There appears to be a connection between estrogen and body weight regulation.  With lower estrogen levels, lab animals tend to eat more and be less physically active.  Levels that are too high or too low appear to lead to fat storage.  And, lower estrogen levels may also slow down your metabolic rate (the speed  at your body converts stored energy into working energy).
When you’re under-rested, your appetite-regulating hormones get short-circuited, so your appetite goes into overdrive, but the hormones that tell you you’re full don’t kick in promptly. Studies also suggest that when you’re sleep-deprived, it alters the way you think about food, so you have stronger cravings for sweets and other less healthful eats.
Additionally, attempts to lose weight on low-calorie diets can lead to even more lost muscle. Studies have found that regular resistance or strength training may be a better alternative than your daily runs to preserve and gain muscle — even when coupled with a low-calorie diet. Aerobic exercise is still important, just don’t make it your only form of activity.

Are you a woman over 40 and noticing it’s getting harder to lose weight?  Got some extra stubborn fluff and puff around the middle?  Maybe you’re finding that the diets you did in your 20’s or 30’s don’t work as fast as they used to or don’t even work at all!  If you’re already well past 40, chances are you’ve found it’s harder to lose weight.  And, those inches around your waistline won’t budge.

A 2014 study found that the type of fat we consume might make all the difference. Participants in the study were asked to eat 750 extra calories every day for seven weeks. Those having excess calories from saturated fats had activated cells that promoted fat storage in the belly and increased insulin resistance. However, individuals who had a high consumption of polyunsaturated fats found in fatty fish, nuts and seeds, gained less abdominal fat and were more likely to increase muscle mass instead.
^{Why that’s so important: “The more muscle we have, the more calories we burn,” Kirkpatrick says. Even if it doesn't actually help you lose weight, it can help keep you from gaining it—along with all the other good things it does for your body, mind, and life. Lots of over-40 guys like HIIT, since its compressed timeframe ends up having a low impact on your schedule.}

Let's get down to business: If you're having a hard time achieving your weight-loss goals after 40, these 16 expert-backed tips for losing weight in your 40s are totally doable and can nudge your body in the right direction again. (And, tbh, they're wise for anyone looking to move the needle to keep in mind—not just those over 40.) You'll be on your way to a stronger, healthier you in no time.

Amy Myers, MD is a two-time New York Times bestselling author and an internationally acclaimed functional medicine physician. Dr. Myers specializes in empowering those with autoimmune, thyroid, and digestive issues to reverse their conditions and take back their health. In addition, she is a wife, mother, and the successful founder and CEO of Amy Myers MD®.

Once you hit 40, losing weight can feel like a lost cause. Dr. Robert Kushner, director of the Center for Lifestyle Medicine at Northwestern Medicine Center in Chicago and author of “Six Factors to Fit: Weight Loss that Works for You,” told TODAY that the total amount of calories burned every day diminishes for most people with each passing decade.

_{To jumpstart your weight loss, the biggest focus should be to develop habits that will help you build or maintain your muscle mass. "The most effective way that women over 40 can boost their metabolism is by building muscle through weight-lifting and resistance training," says Dr. Peterson (more on that to come). But nutrition and sleep habits also play a role here.}
People naturally lose muscle after 40, especially women after menopause. Because muscle burns more calories than fat, this can slow down your metabolism and make it harder to shake those stubborn pounds. Strength-training exercises -- lifting weights or doing body-weight exercises, like push-ups and squats -- at least twice a week can help you keep those muscles.