The United States Food and Drug Administration (FDA) estimates that the average American gets 33 percent of his or her calories from “foods prepared away from home.”

In addition to the dollar amount, the average American adult pays another price for this convenience: unwanted body weight. The difference between eating out once a week or not over a five-year period, the FDA reports, is 10 pounds.

And it’s clear that little if any of this weight gain is positive, the result of muscle mass added through serious workouts. The latest figures provided by the Centers for Disease Control and Prevention (CDC) found the average waist circumference of American males over the age of 20 has increased to 40 inches; females measure 38.1 inches.

Big bellies are a big reason why 70.7 percent of all Americans over the age of 20 are now considered overweight or obese, and the biggest one behind why the FDA now requires menu boards at large chain restaurants, coffee, bakeries, and ice cream shops to list the caloric amount with food choices.

Will this change, officially instituted on May 7, 2018, serve as a runaway truck ramp for all those 18-wheeled eaters who have seemingly lost their brakes while speeding down the Sensible Eating Highway? Hardly. But it may motivate a few leadfoots to go easy on the gas pedal.

More importantly, the rule provides easy access to information that in the past was too often less than easy to obtain. So whether or not you order the 1,950-calorie Cheese Curd Bacon Burger at Buffalo Wild Wings or the 360-calorie Artisan Grilled Chicken Sandwich at McDonald’s, you now know the immediate caloric consequence.

With that immediate knowledge, you gain greater control of your weight, your waistline — and your future.

Gaining greater control of your future is also why you need to know more about the muscle loss that inevitably occurs with aging.

It’s called sarcopenia and begins in your 30s, lessening your lean-muscle mass by as much as 8 percent in a decade. By age 45, the rate usually increases to 1 percent per year, and accelerates significantly sometime in your 60s.

Why does muscle loss happen? On his website, Dr. Gabe Mirkin explains the major reason why: As you age, the neurons that cause nerves to fire die, causing the muscle fibers stimulated by those nerves to atrophy. As a result, the overall muscle gets smaller and weaker.

Another age-related change also encourages muscle loss.

Production of three hormones crucial to maintaining and building muscle (testosterone, growth hormone, and insulin-like growth factor) reduces significantly for all by the fifth decade. Combine the loss of nerve function and the reduction of muscle-helping hormones with the lessening of physical activity — particularly intense physical activity — so typical in middle age, and muscle mass loss is inevitable.

“For example,” Mirkin explains, “the vastus medialis muscle [part of the quadriceps] in the front of your thigh contains about 800,000 muscle fibers when you are 20, but at age 60, it has only about 250,000 fibers.”

That’s a reduction of nearly 70 percent, but your strength does not have to diminish that much because of it. There are ways to counteract the death of neurons and the nerves lost, the reduction of muscle fibers, and the lessening of hormone production, the most important of which may very well be weightlifting.

Performed properly, weightlifting has been found to positively influence the neuromuscular system (meaning nerves fire quicker and don’t die as quickly) and increase decreasing hormone production, thereby mitigating the declining rate of protein synthesis, the process that maintains and grows muscle.

Let’s use my body and the vastus medialis muscle to better explain matters. When I was at my most powerful applying pressure to the pedals on a bicycle (I came to the sport late, so that was actually in my late 30s), the vastus medialis was prominent when I was walking around in shorts. It looked like a doorknob just above the inside of the kneecap and it would pop out even more when I rode.

Now nearly 70 percent of those muscle fibers in my vastus medialis are gone, but — because the body is amazingly adaptive — I haven’t lost that same amount of muscle size.

That’s because when a neuron dies, an adjacent neuron quite often takes over.

But the type of neurons that tend to die first trigger quick-twitch muscle fibers, the type you need to sprint in the final 200 meters of a bicycle race. The type that survive longer trigger slow-twitch muscle fibers, the type you use while pedaling easily and about up to about 80 percent of your maximum on the bicycle.

As a result, you tend to lose power quicker than endurance as you age, which is another reason why you lose muscle size.

But lift weights in the right way and you can turn back the hands of time to some extent — or at the least freeze them in place for a while.