Battling the Midlife Bulge - New Scientist

It is a myth that extra belly fat in middle age is due to a slowing metabolism...[but a recent study] showed that metabolism stays remarkably stable as we age, at least until our 60s. The amount of calories you burn per day from age 20 to 60 remains about the same.

Middle-aged spread is more than just folklore. Studies consistently show an insidious uptick in body weight at this time of life, with most of us putting on the best part of a kilogram each year. Increased abdominal fat is strongly correlated with high amounts of visceral fat, which surrounds the body's internal organs. This dangerous variety of fat is made of particularly active cells that produce hormone-altering signals that disrupt the body's sensitivity to insulin. Visceral fat also pumps proteins called cytokines into the body, affecting the immune system and causing inflammation..[which] increases the risk of chronic conditions, such as type 2 diabetes, cardiovascular disease and cancer as well as heart attacks. Those with just 10 centimetres of extra belly fat, as measured by their waist circumference, have been shown to be at an 11 percent higher risk of early death, and this increased exponentially as waistlines grew.

Metabolism doesn't change from age 20 to age 60 because the body is always working to keep itself within a narrow calorific range... our bodies seem to adapt to exercise, burning similar amounts of calories whether we live very active lifestyles or not. While metabolism remains a constant, middle age is a time when other things change, offering clues as to the cause of the weight gain. The most obvious shift is in hormones.

During the female menopause, the amount of estradiol decreases at the same time that visceral fat increases...this is often termed a 'fat reshuffle'. Fat becomes less pronounced in other parts of the body such as the hips and thighs at the same time as visceral fat begins expanding. Estrogen probably plays an important role - it seems to inhibit the growth of visceral fat. The impact of sleep problems on body weight shouldn't be underestimated. Sleep loss affects our decision-making, and has been repeatedly shown to weaken resolve, leading to poor food choices and less exercise, both of which can result in weight gain [and] has been associated with depleted stores of leptin, a hormone made in our fat cells that inhibits hunger and influences calorie regulation in the body. Simultaneously, a lack of sleep increases levels of ghrelin, also known as the hunger hormone. Poor sleep can interfere with other hormones that cause people to put on fat and lose muscle mass too... sleep deprivation has been shown to trigger higher levels of endocannabinoids, lipids involved in signalling the satisfaction gained from food... men too are affected.

A deficiency of testosterone occurs in upwards of 24 percent of men over the age of 45 [with] a number of causes, from trauma or injury to alcohol misuse, renal failure, cancer, medication use, obesity, diabetes, obstructive sleep apnea, and plain aging. Those who experience low-T are more likely to see a loss of muscle mass and bulk, which can lead to increases in fat accumulation around their middle... low-T usually also means low estrogen in men. While estrogen is less abundant in men, it is still necessary and a drop can cause an increase in visceral fat, as it does for women.

Middle age brings with it another enemy of the waistline: stress. The body makes too much cortisol, which some research has shown can boost our appetite and can cause insomnia. While stress remained largely the same in younger and older age groups as it had in the 1990s, those in middle age in the more recent cohort experience a 50 percent rise in daily negative emotions and 2 to 3 times more daily stress factors.

The causes of middle-age spread are clearly a complex interplay between biology, behaviour and environment.. The place to start: Getting enough sleep.... diet...exercise - at 60 muscle begins to fade. Lean muscle mass makes up half of the total body weight in young adults, but drops to a quarter by age 75. And because muscle burns more energy than fat, this transition causes metabolism to become sluggish. With a slower metabolism, fat starts to accumulate.

Muscle loss is due to a host of age-related changes, but the main factors are a decrease in the body's ability to turn over and repair muscle tissue at the same time as we are decreasing physical exertion which is one of the reasons why muscle-building weight training is recommended for older people.

New Scientist (12 March 2022)