1. Thyroid

The thyroid gland produces T3, T4, and calcitonin—hormones that regulate metabolism, heart rate, sleep, growth, and brain function. When thyroid hormone production is too low (hypothyroidism), metabolism slows. This can lead to fatigue, constipation, depression, and unexplained weight gain, even with minimal food intake.

2. Leptin

Leptin is your body’s “satiety hormone.” It tells your brain when you’re full. Diets high in sugar and ultra-processed foods can cause leptin resistance, where the brain stops responding to leptin’s signal. Fat cells also produce leptin, which can further disrupt communication—leading to overeating and stubborn weight gain.

3. Insulin

Insulin helps move glucose from your bloodstream into cells for energy or storage. Frequent snacking, processed foods, alcohol, artificial sweeteners, and excess sugar can lead to insulin resistance. When cells stop responding properly, glucose stays in the blood and gets stored as fat—often around the abdomen.

4. Estrogen

Both high and low estrogen levels can contribute to weight gain. Excess estrogen can worsen insulin resistance, while low estrogen—common during perimenopause and menopause—signals the body to store more fat. Fat tissue itself produces estrogen, so the body may increase fat storage to compensate, especially in the hips, thighs, and abdomen.

5. Cortisol

Cortisol is the primary stress hormone released by the adrenal glands. Chronic stress, poor sleep, inflammation, and over-exercising can keep cortisol elevated. High cortisol promotes blood sugar imbalances and increased visceral (belly) fat, even when diet appears “clean.”

6. Progesterone

Progesterone works in balance with estrogen. Chronic stress, birth control use, menopause, and exposure to hormone-disrupting chemicals can lower progesterone levels. Low progesterone is often associated with fluid retention, mood changes, anxiety, and weight gain.

7. Ghrelin

Ghrelin is the hunger hormone. It stimulates appetite and fat storage and rises when you’re sleep-deprived, dieting aggressively, or fasting excessively. Elevated ghrelin levels can make weight loss feel like a constant uphill battle, especially during restrictive eating patterns.

8. Testosterone

Women produce testosterone in smaller amounts, primarily from the ovaries and adrenal glands. It supports muscle mass, fat burning, bone strength, and motivation. Chronic stress, inflammation, and aging can lower testosterone levels, contributing to reduced muscle mass and increased fat storage.

9. Melatonin

Melatonin regulates sleep and circadian rhythm. Poor sleep, blue light exposure at night, and irregular schedules disrupt melatonin production. When melatonin drops, growth hormone release is impaired—reducing fat burning and increasing inflammation-related weight gain.

10. Glucocorticoids

Glucocorticoids help regulate inflammation and metabolism. Chronic inflammation and long-term stress can alter how these hormones function, leading to insulin resistance and impaired glucose use. Over time, this contributes to elevated blood sugar levels, fat storage, and metabolic dysfunction.

Functional Medicine Insight
Weight loss becomes much more sustainable when hormones are addressed first. Food, stress, sleep, gut health, detoxification, and nutrient status all influence hormonal balance—and ignoring these factors often leads to frustration.