Understanding Weight Gain Caused by Aging: What You Can and Can’t Control

A plate of eggs and salad on a wooden table in the foreground. A windup clock indicating 7 o'clock in the background beside a cup of coffee on a saucer. There are coffee beans next to the coffee cup.

Ever feel like you can’t believe how quickly your pants size changes these days? If your image of yourself is the 30-year-old version, but your waistline tells a different story, there is a reason. There are both metabolic and lifestyle circumstances that cause weight gain in middle age. Some factors we cannot control, others we can. Let’s break down the science behind weight gain as you age, and the factors you can control.



Genetics: How you lose and gain weight, and where you store fat on your body are genetic. The shape and size of your body are 70% genetically pre-determined. This is important to remember, especially as we age, and our bodies change shape. It doesn’t mean positive habits and behaviors don’t have an impact, but there are limitations. Accepting and allowing our bodies to change naturally as we age is important for mental health.

Human Physiology: The rate at which fat cell turnover decreases with age. This means the rate at which the fat (also called a lipid) inside fat cells empties and creates space for more storage slows. So, if we don’t compensate somehow, we are adding more to our system than can be managed, causing increased body fat even when we do not change our diet and exercise patterns. On average, this can lead to a 20% increase in stored fat. The average middle-aged adult may gain between 10 and 15 lbs annually, depending on circumstances.

Gender: People gain and store weight differently during aging. Males naturally have more muscle cells, and testosterone, in larger areas of the body, allowing them to maintain some more active metabolic tissue into their mid-60s. Females, on the other hand, have naturally more fat cells and less lean tissue, to begin with. Our mitochondria do not stay as active after the age of 40, so maintaining our muscles is a challenge unless we weight-train. Combined with a decline in estrogen levels accompanied by perimenopausal and menopausal shifts, we store fat very easily in mid-life.



The portion size of your meals and snacks: You can control the amount you eat. Often it is a hard adjustment in mid-life to reduce our food intake; our thoughts, mind, and heart’s opinions may get in the way! By this point in life, we have eaten many delicious meals, created ingrained patterns (I have 3 scoops of ice cream, I always have the super-sized meal), have variable emotional well-being, and a lot of life circumstances. We need to listen to our body in mid-life to avoid weight gain and tune out the rest of those cues. Calorie-restricted eating will help with reducing gaining fat mass as you age, but for many, it is a tough pill to swallow. This does not mean drastic “diets” (which do not work), but rather just staying within an appropriate calorie range daily and being very consistent. Most women in mid-life need anywhere from 1600 to 1750 calories daily, and men may do with 2000 to 2300 kcal, however, this is very dependent on lifestyle and requires assessment. It’s inaccurate and difficult to know where you are going wrong, and what your body needs until you begin tracking your habits, and working with a professional. A registered dietitian can do a full assessment of this, creating a plan that syncs your current diet, activity, health history, and future goals.

The timing of when you eat: Eating regular meals daily, at the same time, creates a physiological pattern, with meals about 4 to 5 hours spaced apart and helps you understand and tap into hunger cues. Our hunger cues are masked by everything from stress and work to poor sleep. Eating a high-protein breakfast is important to signal the body and metabolism after fasting, especially for females. Eating breakfast also statistically reduces that mindless, binge eating that can happen into the evening. Eating late in the day, close to sleep, is especially unhelpful.

Intermittent fasting, while a hot topic when it comes to aging, is showing some benefits for glucose regulation and insulin management. But the latest studies show that if you stop eating earlier in the evening (truthfully, even late afternoon) it is more beneficial than skipping breakfast. Most people find this next to impossible, so stopping food intake 3 hours before sleep, and aiming for a 12-hour window with no calories over this evening-night period is a great shift.

The quality of the food you eat: As we age, because we need fewer calories, we need to make sure each bite counts. Aiming to reduce ultra-processed foods, and increase minimally processed foods, to be the bulk of our diet is crucial to flooding our aging body and brain with nutrients. A body that doesn’t receive vitamins, phytochemicals, antioxidants fats, and proteins will store more fat as a protective mechanism. Eat mostly plants, with some animal protein “boosters”. Brightly colored vegetables, some fruit, whole intact grains, beans, nuts, and seeds, along with unprocessed animal products, fish, and a spectrum of fats provide nutrient density for aging brains and hearts. The Mediterranean diet pattern is a wonderful option.

Eliminating “extras”: This is a challenge for everyone. When you were 20 years younger, snacks and alcoholic drinks may not have made a noticeable difference to your waist. Or you could easily “bounce back” after several focused days. Unfortunately, our nervous systems and physiology become less resilient as we age, meaning, an extra 300 to 500 kcal as chips and glasses of wine are no longer going unnoticed. Find ways to fit in your favorite extras but be mindful that these calories add up quickly and are not nourishing. Even being mindful, asking “Will I really enjoy this?” or “Why am I choosing this right now?” before you indulge can help you understand why the extras are there in the first place.

Physical Activity: Getting active, on a consistent basis, is the second most important thing you can do to help manage weight as you age. Research shows this allows your fat cells to turn over more quickly, allowing for less body fat to be stored. Weightlifting and weight-bearing exercise will do this most efficiently. If neither is possible for you, walking at least 50 minutes daily at a brisk pace is beneficial. You can be active at home, thanks to free online resources.

Walking to the subway and back, or walking to do errands, which is less than 30 continuous minutes, increases your daily energy expenditure, but it’s not enough. Find an activity that “moves you” as an adult, not just an activity where you move. And if it includes other people, friends, and the community, the effects are even better!

N.E.A.T.: This acronym stands for Non-Exercise Activity Thermogenesis. This really means the movement you do through the day that is not eating, sleeping, or sport-like exercise. This is the area that many middle-aged adults have eliminated, and it’s a big reason why we gain weight. It can be challenging to have to think of ways to add movement to your regular workday, especially when “chained” to a computer. Taking every opportunity during your day to move, do chores like laundry and yard work breaks, or simply move while you work. And instead of parking yourself in front of the television, make movement a part of your evening routine by prepping for the next day, having an after-dinner stroll, doing stretching or gentle movement are all ways to increase N.E.A.T.

Sleep: Nothing is more impactful on weight than getting 7 to 9 hours of deep, high-quality sleep nightly in middle age. The problem is this these are often the hardest years to get this. With hormonal changes of peri and post menopause, demanding careers, work pressure, raising young children, and taking care of elders, it’s no wonder this is the period deemed most stressful. Prioritizing sleep is really the only answer to the issue. Set a bedtime and stick to it. Eliminate food intake 3 hours before sleep, try herbal teas to soothe your mind 1.5 hours before bed, avoid alcohol, and, frankly, stress. Don’t read emails, work, or watch blue light on screens at least 1 hour before bed. It can be a challenge to break these patterns, but it’s the most impactful thing you can do to manage your weight.

It is possible to stop excessive fat gain as we age with mindfulness and consistency. You do not need restrictive diets. You need to evaluate the reasons behind your behaviors; why are eating late at night and choosing not to exercise? Understanding what amount and type of foods you are choosing daily help immensely. It is inevitable that you may see your body change in middle age, and this can be hard to accept. Instead of focusing solely on your body size, focus on how you feel, how you move, and how you can keep continuing to do the things you love and find new things to enjoy.