insulin, cortisol, thyroid hormones, testosterone, and estrogen are the five main hormones that influence your body weight.

A quick online search for weight loss strategies reveals a plethora of “hormone-balancing” diets, supplements, and medications.

The premise behind these products is that hormones — tiny chemical messengers that regulate physiological processes — get out of balance, causing weight gain or foiling attempts to lose weight.

That seems like a reasonable claim, but is it true? We’ll provide answers on the links between body weight and five of the most talked-about hormone imbalances: those relating to insulin, cortisol, thyroid hormones, testosterone, and estrogen.

Let’s dive in!

1. Insulin

Insulin is the hormone that manages our blood sugar levels. One of its key roles is to signal the uptake of glucose (and nutrients) from the bloodstream into cells. Consuming excess calories — especially from sugary, calorie-laden processed foods — triggers an insulin response: The hormone tells tissues to take up the fuel.

Unneeded calories get converted into body fat. As people grow more overweight or obese, the body’s insulin response starts to malfunction, progressing from insulin sensitivity to insulin resistance, the stage when cells stop responding effectively to insulin. Insulin resistance is a key symptom of type 2 diabetes, which may require medication to restore insulin function.

The more you suffer from overweight or obesity, the worse your insulin sensitivity will typically be, meaning their bodies must pump out more insulin than normal to cope with each meal. Insulin resistance is the end of the spectrum; this is the hallmark of type 2 diabetes.

Because higher insulin levels accompany overeating, it’s tempting to ask: Does more insulin cause weight gain? Yes and no.

Carbohydrates have the biggest impact on insulin output. This led one group of experts to propose the “carbohydrate-insulin model” of obesity, which broadly states that carbohydrates are specifically more fattening than other macronutrients.

While it’s an interesting hypothesis, the research doesn’t back it up, because eating too much fat also consistently induces insulin resistance and weight gain. In short, consuming too many calories — from carbohydrates or fat — leads to weight gain. Excessive weight gain eventually leads to insulin resistance.

In fact, excess energy will endanger any cell because the extra energy ramps up reactive oxygen species and inflammation, scrambling the insulin signal and leading to insulin dysfunction or resistance.

It becomes a vicious cycle: The body’s ability to cope with excess energy gets worse from continuing to consume too many calories, accelerating the downward spiral that ultimately leads to type 2 diabetes and increased risk of death from all causes.

Unfortunately, today’s world of hyper-palatable processed foods available 24/7 makes it difficult to fight off the urge to keep snacking.

To sum up, weight gain is the most common cause of insulin dysfunction (though not all people with type 2 diabetes are overweight).

The bottom line is that insulin resistance goes hand in hand with caloric excess. Moreover, losing weight improves insulin sensitivity regardless of diet.

2. Cortisol

One of the body’s primary stress hormones, cortisol is produced in the adrenal glands, which sit atop the kidneys. When stress activates the sympathetic “fight-or-flight” nervous system, the brain signals the adrenal glands to ramp up cortisol, adrenaline, and noradrenaline production.

The feedback loop between the brain and the adrenal glands — called the hypothalamus-pituitary-adrenal axis (HPA axis) — responds to all types of life stressors, physical, mental, and emotional.

Cortisol affects every cell in the body. It’s a catabolic hormone by nature, breaking down proteins into their amino acid building blocks to fuel the body during stress, infection, illness, trauma, and so on. Does too much stress lead to weight gain? Strictly speaking, no.

If you’re stranded on a desert island, surges in stress hormones like cortisol and adrenaline will increase fat breakdown as you burn fat and tap carbohydrates stored in the muscles and liver, ultimately leading to weight loss.

The rules of the game change, however, when calorie-dense processed foods are easily accessible. While appetite declines during acute bouts of stress, chronic low-grade stress appears to encourage the brain to seek out more energy-dense foods.

This is where the stress-obesity connection comes from. Combining caloric excess (and persistently elevated insulin levels) with chronic low-grade stress appears to be the perfect recipe for weight gain and obesity.

The key to increasing resiliency — the capacity to cope with stress.

3. Thyroid

“My metabolism is broken!”

This common lament often blames weight management woes on the thyroid gland, which sets the body’s metabolic rate and produces hormones that influence how we think, feel, recover, and perform.

Declining thyroid function often invites a diagnosis of hypothyroidism, in which the brain fails to instruct the thyroid gland appropriately, leading to insufficient hormone production. Hypothyroid symptoms may include fatigue, weight gain, brain fog, dry hair and skin, cold intolerance, and more.

Hypothyroidism is strongly associated with weight gain. Many people struggle with symptoms of thyroid dysfunction despite “normal” blood testing, meaning they don’t have a clear medical condition, but they do have suboptimal thyroid output.

Though trainers and even doctors may blame the thyroid for weight gain, the question of hormone balance remains: Is a sluggish thyroid causing the weight gain, or is it just a symptom?

Research suggests that medications can yield modest weight loss benefits for people with hypothyroidism (Agnihothri et al. 2014). The benefits occur in those whose level of thyroid-stimulating hormone (TSH) is above 5.0, well outside the normal TSH high range of 4.0.

Because higher TSH numbers signal lower thyroid output, people with 5.0-plus TSH readings may well have a “sluggish thyroid.” But many people with suboptimal thyroid output are likely to be in the normal TSH range, and drug benefits may not apply to them.

The heavy stress and/or high volume of an intense training program can cause an elevation in thyroid markers. For nonathletes, chronic life stress from too much work, too little sleep, or mental/emotional challenges can yield the same results.

4. Testosterone

For many men, more testosterone means more muscle and a leaner physique, and the notion of improving testosterone levels remains front and center in many men, particularly those over 40.

The blogosphere is full of anecdotes saying that boosting low testosterone — or low T — triggers fat burning and packs on lean mass. But how well do these stories of “hormone hypertrophy” hold up?

Research confirms that training the body leads to acute increases in testosterone, growth hormone, and insulin-like growth factor-1. Moreover, the better the workout, the greater the hormone output. Seems like hormones trigger hypertrophy, right? Not quite.

Caloric restriction, in and of itself, is the biggest signal contributing to low levels of free testosterone (i.e., testosterone that is not bound to proteins in the blood). In fact, the prolonged and sustained caloric deficits required to be an elite bodybuilder mean it takes a pro 2–3 months for testosterone levels to return to normal.

Sleep quality is also a factor. (Sleep apnea, a disorder characterized by pauses in breathing or periods of shallow breathing during sleep, compromises sleep quality.) A recent study by the University of Miami linked poor sleep quality to lower testosterone levels and found that for every hour of sleep loss (under 7 hours), men could expect a drop in testosterone.

5. Estrogen

Social media is awash with claims that too much estrogen causes hormone imbalances and weight gain, particularly in women. Research suggests otherwise. The worldwide obesity epidemic exploded only in the last 40 years.

Why did this “estrogen-dominant” phenotype not cause obesity in the previous 200,000 years of human history? Yes, adults with overweight or obesity often have higher estrogen levels than their slimmer peers — but estrogen isn’t causing the weight gain.

A quick review: Weight gain reflects the accumulation of fat cells that are highly proinflammatory. That disturbs blood glucose and insulin function, contributing to a downward spiral of poor regulation of insulin and cortisol while estrogen levels move higher. Once again, weight gain causes this hormonal disruption — not vice versa.

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