If you’re barely eating but still gaining weight, I see you.

As a Nutritional Therapy Practitioner, this is one of the top complaints I hear from women in their 30s and 40s:

“I’m working out, I barely eat, I think I’m eating clean, but I keep gaining weight.”

Here’s the thing: chronic undereating will stall your metabolism, leading to weight gain over time.

We’ve been told for years to limit calories to lose weight. While this is helpful for people who overeat, are considered obese, and need to lose a lot of weight to avoid metabolic disease, it is not an approach that should be maintained long-term! And it is not an appropriate way to eat for most people outside of that criteria, or simply because you’re a woman, which is something that I see in my work a lot.

A lot of women feel bad for wanting to eat, for being hungry. This is bananas and has to stop.

Your body and its systems are majorly affected when you slash calories. Let’s break down four foundational systems impacted by not eating enough and how they affect your ability to lose weight and have consistent energy levels.

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1. Undereating Wrecks Your Thyroid Function

Your thyroid is your body’s metabolic engine. It needs key nutrients and calories to keep your metabolism humming.

If you’re consistently eating 1200–1500 calories a day, you might be surprised to learn that you need that much (or more!) just to exist—as in, sit around and keep your body functioning. Add workouts, work stress, and everyday life on top? Your needs could easily rise to 2000–2500+ calories per day.

When you chronically underfuel:

• Your thyroid hormone production drops
• Your metabolism slows
• Your energy tanks
• Weight loss becomes harder (and often stalls completely)

🚩 Bonus red flag: Working out fasted (especially high intensity) can add stress to your already taxed system, further suppressing thyroid function.

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2. Blood Sugar Crashes and HPA-axis Dysfunction

The HPA-axis (Hypothalamus, Pituitary, Adrenals) is your body’s stress and blood sugar regulation team. It plays a key role in how your body responds to stress, whether that’s from blood sugar spikes, external stressors like a rude email from your co-worker, or undereating.

Here’s what typically happens in someone who chronically undereats:

• You skip or skimp on breakfast.
• You run on caffeine and carbs.
• Your blood sugar spikes, then crashes.
• Your body sees this as an emergency and releases cortisol and adrenaline to “rescue” you.

This chronic stress cycle keeps your cortisol elevated when it should be winding down. Over time, your HPA-axis becomes dysregulated, leaving you with:

• Insomnia or waking between 2–4am
• Afternoon crashes
• Irritability or anxiety
• Difficulty losing weight, despite effort

Quick breakdown:

• Hypothalamus: Monitors blood sugar and tells the pituitary when there’s an imbalance.
• Pituitary: Sends signals to stabilize blood sugar (often through fat storage).
• Adrenals: Release cortisol and adrenaline in response to the stress of undereating.

It’s a vicious cycle known as “the blood sugar rollercoaster,” and it wreaks havoc on your metabolism and overall well-being. It’s an internal stressor that disrupts several key systems in the body and can leave you feeling anxious, stressed out, hangry, irritable, lethargic, and fatigued.

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3. Your Digestion Slows to a Crawl

Undereating, especially protein, tells your body:

“We must be in a famine. Conserve energy.”

Your body adapts by reducing:

• Stomach acid production
• Enzyme output
• Gut motility

Without these, food sits undigested, bloating increases, toxins build up, and nutrient absorption tanks. That creates a cascade of issues such as inflammation, constipation, hormonal imbalance, and feeling full after just a few bites (even though you’re still undernourished).

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4. Undereating Disrupts Your Hunger Hormones (Leptin + Ghrelin)

Let’s talk about your body’s internal food regulators: leptin and ghrelin. These hormones control your hunger, fullness, and energy regulation.

• Leptin = the “I’m full” hormone
• Ghrelin = the “I’m hungry” hormone

In a healthy, well-fed body, these two stay in balance. But with sustained calorie restriction, this system starts to break down.

When you undereat:

• Leptin levels drop, making it harder to feel full or satisfied.
• Ghrelin levels rise, increasing hunger signals even if you’re trying to “be good” and stick to your low-calorie plan.

Worse, your brain starts ignoring leptin altogether. This is called leptin resistance, and it means:

• You feel hungrier than ever
• You crave quick energy foods (like sugar + caffeine)
• Your body stores fat more easily, especially around the belly

Your body is trying to survive, so it ramps up the signals to eat and slows your metabolism to conserve fuel. And just like that, you’re stuck in a cycle where eating less leads to more fat storage and less energy.

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5. Your Hormones Get Out of Whack

In your 30s and/or 40s your hormones become more sensitive to stressors, including undernutrition.

Not eating enough signals danger to your body, which leads to:

• Suppressed ovulation or irregular periods
• Estrogen dominance
• Low progesterone
• Cortisol stealing resources from sex hormone production

Even if you’re not yet in perimenopause, undereating throws off your hormonal rhythm, and throws your weight loss efforts off with it.

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The Bottom Line: Your Body is Adapting to Stress, not Intentionally Pissing You Off

Weight gain (or plateau) despite eating less isn’t a sign of failure; it’s a sign your body needs support. When you give it consistent nourishment, stress reduction, and strategic care, it will respond.

You can’t hustle your way to healing, but you can nourish your way there.
If you’re ready to get off the blood sugar rollercoaster and finally feel like yourself again, I’d love to help. Check out my Services page for ways to work with me.