split into five equal groups, from under 0.62 g/kg to more than 1.40 g/kg.

Biological aging was measured four ways:

  • Telomere length in white blood cells; the shortest 25% counted as "accelerated aging".
  • AnthropoAge, based on age, BMI and waist-to-height ratio.
  • PhenoAge, based on age and nine routine blood values, such as albumin, glucose and a marker of inflammation.
  • The Klemera–Doubal method, which uses lung function, blood pressure and seven blood values.

For the last three, a person counted as aging faster if their score was higher than expected for their real age. The team adjusted for age, sex, total calories, ethnicity, income, smoking, physical activity, high blood pressure and diabetes, and linked the survey to death records up to the end of 2019.

What they found

  • Less "accelerated aging" with more protein. Compared with the lowest-protein group, the highest-protein group had lower odds of short telomeres (odds ratio 0.40), of a high PhenoAge (0.54) and of a high Klemera–Doubal score (0.53). For AnthropoAge the link was weaker and was clear only in the middle group.
  • Similar across ages, with somewhat stronger links for telomeres and PhenoAge in people over 40.
  • Lower death rate. Higher protein intake was linked to lower overall mortality and lower cancer mortality, but not to deaths from heart disease or stroke.
  • Part of the link ran through the aging scores. In a statistical breakdown, PhenoAge accounted for about 56% of the link between protein and death, AnthropoAge about 53%, the Klemera–Doubal score 23% and telomeres only about 7%.

What to keep in mind

  • A snapshot. Diet and aging markers were measured at the same visit, so the study cannot tell which came first. The authors note that reverse causation cannot be ruled out: people who are already less healthy might eat less.
  • The groups differed a lot. People in the highest-protein group were younger, more often men, had higher incomes and ate more calories overall. People in the lowest group were heavier and more often had obesity, diabetes and high blood pressure. Because protein was divided by body weight, heavier people automatically get a lower number, a point the authors list themselves.
  • One day of eating. A single 24-hour recall may not reflect a person's usual diet.
  • No information on protein sources, so plant and animal protein could not be compared.
  • Old data and few deaths. The surveys date from 1999–2002, and the authors say the cause-specific results and the statistical breakdown should be read with caution and need replication.
  • Not yet peer-reviewed. The authors themselves call for intervention studies.

Why it matters

The study adds to earlier observational work linking protein intake to longer life, and it tries to connect that link to measurable signs of aging in the body. It cannot show that eating more protein slows aging; the differences between the groups and the single snapshot of diet leave room for other explanations. It does point to questions that trials could test, such as whether the amount and type of protein people eat changes these aging scores over time.

Sources