Last Updated on February 8, 2021 by dgvause

A coworker of mine recently remarked about the inevitability of weight gain as we age. She was commenting on her partner’s loss of 20-30 pounds and how it has been all the more remarkable because he is 40-something. This got me thinking about how pervasive this belief is and whether there’s any concrete evidence on which it is based. I’ve always been skeptical of the notion that weight gain in older age is inevitable because of slowing metabolism. In the 1970’s as I was just beginning a lifetime relationship with running, George Sheehan, M.D., my running idol, remarked in a column that weight gain with age was inevitable. I could see no justification for it, aside from a simple observation that everyone in our culture seemed to do so. According to the U.S. Department of Health and Human Services, women on average gain 7 pounds between 29 and 39, while men gain 15.

My arc of life was anything but average. I was to start running, join the Marines, and begin an embrace of all things related to health and fitness. In engineering school, I continued this commitment while working as a fitness instructor. In 1987, in my late 20’s, my 5’7” frame weighed about 137 lb, with a 29 inch waist and less than 10% body fat by weight. I could easily do 20 pull ups and ran about an 18 minute racing 5K. Then came IBM. Twenty two years later, I weighed 180 pounds, was over 30% body fat, and was living a sedentary life (12).

Was it weight gain from getting older?

At 49, I told my concerned general practitioner that I would run the 2005 Marine Corps Marathon. Over the next 13 months, I dropped my weight 38 pounds and ran my first marathon. I started off with a strict clean bodybuilding diet. I watched my percentage body fat drop from 30% to 25% with diet alone. Then something interesting happened. My body fat value plateaued while my weight continued to drop. I knew that this was because I hit the point that every aggressive dieter hits: my body was breaking down muscle to preserve fat. At this point I started to run and lift. By October, 2005, I was 142 lb, and around 13% body fat, and did indeed run my first marathon. Over the past 15 years, my weight has fluctuated between 142 and 148. I’ve done 9 more marathons. 150 pounds is a red line for me. I weigh myself almost every day, a practice consistent with others who have successfully lost weight and kept it off (1).

So what about aging? There is really no evidence that metabolic slowdown is the cause of weight gain (2). There is some indication that metabolic inefficiencies contribute to a slowing metabolism (3). But studies comparing the metabolisms of peopled aged 20-34 and 60-74 indicate that increased metabolic inefficiency equates to a decrease in roughly 24 calories on average daily (3). Instead, weight gain with increasing age is strongly associated with increased food intake, decreased activity levels, and muscle loss (4).

As for muscle loss, the numbers are surprising. An average male between 18-35 year has 40-44% muscle. This drops to 32-35% for the 56-75 year cohort (5). A 170 pound average 20-something male will on average lose 13.6 pounds of muscle by the time he’s 60. Much of this is discretionary (6) and reversible (7). A pound of muscle burns a small, but over time significant, amount of energy. Various studies place the rate at 4.5-10 calories per day (8)(9)(10), not the often hyped 50 calories per day.

So what does this mean over a lifetime? The loss of a single pound of muscle results in a 1,642 calorie surplus over a year, assuming the lowest metabolic activity of 4.5 cal. per day. Over the course of 20 years, on pound of muscle loss results in 9.4 pounds of excess calories not burned. The numbers compound. The loss of say 10 pounds of muscle or more over a lifetime can become very significant.

While preventing muscle loss or, even better, achieving muscle gain is important for long term weight control and quality of life as a senior, it will not significantly help in the short term. Resting muscle tissue just doesn’t but that many calories. Running or walking is perhaps the most time-efficient way to burn calories. Running burns roughly 11.4 to 17 calories per minute depending on body weight. And it comes with a host of other cardiovascular and psychological benefits (11).

The rest is simple, but difficult. To lose weight and keep it off, you need to strength train to preserve your muscle and try to burn more calories. Cardiovascular exercise will goose your metabolism, make your heart healthy, and burn a lot of calories, if you become an endurance athlete. But the battle is won or lost at the dinner table. The wrong nutrition can destroy any exercise regimen.

(1) National Weight Control Registry
(2) Mayo Clinic: Is a slow metabolism the reason I’m overweight?
(3) Healthline: Why Your Metabolism Slows Down With Age
(4) Science Alert: The Biggest Reason You Gain Weight as You Age Has Nothing to Do With Your Metabolism
(5) Healthline: How Much Muscle Mass Should I Have, and How Do I Measure It?
(6) Harvard Medical School: Preserve your muscle mass.
(7) NPR: Seniors Can Still Bulk Up On Muscle By Pressing Iron.
(8) University of New Mexico: Controversies in Metabolism
(9) Built Lean: How many calories does 1lb of muscle burn?
(10) Verywell Fit: The Amount of Calories Muscles Burn
(11) Healthline: How Many Calories Do You Burn Running a Mile?
(12) Why It’s Harder to Lose Weight as You Age
(13) Mean Body Weight, Height, and Body Mass Index,United States 1960–2002
(14) Why people gain weight as they get older

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