The Truth About Protein, Part 1: A Look at Amino Acids and Why Adults Over Age 40 Need Protein

As proteins are the building blocks of all human life, it’s unanimously agreed upon that we need to eat this essential macronutrient. But researchers have debated the specifics for years—like how much protein? From what sources? Do our protein needs change over the lifespan? And should we consume more or less to extend longevity? 

In this first article in a series of three, learn more about the basics of protein, including details about essential amino acids—plus which ones protein experts think are the most critical—and the top benefits of eating protein in adults over 40. In the following two articles, we’ll cover how much protein you really need, how protein impacts longevity (we’ll tackle the mTOR issue), and which protein sources are best for middle-aged and older adults.  

Protein 101: Essential Amino Acids 

Most people are aware of which foods contain high amounts of protein. But whereas fat- and carbohydrate-rich foods are broken down into subcategories, like polyunsaturated and saturated fat or sugar and fiber, protein just gets one overarching category. However, it’s a bit more complicated than that, as all proteins are composed of amino acids—we just don’t see them on the nutrition label (sports supplements and protein powders aside). 

Humans have 20 amino acids, all of which perform different—and critical—functions in the body. Of these 20, nine are considered essential amino acids—histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine—as we cannot produce them on our own. Many protein-rich foods (namely animal proteins) contain all nine, which are dubbed “complete proteins.” Conversely, most plant foods, like beans, nuts, and seeds, are incomplete proteins (although a few plant proteins, like soy, quinoa, and hemp, are complete).

Above and beyond those nine essential amino acids, six to eight others (another debated topic) are conditionally essential—meaning, they become essential to consume in the diet under certain conditions. These conditions can include pregnancy, injury, high stress in the body, trauma, or intense exercise. 

Although all amino acids are important for different functions, protein expert Don Layman, Professor of Food Science and Human Nutrition at the University of Illinois Urbana-Champaign, has pinpointed three that are the most critical for muscle health and aging—leucine, methionine, and lysine. 

Lysine is required for collagen formation—the protein most essential for skin, bone, and cartilage structure—and acts as a signal for muscle protein synthesis. Leucine is vital for muscle repair and influences lipid and energy metabolism, as it is a rare amino acid that activates the fatty acid oxidation pathway—the way we break down and use fat for energy. Methionine is needed to make and repair DNA, RNA, other amino acids, and antioxidants like glutathione—and most plant foods are severely limited in it. 

Top Benefits of Protein for Adults Over Age 40

While there are dozens—if not hundreds—of benefits of protein and amino acids in the body, let’s take a look at the leading benefits to adults over age 40.

Supports Muscle Mass and Prevents Sarcopenia

Every gym-goer knows that protein is necessary for maintaining or building muscle mass. But this becomes especially important as we age, as we lose about 4% of our muscle mass per decade after age 40. How much skeletal muscle we have impacts our metabolism—so, if we lose muscle year after year, our metabolic rate lowers, and fat accumulation can occur. That is unless we make up for this decline by boosting protein intake and prioritizing strength and resistance training. 

Age-related loss of muscle mass, strength, and function, known as sarcopenia, is linked to increased morbidity, mortality, falls, fractures, and loss of independence. Therefore, it’s crucial to maintain muscle mass as we age—which can be supported with healthy protein intake. 

Maintaining high protein consumption can also help prevent muscle loss that occurs during weight loss—which, as we saw in this recent article, is linked to poor health outcomes and lessened longevity. 

Supports Protein Turnover

Each protein in the body—made up of different amino acid combinations—has a different turnover rate, which is when older proteins are replaced with newer ones as they are broken down in the cell. As protein turnover is constantly occurring, we need to balance out protein breakdown with new protein synthesis. 

While each protein turnover rate is different, they all require new proteins to do so—and if it’s not coming from your diet, it will come from your muscles and other parts of the body, which is one reason why dietary protein is so essential. 

Increases Satiety and Supports a Healthy Weight

Of the three macronutrients, protein is considered the most satiating. Most people intuitively know this, as consuming 1,000 calories of grilled chicken is much more challenging than the same calories in a bowl of pasta. The satiating effects of protein occur because it reduces ghrelin levels—our hunger hormone—while boosting peptide YY levels, our “feel-full” hormone. 

Studies have shown how powerful the effects of eating protein are on satiety. In one study, overweight women who increased their protein intake from 15% of daily calories to 30% consumed 440 fewer calories each day. The satiety effects of protein become even more beneficial as we age because it can fight back against the commonly seen age-related fat accumulation. 

Supports Bone Health

Older adults—especially older women—are prone to bone loss, which can lead to fractures, falls, and loss of mobility. An often-touted myth is that excess protein is bad for bones because it leaches calcium from them, but research has found that protein is actually highly beneficial for strengthening bones. 

In clinical studies, researchers have found that relatively high protein intakes (including animal protein) are linked to increased bone mineral mass and a reduced risk of osteoporotic fractures. This is because protein helps with calcium absorption, enhances lean body mass, and stimulates the secretion of IGF-1, a hormone that benefits skeletal development and bone formation. 

Key Takeaway 

Protein is vital to consume at every age—but adults in their 40s and beyond may need to pay particular attention to the protein on their plates. With benefits including supporting muscle mass, preventing sarcopenia, promoting bone growth, and increasing satiety, adequate protein consumption can combat many common age-related ailments. For details about how much protein to eat—and from what sources—plus how protein impacts lifespan, stay tuned for the following two articles in this series.