Contributed by: Annabelle Hutchinson
When it comes to longevity, one of the first questions people ask is what they should eat. Unfortunately, nutritional epidemiology is plagued by faulty methods of measurement and analysis that lead to biased results, low internal validity, and misplaced claims of causality. The result? We are bombarded by contradictory and confusing nutrition advice. However, there is one area where the scientific literature is relatively clear – dietary protein.
Proteins are the building blocks of muscles and sine qua non of muscle protein synthesis. Most people assume that increased protein intake or supplementation is reserved for bodybuilders and athletes, but the general population, particularly older adults, can benefit from higher levels of dietary protein. Lean body mass tends to drop precipitously after the age of 75, leading to a host of physical ailments. Aging is associated with the deterioration of muscular strength and endurance, leading to instability, injury, and pain. Consuming an adequate amount of dietary protein can slow down the progressive loss of muscle mass and function. This means it is easier to maintain physical vitality and overall health (and happiness!) as we age.
So, how much protein should we be eating? The UK’s Reference Nutrient Intake (RNI) for adults sets daily protein consumption at a modest 0.75 grams per kilogram of body weight, while the US’s Recommended Daily Allowance (RDA) for protein is 0.8 grams of protein per kilogram of body weight. Based on these guidelines, adults weighing 70 kilograms should aim to consume 52.5-56 grams of protein per day.
While these reference ranges are often read as recommendations, the RDA for protein actually reflects the minimum amount of dietary protein required to meet indispensable needs. They are not necessarily the optimal level for human health and longevity, particularly for physically active adults, and they do not communicate the best guidance from the scientific literature. They simply give us a baseline below which people are not meeting their most basic needs.
There is robust evidence documenting the benefits of consuming protein at levels beyond this baseline. These benefits include preventing or attenuating age-related osteoporosis and sarcopenia, as well as limiting metabolic disorders. Higher levels of dietary protein were found in several studies to reduce bone fracture and bone mineral density loss, two features of age-related decline in older people.
For optimal bone maintenance throughout life, a 2017 meta-analysis recommends that dietary protein intake should exceed the 0.8 gram/kilogram of body weight standard. A 2018 study advised that daily protein intake should be 1.6-2.2 grams per kilogram of body weight per day. For an adult weighing 70 kilograms, this means consuming between 112-154 grams of protein per day, more than twice the RDA recommendation. Importantly, the study also advises engaging in frequent exercise to promote muscle synthesis.
“For an adult weighing 70 kilograms, this means consuming between 112-154 grams of protein per day, more than twice the RDA recommendation.”
Protein intake should be achieved by splitting protein consumption between 3-4 meals throughout the day. A 2014 study revealed that the body is less efficient at consuming a high dose (>60 grams) of protein in a single meal skewed toward the end of the day. By switching breakfast from a carbohydrate-dominant meal (e.g. cereal, oats, toast) to a protein-dominant meal (e.g. eggs, lean meat, high-protein vegetables), adults can distribute their protein more evenly throughout the day.
Bear in mind that not all proteins are created equal. Protein quality matters, and heavily processed proteins with unhealthy fats or sugars may not provide health benefits. Proteins that include all nine essential amino acids are better able to support tissue growth, development, and maintenance – all important for reducing age-related sarcopenia and osteoporosis. Plant-based proteins are not as bioavailable for muscle synthesis as animal-based proteins, but it is possible to consume an adequate amount of protein on a plant-based diet. If you are plant-based, it is advisable to consume protein at the high-end of the optimal reference range of 1.6-2.2 grams/kilogram of body weight to account for lower rates of protein synthesis.
As humans age, we become weaker, less stable, and less able to engage in the physical activities that once brought us joy. To live longer and better, preserving muscle mass and function is critical. Consuming adequate dietary protein is a well-researched path to stronger muscles and better health outcomes as we age.