In your forties, your body may have an increasingly difficult time digesting carbohydrates, which may lead to weight gain. Living a stressful life can lead to an increase in the stress-hormone called cortisol, which can make you more prone to gaining belly fat. Estrogen loss may also lead to fat redistribution in your body and cause belly fat gain.11
As we age, we tend to become more insulin resistant which can put us at risk for type 2 diabetes. When you eat foods that break down into sugar, the pancreas pumps out insulin to escort the sugar out of your blood. People with Insulin resistance don’t use insulin effectively so that cells have trouble absorbing sugar which causes a buildup of sugar and insulin in the blood. Researchers still aren’t 100% in agreement as to why, but at the end of the day, people with insulin resistance gain weight, particularly around the middle. And some research shows that lack of estrogen may cause insulin resistance.
Your metabolic rate naturally continues to decline 5 percent each decade once you hit 40.3 Your resting metabolic rate (RMR) determines how many calories you just to survive. It is determined by a variety of chemical reactions inside your body. These reactions rely on your mitochondrial function and sodium-potassium pumps. Your mitochondria help to create energy, while your sodium-potassium pumps generate muscle contractions and nerve impulses.4,5,6,7,8 Both of these processes become less effective over the years and slow your metabolism.9,10 If you eat more than your RMR yet lead a sedentary life, you set yourself up for weight gain.
Hormonal changes are one of the main reasons that women tend to lose more muscle as they approach menopause. Diet and exercise also play a role.12 On average, adults lose 3 to 8 percent muscle every decade after age 30.13,14 By the time you reach 80, you may have about 30 percent less muscle than you had at age 20.15,16 Muscle loss over time can lead to slower RMR, increased fat, weight gain, weakness, and fractures.17
I am 59 and have been on a injury / weight gain cycle for several years. I have never been overweight till my first accident , then I gained weight and kept gaining and now that I am almost 60 , I want that great body and high energy back. The older I get the more problems my weight causes , legs hurt , falling asleep in my chair , I am too young for that. So I am eating better and boxing , which is a great workout . I plan to sky dive for my 60th next year.
When you were young, you probably didn't spend too much time thinking about preparing your body for the future. In your teens and twenties, you're in peak condition and it's the perfect time to start exercising. Cut to 20 years later and, if you didn't start exercising, you probably wish you had since there's something we all start to experience in our 40's—weight gain.