How much muscle we have tells us more about how we are aging than body weight or BMI ever could. Here's a startling fact. After the age of 50, the average person loses about 1% of their muscle mass every single year. And it's not just muscle mass. Strength plummets even faster, dropping around 3% annually. By the time you reach 75, if you're not engaging in regular strength training, you could be losing up to 4% of your strength every year. So what can we do about this? Exercise, both before you need it, building muscle reserve, but also in old age to slow and reverse the decline. While resistance training is the most important factor for building and maintaining muscle mass and strength, protein intake plays an important role too.

A meta-analysis from Dr. Stuart Phillips and colleagues highlights the importance of protein intake by showing that people who engage in resistance training And supplemented with additional protein, taking their total daily protein intake up to 1.6 grams per kilogram body weight, increased their muscle mass by 27% and their strength by 10% more than those who did resistance training without additional protein supplementation. So these people were getting around 1.2 grams of protein per kilogram body weight. So dialing in that protein intake matters for both muscle mass and strength when combined with resistance training. Skeletal muscle makes up around 30 to 40% of our lean body mass. More muscle doesn't just mean more strength.

It means better metabolism, enhanced insulin sensitivity, and a pretty good defense against type 2 diabetes. It also dramatically decreases frailty and the risk for sarcopenia, one of the main risk factors for falls and fractures in older adults. Research has shown that individuals who suffer from a fragility fracture are twice as likely to die compared to those without such fractures. And between 22 to 58% of people with a hip fracture pass away within just 12 months after the injury. In old age, falling and breaking a hip can literally be a death sentence. A better body composition dramatically improves quality of life and reduces disability risk. Having a higher muscle mass can decrease the risk of early death by 30%, whereas having a high fat mass can increase that risk by 56%.

So what explains our greater susceptibility to lose muscle mass as we get older? There are a few factors that play a role in this, but a big player here is a phenomenon called anabolic resistance. So as we age, our muscles become less responsive to amino acids, meaning they don't trigger muscle protein synthesis in response to protein intake As effectively. So for older individuals, the same amount of protein results in a smaller increase in muscle protein synthesis compared to younger people. Some studies have shown that an older person requires almost twice as much protein for the same response.

For example, around 0.24 grams of protein per kilogram body weight, or 0.1 grams per pound— that's 20 grams of protein for about an 80-kilogram man— maximally stimulates muscle protein synthesis in someone young. But this dose is higher for older adults who need about 0.4 grams of protein per kilogram or 0.18 grams per pound of protein per dose. An older adult man weighing about 80 kilograms would need about 32 grams of protein to maximally stimulate muscle protein synthesis. By the way, for anyone taking notes, this suggests that the optimal amount of protein per dose is between 20 and as high as 35 grams of protein, depending on your personal level of anabolic resistance. So this means a few things.

The first is that if you're older, you need a higher total daily protein intake to maintain or increase muscle mass. It also means that you need a higher dose of protein at each meal to stimulate muscle protein synthesis. But anabolic resistance is not inevitable or only due to aging, as some might suggest. In fact, physical inactivity may actually be the biggest contributor. Reducing physical activity worsens anabolic resistance. For example, taking fewer steps for just 2 weeks causes anabolic resistance in older adults and reduces their insulin sensitivity. Imagine what decades of inactivity can do. That's the bad news. But the good news is that exercise makes muscle more sensitive to protein and essentially negates anabolic resistance.

When older adults exercise before protein intake, their muscle anabolic response is identical to that of a younger adult. So how do I interpret this? Active older adults probably don't experience as much anabolic resistance as inactive people, and therefore it might not be such an issue for people that are physically active. The most effective way to combat anabolic resistance as we age is through regular physical activity combined with a higher daily protein intake, ideally around 1.6 grams per kilogram body weight. We do not have to be frail in old age. We can build muscle into our 40s, 50s, 60s, and even our 70s and beyond. And we can definitely increase muscle strength and power output at this age.

In one study that recruited adults aged 90 years and older, 8 weeks of high-intensity strength training produced a 174% increase in muscle strength and a 48% increase in the size of their leg muscles. Muscle strength and size increased even in the 9th decade of life, an age when most people wouldn't even think twice about touching a weight.