6 Possible Reasons Why You’re Gaining Weight During Middle Age

You probably noticed that as you age, it gets harder and harder to manage your weight. It’s a common complaint among middle-aged adults; in fact, about 44 percent of Americans ages 40 to 59 are considered obese, according to the U.S. Centers for Disease Control and Prevention.  

For some people, middle age weight gain is just a few pounds. For others, it’s significant, raising the chances for heart disease, type 2 diabetes, some cancers and arthritis. Some middle-aged adults may maintain their weight, but they experience a body composition shift toward a higher body fat percentage, risking being classified as “metabolically obese, normal weight” or in other words, skinny fat. Being skinny fat has ties to dementia, type 2 diabetes and heart disease.  

This weight gain can be very frustrating for many people, particularly if they’re living a healthy lifestyle. Many women write off the weight gain as part of menopause, which is understandable. But it’s also common for men to gain weight during middle age. Researchers have been studying this issue for years, which has led to a handful of scientific theories.  

Reason 1: Stem Cells

Stem cells are cells that can develop into many different types of cells in the body. There are two types – embryotic and adult. Small numbers of adult stem cells are found in most tissues throughout the body, including brain, bone marrow, blood vessels, skin, teeth and heart. However, as we age, a new type of stem cell develops that shifts the production of new fat cells into overdrive, causing fat to accumulate in our midsection, according to a study published in Science. Researchers studied mice and human tissues, finding that the rise in body fat percentage also raises the risk for developing chronic conditions.  

Reason 2: Hormones

It’s not news that hormones affect weight. A handful of hormones influence appetite, body fat distribution and metabolism. They are:

Leptin – prevents hunger cues when your body doesn’t need energy. White fat cells produce and release leptin, which means the more fat you have, the higher your leptin levels. This is why you’ll feel hungry after losing fat mass; your body thinks it’s starving and needs more calories, making it tougher to lose weight while dieting. Another problem is leptin resistance, which prevents you from feeling full, even though you’ve had enough calories, and your body has enough fat stores.  

Insulin – controls blood sugar levels. After you eat, most of your food is broken down into blood sugar and released into the bloodstream. Insulin escorts blood sugar into cells to be used as energy. However, if your body is resistant to insulin, blood sugar levels will rise, triggering your body to store the excess sugar in liver, muscles and fat, causing weight gain.    

Estrogen and progesterone – are female sex hormones. Estrogen regulates the menstrual cycle, affects the reproductive and urinary tracts, heart, blood vessels, bones, breasts, skin, hair, mucous membranes, pelvic muscles and brain, while progesterone supports menstruation and early stages of pregnancy. As women age, estrogen and progesterone levels diminish, muscle mass decreases, mostly from the midsection, and replaced with fatty tissue deposits. The decrease in muscle mass also means you’ll burn less calories and need less calories to sustain your weight. The shift in hormone levels is notorious for affecting sleep cycles – another potential cause of weight gain.      

Androgens – are male sex hormones and include testosterone, dihydrotestosterone (DHT), dehydroepiandrosterone (DHEA) and sulfonylated derivative (DHEAS). All of us produce less testosterone as we age; however, some men (and some women) produce drastically less testosterone; it’s referred to as low testosterone (or low-T) and it causes people to feel lethargic, lacking motivation to exercise. It also can slow your metabolism. The combination results in weight gain.

Growth hormone – is a hormone produced by the pituitary gland. In children, it promotes growth and in adults, it supports metabolism, bone structure and healthy blood sugar levels. If the pituitary gland is damaged, it could decrease the production of growth hormone, increasing body fat.  

Reason 3: Loss of Muscle Mass

Having a higher muscle mass is helpful for managing weight because it helps you use more calories and burn more fat. However, muscle mass wanes during middle age for several reasons. First, sarcopenia (muscle loss) is part of the natural aging process and usually begins in your 30s or 40s. Second, middle-aged adults tend to be less active than they were when they were younger, and exercise, particularly strength training, helps maintain muscle mass. Third, as we age, the rate at which muscles produce protein slows. It’s referred to as muscle protein synthesis and along with muscle protein breakdown determines the muscle protein balance – an important component of maintaining and building muscle.    

Reason 4: Slower Metabolism    

For years, slower metabolism was considered a part of the aging process and the primary culprit of middle-age weight gain. However, in 2021, researchers found this isn’t accurate. Metabolic rates remain consistent between ages 20 and 60, decreasing by only 0.7 percent each year after a 60, according to a study published in the journal Science. But when your metabolism slows, managing weight becomes more difficult because you need less calories, while your appetite may remain the same.  

Reason 5: Genes

If you’re an overweight middle-aged adult, chances are, your parents’ weight status is influencing your weight; if both of your parents were obese during middle age, you are six times more likely to also be obese during middle age, according to a study conducted by the University of Norway and presented at the European Congress on Obesity (ECO 2024). Of course, even if you inherited genes that raise the probability of middle age weight gain, lifestyle is still a reigning component of weight management.    

Reason 6: Oxidative Stress

Obesity is a state of chronic low-grade inflammation – a prolonged immune response to diseases, injuries and foreign invaders that results in the immune system attacking healthy organs and tissues and producing low-grade inflammation. Chronic inflammation triggers oxidative stress -- an imbalance of free radicals (unstable oxygen molecules that can damage cell membranes, proteins, fats and DNA) and antioxidants (substances that protects cells from free radical damage). Meanwhile, oxidative stress triggers inflammation. The processes are interconnected – like a chicken-or-egg situation — and involved with weight gain.

Chronic inflammation impairs the body’s ability to process insulin, leading to higher blood sugar levels, which causes weight gain. It also causes fat to accumulate in the liver, disrupting metabolism, hindering the processing of fats and insulin and causing fat to accrue in other organs and tissues, which also can lead to weight gain.  

Oxidative stress has been found to cause white fat to accumulate, speed the development of new fat cells and enlarge mature fat cells, according to a study published in the journal Metabolic Syndrome and Related Disorders. Furthermore, there’s a correlation between increased oxidative stress and higher body mass index (BMI), trunk fat percentage and visceral fat mass (fat around vital organs), according to a study published in the journal Cells.  

Tips for Middle Age Weight Management  

Middle age weight gain might be inevitable for most people, however, you can take steps to control the amount of weight you could potentially gain, as well as any unhealthy changes in your body composition.    

Eat plenty of fruit and vegetables – they’re a great source of polyphenols. These are micronutrients that occur in fruits, vegetables, herbs and teas. Polyphenols are strong antioxidants that neutralize free radicals. They’re abundant in berries, oranges, spinach, broccoli, carrots, potatoes, artichokes, cabbage, asparagus, avocadoes, beetroot, radish, lettuce, sweet potato, squash, pumpkin, collard greens and kale. An easy way to get fruit and vegetables into your diet is by following a Mediterranean diet.

Prioritize protein intake – it helps support healthy muscles. Make sure you understand how much protein you need and that you’re getting it from quality sources.  

Exercise – it helps burn calories and fat and maintain muscle mass. Your workout routine should include aerobic exercise, strength training, stretching and balance practice.  

Manage your blood sugar – it can help prevent and control insulin resistance.    

Avoid toxins – they contribute to oxidative stress. Common toxins include UV radiation, pollution, tobacco smoke and industrial chemicals.  

Drink herbal tea – it’s a great source of antioxidants, particularly calming teas like lavender and chamomile, and most herbal teas are decaffeinated, which is good news if you’re watching your caffeine intake.

Watch your sugar intake – it can affect leptin.  

Get between seven and nine hours of good sleep – it can help control junk food cravings.  

Before you make changes to your diet or begin an exercise routine, talk to your primary care physician. Don’t have a primary care physician? Consider joining an MDVIP-affiliated practice. MDVIP-affiliated physicians have more time to help you in your pursuit of a healthier lifestyle. Find a physician near you and begin your partnership in health »