What Causes PCOS-Related Weight Gain? A Nutritionist Explains

If you’re eating well, exercising regularly and still feel stuck with your weight, you’re not doing anything wrong, your hormones may be working against you.

Polycystic ovary syndrome (PCOS) affects how your body processes food, stores fat, and responds to insulin.

That means weight gain, especially around your middle, is not just about willpower. It’s a metabolic issue rooted in hormone imbalance, inflammation and insulin resistance.

In this post, I’ll explain the real reasons weight gain is so common with PCOS, why traditional diets don’t work long-term, and what I focus on in clinic to help women feel more in control of their weight again, without going to extremes.

Why PCOS Makes Losing Weight So Difficult

Weight gain in PCOS isn’t about laziness or lack of discipline. It’s driven by a combination of biological and hormonal factors, including:

1. Insulin Resistance

This is one of the most common drivers of PCOS-related weight gain. Insulin is a hormone that helps move sugar (glucose) out of your blood and into your cells. But in PCOS, your cells often become less responsive to insulin, leading to higher insulin levels in the blood.

High insulin:

• Promotes fat storage, especially around the waist

• Triggers more hunger and sugar cravings

• Increases androgens (like testosterone), which worsens hormonal symptoms

Insulin resistance can exist even if your blood sugar is “normal” on a standard test. This is why weight gain and difficulty losing weight are often early signs of metabolic imbalance in PCOS.

2. Hormonal Imbalances

Women with PCOS often have elevated androgens (male-type hormones) and disrupted ratios of oestrogen and progesterone. These hormone shifts can affect your appetite, fat distribution and metabolism.

Hormone imbalances also:

• Disrupt sleep

• Increase cravings and emotional eating

• Worsen PMS and water retention

• Reduce your ability to build lean muscle

This is why hormonal support – not just calories in/calories out – is crucial.

3. Chronic Inflammation

PCOS is now recognised as a low-grade inflammatory condition, which contributes to insulin resistance, fatigue, and stubborn weight gain.

Inflammation can:

• Slow metabolism

• Interfere with hunger and satiety signals

• Cause fluid retention and puffiness

• Increase cortisol (your stress hormone)

Supporting inflammation through the right foods, gut health, and lifestyle changes is one of the most important (and often overlooked) parts of weight loss with PCOS.

4. Stress and Cortisol

If you’re always “switched on” rushing, pushing through exhaustion, or unable to rest, high cortisol could be part of the picture.

Chronic stress raises cortisol, which:

• Promotes fat storage (especially around your belly)

• Disrupts sleep and blood sugar

• Lowers progesterone and worsens hormonal imbalance

In clinic, I often see women who are trying so hard to “do the right things” but are stuck in a stress-metabolism trap.

5. Thyroid Dysfunction

PCOS and thyroid issues often go hand-in-hand, especially Hashimoto’s. An underactive thyroid slows down metabolism, making weight gain more likely and weight loss harder, even with a good diet.

Signs your thyroid might be involved:

• Tired all the time

• Feeling cold often

• Constipation

• Hair thinning

• Irregular or heavy periods

If you’re doing all the right things and still feel stuck, your thyroid is worth checking.

Why Restrictive Diets Don’t Work with PCOS

Low-calorie, low-carb, or “quick fix” plans might work short-term, but often backfire long-term.

Restricting food too much:

• Slows your metabolism

• Increases cravings

• Disrupts hormones further

• Raises cortisol (making it harder to lose fat)

Instead of restriction, my approach is focused on regulating blood sugar, calming inflammation, supporting hormone balance, and making your metabolism more efficient — using real food and sustainable steps.

What Does Work: A Root Cause, Food-First Strategy

You don’t need to go carb-free, starve yourself, or spend hours in the gym to lose weight with PCOS.

Instead, I focus on:

✔ Balancing blood sugar with smart carbs + protein + healthy fats

✔ Nutrient repletion (magnesium, zinc, omega-3s, B vitamins)

✔ Reducing inflammation through targeted food swaps

✔ Supporting metabolism with strength-building movement and gut health

✔ Addressing hormone blockers (like stress, poor sleep, and digestive issues)

Weight loss becomes possible when your body feels safe, nourished and supported.

You’re Not Lazy You’re Likely Undersupported

If you’ve been made to feel like weight gain is your fault, or that you just need to try harder, I want you to know: it’s not true. PCOS changes how your body responds to food, stress, and exercise. And with the right plan, it can change.

Next Steps

If you’re ready to stop dieting and start understanding what your body actually needs to shift stubborn weight, I can help.

Want to understand why your body is stuck in fat-storage mode?

Download your free Hormone Health Snapshot — a practical guide to the common blocks I see in PCOS weight and metabolism.

Feel like nothing is working for your weight and hormones?

Book a free 30-minute call to explore whether my personalised 12-week PCOS programme could help you rebalance hormones and support sustainable weight loss.

Final Thought

If you’ve been stuck in a cycle of trying harder and getting nowhere, know that it’s not just about food or willpower. PCOS weight gain is complex, but it’s not unchangeable. When you work with your hormones instead of against them, real progress becomes possible.

Updated in June 2025 to reflect new PCOS research and nutrition strategies.

Disclaimer

This blog is for informational purposes only and does not replace personalised medical or nutritional advice.