Perimenopausal Weight Gain: What You Need To Know

Frustrated by perimenopausal weight gain? Wondering how to lose weight in your 40s?

Gaining weight, particularly around the middle, can be one of the most frustrating characteristics of perimenopause for many women. It can feel like it happens overnight despite not having changed anything you do or eat. What can be even more frustrating is that the things you used to turn to when you needed to ‘get in shape’ or lose a few pounds no longer work like they used to, if at all. Sound familiar?

So what’s going on? What’s changing in your body to create this situation now? What can you do about it? This is exactly what this blog is all about. Gaining extra pounds in perimenopause and or menopause is NOT inevitable, it’s just more likely. But trust me, there ARE things you can do to prevent or reverse it!

Why am I gaining weight in my 40s?

The hormonal changes from late 30s create metabolic shifts that make women three times more likely to gain weight. Perimenopausal weight gain is driven by oestrogen behaving erratically and declining levels of progesterone. The new hormonal picture starts to create a level of ‘metabolic dysfunction’, making you more prone to insulin resistance. Not only does this lead to an increase in fat mass, but a redistribution of fat mass in the body. For example fat stores moving from the hips, breasts, and thighs to the abdomen. Left unaddressed, this can eventually lead to the typical apple shape commonly seen in post menopausal women. 

Let’s look at some of the factors at play in perimenopause that impact metabolic function and insulin control.

1) Declining Muscle Mass

From around age 35, muscle mass declines at a rate of 1-2% per year, contributing to a slowing of metabolism. This is called sarcopenia, which is defined as age related, involuntary loss of skeletal muscle mass and strength. It applies to both men and women.

Muscle mass is one of the largest determining factor of how much energy (calories) you burn each day. The less muscle you have the less energy you will burn and the more body fat you will hold onto. Muscle is its own organ, known as the organ of longevity, muscle is essential for many aspects of health, from immune function to a healthy metabolism and body composition.

The good news is that YOU CAN counteract muscle loss as you age! By doing things that help you to keep BUILDING new muscle and maintaining it!

The WORST thing you can do past age 35 is to NOT be doing exercise that builds muscle. Focusing on cardio and HIIT workouts isn’t going support muscle building, but lifting heavy weights (strength training) IS.

In fact, past age 40, too much long duration cardio, HIIT classes, spin classes, and ‘boot camps’ can be ‘catabolic’, which means having the ability to break your muscle down. The opposite of catabolic is ‘anabolic’, which builds new muscle. Lifting, pushing and pulling heavy weights (YOUR heavy) is anabolic. Studies suggest strength training 2 – 3 times per week for 20-40 minutes is ideal.

​​Optimal protein intake is also KEY for building and maintaining muscle mass. The minimal optimal daily intake of protein is 1.5 grams per kilo of your own body weight, split out across three meals. This can be up to 2g per kilo of body weight if you have more body fat to lose, are lifting pretty intensely each week or just want to really optimise health and body composition.

2) Changes To Carbohydrate Tolerance

The erratic fluctuations in oestrogen levels throughout perimenopause and its subsequent decline the nearer you get to reaching menopause makes our cells less sensitive to insulin, and instead more resistant to insulin. This situation reduces our tolerance to higher carbohydrate meals and carbohydrates in general. This doesn’t mean that you should completely avoid all carbohydrate foods, but that you would benefit from being more mindful of your portion sizes and types of carbohydrates you rely on.

All carbohydrate foods – from lentils, quinoa and sweet potato to white flour wraps, bagels and chips – break down into glucose (sugar). This glucose enters your bloodstream. The speed at which they break down into glucose, and the amount of glucose they break down into, matters from now on more than ever.


Because the sharper and higher your glucose spike, the more insulin your pancreas needs to make in order to move the glucose out of your blood stream and into your cells. Once inside the cells, glucose can be used for energy, either straight away or stored for use later on (in the form of glycogen). Any excess glucose, for example when there was too much in the blood stream at one time, gets stored in fat cells, predominantly ones around the middle.

In your 20s and earlier 30s, your muscle cells were sensitive to insulin, which means they were more efficient at soaking up glucose when insulin asked them to. In your 40s however, your cells can start to become less sensitive (resistant) to insulin’s request. This results in some or all of the glucose (depending on how resistant your cells have become) remaining in the blood stream. The pancreas then needs to secrete more insulin in order to process the remaining glucose, resulting in the glucose being moved into fat cells instead, as it has nowhere else to go. Hello perimenopausal weight gain!

The more carbs on your plate, even healthier types, the more glucose they will break down into. The more refined versions of carbs you eat, the more glucose you will make. Therefore, a slight change to your relationship with carbs can make a big difference. Switching to complex (slow-release) carbs AND being mindful of your portion size, is a powerful change to make in perimenopause.

3) Insulin Resistance

You can click here to read my blog post where I dive deeper into this topic. For the purpose of this blog, I’ll explain why body cells become more resistant to insulin as we pass 40, leading to perimenopausal weight gain.

Oestrogen keeps your cells ‘sensitive’ to insulin and the high and fluctuating levels of oestrogen that we see in the earlier perimenopause years (early 40s) can impact how sensitive your cells are at various times in the day and month. In the later stages of perimenopause (mid to late 40s) when oestradiol levels start to decline, and post menopause when levels are almost nonexistent, cells become EVEN more prone to insulin resistance. In addition to increases in body fat, insulin resistance can also drive high cholesterol, high triglycerides and ‘fatty liver’, which is the accumulation of fat in the liver.

4) Declining Progesterone 

Progesterone also plays a role in your body’s ability to burn fat and build muscle. Declining progesterone as you move past 40 is another factor potentially contributing to fat gain or trouble losing it. Low progesterone also leaves oestrogen ‘unopposed’ and unopposed oestrogen is another cause of weight gain. 

5) Low Thyroid Hormone Production

The thyroid gland is your metabolism regulator. Declining progesterone and unopposed oestrogen impacts the thyroid gland’s ability to produce thyroid hormone. For most women, less thyroid hormone is made, which is known as hypothyroidism or under active thyroid. From late 30s, it’s helpful (and important) to check in with how your thyroid is doing about once per year. Key thyroid markers to check are TSH, T4, T3 and the two main thyroid antibodies; Thyroglobulin (Anti-Tg) and Peroxidase (Anti-TPO).

If these thyroid markers are within optimal ranges it’s much easier for your body to burn fat. It’s important to bare in mind that the conventional reference ranges for TSH and T4 are rather wide. This can mean you are told your levels are normal when actually they are below par and causing issues. T3 is the ACTIVE thyroid hormone, it’s the one that does all the work. Most GPs do not test T3, but we must know this number because T4 is converted into T3. Therefore normal T4 does not necessarily mean good thyroid hormone levels.

6) Chronic Stress and Generally Overdoing Life

Chronic modern day stress really does play a significant role in weight gain and the ability to lose weight after 40. Cortisol, your body’s main stress hormone, is a big reason for the so-called ‘muffin top’! Cortisol has the ability to break down muscle tissue and convert it into glucose (a process called gluconeogenesis), most of which is stored around your middle. Furthermore, as progesterone levels decline and oestrogen levels fluctuate on its erratic rollercoaster, cortisol levels naturally rise. This means that stress management is more important in your 40s (onwards) than ever before. This new naturally higher cortisol state means high or chronic stress (including blood sugar imbalances and cortisol-inducing exercise) adds fuel to the fire.

How to lose weight in your 40s?

THE GOOD NEWS is that simple diet and lifestyle interventions make a profound difference to perimenopausal weight gain! In my next blog, I give you 7 Ways To Lose Weight In Your 40s.

Hi, I'm Francesca

I’m a Registered Nutritional Therapist who helps womens in their 40s find vibrant health and vitality, and thrive through perimenopause and beyond.

With nearly 10 years of experience working with hundreds of people, I empower and support women to support their bodies and hormones for a smooth and happy ride in their 4os.

Through our work together, clients have improved their energy, their periods and cycles, their mood, sleep, brain fog and digestion, and learned how to better manage their weight.

I am here to help you get back to YOU so you can have a fantastic time in your 40s.

My signature nutrition and lifestyle coaching approach to supporting women with their health and wellbeing is refreshing, down-to-earth and realistic.

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Learn more about my signature course – Thrive Through Perimenopause – to start taking care of your hormone health once and for all, for a MUCH smoother ride in your 40s and beyond!

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